Inductively coupled plasma mass spectrometry-based immunoassay: a review.

INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRYBASED IMMUNOASSAY: A REVIEW Rui Liu,1,2 Peng Wu,3 Lu Yang,4 Xiandeng Hou,1,3 and Yi Lv1* 1

College of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, P.R. China 2 Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu, Sichuan, 610059, P.R. China 3 Analytical & Testing Center, Sichuan University, Chengdu, Sichuan, 610064, P.R. China 4 Chemical Metrology, National Research Council Canada, Ottawa, Ontario, Canada, K1A 0R6 Received 16 November 2012; revised 15 May 2013; accepted 29 May 2013 Published online 22 November 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mas.21391

The last 10 years witnessed the emerging and growing up of inductively coupled plasma mass spectrometry (ICPMS)-based immunoassay. Its high sensitivity and multiplex potential have made ICPMS a revolutionary technique for bioanalyte quantification after element-tagged immunoassay. This review focuses on the major developments and the applications of ICPMSbased immunoassay, with emphasis on methodological innovations. The ICPMS-based immunoassay with elemental tags of metal ions, nanoparticles, and metal containing polymers was discussed in detail. The recent development of multiplex assay, mass cytometry, suspension array, and surface analysis demonstrated the versatility and great potential of this technique. ICPMS-based immunoassay has become one of the key methods in bioanalysis. # 2013 Wiley Periodicals, Inc. Mass Spec Rev 33:373–393, 2014 Keywords: inductively coupled plasma mass spectrometry (ICPMS); laser ablation; metal label; gold nanoparticles (AuNPs); immunoassay; cytometry; suspension array; Western blotting

I. INTRODUCTION Protein quantification is of great importance in biological research since many specific functions in a biological cell or an organism are controlled by changes in protein expression levels under different physiological conditions (Hamdan & Righetti, 2002; Ong & Mann, 2005; Becker & Jakubowski, 2009; Mounicou et al., 2009). Currently, antibody based immunoassays are the primary tools for the targeted quantification of specific proteins. Immunoassays have been in use since the late 1950s when radioimmunoassays (RIA) were first applied to quantify insulin in plasma samples using radioisotope labeled antibodies that could subsequently be detected by scintillation counters (Yalow & Berson, 1959). Although RIA methods are

Contract grant sponsor: National Natural Science Foundation of China; Contract grant numbers: 20835003, 21075084, 21128006. Correspondence to: Y. Lv, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, P.R. China. E-mail: [email protected]

Mass Spectrometry Reviews, 2014, 33, 373–393 # 2013 by Wiley Periodicals, Inc.

reliable, accurate, and highly sensitive, they suffer from the problems associated with radioisotopes (such as health hazard, waste disposal problems, and limited stability), which restrict their use to specialized laboratories. Consequently, several types of nonradio immunoassays based on alternative detection techniques have been proposed (Hage, 1999), involving enzyme linked immunosorbent assay (ELISA) (Engvall & Perlmann, 1971; Lequin, 2005), chemiluminescent immunoassay (CLIA) (Schroeder et al., 1976; Zhao et al., 2009a), time resolved fluorescence immunoassay (TRFIA) (Soini & Hemmila, 1979; Hagan & Zuchner, 2011), electrochemiluminescent immunoassay (ECLIA) (Blackburn et al., 1991; Kenten et al., 1991; Forster et al., 2009), etc. In the last 50 years, they have been successfully applied to a large number of molecules that vary widely in size, chemical and physical properties, and biological activity. Attributed to their high sensitivity, high specificity, and cost effectiveness, immunoassays have advanced to become routine methods for the detection and quantification of hundreds of types of molecules both native to living organisms (e.g., hormones), and foreign molecules (e.g., pharmaceuticals). However, these conventional immunoassay detection techniques are often significantly limited in dynamic range and in some cases sensitivity. Moreover, the overlap of signals occurs, prohibiting their usage to meet today’s high-throughput requirement of simultaneous multianalyte quantification. For instance, the emission bands of fluorescent dyes (or even quantum dots) are quite broad that the spectral overlap is inevitable when simultaneous measurements are made with multiple dyes (Han et al., 2001; Chattopadhyay et al., 2006; Biju et al., 2010; Wu et al., 2011). The comparison of commonly used immunoassays is summarized in Table 1. Inductively coupled plasma mass spectrometry (ICPMS) is undoubtedly the predominant and the most sensitive commercial instrument for the determination of a wide range of metals and several nonmetals (Bings et al., 2010; Zheng et al., 2010; Gao et al., 2012; Profrock & Prange, 2012). The advantages of ICPMS as an elemental detector include low detection limits (pg mL1 level for most elements), low matrix effects, wide dynamic ranges, and high spectral resolution for elements and isotopes, which is commendable for immunoassays with an elemental tag (Baranov et al., 2002b; Bettmer et al., 2006;

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Table 1. The comparison of different types of immunoassays R-IA

Invention year

1959(Yalow&

Berson,

ELISA

CL-IA

TRF-IA

ECL-IA

ICPMS-IA

2001(Zhang, et al.,

1971(Engvall&

1976(Schroeder, et al.,

1979(Soini&

1991(Blackburn, et al., 1991; Kenten, et al.,

1959)

Perlmann, 1971)

1976)

Hemmila, 1979)

1991)

2001)

Sensitivity

High

Medium

High

High

High

High

Labeling reagent feature

Radioactive

Produce CL

Produce TRF

Produce ECL

Produce

colorimetric

signal

No special requirement

Reagents shelf life

Short

Medium

Medium

Medium

Medium

Long

Stability

Medium

High

Medium

Medium

Medium

High

Multiplex potential

Low

Low

Low

Low

Low

Excellent

Medium

Low

Medium

Medium

Medium

High

Instrumentation

and

operation cost

Prange & Proefrock, 2008; Becker & Jakubowski, 2009; Bettmer et al., 2009; Careri et al., 2009; Mounicou et al., 2009; Bomke et al., 2010; Sanz-Medel, 2010; Tholey & Schaumloffel, 2010; Wang et al., 2010). Therefore, ICPMS-based immunoassay has become a fast growing research field in immunoassay since it was first reported by Zhang et al. (2001). This is because that ICPMS as a detection technique does not require labeled reporters to possess the radioactive, optical, electric, electrochemical, magnetic, or any other special properties since atomic ions from the labels are directly detected. Second, ICPMS-based immunoassay has the great multiplexing potential for biological analytes endowed by the excellent element isotopic spectral resolution of the mass spectrometer. Third, high sensitivity could be easily obtained by the use of the nanoparticle tag instead of metal ions, because of large quantity of detectable atoms in each nanoparticle tag. Methods for the detection of biological analytes such as small biomolecules, proteins, nucleic acids, and even cells have been proved to be successful. Moreover, it has been demonstrated to be the ideal technique for the next generation of flow cytometer (Benoist & Hacohen, 2011; Doerr, 2011; Janes & Rommel, 2011; Darzynkiewicz, 2012; de Souza, 2012). Despite some excellent reviews relevant to ICPMS-based immunoassay (Baranov et al., 2002b; 2003; Wind & Lehmann, 2004; Bettmer et al., 2006; Prange & Proefrock, 2008; SanzMedel et al., 2008; Scheffer et al., 2008; Becker & Jakubowski, 2009; Bettmer et al., 2009; Careri et al., 2009; Mounicou et al., 2009; Bomke et al., 2010; Fernandez et al., 2010; Ornatsky et al., 2010; Sanz-Medel, 2010; Tholey & Schaumloffel, 2010; Wang et al., 2010; Careri & Mangia, 2011; Engelhard, 2011; Giesen et al., 2012; Konz et al., 2012), to the best of our knowledge, there has been no comprehensive summary of this emerging technique to date. Herein, the present review aims to present major developments as well as applications of this stateof-the-art ICPMS-based immunoassay with emphasis on methodological innovations. The advantages and the limitations of this technique are discussed in details. Besides ICPMS immunoassays, the bioassays based on similar principles such as nucleic acid hybridization and aptamer-based assays are included in this review. 374

II. THE BASICS OF ICPMS AND IMMUNOASSAY A. The Basics of ICPMS Inductively coupled plasma mass spectrometry (ICPMS) was invented in the early 1980s (Houk et al., 1980) and the first commercially available ICPMS instrument was introduced in 1983 by PerkinElmer SCIEX. An ICPMS usually consists of a sample introduction system, an ICP system, and a mass detector (Thomas, 2001). The sample, typically in liquid form, is pumped into the sample introduction system, which is made up of a spray chamber and a nebulizer. It emerges as an aerosol and eventually finds its way into the base of the plasma. As it travels through the different heating zones of the plasma torch, it is dried, vaporized, atomized, and ionized. During this process, the sample is transformed from a liquid aerosol to solid particles, then into gas. When it finally arrives at the analytical zone of the plasma, at approximately 7,500–10,000 K, it turns into excited atoms and ions, representing the elemental composition of the sample. There is enough energy in the plasma to remove an electron from its orbital to generate an ion. It is the generation, transportation, and detection of significant numbers of these positively charged ions that give ICPMS characteristic ultratrace detection capabilities. The ICPMS instrument measures most of the elements in the periodic table. The elements shown in light blue color in Figure 1 can be analyzed by ICPMS with detection limits at or below the pg mL1 (part per trillion, ppt) range (PerkinElmer, 2003). Elements that are in white are either not measurable by ICPMS (the upper right hand side) or do not have naturally occurring isotopes. The bars for each element in Figure 1, sometimes referred to as the isotopic fingerprint, depict the number and relative abundance of the natural isotopes for each element. The naturally occurring isotopes of each element have the same atomic number (number of protons in the nucleus), but differ by the atomic mass. This is the result of the different number of neutrons present in the nucleus of each isotope. Practically, there are more than one hundred isotopes can be simultaneously detected by ICPMS, all with high sensitivity and high resolution (typical quadrupole Mass Spectrometry Reviews DOI 10.1002/mas

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FIGURE 1. Elements and isotopes determined by ICPMS and the approximate detection capability (PerkinElmer, 2003). Reproduced by permission of PerkinElmer, Inc. Copyright # 1998–2010 PerkinElmer, Inc., U.S.A. All rights reserved.

mass spectrometers used in ICPMS have resolutions between 0.7 and 1.0 amu).

B. The Basics of Immunoassay An immunoassay is a type of biochemical test that uses antibodies raised against an analyte of interest (antigen) as a means of detecting the presence of that analyte. The high specificity and affinity of an antibody for its antigen allows a selective binding of the antigen, which is present in the matrices of hundreds of other substances, even if they exceed the analyte concentration by 2–3 orders of magnitude. Thus, immunoassays can handle samples without any analyte enrichment, purification or pretreatment, which is normally necessary for standard methods such as high performance liquid chromatography (HPLC), gas chromatography (GC), and molecular mass spectrometry (MS). Especially for clinical diagnostics, where complex samples such as whole blood, serum or urine consists of many different substances (i.e., proteins, amino acids, sugars, hormones, etc.) have to be analyzed, immunoassays have considerable advantages over other standard methods with respect to analysis time and sensitivity. Since it is hard to detect antibodies and their binding to antigens, the use of antibodies as detection reagents often requires the labeling of the antibodies with an easily detectable reporter molecule (e.g., a radioMass Spectrometry Reviews DOI 10.1002/mas

isotopes, enzyme, small molecule light absorbers, or fluorophores). As a result, the use of immunoassays in bioanalysis has grown rapidly from 1959, when Yalow and Berson demonstrated the first radioimmunoassay with a radioisotope as a label (Yalow & Berson, 1959), for which Yalow received the Nobel Prize. In case of making the antibodies “visible” by ICPMS, an elemental tag sensitively detectable by ICPMS should be labeled on the antibodies. Antibodies including polyclonal antibodies, monoclonal antibodies, and recombinant antibodies are commonly used recognition elements for bioassays. Great success in antibody engineering has been achieved in the last 20 years (Leavy, 2010). To date, many animals (e.g., rabbits, sheep, chickens, and cattle) have been used to produce polyclonal antibodies, which are relatively inexpensive for large quantities. However, these antibodies can cross react with structurally similar compounds and the co-contaminants presented in analytes which cause matrix effects on the polyclonal antibodies based assay. While monoclonal antibodies are usually produced from mice, they possess specific binding characteristics. The monoclonal antibodies-based assay is generally more sensitive than polyclonal antibodies based assay. The main drawback of producing monoclonal antibodies is that they are expensive, and technically demanding to generate and to maintain a hybridoma cell line. The development of molecular methods for expression of 375

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antibody fragments and techniques for producing and screening combinatorial libraries have opened up a wide range of opportunities for selecting and engineering recombinant antibodies. Recombinant antibodies offer advantages over traditional polyclonal antibodies or monoclonal antibodies in terms of ease of production, increased repertoire for selection, and versatility. Generally, depending on the antibody-analyte binding is monitored via displacement of a labeled antigen or directly, immunoassays are classified in two different categories: competitive and noncompetitive. The basic procedures for common competitive immunoassays and noncompetitive immunoassays are illustrated in Figure 2. In competitive immunoassays, the labeled analyte competes with the analyte for the antigen binding sites of the antibody. The competitive immunoassays are often simple and fast, benefiting from their one-step immunoreaction. The sensitivity of a competitive immunoassay is determined by the affinity of the antibody for its antigen. In noncompetitive immunoassays (mostly sandwich immunoassay), a significant excess of antibodies over the antigen is used. Here, diffusion processes are much more important than the affinity of the antibody used. Noncompetitive methods are potentially capable of measuring concentrations that are several orders of magnitude lower than their respective competitive immunoassay (Jackson & Ekins, 1986). Moreover, noncompetitive immunoassays generally have a larger working range and higher accuracy than that of

competitive immunoassays. Depending on whether the immunoreaction occurs on a solid phase or in solution, immunoassays can also be classified into homogeneous and heterogeneous formats. Homogeneous immunoassays rely on a change in the activity of the labeled immunoreagent that occurs when the antigen binds with antibody to form immunocomplex, and do not require any separation step. In contrast, heterogeneous immunoassays require a physical separation of the labeled immunoreagent bound to the immunocomplex from the free labeled immunoreagent. Typical solid phases, including microtiter plates, membranes, and tissue sections, are applied to facilitate the physical separation. Although this separation step complicates the procedure, the heterogeneous immunoassays often provide superior limits of detection to homogeneous immunoassays, making them the most frequently adopted methods. In recent years, immunoassays have been adapted to separation techniques such as chromatography, electrophoresis, and microfluidic chip. Usually a highly sensitive detector is situated downstream of the separation device and detects the labeled immunoreagents.

III. ICPMS-BASED QUANTITATIVE IMMUNOASSAY Immunoassay is a very important method for detecting and measuring specific proteins or other substances through their properties as antigens or antibodies. For the ultimate purpose of

FIGURE 2. Two representative immunoassay formats: (A) heterogeneous competitive immunoassay, and (B) heterogeneous noncompetitive (sandwich) immunoassay in microtiter plates.

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human disease diagnosis and therapy, novel antibody-based immunoassays have been proposed to identify and locate intracellular and extracellular proteins, to separate proteins from other molecules in a cell lysate, as well as to detect and quantify proteins. In principle, immunoassays are based on the use of an antibody that reacts specifically with the substance (antigen) to be tested, and quantification is generally achieved by measuring the specific activity of a label, that is, its radioactivity, enzyme activity, fluorescence, or chemiluminescence. To obtain special detectability, the labeling reagents often require laborious design and synthesis, which limited their availability and made them considerably expensive. In addition, the maintenance of their stabilities is also challenging. What’s more, the development of sensitive and simultaneous multianalyte immunoassays is of great significance and urgently needed, since only the comprehensive survey of vast number of biomarkers can provide accurate clinical diagnosis. However, conventional immunoassay detection methods, such as radioimmunoassay, fluorescence immunoassay, and chemiluminescent immunoassay are often challenged by limited dynamic range, low sensitivity, and the overlap of detection signals. Thus, the parallel single-analyte immunoassay is the current dominating clinical method. To overcome problems associated with the radioisotopic, fluorescent, or enzyme labels, element-tagged immunoassays by using atomic spectrometry detection were proposed 30 years ago (Cais et al., 1977). The detection is based on the intrinsic elemental composition of labeling reagents (atomic spectrometry), thus largely alleviate the worry about their synthesis and stability. However, due to either the lack of multiplex potential or low sensitivity, the detection by atomic spectrometry including atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), and atomic emission spectrometry (AES) are useful but not attractive (Mariet et al., 1990; Remy et al., 1991; Wang et al., 2001; Wu et al., 2007; Liang et al., 2011a; Liu et al., 2012b; Tung et al., 2012). Only after the distinct merits of multiplex potential and high sensitivity were brought by ICPMS, the combination of atomic spectrometry and element-tagged immunoassay opened up a new avenue for quantitative bioanalysis. Practically, more than 100 ICPMS discernible elemental isotopes could be employed for antibodies labeling, which endow a highly multiplexing potential. Moreover, the barcode “Suspension Array” technique can be adopted to provide an even more fascinating future of high throughput immunoassay (Han et al., 2001). The published applications of ICPMS-based immunoassay for quantitative bioanalysis are summarized in Table 2.

A. Metal Ions as Labels for ICPMS Immunoassay In the year 2001, Zhang’s group reported the pioneering works of ICPMS-based immunoassay for thyroid stimulating hormone (TSH) and total thyroxine (T4) quantitative determination (Zhang et al., 2001, 2002a). Europium macrocyclic compound (N’-(p-isothiocyanatobenzyl)-diethylenetriamine-N1, N2, N3, N3-tetraacetate-Eu3þ, DTTA-Eu3þ), which is often used as a tag in TRF-IA (Bunzli, 2010), was used as an elemental tag linked to antibody and subsequently detected by ICPMS. The rare earth element Eu resulted in low blank signal, due to its very low natural concentration in biological matrices. The results obtained by this method correlated well with those obtained by the traditional radioimmunoassay and chemiluminescent Mass Spectrometry Reviews DOI 10.1002/mas

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immunoassay. The analytical figures of merit, that is, limit of detection, linear range, relative standard deviation, etc., are comparable with those of traditional methods. Careri et al. determined peanuts allergen in food samples (Careri et al., 2007) and conducted a comparison of the ICPMSbased immunoassay and LC/electrospray ionization (ESI)-MS/ MS methods (Careri et al., 2008). The method can detect low amounts of peanuts (approximately 2 mg peanuts g1 cerealbased matrix) by using an Eu tagged antibody (Careri et al., 2007). While applied to complex sample matrix, the main limitation of LC/MS/MS method was related to the ESI source, which led to an inaccurate quantitative result. On the other hand, in the ICPMS-based method, no significant instrumental drawbacks were observed except the memory effect of the injection valve, and the inaccuracy was derived from the immunoassay. Much better limit of detection was obtained with ICPMS-based immunoassay even by using an antibody not optimized for ICPMS immunoassay (Careri et al., 2008). In another study, carcinoembryonic antigen (CEA) was measured by using mercury labeled antibody (Peng et al., 2011). Before element tagging, mercury was chelated with diethylenetriamine pentaacetic acid (DTPA) (log K ¼ 26.4), which is often used in the field of radio pharmacology for the covalent modification of proteins and peptides. Magnetic nanoparticles were used as the support of immobilized proteins due to their advantages of enhanced specific surface area and fast separation by the application of a magnetic field. Ferrocene containing Fe element in the center of dicyclopentadienyl has been widely used in electrochemistry as a mediator to enhance the electron transfer between electrode and solution. When it is used in quadrupole (q) ICPMS immunoassay, the dynamic reaction cell (DRC) and/or collision cell apartment should be applied to alleviate isobaric interferences from various polyatomic ions. The DRC ICPMS-based immunoassay (Deng et al., 2002) using ferrocene as label for the determination of 2,4-dichlorophenoxyacetic acid in the dynamic range of 0.1–1,000 ng mL1 was presented by Deng et al. Generally, the most published metal ion labels for ICPMSbased immunoassay are adopted from traditional immunoassays, such as iodine compounds from RIA, lanthanides macrocyclic compounds from TRFIA. The metal labels should be sensitive for ICPMS detection and possess low isobaric interferences (Liu et al., 2013). Some other widely used metal ion labels, such as organic mercury compounds (Takatera & Watanabe, 1993; Kutscher & Bettmer, 2009; Xu et al., 2010) bis (pyridine)iodonium tetrafluoroborate, (Navaza et al., 2009), ruthenium-NHS ester (Liu et al., 2012a), etc., may also be adopted to ICPMS-based immunoassay with good applicability. However, these adopted metal labels often bring high steric hindrance (such as macrocyclic compounds) or high toxicity (such as mercury compounds). Therefore, the research on special designed metal ion labels for ICPMS immunoassay is also of great importance.

B. Metal Nanoparticles and Polymer-Based Elemental Tags for Sensitive ICPMS Immunoassay

1. Nanoparticles Nanoparticles tags for ICPMS-based immunoassay have intrigued many research interests. The beauty of ICPMS for 377

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Table 2. The applications of ICPMS-based immunoassay for quantitative bioanalysis Analyte

Immunoreaction type

Elemental tag

LOD

Reference

Thyroid stimulating hormone

Microwells/Sandwich

Eu-labeled streptavidin

0. 5mIU L-1

(Zhang, et al., 2001)

Thyroxin

Microwells/Competitive

Eu-labeled streptavidin

7.4 ng mL-1


2,4-dichlorophenoxyacetic acid


Fe labeled antibody

0.044 ng mL-1

(Deng, et al., 2002)

Peanut allergens

Microwells/Indirect

Eu labeled rabbit anti-mouse antibody

1.5 ng mL-1 (solution) 2.2 μg g-1 (peanut matrix) -1

(Careri, et al., 2007; Careri, et al., 2008)

CEA

Magnetic beads/Sandwich

Hg labeled antibody

0.041 ng mL

Goat anti E. coli

Microwells

Iodine labeled antibody

120 ng mL-1

(Li et al., 2010)

Rabbit anti-human IgG

Microwells/Sandwich

Au NPs labeled antibody

0.4 ng mL-1


Human IgG

Filter

Goat anti-human Fab' -nanogold

3 ng mL-1

Human IgG

Protein Sepharose A

Goat anti-human Fab' -nanogold

0.075 ng mL-1

AFP

Microwells/Sandwich

Eu-labeled antibody

0.22 ng mL-1

hCG

Microwells/Sandwich

Eu-labeled antibody

0.0023 kU L-1

Estriol


Eu-labeled antibody

2.5 nmol L-1

Human vascular endothelial growth factor

Microwells/Sandwich


0.029 ng mL-1

Anti-erythropoietin antibody

Microwells/Sandwich


10.7 ng mL-1

(Lu, et al., 2009)

Ochratoxin A



0.003 ng mL-1

(Giesen et al., 2010)


0.2 pmol

(Merkoci, et al., 2005)

Au NPs labeled oligonucleotide probe

80 zmol

(Hsu, et al., 2011)

Peptide-modified DNA

Nitrocellulose membrane/Noncompetitive

(Peng, et al., 2011)

(Baranov, et al., 2002)

(Thompson, et al., 2010)

Virus-specific RNA


Human α-thrombin


AuNPs labeled aptamer

0.5 fmol

(Zhao, et al., 2009)

E. coli O157:H7 cell

Homogeneous


500 CFU mL-1

(Li, et al., 2010)

Chloramphenicol



4.52 ng mL-1

Human IgG Transferrin adduct CEA

Immunoaffinity

CdSe NPs labeled antibody

chromatography/Sandwich Immunoaffinity chromatography On

chip/Magnetic

Ru drug labeled transferrin adduct

with

ETV-ICPMS detection

PbS NPs labeled antibody

0.058 ng mL-1 (Cd), 0.097 ng mL-1 (Se) -

(Jarujamrus, et al., 2012) (Chen, et al., 2010) (Hann et al., 2010)

0.058 ng mL

-1

(Chen, et al., 2011)

-1

Progesterone


CdSe/ZnS QDs labeled antibody

0.028 ng mL

(Bustos, et al., 2012)

Prostate-specific antigen

Magnetic nanoparticles

TiO2 nanoparticles

1.16 fg mL-1

(Cho& Lim, 2013)

Au NPs

0.03 ng mL-1

(Liu, et al., 2011)


0.016 ng mL-1

(Hu, et al., 2009)


0.1 ng mL-1

(Liu, et al., 2010)


1 pmol

(Han, et al., 2011)

AuNPs and Eu labeled antibody

-

(Quinn, et al., 2002)

Eu labeled antibody

1.2 ng mL-1

Sm labeled antibody

1.7 ng mL-1

CEA

AFP

Rabbit-anti-human IgG

DNA Smad2, Smad4, Human IgG, Met-3xFLAG™-BAP

AFP hCG

Microwells/Sandwich

with

Ag

enhancement Microwells/Competitive with single particle ICPMS Microwells/Sandwich with single particle ICPMS Homogenous/Sandwich with single particle ICPMS Microwells/Maleylation

Microwells/Sandwich

Growth factor PDGF-AA

Microwells/Maleylation

Tb labeled antibody

p53 protein

Microwells/Sandwich

Tm labeled antibody

p53 DNA-binding

Microwells

Tm labeled antibody

α-fetoprotein (AFP) Human chorionic gonadotropin (hCG) Carcinoembryonic antigen (CEA)

378

Liquid phase with SEC-ICPMS detection

(Razumienko, et al.,

-

2008) -1

Pr-labeled AFP antibody

8.2 ng mL

Eu-labeled hCG antibody

3.0 mIU mL-1

Gd-labeled CEA antibody

2.6 ng mL


-1

(Terenghi, et al., 2009)



&

Table 2. (Continued) Ovarian tumor antigen (CA125 /MUC6)

Ho-labeled CA125 antibody

6.02 IU mL-1

Gastrointestinal tumor antigen (CA19-9)

Tb-labeled CA19-9 antibody

8.5 IU mL-1

Eu labeled monoclonal antibody

0.01

(Hutchinson et al.,

Sm labeled monoclonal antibody

0.02

2004)

Au NPs labeled aptamer

1.5 fmol

Ag NPs labeled antibody

5.5 fmol

Free prostate specific antigen (IPSA) Total prostate specific antigen Cytochrome c Insulin Messenger RNAs

α-chymotrypsin

Flow injection/Sandwich

Magnetic microparticles

Streptavidin

Streptavidin

and metalloprotease-10

bead/Homogenous

Chymotrypsin DNA

labeled streptavidin agarose

bead/Homogenous

Calpain-1, caspase-3, matrix metalloprotease-9, a disintegrin

Trypsin

Au NPs and Eu labeled antibody, Tb

In situ hybridization

substrate agarose

Human stem cell factor receptor c-Kit

SiO2 NPs / Homogenous

Cell surface antigen CD38, CD110, CD61, CD45, CD54, CD49d Cell surface antigen CD33, CD34, CD38, CD45, CD64, HLA-DR

2006) (Lathia, et al., 2010)

-

(Lathia, et al., 2011)

0.5 pM - 0.12 nM

Tb labeled chymotrypsin specific peptide

1.3 pM - 0.42 nM

isotopes labeled oligonucleotides

(Ornatsky, et al.,

2 pM

Ho labeled trypsin specific peptide

Rare-earth elements, indium, and stable

Magnetic microparticles

0.5 pM -2 pM

(Yan, et al., 2011)

(Han, et al., 2013)

Au NPs labeled antibody Sm labeled antibody

Immunophenotyping

Eu labeled antibody

Integrin receptor VLA-4 Cell surface antigen CD33, CD34, CD38, CD45, CD54

Tm, Gd, Tb, Ho labeled protease specific peptide substrate

Intracellular oncogenic kinase BCR/Abl Myeloid cell surface antigen CD33

Lu labeled chymotrypsin specific peptide

-

(Liu& Yan, 2011)

-

(Ornatsky, et al., 2006)

Tb labeled antibody Immunophenotyping

Pr, Tb, Ho, Eu, Tm labeled antibody

-

(Lou, et al., 2007)

Immunophenotyping

La, Eu, Dy, Ho, Nd, Pr labeled antibody

-

(Tanner, et al., 2007)

Pr, Tm, Ho, Tb, Eu, Eu, Sm labeled

Immunophenotyping

antibody

-

(Ornatsky, et al., 2008) (Ornatsky, et al.,

Cell surface antigen CD34, CD33, HLA-DR, CD45

Immunophenotyping

Tm, Pr, Sm, Tb labeled antibody

-

Glycoproteins

Glycoprofiling

Tb, Eu, Gd, Yb, Dy labeled lectins

-

(Lelpold, et al., 2009)


0.2 amol for antibody

(Muller, et al., 2005) (de Bang, et al., 2013)

Mre-11 protein Plant thylakoid proteins AFP CEA Human IgG

lmmunohistochemistry

with

LA-ICPMS Western blots with LA-ICPMS Microarrays/Sandwich LA-ICPMS

with

Lanthanide-labeled antibodies

-

Sm labeled antibody

0.20 ng mL-1

Eu labeled antibody

0.14 ng mL-1


0.012 ng mL-1

2008)

(Hu, et al., 2007)

Holoceruloplasmin

Microarrays with LA-ICPMS

Cu inside holoceruloplasmin

126 nM

(Joo& Lim, 2012)

Cytochromes

Microarrays with LA-ICPMS

Lanthanide-labeled antibodies

0.003-0.734 amol

(Waentig, et al., 2013)

nanoparticle detection is that high sensitivity can be easily obtained because of large quantities of detectable atoms in each nanoparticle tag (for instance, ca. 30,000 Au atoms in an Au NPs of 10 nm diameter). Among the nanoparticles, colloidal Au nanoparticles are ideal markers in bioanalytical systems for several reasons: first, they can be readily prepared in a wide range of diameters, from approximately 2 nm to above 100 nm; second, the specific activities of biomolecules can be retained when coupling biomolecules to colloidal Au nanoparticles; third, the gold particles can be easily visualized within biological entities in the transmission electron microscopy with high contrast (Zhang et al., 2002b). Using gold nanoparticles tag instead of lanthanide ions, enhanced sensitivity was first reported by Zhang et al. (2002b). A limit of detection of 0.4 ng mL1 was achieved for rabbit anti human IgG. Almost at the same time, Baranov et al. investigated four different ICPMS-based immunoassays (using centrifugal filtration, protein A affinity, size exclusion gel filtration, and ELISA) by employing Au nanoparticles and Eu ions tags to produce a fast and efficient means for detecting proteins of interest with exceptional sensitivity and precision in complicated biological samples (Baranov et al., 2002a). Thanks to the Mass Spectrometry Reviews DOI 10.1002/mas

high sensitivity endowed by Au nanoparticles, ICPMS-based bioassay have found applications for different analytes, including chloramphenicol (Jarujamrus et al., 2012), c-myc peptide contained oligonucleotides (Merkoci et al., 2005), virus-specific RNA (Hsu et al., 2011), anti-erythropoietin antibodies (Lu et al., 2009), human alpha-thrombin (Zhao et al., 2009b), human vascular endothelial growth factor (Thompson et al., 2010), and even Escherichia coli O157:H7 bacteria (Li et al., 2010a). Besides Au NPs, Hu et al. reported CdSe NPs (Chen et al., 2010) and PbS NPs (Chen et al., 2011) labels for the ICPMSbased immunoassay. The immunoaffinity monolithic capillary microextraction using CdSe NPs labels coupled with microconcentric nebulizer ICPMS was proposed for the determination of human IgG in human serum. The established method presented LODs of 0.058 ng mL1 based on the Cd signal and 0.097 ng mL1 based on the Se signal. After PbS NPs labeling, a microfluidic chip magnetic immunoassay in combination with electrothermal vaporization (ETV) ICPMS was proposed for the determination of CEA. The concentrations of CEA can be correlated with that of acid dissolved PbS NPs. A LOD of 0.058 ng mL1 was obtained for CEA determination. SanzMedel et al. reported a critical appraisal of elemental mass 379

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spectrometry and molecular fluorescence detection for quantum dots based immunoassays (Bustos et al., 2012). Adequate agreement between results obtained using both elemental and molecular techniques for the determination of progesterone in cow milk has been obtained. Moreover, results from the comparison showed that fluorescence detection of the QDs is simpler, less time-consuming, and less expensive. However, ICPMS detection affords internal validation, matrix-independent quantification, and better sensitivity. IC10 of 0.028 ng mL1 using ICPMS was obtained, versus 0.11 ng mL1 using conventional fluorimetric detection, just by using lower reagents concentrations. Although sensitive, the disadvantage of using nanoparticle in ICPMS-based immunoassay is that nanoparticles often have a high affinity to the surfaces of immunoreaction vessels and/or typical ICPMS sample introduction system (Baranov et al., 2002a). However, it was observed that this effect is significantly reduced in the presence of proteins in a sample, probably due to complexation and/or passivation of surfaces. Continuing efforts are required to alleviate the interference of nonspecific binding, by careful design and optimization of blocking reagents such as bovine serum albumin, milk, Tween 20, Triton X-100, sodium dodecyl sulfate (SDS), polyvinylalcohol (PVA), polyvinylpyrrolidone (PVP), and polyethyleneglycol (PEG) (Zhang et al., 2011). Moreover, compared to noncovalent binding (often used in Au NPs bioconjugating), the formation of NP conjugates via controllable covalent chemisorption methods may be preferable to unspecific physisorption in terms of stability and reproducibility of the surface functionalization.

2. Polymer-Based Elemental Tags Owing to the delicate control of organic synthesis, a polymerbased elemental tag (MAXPARTM, DVS Sciences, Inc., Sunnyvale, Canada) for highly sensitive ICPMS immunoassay, possessing 33 units per chain, was developed by Lou et al. (as shown in Fig. 3) (Lou et al., 2007). The use of a metal-chelating polymeric tag allows incorporating multiple numbers of a given ion, which leads to an increase in the sensitivity, since the ICPMS signal increases linearly with the number of atoms of a given element. Ornatsky et al. investigated the possibility of using these polymer-based elemental tags for protein detection and quantification in microwells format, and compared the results with conventional immunoassays, such as ELISA and Western blotting (Razumienko et al., 2008). The technique was further employed to measure low levels and DNA-binding activity of transcription factor p53 in leukemia cell lysates through its interaction with immobilized oligonucleotides and recognition by element-tagged antibodies. To increase the number of metal binding sites per polymer chain for further sensitivity enhancement, the metal chelating polymers was synthesized with a high degree of polymerization, high diethylenetriaminepentaacetic acid (DTPA) functionality (Majonis et al., 2010, 2011), and a maleimide as an orthogonal functional group for conjugation to antibodies. Isothermal titration calorimetry (ITC) results showed each polymer chain binds 68 7 lanthanide ions. Secondary goat anti-mouse IgG was covalently labeled with the maleimide form of the DTPA polymer carrying 159Tb. ICPMS analysis of this conjugate showed each antibody carried an average of 161 4 159Tb 380

FIGURE 3. Experimental design for tagging antibodies with metal-chelating polymers. The antibody of interest is subjected to selective reduction of –S–S– groups to produce reactive –SH groups, which are reacted with the terminal maleimide groups of a polymer bearing metal-chelating ligands along its backbone. The polymer-bearing antibodies are purified, treated with a given lanthanide ion, and then purified again. Each type of antibody is labeled with a different element (Lou et al., 2007). Reproduced by permission of John Wiley and Sons.

atoms. This result combined with the ITC result show that there are 2.4 0.3 polymer chains on average attached to each antibody. Eleven monoclonal primary antibodies were labeled with different lanthanide isotopes using the same labeling methodology. The polymer-based ICPMS immunoassays feature increased sensitivity, wide dynamic range, and minimal interference from complex matrices. Since large number of elements and isotopes present in low abundance in biological systems, multiple polymer tags can be used simultaneously for high throughput multianalyte immunoassay.

3. Single Nanoparticle Analysis or Signal Amplification for Further Sensitivity Enhancement Since even a few molecules of proteins are sufficient to affect the biological functions of cells and trigger pathophysiological processes, a highly sensitive technique for protein quantification plays an important role in the early diagnosis and elucidation of molecular mechanisms for many diseases. Commonly, the labeled nanoparticles are detected by using traditional integral mode detection as analytes dissolved in solution. Those methods are not sensitive enough to achieve ultrasensitive detection and ultimately single molecular detection, thus further sensitivity enhancement are expected. The feasibility of using single nanoparticle analysis by ICPMS in a time resolved analysis (TRA) mode for the immunoassays of AFP and rabbit anti human IgG has been studied by Zhang et al. (Hu et al., 2009; Liu et al., 2010). The transient signals induced by the flash of ions arising from the ionization of nanoparticles in the plasma torch Mass Spectrometry Reviews DOI 10.1002/mas


can be detected and measured by the mass spectrometer individually as only one transient appears during a given dwell time. The frequency of transient signals is directly correlated to the concentration of nanoparticle tags, and thus the concentration of nanoparticle-tagged antibodies can be quantified by the frequency of transient signals. Characteristics of the signals obtained from Au-NPs of 20, 45, and 80 nm in diameters were discussed. The analytical figures of merit for the determination of Au-labeled IgG using ICPMS in conventional integral mode and single particle mode were compared in detail (Liu et al., 2010). This single particle mode ICPMS analysis affords the possibility of developing highly sensitive immunoassay strategies. The limit of detection is 0.016 ng mL1 for human AFP and 0.1 ng mL1 for rabbit-anti-human IgG after immunoreactions. A method for one-step homogeneous DNA assay has been proposed using single nanoparticle analysis of ICPMS, as shown in Figure 4 (Han et al., 2011). The first step was to functionalize citrate protected AuNPs with two sets of single-stranded DNA, probe 1 and probe 2. Then DNA targets were hybridized with AuNP-probe 1 and AuNP-probe 2 in buffer solution. The contact of DNA targets with DNA probes immobilized on the surface of the AuNPs resulted in the formation of dimers, trimers, or even large aggregates of AuNPs. This polymeric network aggregation led to decreased concentrations of the whole AuNPs population as well as increased individual sizes. These changes were detected by single particle ICPMS quantitatively, and thus the amount of DNA was obtained. The solution of AuNP aggregates was introduced into the plasma torch by the nebulizer and then AuNPs underwent desolvation, particle vaporization, atomization, and ionization in the ICP zone at approximately 7,500– 10,000 K. Finally, the frequency and intensity of the 197Auþ pulse signals were recorded. With this method, DNA at concentration as low as 1 pM could be detected. Besides single nanoparticle detection, high sensitivity can also be obtained using a signal amplification procedure (Liu

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et al., 2013). To further improve the sensitivity for human CEA, an immunogold-silver enhancement method has been developed for signal amplification (Liu et al., 2011). After a 15 min signal amplification procedure, the LOD of the method was around two orders of magnitude lower than that by the widely used ELISA, and one order of magnitude lower than that by clinical routine CLIA or TRFIA. Other signal amplification schemes (Lei & Ju, 2012), such as rolling circle amplification, avidin–biotin amplification, and exponential isothermal amplification, may also exhibit some intriguing advantages for bioanalyte analysis by coupling to the sensitive ICPMS immunoassay.

C. Multiplex Immunoassay Simultaneous multianalyte determinations are important for biological studies. Multianalyte immunoassays present several advantages, such as low sample consumption, reduced analysis time, minimized repetitions of tedious procedures, and low cost per test. The limitations of the reported approaches in the literatures for multianalyte simultaneous determination include difficulty in finding a sufficient number of suitable labels that can be prepared easily and can be detected distinctly with similar sensitivities by a single detection technique. As shown in Figure 1, more than 100 stable isotopes can be detected by ICPMS with high sensitivities. As an excellent element specific detection technique, ICPMS offers parts per billion to parts per trillion detection limits for most elements. Elements such as rare earths and noble metals, as well as some of the transition metals, have the highest sensitivity with detection limits down to parts per trillion. Those elements, their stable isotopes, or the unique combination of them are candidates for labeling bioactive molecules, especially those that occur at naturally low concentrations in the body and environment. Simultaneous determination of proteins using an element tagged immunoassay coupled with ICPMS detection was first achieved for IgG and FLAG-BAP by Tanner et al. using AuNPs

FIGURE 4. DNA hybridization assay with AuNPs probes using single particle analysis by ICPMS (Han et al., 2011). Reproduced by permission of John Wiley and Sons.


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and Eu3þ labels (Quinn et al., 2002). It was demonstrated that at least two target proteins can be determined simultaneously, yielding a linear response for both proteins in a concentration range of 2–100 ng mL1 using a sample volume of 0.5 mL. Later, to illustrate the applicability of this method for multianalyte analysis in clinical samples, simultaneous determination of AFP and hCG in clinical human serum samples was realized by Zhang et al. using Eu3þ and Sm3þ labels (Zhang et al., 2004). The measurable ranges of AFP and hCG were 4.6–500 and 5.0– 170 ng mL1, respectively, with detection limits of 1.2 and 1.7 ng mL1, respectively. A homogeneous immunoassay was developed for the simultaneous determination of five cancer biomarker proteins: AFP, human chorionic gonadotropin, CEA, ovarian tumor antigen (CA125/MUC16), and gastrointestinal tumor antigen (CA199) followed by size exclusion chromatography (SEC) separation (Terenghi et al., 2009). The method was based on the incubation of a serum (or tissue cytosol) with five antibodies, each labeled with a different lanthanide (Pr3þ, Eu3þ, Gd3þ, Ho3þ, and Tb3þ, respectively) followed by the specific determination of the immunocomplex by SEC-ICPMS. The sensitivity of the method was comparable to that of ELISA or radioimmunoassay, but with the advantages of multiplexed analysis capacity and virtually no sample preparation needed. To get a highly sensitive and specific detection of multiple biomarkers simultaneously in biological samples, multiple nanoparticles can be employed, as long as they have high sensitivity and interferences free for ICPMS detection, occurring at naturally low concentrations in the body and the environment, and having good biocompatibility as well as the ability to easily conjugate to biomolecules. For example, aptamer modified gold nanoparticles and antibody modified silver nanoparticles have been employed as specific element tags for cytochrome c and insulin, with high sensitivities (Liu & Yan, 2011). The surface functionalized magnetic microparticles were used to achieve efficient and fast magnetic separation. Under optimal conditions, the developed method had LODs of 1.5 fmol for cytochrome c and 5.5 fmol for insulin, respectively. Furthermore, Nitz et al. have carried out ICPMS-based multiplex profiling of glycoproteins using lectins conjugated to lanthanide chelating polymers (Lelpold et al., 2009). After in situ hybridization, commercial antibodies conjugated to Eu and gold NPs together with biotinylated oligonucleotide probes reacted with terbium labeled streptavidin, were used to demonstrate simultaneous mRNA and protein detection by ICPMS in leukemia cells (Ornatsky et al., 2006a). The single and multiplexed protease assays were realized by Nitz’s group (Lathia et al., 2010; Lathia et al., 2011) and Wang’s group (Yan et al., 2011), separately. A lanthanide-coded protease-specific peptidenanoparticle probe was well designed as shown in Figure 5 (Yan et al., 2011). This technique gave a new way for efficient and accurate label free multiplex protease assay. Absolute and relative quantification of multiple DNAs based on elemental labeling was accomplished by Zhang et al. (Han et al., 2013) Rare-earth elements, indium, and stable isotopes macrocyclic compounds were labeled to oligonucleotides serving as DNA probes. Fifteen clinical diseases (cancer, heredopathia, and virus) associated DNA targets were simultaneously detected. Despite the need of more practices in various clinical and biological sample matrices, the ICPMS-based immunoassay has 382

demonstrated several significant benefits compared to other routine methods in quantitative bioanalysis: 1. Owning to its specific and multi-element detection capability, ICPMS provides a great potential for multiplex immunoassays. 2. ICPMS as a readout tool does not require tags to possess the optical, electric, electrochemical, magnetic, or any other special properties since atoms from tags are directly discriminated and detected. This feature greatly eases the difficulty of tag synthesis and subsequently endows a vast availability of tags. 3. ICPMS provides high sensitivity and stability for the determination of elemental and isotopic tags. 4. ICPMS processes wide dynamic linear ranges for elemental and isotopic tags, which is of great importance, since the difference between high abundance and low abundance proteins in a biological sample can span up to twelve orders of magnitude (Corthals et al., 2000). 5. Selected target elements usually do not exist in sample matrices, resulting in low background and high signal to noise ratio. Unlike optical signal derived from reflection of sample vessel or biological matrices, the only background signals of ICPMS are originated from nonspecific binding. 6. High sensitivity can be easily obtained by the use of the nanoparticle tag instead of metal ions, due to large quantities of detectable atoms in each nanoparticle tag. In addition, signal amplification is easily obtained. However, there are a few disadvantages associated with the use of ICPMS as a detector. ICPMS is relatively expensive and complex to use, and thus operators need special training. Most ICPMS users are inorganic analytical chemists or geologists that not familiar with bioassays, thus more interdisciplinary collaborations are expected for the further development of methods for quantitative bioanalysis.

IV. ICPMS-BASED MASS CYTOMETRY FOR SINGLE CELL ANALYSIS AND SUSPENSION ARRAY A. Single Cell Analysis Over the past two decades, fluorescence-based flow cytometry has become a mainstay of biological and clinical single cell research (Janes & Rommel, 2011). The unambiguous functional and phenotypical identification of cells in heterogeneous populations requires quantitative determination of many biomarkers simultaneously in individual cells. A similar requirement for multiparameter assays is shared by genomic and proteomic researchers interested in understanding the complex interaction of many genes, proteins, and small molecules which lead to the transformation of a normal cell into a disease causing cell. Antibodies targeting markers of interest are labeled with different color fluorophores, allowing the markers to be quantified and thus yielding insights into what defines a cell subtype or activation of a specific pathway in a cell subtype. Although hundreds, if not thousands, of fluorescent dyes are currently available for such measurements (i.e., organic dyes or quantum dots), the main limitations of the existing flow cytometers are related to the spectral overlap between signals from fluorescent labels used in analysis, although the quantum dots have a Mass Spectrometry Reviews DOI 10.1002/mas


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FIGURE 5. A: Synthesis of an Ln-coded protease-specific peptide–NP probe. B: Protease assay procedures (Yan et al., 2011). Reproduced by permission of John Wiley and Sons.

narrower emission bandwidth (30 nm full width at halfmaximum). The spectral overlap between these options routinely limits the capacity of flow cytometry to simultaneous quantification of commonly only six to ten parameters (Chattopadhyay et al., 2008). After the careful design of multiple lasers with panels of antibodies tagged with either dyes or quantum dots that fluoresce at different wavelengths, up to 18 distinct antigens is allowed to be identified simultaneously from a sample (Chattopadhyay et al., 2006). However, the complications caused by signal overlap and cellular autofluorescence require a considerable amount of optimization for this level of multiplexing. Intrigued by the multiplexing potential of ICPMS-based immunoassay, Tanner et al. made continuing efforts on multiple cellular antigen detection, towards a massively multivariate single-cell technology (Ornatsky et al., 2006b, 2008a,b; Tanner et al., 2007). The multi-element simultaneous detection capability of ICPMS provides a great innovation to conventional fluorescence-based cytometry. Towards this destination, they first developed an ICPMS-linked metal-tagged immunophenotyping for four-plexed proteomic analysis (Ornatsky et al., 2006b). Expression of intracellular oncogenic kinase BCR/Abl, Mass Spectrometry Reviews DOI 10.1002/mas

myeloid cell surface antigen CD33, human stem cell factor receptor c-Kit, and integrin receptor VLA-4 were investigated using model human leukemia cell lines. Four commercially available tags (Au, Sm, Eu, and Tb) conjugated to secondary antibodies enabled the assay. Results obtained by ICPMS were validated by comparing with the data from fluorescence activated cell sorter. They further used commercially available secondary immunolabeling reagents for leukemic cell lines (Tanner et al., 2007; Ornatsky et al., 2008a). Multiplex analysis was shown with tag reagents based on functionalized carriers that bind lanthanide ions. DNA quantification using metallointercalation allowed for cell enumeration or mitotic state differentiation. In situ hybridization permitted the determination of cellular RNA. The results provided a feasibility basis for the development of a multivariate assay tool for individual cell analysis based on ICPMS in a cytometer configuration. Though commercial quadrupole ICPMS has long been used for cell uptake analysis (deLlano et al., 1996; Andreu et al., 1998; Koellensperger et al., 2009; Vancaeyzeele et al., 2007), and single cell metal uptake analysis has been carried out (Ho & Chan, 2010; Tsang et al., 2011), this technique could not be applied to multielement analysis in individual intact cells for 383

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several reasons (Ornatsky et al., 2010). The quadrupole mass analyzer in common ICPMS has a settling time of 50–300 msec for stabilization of the mass filter between individual isotope measurements. This time is comparable to the duration of the ion cloud produced in the argon plasma from an individual microparticle or cell (Degueldre et al., 2006; Tanner et al., 2007). Consequently, the measurement of two or more isotopes during a transient event of such short duration is virtually impossible with available quadrupole mass spectrometry instruments. The required sampling frequency of the cell-induced transient should be 50,000–100,000 spectra/sec to obtain ten or more individual spectra per cell (typically, 200–300 msec per cell), to discriminate the transients from overlapping cells. Thus, scanning instruments like quadrupole MS or scanning sector field MS are fundamentally restricted (Tanner & Gnther, 2009). A new type of instrument is required to interrogate individual cells. Multiple collector sector field MS is capable of monitoring multi-isotopes in a short transient. However, drifting isotope ratios are observed in transient signals using these instruments (Tanner & Gnther, 2009), thus limiting the precision and leaving unknowns in quantitative results. Inductively coupled plasma time of flight mass spectrometry (ICP-TOF-MS) in principle provides fast simultaneous multi-element detection in short transients. After a series of efforts (Tanner et al., 2007, 2008; Bandura et al., 2009), Tanner et al. constructed a mass cytometry based on ICP-TOF-MS (CyTOFTM, DVS Sciences, Inc.). By circumventing the limitations of emission spectral overlap associated with fluorochromes utilized in traditional flow cytometry, mass cytometry currently allows measurement of up to 37 parameters per cell (Newell et al., 2012). The instrument comprises a three aperture plasma-vacuum interface, a dc quadrupole turning optics for decoupling ions from neutral components, a rf quadrupole ion guide discriminating against low-mass dominant plasma ions, a point-to-parallel focusing dc quadrupole doublet, an orthogonal acceleration reflectron analyzer, a discrete dynode fast ion detector, and an 8-bit 1 GHz digitizer. A high spectrum generation frequency provides capability for collecting multiple spectra from each particle-induced transient ion cloud. It was shown that the transients can be resolved and characterized individually at a peak frequency of 1,000 cells per second. The new instrument has the mass resolution (full width at halfmaximum) M/DM > 900 for m/z 159, and the sensitivity of >1.4 108 ion counts per second per mg L1 of Tb with a standard sample introduction system. The mass range (m/z, 125– 215) and abundance sensitivity are sufficient for elemental immunoassay with up to 60 distinct available elemental tags. When 500) can be used, which provides > 2.4 108 cps per mg L1 of Tb. A real-time single cell 20 antigen expression assay of model cell lines and leukemia patient samples was presented after immunolabeled with lanthanide-tagged antibodies. The metal-containing polystyrene beads of narrow bead-to-bead variation can served as standards for mass cytometry (Abdelrahman et al., 2010), to monitor instrument drift and yield consistent results. Furthermore, to illustrate the highly multi-parametric analysis by mass cytometry, researchers presented applications in leukemia patient cell type sub-classification, intracellular antigen analysis, and live/dead cell discrimination (Ornatsky et al., 2010). The logarithmic radial plots of mean intensity values for 22 metal-tagged 384

FIGURE 6. Logarithmic radial plots of mean intensity values for 22 metaltagged antibodies detected by mass cytometric analysis of human leukemia cell lines (KG1a, HL-60, Ramos, and Jurkat). All metal-labeled antibodies were combined in one mixture at predetermined concentrations (Ornatsky et al., 2010). Reproduced by permission of Elsevier B.V.

antibodies detected by mass cytometry analysis of human leukemia cell lines are shown in Figure 6. Besides the analysis of large eukaryotic cells, the mass cytometry have also been applied for the interrogation of bacteria (Leipold et al., 2011). Using a combination of a metalbased membrane stain and lectins conjugated to lanthanidechelating polymers, individual E. coli cells can be differentiated based on their cell surface polysaccharides using elementtagged concanavalin A and wheat germ agglutinin lectins. This technique enabled experiments designed to follow the export of O-antigen substituted lipopolysaccharide in a conditional mutant. These studies revealed that the culture responds as a uniform population and that lipopolysaccharide export is approximately 10 times faster than the logarithmic bacterial doubling time. In a recent article published in Science, Nolan et al. and Tanner et al. have reported the application of the single-cell mass cytometer to dissecting the functional complexity of hematopoiesis (Bendall et al., 2011). They examined healthy human bone marrow, measuring 34 parameters simultaneously in single cells (binding of 31 antibodies, viability, DNA content, and relative cell size). The workflow summary is shown in Figure 7. The signaling behavior of cell subsets spanning a defined hematopoietic hierarchy was monitored with 18 simultaneous markers of functional signaling states perturbed by a set of ex vivo stimuli and inhibitors. To extract cellular hierarchy from massive high-dimensional cytometry data, spanning-tree progression analysis of density normalized events (SPADE) (Qiu et al., 2011), as a novel algorithm that organizes cells into hierarchies of related phenotypes, was applied to facilitate the visualization of massive resulting data. In this manner, the analysis revealed previously unappreciated instances of both precise signaling responses that were bounded within conventionally defined cell subsets and more continuous phosphorylation responses that crossed cell population boundaries in Mass Spectrometry Reviews DOI 10.1002/mas


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FIGURE 7. Workflow summary of mass cytometry analysis for immune cell response patterns (Bendall et al., 2011). Reproduced by permission of American Association for the Advancement of Science.

unexpected manners yet tracked closely with cellular phenotype. In a single experiment, enough markers can be measured to identify and compare functional immune activities across nearly all cell types in the human hematopoietic lineage. In another study, the phenotypic and functional characteristics of human CD8þ T cells was analyzed by measuring 17 cell surface markers, six cytokines, two cytotoxic granule components and three viral antigen peptide-MHC tetramers on human CD8þ T cells (Newell et al., 2012). These parameters covered nine functional attributes and distinguished all reported CD8þ T-cell subsets, such as naive, central memory, effector memory, terminal effector, long-lived memory precursor effector cells and short-lived effector cells. With 3-dimensional principal component analysis (3D-PCA) to display phenotypic diversity, a relatively uniform pattern of variation in all tested subjects was observed, highlighting the interrelatedness of previously described subsets and the continuous nature of CD8þ T cell differentiation. The results illustrated a much greater functional complexity of CD8þ T cells than previously appreciated. Mass cytometry has been adapted to measurements of the cell cycle (Behbehani et al., 2012). The cyclin A and cyclin B1 were identified with the respective antibodies tagged with the transition elements. Iododeoxyuridine was successfully used as a marker of DNA replicating cells and histone H3 phosphorylated on Ser10, detected with the transition element-tagged phosphospecific antibody, was the marker of mitotic cells. The DNA intercalating ligand containing iridium was applied to mark DNA and assess its content, whereas immunocytochemical detection of phosphorylated on Ser807 and Ser811 retinoblastoma protein (Rb) epitope was helpful to distinguish cycling from noncycling (G0) cells. Sample multiplexing techniques currently used in flow cytometry, such as fluorescent cell barcoding (Krutzik & Nolan, 2006), were adapted to mass cytometry for the profiling of the cellular states perturbed by small-molecule regulators (Bodenmiller et al., 2012). Use of mass-tag cellular barcoding, allows the increase of mass cytometry throughput by using n metal ion tags to multiplex up to 2n samples. Mass Spectrometry Reviews DOI 10.1002/mas

Benefited from the high multiplexing ability, this mass cytometry is a great revolution and is believed to be a “gamechanger” and “opening a new chapter” in single cell biology (Benoist & Hacohen, 2011; Cheung & Utz, 2011; Janes & Rommel, 2011; Darzynkiewicz, 2012; Chen & Weng, 2012). The results from mass cytometry, such as antigen quantification (Wang et al., 2012), cell viability (Fienberg et al., 2012), are all validated by fluorescence-based cytometry. Like any new technology, the mass cytometry has its own limitations. These include: 1. Unlike conventional fluorescence-based cytometry, mass cytometry is a destructive technique. It can replace fluorescence cytometry in multiplex cell analysis, but cannot perform cell sorting. 2. The sample introduction system is very different from that used in fluorescence cytometry and is designed to strip the buffer from cells or beads utilizing pneumatic nebulization. The sample introduction efficiency of pneumatic nebulization is currently 30% (Bendall et al., 2012), which means only 30% of cells can be transported to the mass detector. 3. The radial dispersion of ion cloud derived from the individual cell or individual particle may cause high RSD from cell to cell (Degueldre et al., 2006). 4. In mass cytometry, cells are introduced into the hot plasma region stochastically. Two or more cells might be introduced simultaneously into the hot plasma region.

B. Mass Suspension Array Suspension array is a flow cytometry based high throughput, large-scale, and multiplexed screening platform used in molecular biology (Han et al., 2001; Pregibon et al., 2007). It has been widely applied to genomic and proteomic research, such as single nucleotide polymorphism genotyping, genetic disease 385

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FIGURE 8. Concept of the ICPMS-based suspension array (Tanner et al., 2008). Beads are synthesized containing a number of metals at various concentrations. The beads are functionalized to allow surface attachment of antibodies or antisense oligonucleotides, such that similarly encoded beads carry the same affinity reagent, and can be distinguished with differently functionalized beads of other compositions. Exposure of the beads to a cell lysate caused complexation of the antigens (proteins to antibodies, genes to oligonucleotides) that are subsequently quantified through a secondary tagging with a universal reporter element. Concomitance of the bead encoding and reporter tags identifies the antigen (bead encoding) and its quantification (reporter tag). Reproduced by permission of International Union of Pure and Applied Chemistry.

screening, gene expression profiling, drug discovery screening, and clinical diagnosis. In cytometry detection, two markers are required, that is, the “classifier” marker and the “reporter” marker. To introduce suspension array technology to mass cytometry, the elemental “classifier” and “reporter” markers should be designed and synthesized specifically for ICPMS detection. The “classifier” particles must be large (>500 nm) and monodispersed with respect to particle size, but not too large (>5 mm), to burn completely in the plasma torch. Since the composition of “classifier” particles on an individual basis is measured, the metal element (usually lanthanide) content distribution must be narrow. The “classifier” particles must be loaded with a significant quantity of lanthanide (e.g., more than 106 ions per particle) for a high quality MS signal. Finally, the particles should have a surface that permits bioconjugation of antibodies and oligonucleotides, with minimal nonspecific adsorption. The concept of the ICPMS-based suspension array is shown in Figure 8. Using a combination of surfactant-free emulsion polymerization (SFEP) and seeded emulsion polymerization (Thickett et al., 2010), lanthanide elements encoded polystyrene (PS) particles with diameters of 800 nm and with carboxyl groups on the surface were synthesized. NeutrAvidin, a deglycosylated form of avidin, was conjugated to the surface of these particles using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) chemistry. As a proof-of concept immunoassay, these particles were further functionalized via exposure to biotin-labeled immunoglobulin. These IgG-functionalized particles were able to capture goat anti-mouse IgG, which was labeled with a metal chelating polymer as a reporter group carrying multiple copies of a lanthanide ion different from that encoded in the PS particles. Although the bioassay appeared to work, the particles themselves suffered from a broad particleto-particle distribution of lanthanide ion content. This broad 386

distribution limits their resolving power and applicability in highly multiplexed immunoassays. In another approach, two-stage dispersion copolymerization of styrene and acrylic acid (AA) (Abdelrahman et al., 2009) or methacrylic acid (MAA) (Liang et al., 2011b) in ethanol in the presence of poly(N-vinylpyrrolidone) (PVP) was employed. Dispersion polymerization of styrene in ethanol in the presence of polymeric stabilizers like PVP was effective for the synthesis of particles with micrometer diameters and an exceptionally narrow size distribution. In the reactions, the 2 mm diameter mono-dispersed Ln-encoded particles were synthesized, with coefficients of variation of the diameters on the order of 1% and with narrow Ln ion distributions. In the copolymerization reactions, the AA was added to the reaction mixture 1 hr after initiation along with much smaller amounts of the relevant lanthanide salt(s) to chelate the Ln ions within the particles. The AA comonomer also provided surface carboxyl functionality, which could be quantified by conductometric titration. These reactions led to good control over the Ln loading with a relatively narrow particle-to-particle Ln distribution, which is an improvement on the seeded emulsion polymerization process. This method is effective for synthesizing beads of constant and known Ln ion composition that can be used to calibrate the mass cytometer (Abdelrahman et al., 2010). However, there are only limited numbers of biomolecules attached to the “classifier” particles synthesized in model bioassays. For example, only small amounts of NeutrAvidin could be attached to the particle surface in spite of a large number of surface COOH groups determined by titration. These particles were sterically stabilized by a corona of PVP. While this polymer is effectively suppressed nonspecific protein adsorption to the particles, PVP chains also appeared to interfere with bioconjugation to the carboxyl groups under the corona at the particle surface. The formation of poly(glycidyl methacrylate) (PGMA) shells by seeded emulsion polymerization is a very promising approach Mass Spectrometry Reviews DOI 10.1002/mas


for solving this problem (Abderahman et al., 2011). The incorporation of PGMA onto the surface of the particles increased the amount of protein conjugation by a factor of 10 or more relative to the original particles, while retaining particle colloidal stability, a narrow particle size distribution, and a low Ln ion content variation. The release of lanthanide ions from metal-encoded poly(styrene-co-MAA) microspheres and poly (styrene-co-AA) microspheres, which were synthesized by twostage or three-stage dispersion polymerizations, was systematically studied (Liang et al., 2012). The results showed that in the absence of strong chelating agents (such as DTPA and EDTA), these particles are stable against ion leakage, even upon prolonged storage and stirring. Microgels can act as transport vehicles for LaF3:Ln NPs (Ln NPs ¼ Eu, Tb, Pr, Gd NPs, or NPs mixtures) nanoparticles through fluid media. In this context, microgels can be used as an alternative for polystyrene microbeads (Pich et al., 2008; Berger et al., 2010), to attach bioaffinity reagents to the particles, which is difficult for polystyrene microbeads due to the interference of the PVP chains on the surface. The functionality was introduced during NP synthesis by employing a combination of two ligands: aminoethyl phosphate (AEP) and ethylene glycol methacrylate phosphate (EGMAP). AEP and EGMAP bind to the NP surface through the phosphate group, and provide colloidal stabilization of the NPs in water. The modification of the LaF3:Ln nanoparticle surface with reactive double bonds allows effective incorporation of the NPs into the nanogel structure. This approach ensures effective encapsulation of varying amounts of NPs into the nanogel interior with a loading efficiency close to 95%. The NPs are covalently bound to the nanogel core, and no NP leakage occurs. Hybrid nanogels with excellent colloidal and temperature-sensitive properties are easily taken up by living cells, presumably by nonspecific endocytosis. In another report, highly carboxylated microgels based upon a poly(N-isopropylacrylamide) copolymer framework with diameters of 1 mm was synthesized as a template for incorporating Eu3þ ions (Lin et al., 2011). These experiments showed that by adjusting the Eu3þ to COOH group ratio, the Eu content of the microgels could be controlled within the range of 106 to 107 Eu ions per microgel. Their application in bioconjugation and subsequent suspension array is expected. Generally, the reported work of mass cytometry based suspension arrays is still in the proof of concept stage. To illustrate its great potential, more efforts are needed in the development of applications for real biological and clinical sample matrices.

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level without any sample preparation. LA-ICPMS was introduced to element-tagged immunoassay by McLeod et al. for immunohistochemical imaging (Hutchinson et al., 2005; Seuma et al., 2008), and later symmetrically investigated by Jakubowski et al. for imaging and Western blotting (Jakubowski et al., 2008a,b; Roos et al., 2008; Waentig et al., 2009; Giesen et al., 2011a,b; Waentig, Jakubowski, & Roos, 2011a; Waentig et al., 2011b). As advocated by several recent reviews (Becker & Salber, 2010; Giesen et al., 2012; Konz et al., 2012), LA-ICPMS is expected to get valuable information for the early detection (diagnosis) and treatment (drug targets) of diseases, including cancer and neurodegenerative conditions.

A. LA-ICPMS for Imaging and Spatial Distribution Analysis The detection and imaging of b-amyloid protein in immunohistochemical sections from the brains of a transgenic mouse model of Alzheimer’s disease was first realized by McLeod et al. The distribution of b-amyloid deposits in tissue was based on

V. LA-ICPMS-BASED IMMUNOASSAY FOR SURFACE ANALYSIS Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is a powerful analytical technology that enables highly sensitive elemental and isotopic analysis to be performed directly on solid samples. LA-ICPMS begins with a laser beam focused on the sample surface to generate fine particles. The ablated particles are then transported to the secondary excitation source (ICP) of the ICPMS instrument for digestion and ionization of the sampled mass. The excited ions in the plasma torch are subsequently introduced to a mass spectrometer for both elemental and isotopic analysis. LA-ICPMS can perform fast and highly sensitive detection down to part per billion (ppb) Mass Spectrometry Reviews DOI 10.1002/mas

FIGURE 9. Multiplex LA-ICPMS images of 5 mm breast cancer tissue, simultaneously incubated with (A) HER 2 (Ho), (B) CK 7 (Tm), and (C) MUC 1 (Tb) (Giesen et al., 2011a). Reproduced by permission of American Chemical Society.

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FIGURE 10. Concomitant detection of CYP1A1 (A) and CYP2E1 (C) with a europium labeled and an iodine labeled antibody, respectively. Blot membranes were scanned and analyzed by LA-ICP-MS for 127Iþ and 153Euþ. B: The 5 and 10 mg samples as in (C) but developed via the CYP2E1-antibody by luminescence detection on the blot membrane. Samples: liver microsomes of 3-methylcholanthrene treated rats (Roos et al., 2008). Reproduced by permission of Springer.

measurement of Eu and Ni coupled antibodies. The laser-based methodologies (spot ablation, single line raster, and twodimensional imaging) were also used to detect and map trace element distributions and thus provide a novel probe for both element and protein data (Hutchinson et al., 2005). The distribution of two breast cancer-associated proteins (MUC 1 and HER 2) in tissue sections was studied based on multiple line rastering and measurement of relevant Au/Ag tagged antibodies bound to the tissue (Seuma et al., 2008). Compared to optical microscopy, LA-ICPMS technique showed extremely high sensitivity and sufficiently good resolution to permit fine scale feature mapping at the cellular level. Application to the quantitative assessment of HER 2 expression in tissue microarrays was demonstrated as well. Multiplexed immunohistochemical detection of three tumor markers (HER 2, CK 7, and MUC 1) in a 5 mm thin breast cancer tissue was reported (Figure 9) (Giesen et al., 2011a). The lanthanides were used to label primary antibodies for the subsequent LA-ICPMS detection. The single cell and cell nucleus imaging was developed by the same authors using iodine as an elemental dye (Giesen et al., 2011b). At an 388

incubation time of 60 sec, iodine is located mainly within the cell nuclei. Jakubowski et al. made contributions in protein detection by LA-ICPMS after they were element-labeled, separated by SDS–PAGE, and electroblotted onto NC membranes. Before SDS–PAGE separation, proteins were labeled with iodine (Jakubowski et al., 2008a) or lanthanides (Jakubowski et al., 2008b) directly. Detection limits at fmol level were achieved. After SDS–PAGE separation, proteins (Roos et al., 2008; Waentig et al., 2009) or whole proteomes (Waentig et al., 2011a) can be labeled with iodine or lanthanides labeled antibodies. In comparison to conventional chemiluminescence detection, the Western blotting procedure in combination with LA-ICPMS detection is less time consuming and the elemental signatures on the blots show long-term stability. More importantly, LAICPMS offers multiplexing capabilities and therefore simultaneous detection of two proteins (CYP1A1 and CYP2E1) with an europium-labeled antibody and an iodine-labeled antibody is demonstrated, as shown in Figure 10 (Roos et al., 2008). Moreover, detection of five differentially labeled antibodies in one single Western blot assay is achieved (Waentig et al., Mass Spectrometry Reviews DOI 10.1002/mas


2011b). Three commercially available labeling reagents (i.e., MeCAT, MAXPARTM, and SCN-DOTA) were compared (Waentig et al., 2012). The results shows lower fmol range LOD can be reached in the Western blot immunoassay using MeCAT and MAXPARTM as element labeling reagents, whereas even sub fmol LOD can be achieved in a dot blot experiment for the pure antibodies.

B. LA-ICPMS Quantification Similar to protein imaging, the quantification can be achieved by LA-ICPMS. After protein separation by regular 1D SDS– PAGE and transfer to a blotting membrane, the protein was marked subsequently with a primary antibody and a mouse-antirabbit antibody covalently coupled to a gold cluster (Muller et al., 2005). Quantification of the labeled antibodies was carried out by calibration using matrix matched standards. The detection limit of approximately 0.20 amol for gold cluster labeled antibody and excellent linearity were achieved. Recently, multiplexed quantification of plant thylakoid proteins on western blots was realized using lanthanide-labeled antibodies (de Bang et al., 2013). Cerium-labeled lysozyme was introduced as an internal reference protein, enabling correction for up to 50% difference in transfer efficiency during the blotting of membranes. The sensitivity of LA-ICPMS detection was comparable to chemiluminescence detection, and was further improved 20fold by using a polymer tag capable of carrying multiple labels. The strong desire of high throughput methods, together with accurate quantitative data, stimulates the combination of protein microarray technology with the multiplex ICPMS-based immunoassay. Zhang et al. demonstrated the potential of laser ablation ICPMS for the detection of multiple proteins on each spot of the immuno-microarray (Hu et al., 2007). AFP, CEA, and human IgG were detected as model proteins in sandwich format on a microarray with Sm3þ labeled AFP antibody, Eu3þ labeled CEA antibody, and Au NPs labeled IgG antibody as elemental tag. The detection limits were 0.20, 0.14, and 0.012 ng mL1 for AFP, CEA, and human IgG, respectively. This method demonstrated the possibility to detect multiple analytes on each spot of the microarray with a spatial resolution in the micrometer range. The further simultaneous analysis of eight cytochromes in reverse phase microarrays was achieved using LA-ICPMS by Waentig et al. (2013). The detection limits in the lower amol range and linearity of R2 > 0.9996 were obtained.

VI. CONCLUSIONS AND FUTURE PROSPECTS The development of new strategies for large-scale biomarker discovery and detection is one of the hottest topics in recent years. In this context, highly sensitive, high-throughput, diseasespecific antibody-based methods are used for highly specific clinical immunoassay. The combination of this approach with ICPMS, which is capable of performing sensitive and multiplex quantitative analysis, represents an excellent platform. The research of nanoparticle engineering and subsequent signal amplification will brings more excitation of higher sensitivity to ICPMS-based immunoassay. Since most ICPMS instruments are design for large volume solution analysis, the design and optimization of specific ICPMS-based instrumentation for practical clinical and biological applications are expected. After Mass Spectrometry Reviews DOI 10.1002/mas

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all, the technology is gradually becoming matured and the commercial mass cytometry is available (Bandura et al., 2009). The vast practical clinical and biological applications and demonstrations in microtiter plate, microarray, Western blotting, cell cytometer, and suspension array are demanded, in which more participations and contributions from medical and biological scientist are desired.

ACKNOWLEDGMENTS Authors acknowledge the financial support for this project from the National Natural Science Foundation of China (nos. 20835003, 21075084, and 21128006).

REFERENCES Abdelrahman AI, Dai S, Thickett SC, Ornatsky O, Bandura D, Baranov V, Winnik MA. 2009. Lanthanide-containing polymer microspheres by multiple-stage dispersion polymerization for highly multiplexed bioassays. J Am Chem Soc 131:15276–15283. Abdelrahman AI, Ornatsky O, Bandura D, Baranov V, Kinach R, Dai S, Thickett SC, Tanner S, Winnik MA. 2010. Metal-containing polystyrene beads as standards for mass cytometry. J Anal At Spectrom 25:260–268. Abderahman AI, Thickett SC, Liang Y, Ornatsky O, Baranov V, Winnik MA. 2011. Surface functionalization methods to enhance bioconjugation in metal-labeled polystyrene particles. Macromolecules 44:4801–4813. Andreu EJ, de Llano JJM, Moreno I, Knecht E. 1998. A rapid procedure suitable to assess quantitatively the endocytosis of colloidal gold and its conjugates in cultured cells. J Histochem Cytochem 46:1199–1201. Bandura DR, Baranov VI, Ornatsky OI, Antonov A, Kinach R, Lou XD, Pavlov S, Vorobiev S, Dick JE, Tanner SD. 2009. Mass cytometry: Technique for real time single cell multitarget immunoassay based on inductively coupled plasma time-of-flight mass spectrometry. Anal Chem 81:6813–6822. Baranov VI, Quinn Z, Bandura DR, Tanner SD. 2002a. A sensitive and quantitative element-tagged immunoassay with ICPMS detection. Anal Chem 74:1629–1636. Baranov VI, Quinn ZA, Bandura DR, Tanner SD. 2002b. The potential for elemental analysis in biotechnology. J Anal At Spectrom 17:1148–1152. Baranov VI, Quinn ZA, Bandura DR, Tanner SD. 2003. New challenges for ICP-MS instrumentation and data acquisition. Solving problems of real life biology. In: Holl JG, Tanner SD, editors. Plasma source mass spectrometry. London: Royal Society of Chemistry. p 16–27. Becker JS, Jakubowski N. 2009. The synergy of elemental and biomolecular mass spectrometry: New analytical strategies in life sciences. Chem Soc Rev 38:1969–1983. Becker JS, Salber D. 2010. New mass spectrometric tools in brain research. Trac-Trends Anal Chem 29:966–979. Behbehani GK, Bendall SC, Clutter MR, Fantl WJ, Nolan GP. 2012. Singlecell mass cytometry adapted to measurements of the cell cycle. Cytom Part A 81A:552–566. Bendall SC, Simonds EF, Qiu P, Amir EAD, Krutzik PO, Finck R, Bruggner RV, Melamed R, Trejo A, Ornatsky OI, Balderas RS, Plevritis SK, Sachs K, Pe’er D, Tanner SD, Nolan GP. 2011. Single-cell mass cytometry of differential immune and drug responses across a human hematopoietic continuum. Science 332:687–696. Bendall SC, Nolan GP, Roederer M, Chattopadhyay PK. 2012. A deep profiler’s guide to cytometry. Trends Immunol 33:323–332. Benoist C, Hacohen N. 2011. Flow cytometry, amped up. Science 332: 677–678. Berger S, Ornatsky O, Baranov V, Winnik MA, Pich A. 2010. Hybrid nanogels by encapsulation of lanthanide-doped LaF3 nanoparticles as elemental tags for detection by atomic mass spectrometry. J Mater Chem 20:5141–5150.

389

&

LIU ET AL.

Bettmer J, Jakubowski N, Prange A. 2006. Elemental tagging in inorganic mass spectrometric bioanalysis. Anal Bioanal Chem 386:7–11. Bettmer J, Bayon MM, Encinar JR, Sanchez MLF, de la Campa MDF, Medel AS. 2009. The emerging role of ICP-MS in proteomic analysis. J Proteomics 72:989–1005. Biju V, Itoh T, Ishikawa M. 2010. Delivering quantum dots to cells: Bioconjugated quantum dots for targeted and nonspecific extracellular and intracellular imaging. Chem Soc Rev 39:3031–3056. Bings NH, Bogaerts A, Broekaert JAC. 2010. Atomic spectroscopy: A review. Anal Chem 82:4653–4681. Blackburn GF, Shah HP, Kenten JH, Leland J, Kamin RA, Link J, Peterman J, Powell MJ, Shah A, Talley DB, Tyagi SK, Wilkins E, Wu TG, Massey RJ. 1991. Electrochemiluminescence detection for development of immunoassays and dna probe assays for clinical diagnostics. Clin Chem 37:1534–1539. Bodenmiller B, Zunder ER, Finck R, Chen TJ, Savig ES, Bruggner RV, Simonds EF, Bendall SC, Sachs K, Krutzik PO, Nolan GP. 2012. Multiplexed mass cytometry profiling of cellular states perturbed by small-molecule regulators. Nat Biotechnol 30:858–867. Bomke S, Sperling M, Karst U. 2010. Organometallic derivatizing agents in bioanalysis. Anal Bioanal Chem 397:3483–3494. Bunzli JCG. 2010. Lanthanide luminescence for biomedical analyses and imaging. Chem Rev 110:2729–2755. Bustos ARM, Trapiella-Alfonso L, Encinar JR, Costa-Fernandez JM, Pereiro R, Sanz-Medel A. 2012. Elemental and molecular detection for Quantum Dots-based immunoassays: A critical appraisal. Biosens Bioelectron 33:165–171. Cais M, Dani S, Eden Y, Gandolfi O, Horn M, Isaacs EE, Josephy Y, Saar Y, Slovin E, Snarsky L. 1977. Metallo-immunoassay. Nature 270:534– 535. Careri M, Mangia A. 2011. Trends in analytical atomic and molecular mass spectrometry in biology and the life sciences. Anal Bioanal Chem 399:2585–2595. Careri M, Elviri L, Mangia A, Mucchino C. 2007. ICP-MS as a novel detection system for quantitative element-tagged immunoassay of hidden peanut allergens in foods. Anal Bioanal Chem 387:1851–1854. Careri M, Elviri L, Maffini M, Mangia A, Mucchino C, Terenghi M. 2008. Determination of peanut allergens in cereal-chocolate-based snacks: Metal-tag inductively coupled plasma mass spectrometry immunoassay versus liquid chromatography/electrospray ionization tandem mass spectrometry. Rapid Commun Mass Spectrom 22:807–811. Careri M, Elviri L, Mangia A. 2009. Element-tagged immunoassay with inductively coupled plasma mass spectrometry for multianalyte detection. Anal Bioanal Chem 393:57–61. Chattopadhyay PK, Price DA, Harper TF, Betts MR, Yu J, Gostick E, Perfetto SP, Goepfert P, Koup RA, De Rosa SC, Bruchez MP, Roederer M. 2006. Quantum dot semiconductor nanocrystals for immunophenotyping by polychromatic flow cytometry. Nat Med 12:972–977. Chattopadhyay PK, Hogerkorp CM, Roederer M. 2008. A chromatic explosion: The development and future of multiparameter flow cytometry. Immunology 125:441–449. Chen GB, Weng NP. 2012. Analyzing the phenotypic and functional complexity of lymphocytes using CyTOF (cytometry by time-offlight). Cell Mol Immunol 9:322–323. Chen BB, Peng HY, Zheng F, Hu B, He M, Zhao W, Pang DW. 2010. Immunoaffinity monolithic capillary microextraction coupled with ICP-MS for immunoassay with quantum dot labels. J Anal At Spectrom 25:1674–1681. Chen BB, Hu B, Jiang P, He M, Peng HY, Zhang X. 2011. Nanoparticle labelling-based magnetic immunoassay on chip combined with electrothermal vaporization—Inductively coupled plasma mass spectrometry for the determination of carcinoembryonic antigen in human serum. Analyst 136:3934–3942. Cheung RK, Utz PJ. 2011. SCREENING CyTOF-the next generation of cell detection. Nat Rev Rheumatol 7:502–503.

390

Cho HK, Lim HB. 2013. Determination of prostate-specific antigen (PSA) tagged with TiO2 nanoparticles using ICP-MS. J Anal At Spectrom 28:468–472. Corthals GL, Wasinger VC, Hochstrasser DF, Sanchez JC. 2000. The dynamic range of protein expression: A challenge for proteomic research. Electrophoresis 21:1104–1115. Darzynkiewicz Z. 2012. Cycling into future: Mass cytometry for the cellcycle analysis. Cytom Part A 81A:546–548. de Bang TC, Pedas P, Schjoerring JK, Jensen PE, Husted S. 2013. Multiplexed quantification of plant thylakoid proteins on western blots using lanthanide-labeled antibodies and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Anal Chem 85:5047–5054. de Souza N. 2012. Single-cell methods. Nat Methods 9:35–35. Degueldre C, Favarger PY, Wold S. 2006. Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode. Anal Chim Acta 555:263–268. deLlano CJM, Andreu EJ, Knecht E. 1996. Use of inductively coupled plasma-mass spectrometry for the quantitation of the binding and uptake of colloidal gold low-density lipoprotein conjugates by cultured cells. Anal Biochem 243:210–217. Deng AP, Liu HT, Jiang SJ, Huang HJ, Ong CW. 2002. Reaction cell inductively coupled plasma mass spectrometry-based immunoassay using ferrocene tethered hydroxysuccinimide ester as label for the determination of 2,4-dichlorophenoxyacetic acid. Anal Chim Acta 472:55–61. Doerr A. 2011. A flow cytometry revolution. Nat Methods 8:531–531. Engelhard C. 2011. Inductively coupled plasma mass spectrometry: Recent trends and developments. Anal Bioanal Chem 399:213–219. Engvall E, Perlmann P. 1971. Enzyme-linked immunosorbent assay (ELISA) quantitative assay of immunoglobulin-G. Immunochemistry 8:871. Fernandez B, Costa JM, Pereiro R, Sanz-Medel A. 2010. Inorganic mass spectrometry as a tool for characterisation at the nanoscale. Anal Bioanal Chem 396:15–29. Fienberg HG, Simonds EF, Fantl WJ, Nolan GP, Bodenmiller B. 2012. A platinum-based covalent viability reagent for single-cell mass cytometry. Cytom Part A 81A:467–475. Forster RJ, Bertoncello P, Keyes TE. 2009. Electrogenerated chemiluminescence. Annu Rev Anal Chem 2:359–385. Gao Y, Peng XH, Shi ZM, Zhang RX, Xia XF, Yue FR, Liu R. 2012. Determination of mercury in alcoholic drinks by ICP-MS after matrixassisted photochemical vapor generation. Atom Spectrosc 33:73–77. Giesen C, Jakubowski N, Panne U, Weller MG. 2010. Comparison of ICPMS and photometric detection of an immunoassay for the determination of ochratoxin A in wine. J Anal At Spectrom 25:1567–1572. Giesen C, Mairinger T, Khoury L, Waentig L, Jakubowski N, Panne U. 2011a. Multiplexed immunohistochemical detection of tumor markers in breast cancer tissue using laser ablation inductively coupled plasma mass spectrometry. Anal Chem 83:8177–8183. Giesen C, Waentig L, Mairinger T, Drescher D, Kneipp J, Roos PH, Panne U, Jakubowski N. 2011b. Iodine as an elemental marker for imaging of single cells and tissue sections by laser ablation inductively coupled plasma mass spectrometry. J Anal At Spectrom 26:2160–2165. Giesen C, Waentig L, Panne U, Jakubowski N. 2012. History of inductively coupled plasma mass spectrometry-based immunoassays. Spectroc Acta Part B At Spectrosc 76:27–39. Hagan AK, Zuchner T. 2011. Lanthanide-based time-resolved luminescence immunoassays. Anal Bioanal Chem 400:2847–2864. Hage DS. 1999. Immunoassays. Anal Chem 71:294R–304R. Hamdan M, Righetti PG. 2002. Modern strategies for protein quantification in proteome analysis: Advantages and limitations. Mass Spectrom. Rev 21:287–302. Han MY, Gao XH, Su JZ, Nie S. 2001. Quantum-dot-tagged microbeads for multiplexed optical coding of biomolecules. Nat Biotechnol 19:631–635.



Han GJ, Xing Z, Dong YH, Zhang SC, Zhang XR. 2011. One-step homogeneous DNA assay with single-nanoparticle detection. Angew Chem Int Ed 50:3462–3465. Han GJ, Zhang SC, Xing Z, Zhang XR. 2013. Absolute and relative quantification of multiplex DNA assays based on an elemental labeling strategy. Angew Chem Int Ed 52:1466–1471. Hann S, Boeck K, Koellensperger G. 2010. Immunoaffinity assisted LCICP-MS-a versatile tool in biomedical research. J Anal At Spectrom 25:18–20. Ho KS, Chan WT. 2010. Time-resolved ICP-MS measurement for singlecell analysis and on-line cytometry. J Anal At Spectrom 25:1114– 1122. Houk RS, Fassel VA, Flesch GD, Svec HJ, Gray AL, Taylor CE. 1980. Inductively coupled argon plasma as an ion-source for mass-spectrometric determination of trace-elements. Anal Chem 52:2283–2289. Hsu IH, Chen WH, Wu TK, Sun YC. 2011. Gold nanoparticle-based inductively coupled plasma mass spectrometry amplification and magnetic separation for the sensitive detection of a virus-specific RNA sequence. J Chromatogr A 1218:1795–1801. Hu SH, Zhang SC, Hu ZC, Xing Z, Zhang XR. 2007. Detection of multiple proteins on one spot by laser ablation inductively coupled plasma mass spectrometry and application to immuno-microarray with elementtagged antibodies. Anal Chem 79:923–929. Hu SH, Liu R, Zhang SC, Huang Z, Xing Z, Zhang XR. 2009. A new strategy for highly sensitive immunoassay based on single-particle mode detection by inductively coupled plasma mass spectrometry. J Am Soc Mass Spectrom 20:1096–1103. Hutchinson RW, Ma RL, McLeod CW, Milford-Ward A, Lee D. 2004. Immunoassay with FI-ICP-MS detection—Measurement of free and total prostate specific antigen in human serum. Can J Anal Sci Spectrosc 49:429–435. Hutchinson RW, Cox AG, McLeod CW, Marshall PS, Harper A, Dawson EL, Howlett DR. 2005. Imaging and spatial distribution of beta-amyloid peptide and metal ions in Alzheimer’s plaques by laser ablationinductively coupled plasma-mass spectrometry. Anal Biochem 346:225–233. Jackson TM, Ekins RP. 1986. Theoretical limitations on immunoassay sensitivity—Current practice and potential advantages of fluorescent Eu3þ chelates as nonradioisotopic tracers. J Immunol Methods 87: 13–20. Jakubowski N, Messerschmidt J, Anorbe MG, Waentig L, Hayen H, Roos PH. 2008a. Labelling of proteins by use of iodination and detection by ICP-MS. J Anal At Spectrom 23:1487–1496. Jakubowski N, Waentig L, Hayen H, Venkatachalam A, von Bohlen A, Roos PH, Manz A. 2008b. Labelling of proteins with 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra acetic acid and lanthanides and detection by ICP-MS. J Anal At Spectrom 23:1497– 1507. Janes MR, Rommel C. 2011. Next-generation flow cytometry. Nat Biotechnol 29:602–604. Jarujamrus P, Chawengkirttikul R, Shiowatana J, Siripinyanond A. 2012. Towards chloramphenicol detection by inductively coupled plasma mass spectrometry (ICP-MS) linked immunoassay using gold nanoparticles (AuNPs) as element tags. J Anal At Spectrom 27:884–890. Joo J-Y, Lim HB. 2012. LA-ICP-MS with microarray chip sampling to determine holoceruloplasmin in serum. J Anal At Spectrom 27:1069– 1073. Kenten JH, Casadei J, Link J, Lupold S, Willey J, Powell M, Rees A, Massey R. 1991. Rapid electrochemiluminescence assays of polymerase chainreaction products. Clin Chem 37:1626–1632. Koellensperger G, Groeger M, Zinkl D, Petzelbauer P, Hann S. 2009. Quantification of elemental labeled peptides in cellular uptake studies. J Anal At Spectrom 24:97–102. Konz I, Fernandez B, Fernandez ML, Pereiro R, Sanz-Medel A. 2012. Laser ablation ICP-MS for quantitative biomedical applications. Anal Bioanal Chem 403:2113–2125.


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Krutzik PO, Nolan GP. 2006. Fluorescent cell barcoding in flow cytometry allows high-throughput drug screening and signaling profiling. Nat Methods 3:361–368. Kutscher DJ, Bettmer J. 2009. Absolute and relative protein quantification with the use of isotopically labeled p-hydroxymercuribenzoic acid and complementary MALDI-MS and ICPMS detection. Anal Chem 81:9172–9177. Lathia US, Ornatsky O, Baranov V, Nitz M. 2010. Development of inductively coupled plasma-mass spectrometry-based protease assays. Anal Biochem 398:93–98. Lathia US, Ornatsky O, Baranov V, Nitz M. 2011. Multiplexed protease assays using element-tagged substrates. Anal Biochem 408:157–159. Leavy O. 2010. Foreword. Therapeutic antibodies: Past, present and future. Nat Rev Immunol 10:297. Lei JP, Ju HX. 2012. Signal amplification using functional nanomaterials for biosensing. Chem Soc Rev 41:2122–2134. Leipold MD, Ornatsky O, Baranov V, Whitfield C, Nitz M. 2011. Development of mass cytometry methods for bacterial discrimination. Anal Biochem 419:1–8. Lelpold MD, Herrera I, Ornatsky O, Baranov V, Nitz M. 2009. ICP-MSbased multiplex profiling of glycoproteins using lectins conjugated to lanthanide-chelating polymers. J Proteome Res 8:443–449. Lequin RM. 2005. Enzyme immunoassay (EIA)/enzyme-linked immunosorbent assay (ELISA). Clin Chem 51:2415–2418. Li F, Zhao Q, Wang CA, Lu XF, Li XF, Le XC. 2010a. Detection of Escherichia coli O157: H7 using gold nanoparticle labeling and inductively coupled plasma mass spectrometry. Anal Chem 82:3399– 3403. Li JX, Wang XR, Zhuang ZX, Cui WG. 2010b. Nonradioactive iodinelabeled antibodies-inductively coupled plasma mass spectrometry for immunoassay. Spectrosc Spectr Anal 30:788–791. Liang AH, Tang ML, Tang YF, Liu QY, Wen GQ, Li TS, Jiang ZL. 2011a. A new immunonanogold graphite furnace atomic absorption spectral assay for human chorionic gonadotrophin. Anal Lett 44:2162–2169. Liang Y, Abdelrahman AI, Baranov V, Winnik MA. 2011b. The synthesis and characterization of lanthanide-encoded poly(styrene-co-methacrylic acid) microspheres. Polymer 52:5040–5052. Liang Y, Abdelrahman AI, Baranov V, Winnik MA. 2012. The release and extraction of lanthanide ions from metal-encoded poly (styrene-comethacrylic acid) microspheres. Polymer 53:998–1004. Lin WJ, Ma XM, Qian JS, Abdelrahman AI, Halupa A, Baranov V, Pich A, Winnik MA. 2011. Synthesis and mass cytometric analysis of lanthanide-encoded polyelectrolyte microgels. Langmuir 27:7265– 7275. Liu J-M, Yan X-P. 2011. Ultrasensitive, selective and simultaneous detection of cytochrome c and insulin based on immunoassay and aptamer-based bioassay in combination with Au/Ag nanoparticle tagging and ICP-MS detection. J Anal At Spectrom 26:1191–1197. Liu R, Xing Z, Lv Y, Zhang SC, Zhang XR. 2010. Sensitive sandwich immunoassay based on single particle mode inductively coupled plasma mass spectrometry detection. Talanta 83:48–54. Liu R, Liu X, Tang YR, Wu L, Hou XD, Lv Y. 2011. Highly sensitive immunoassay based on immunogold—Silver amplification and inductively coupled plasma mass spectrometric detection. Anal Chem 83:2330–2336. Liu R, Lv Y, Hou XD, Mester Z, Yang L. 2012a. Protein quantitation using Ru-NHS ester tagging and isotope dilution high-pressure liquid chromatography—Inductively coupled plasma mass spectrometry determination. Anal Chem 84:2769–2775. Liu X, Liu R, Tang Y, Zhang L, Hou X, Lv Y. 2012b. Antibody-biotemplated HgS nanoparticles: Extremely sensitive labels for atomic fluorescence spectrometric immunoassay. Analyst 137:1473–1480. Liu R, Hou X, Lv Y, McCooeye M, Yang L, Mester Z. 2013. Absolute quantification of peptides by isotope dilution liquid chromatographyinductively coupled plasma mass spectrometry and gas chromatography/mass spectrometry. Anal Chem 85:4087–4093.

391

&

LIU ET AL.

Liu R, Zhang Y, Zhang SY, Qiu W, Gao Y. 2013. Silver enhancement of gold nanoparticles for biosensing: From qualitative to quantitative. Appl Spectrosc Rev DOI: 10.1080/05704928.2013.807817 Lou XD, Zhang GH, Herrera I, Kinach R, Ornatsky O, Baranov V, Nitz M, Winnik MA. 2007. Polymer-based elemental tags for sensitive bioassays. Angew Chem Int Ed 46:6111–6114. Lu YY, Wang WJ, Xing Z, Wang SD, Cao P, Zhang SC, Zhang XR. 2009. Development of an ICP-MS immunoassay for the detection of antierythropoietin antibodies. Talanta 78:869–873. Majonis D, Herrera I, Ornatsky O, Schulze M, Lou XD, Soleimani M, Nitz M, Winnik MA. 2010. Synthesis of a functional metal-chelating polymer and steps toward quantitative mass cytometry bioassays. Anal Chem 82:8961–8969. Majonis D, Ornatsky O, Kinach R, Winnik MA. 2011. Curious results with palladium- and platinum-carrying polymers in mass cytometry bioassays and an unexpected application as a dead cell stain. Biomacromolecules 12:3997–4010. Mariet F, Brossier P, Dicaire F, Ismail AA. 1990. Comparison of FT-IR and AAS for metalloimmunoassay of a tricyclic antidepressant drug (desipramine). J Pharm Biomed Anal 8:979–982. Merkoci A, Aldavert M, Tarrason G, Eritja R, Alegret S. 2005. Toward an ICPMS-linked DNA assay based on gold nanoparticles immunoconnected through peptide sequences. Anal Chem 77:6500–6503. Mounicou S, Szpunar J, Lobinski R. 2009. Metallomics: The concept and methodology. Chem Soc Rev 38:1119–1138. Muller SD, Diaz-Bone RA, Felix J, Goedecke W. 2005. Detection of specific proteins by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using gold cluster labelled antibodies. J Anal At Spectrom 20:907–911. Navaza AP, Encinar JR, Ballesteros A, Gonzalez JM, Sanz-Medel A. 2009. Capillary HPLC-ICPMS and tyrosine iodination for the absolute quantification of peptides using genetic standards. Anal Chem 81:5390–5399. Newell EW, Sigal N, Bendall SC, Nolan GP, Davis MM. 2012. Cytometry by time-of-flight shows combinatorial cytokine expression and virusspecific cell niches within a continuum of CD8(þ) T cell phenotypes. Immunity 36:142–152. Ong SE, Mann M. 2005. Mass spectrometry-based proteomics turns quantitative. Nat Chem Biol 1:252–262. Ornatsky O, Baranov V, Bandura D, Tanner S, Dick J. 2006a. Messenger RNA detection in leukemia cell lines by novel metal-tagged in situ hybridization using inductively coupled plasma mass spectrometry. Transl Oncogenomics 1:1–9. Ornatsky O, Baranov V, Bandura DR, Tanner SD, Dick J. 2006b. Multiple cellular antigen detection by ICP-MS. J Immunol Methods 308:68–76. Ornatsky OI, Kinach R, Bandura DR, Lou X, Tanner SD, Baranov VI, Nitz M, Winnik MA. 2008a. Development of analytical methods for multiplex bio-assay with inductively coupled plasma mass spectrometry. J Anal At Spectrom 23:463–469. Ornatsky OI, Lou X, Nitz M, Schafer S, Sheldrick WS, Baranov VI, Bandura DR, Tanner SD. 2008b. Study of cell antigens and intracellular DNA by identification of element-containing labels and metallointercalators using inductively coupled plasma mass spectrometry. Anal Chem 80:2539–2547. Ornatsky O, Bandura D, Baranov V, Nitz M, Winnik MA, Tanner S. 2010. Highly multiparametric analysis by mass cytometry. J Immunol Methods 361:1–20. Peng HY, Chen BB, He M, Zhang Y, Hu B. 2011. Magnetic quantitative immunoanalysis of carcinoembryonic antigen by ICP-MS with mercury labels. J Anal At Spectrom 26:1217–1223. PerkinElmer, Inc. 2003. The 30-minute guide to ICP-MS. http://www.perkinelmer.com/CMSResources/Images/44-74849tch_ icpmsthirtyminuteguide.pdf Pich A, Zhang FB, Shen L, Berger S, Ornatsky O, Baranov V, Winnik MA. 2008. Biocompatible hybrid nanogels. Small 4:2171–2175.

392

Prange A, Proefrock D. 2008. Chemical labels and natural element tags for the quantitative analysis of bio-molecules. J Anal At Spectrom 23:432–459. Pregibon DC, Toner M, Doyle PS. 2007. Multifunctional encoded particles for high-throughput biomolecule analysis. Science 315:1393–1396. Profrock D, Prange A. 2012. Inductively coupled plasma-mass spectrometry (ICP-MS) for quantitative analysis in environmental and life sciences: A review of challenges, solutions, and trends. Appl Spectrosc 66: 843–868. Qiu P, Simonds EF, Bendall SC, Gibbs KD, Bruggner RV, Linderman MD, Sachs K, Nolan GP, Plevritis SK. 2011. Extracting a cellular hierarchy from high-dimensional cytometry data with SPADE. Nat Biotechnol 29:886–891. Quinn ZA, Baranov VI, Tanner SD, Wrana JL. 2002. Simultaneous determination of proteins using an element-tagged immunoassay coupled with ICP-MS detection. J Anal At Spectrom 17:892–896. Razumienko E, Ornatsky O, Kinach R, Milyavsky M, Lechman E, Baranov V, Winnik MA, Tanner SD. 2008. Element-tagged immunoassay with ICP-MS detection: Evaluation and comparison to conventional immunoassays. J Immunol Methods 336:56–63. Remy I, Brossier P, Lavastre I, Besancon J, Moise C. 1991. Potentiality of an organometallic labeled streptavidin biotin system in metalloimmunoassay. J Pharm Biomed Anal 9:965–967. Roos PH, Venkatachalam A, Manz A, Waentig L, Koehler CU, Jakubowski N. 2008. Detection of electrophoretically separated cytochromes P450 by element-labelled monoclonal antibodies via laser ablation inductively coupled plasma mass spectrometry. Anal Bioanal Chem 392: 1135–1147. Sanz-Medel A. 2010. ICP-MS for multiplex absolute determinations of proteins. Anal Bioanal Chem 398:1853–1859. Sanz-Medel A, Montes-Bayon M, de la Campa M, Encinar JR, Bettmer J. 2008. Elemental mass spectrometry for quantitative proteomics. Anal Bioanal Chem 390:3–16. Scheffer A, Engelhard C, Sperling M, Buscher W. 2008. ICP-MS as a new tool for the determination of gold nanoparticles in bioanalytical applications. Anal Bioanal Chem 390:249–252. Schroeder HR, Vogelhut PO, Carrico RJ, Bogulaski RC, Buckler RT. 1976. Competitive protein-binding assay for biotin monitored by chemiluminescence. Anal Chem 48:1933–1937. Seuma J, Bunch J, Cox A, McLeod C, Bell J, Murray C. 2008. Combination of immunohistochemistry and laser ablation ICP mass spectrometry for imaging of cancer biomarkers. Proteomics 8:3775–3784. Soini E, Hemmila I. 1979. Fluoroimmunoassay—Present status and key problems. Clin Chem 25:353–361. Takatera K, Watanabe T. 1993. Determination of sulfhydryl-groups in ovalbumin by high-performance liquid-chromatography with inductively-coupled plasma-mass spectrometric detection. Anal Chem 65: 3644–3646. Tanner M, Gu¨nther D. 2009. Short transient signals, a challenge for inductively coupled plasma mass spectrometry, a review. Anal Chim Acta 633:19–28. Tanner SD, Ornatsky O, Bandura DR, Baranov VI. 2007. Multiplex bioassay with inductively coupled plasma mass spectrometry: Towards a massively multivariate single-cell technology. Spectroc Acta Part B At Spectrosc 62:188–195. Tanner SD, Bandura DR, Ornatsky O, Baranov VI, Nitz M, Winnik MA. 2008. Flow cytometer with mass spectrometer detection for massively multiplexed single-cell biomarker assay. Pure Appl Chem 80:2627– 2641. Terenghi M, Elviri L, Careri M, Mangia A, Lobinski R. 2009. Multiplexed determination of protein biomarkers using metal-tagged antibodies and size exclusion chromatography-inductively coupled plasma mass spectrometry. Anal Chem 81:9440–9448. Thickett SC, Abdelrahman AI, Ornatsky O, Bandura D, Baranov V, Winnik MA. 2010. Bio-functional, lanthanide-labeled polymer particles by



seeded emulsion polymerization and their characterization by novel ICP-MS detection. J Anal At Spectrom 25:269–281. Tholey A, Schaumloffel D. 2010. Metal labeling for quantitative protein and proteome analysis using inductively-coupled plasma mass spectrometry. Trac-Trends Anal Chem 29:399–408. Thomas R. 2001. Spectroscopy tutorial—A beginner’s guide to ICP-MS— Part I. Spectroscopy 16:38–42. Thompson DF, Eborall W, Dinsmore A, Smith CJ, Duckett CJ. 2010. Development and validation of a NANOGold (TM) immunoassay for the detection of vascular endothelial growth factor (VEGF) in human serum using inductively coupled plasma mass spectrometry. Rapid Commun Mass Spectrom 24:927–932. Tsang CN, Ho KS, Sun HZ, Chan WT. 2011. Tracking bismuth antiulcer drug uptake in single Helicobacter pylori cells. J Am Chem Soc 133:7355–7357. Tung NH, Chikae M, Ukita Y, Viet PH, Takamura Y. 2012. Sensing technique of silver nanoparticles as labels for immunoassay using liquid electrode plasma atomic emission spectrometry. Anal Chem 84:1210–1213. Vancaeyzeele C, Ornatsky O, Baranov V, Shen L, Abdelrahman A, Winnik MA. 2007. Lanthanide-containing polymer nanoparticles for biological tagging applications: Nonspecific endocytosis and cell adhesion. J Am Chem Soc 129:13653–13660. Waentig L, Roos PH, Jakubowski N. 2009. Labelling of antibodies and detection by laser ablation inductively coupled plasma mass spectrometry. J Anal At Spectrom 24:924–933. Waentig L, Jakubowski N, Hayen H, Roos PH. 2011a. Iodination of proteins, proteomes and antibodies with potassium triodide for LA-ICP-MS based proteomic analyses. J Anal At Spectrom 26:1610–1618. Waentig L, Jakubowski N, Roos PH. 2011b. Multi-parametric analysis of cytochrome P450 expression in rat liver microsomes by LA-ICP-MS. J Anal At Spectrom 26:310–319. Waentig L, Jakubowski N, Hardt S, Scheler C, Roos PH, Linscheid MW. 2012. Comparison of different chelates for lanthanide labeling of antibodies and application in a Western blot immunoassay combined with detection by laser ablation (LA-)ICP-MS. J Anal At Spectrom 27:1311–1320. Waentig L, Jakubowski N, Techritz S, Roos P. 2013. A multi-parametric microarray for protein profiling: Simultaneous analysis of 8 different cytochromes via differentially element tagged antibodies and laser ablation ICP-MS. Analyst DOI: 10.1039/C3AN00468F http://pubs.rsc. org/en/content/articlelanding/2013/AN/C3AN00468F Wang GL, Yuan JL, Gong BL, Matsumoto K, Hu ZD. 2001. Immunoassay by graphite furnace atomic absorption spectrometry using a metal chelate as a label. Anal Chim Acta 448:165–172. Wang M, Feng WY, Zhao YL, Chai ZF. 2010. ICP-MS-based strategies for protein quantification. Mass Spectrom Rev 29:326–348. Wang LL, Abbasi F, Ornatsky O, Cole KD, Misakian M, Gaigalas AK, He HJ, Marti GE, Tanner S, Stebbings R. 2012. Human CD4(þ)


&

lymphocytes for antigen quantification: Characterization using conventional flow cytometry and mass cytometry. Cytom Part A 81A:567– 575. Wind M, Lehmann WD. 2004. Element and molecular mass spectrometry— An emerging analytical dream team in the life sciences. J Anal At Spectrom 19:20–25. Wu LL, Qiu LW, Shi CS, Zhu J. 2007. A nanoparticle-based solution DNA sandwich assay using lCP-AES for readout. Biomacromolecules 8:2795–2800. Wu P, Miao LN, Wang HF, Shao XG, Yan XP. 2011. A multidimensional sensing device for the discrimination of proteins based on manganesedoped ZnS quantum dots. Angew Chem Int Ed 50:8118–8121. Xu M, Yan XW, Xie QQ, Yang LM, Wang QQ. 2010. Dynamic labeling strategy with Hg-204-isotopic methylmercurithiosalicylate for absolute peptide and protein quantification. Anal Chem 82:1616–1620. Yalow RS, Berson SA. 1959. Assay of plasma insulin in human subjects by immunological methods. Nature 184:1648–1649. Yan XW, Yang LM, Wang QQ. 2011. Lanthanide-coded protease-specific peptide-nanoparticle probes for a label-free multiplex protease assay using element mass spectrometry: A proof-of-concept study. Angew Chem Int Ed 50:5130–5133. Zhang C, Wu FB, Zhang YY, Wang X, Zhang XR. 2001. A novel combination of immunoreaction and ICP-MS as a hyphenated technique for the determination of thyroid-stimulating hormone (TSH) in human serum. J Anal At Spectrom 16:1393–1396. Zhang C, Wu FB, Zhang XR. 2002a. ICP-MS-based competitive immunoassay for the determination of total thyroxin in human serum. J Anal At Spectrom 17:1304–1307. Zhang C, Zhang ZY, Yu BB, Shi JJ, Zhang XR. 2002b. Application of the biological conjugate between antibody and colloid Au nanoparticles as analyte to inductively coupled plasma mass spectrometry. Anal Chem 74:96–99. Zhang SC, Zhang C, Xing Z, Zhang XR. 2004. Simultaneous determination of alpha-fetoprotein and free beta-human chorionic gonadotropin by element-tagged immunoassay with detection by inductively coupled plasma mass Spectrometry. Clin Chem 50:1214–1221. Zhang W, Ang WT, Xue C-Y, Yang K-L. 2011. Minimizing nonspecific protein adsorption in liquid crystal immunoassays by using surfactants. ACS Appl Mater Interfaces 3:3496–3500. Zhao LX, Sun L, Chu XG. 2009a. Chemiluminescence immunoassay. Trac-Trends Anal Chem 28:404–415. Zhao Q, Lu XF, Yuan CG, Li XF, Le XC. 2009b. Aptamer-linked assay for thrombin using gold—Mass spectrometry detection. Anal Chem 81:7484–7489. Zheng CB, Yang L, Sturgeon RE, Hou XD. 2010. UV photochemical vapor generation sample introduction for determination of Ni, Fe, and Se in biological tissue by isotope dilution ICPMS. Anal Chem 82: 3899–3904.

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Quantitative aspects of inductively coupled plasma mass spectrometry.

Single particle inductively coupled plasma mass spectrometry: a powerful tool for nanoanalysis.

Validation of a Metallomics Analysis of Placenta Tissue by Inductively-Coupled Plasma Mass Spectrometry.

Fractionation analysis of manganese in Turkish hazelnuts (Corylus avellana L.) by inductively coupled plasma-mass spectrometry.

Precise determination of seawater calcium using isotope dilution inductively coupled plasma mass spectrometry.

Isotope ratio and isotope dilution analysis of lead in wine by inductively coupled plasma-mass spectrometry.

Accurate determination and certification of bromine in plastic by isotope dilution inductively coupled plasma mass spectrometry.

Multiplexed microRNA detection using lanthanide-labeled DNA probes and laser ablation inductively coupled plasma mass spectrometry.

Determination of 241Am in Urine Using Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS).

Imaging Metals in Brain Tissue by Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS).

Multiplex DNA assay based on nanoparticle probes by single particle inductively coupled plasma mass spectrometry.

Speciation of tissue and cellular iron with on-line detection by inductively coupled plasma-mass spectrometry.

Elemental Bioimaging by Means of Fast Scanning Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry.

Quantitative analysis of gold nanoparticles in single cells by laser ablation inductively coupled plasma-mass spectrometry.

Thin-layer chromatography combined with diode laser thermal vaporization inductively coupled plasma mass spectrometry.

Imaging gold nanoparticles in mouse liver by laser ablation inductively coupled plasma mass spectrometry.

Laser ablation inductively coupled plasma mass spectrometry imaging of metals in experimental and clinical Wilson's disease.

Rapid cell mode switching and dual laser ablation inductively coupled plasma mass spectrometry for elemental bioimaging.

Arsenic speciation by ion chromatography with inductively coupled plasma mass spectrometric detection.

Speciation of cisplatin in environmental water samples by hydrophilic interaction liquid chromatography coupled to inductively coupled plasma mass spectrometry.

Isotopic analysis of tungsten using multiple collector-inductively coupled plasma-mass spectrometer coupled with electrothermal vaporization technique.

Determination of 236U in environmental samples by single extraction chromatography coupled to triple-quadrupole inductively coupled plasma-mass spectrometry.

A Practical Guide on Coupling a Scanning Mobility Sizer and Inductively Coupled Plasma Mass Spectrometer (SMPS-ICPMS).

Determination of selenium by inductively coupled plasma mass spectrometry utilizing a new hydride generation sample introduction system.