View Article Online View Journal

Analyst Accepted Manuscript

This article can be cited before page numbers have been issued, to do this please use: X. Du, D. Jiang, Q. Liu, G. Zhu, H. Mao and K. Wang, Analyst, 2014, DOI: 10.1039/C4AN01752H.

This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.

www.rsc.org/analyst

Page 1 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Fabrication of Graphene Oxide Decorated with Nitrogen-Doped Graphene Quantum Dots and its Enhanced Electrochemiluminescence for Ultrasensitive Detection of Pentachlorophenol Xiaojiao Dua, Ding Jiangb, Qian Liua, Gangbing Zhuc, Hanping Maoa and Kun Wanga∗ a

Key Laboratory of Modern Agriculture Equipment and Technology, School of Chemistry and

Chemical Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China. b

School of Food and Biological Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China.

c

School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, P.R.

China.

∗ Corresponding author. Tel.: +86 511 88791800; fax: +86 511 88791708.

E-mail address: [email protected]

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 2 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Nitrogen-doped graphene quantum dots (NGQDs), as a new class of quantum dots, have potential applications in fuel cells and optoelectronics fields due to their electrocatalytic activity, tunable luminescence and biocompatibility. Herein, a facile hydrothermal approach for cutting nitrogen-doped graphene into NGQDs has been proposed for the first time. Then the resulting NGQDs were homogeneously modified onto the surface of graphene oxide (GO) to form the NGQDs-GO nanocomposites. Compared with NGQDs-only, the as-prepared NGQDs-GO nanocomposites exhibited excellent electrochemiluminescence (ECL) performances including 3.8-fold enhanced ECL intensity and 200 mV decreased ECL onset potential, which was ascribed to the introduction of GO. Based on the selective inhibitory effect of pentachlorophenol (PCP) on the ECL intensity of the NGQDs-GO system, a novel ECL sensor for PCP determination was constructed, with a wide linear response ranging from 0.1 to 10 pg/mL and a detection limit of 0.03 pg/mL. The practicability of the sensing platform in real water samples showed satisfactory results, which could open an avenue of NGQDs-based nanocomposites in the electroanalytical field.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 3 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Introduction Carbon-based quantum dots, including carbon dots (C-Dots), and the emerging graphene quantum dots (GQDs), have been employed as potential candidates to replace traditional quantum dots (QDs) and applied in many fields, such as bioimaging, sensing, catalysts and photovoltaic devices for their low-toxicity, good biocompatibility and photostability.1-7 GQDs, unlike their cousins C-Dots, clearly possess a graphene structure inside the dots, regardless of the dot size, which endows them with some of the unusual properties of graphene, and thus are attracting increasing interests among various fields in the recent years.2-7 Since Bards’s group reported the electrochemiluminescence (ECL) of Si QDs, ECL systems based on QDs have been extensively studied for biological applications due to their unique properties.8 In the past few years, GQDs were also found to be ECL active as luminophores, in which both extrinsic coreactant S2O82− and H2O2 have been utilized to enhance GQDs ECL intensity.9,10 For example, Zhu’s group reported a facile one-pot microwave-assisted approach for the preparation of yellow-luminescent GQDs, and further developed a novel ECL sensor for Cd2+ based on the competitive coordination between cysteine and luminophore GQDs for metal ions.9 Lu and her co-workers demonstrated a simple method to obtain water-soluble GQDs and proposed an ultrasensitive ECL aptamer sensor with GQDs as luminophore.10 These results indicate that GQDs show great potential to fabricate the ECL sensing interface. With the development of material science and the need of applied research, two strategies have been reported to improve the intrinsic properties of GQDs and explore

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 4 of 29 View Article Online

DOI: 10.1039/C4AN01752H

their potential applications. In one perspective, the small particle size, supernal conductivity, rapid electron transfer, and electron reservoir properties of GQDs make it much easier to form composites and thus can further enhance the catalytic activities of the original materials, such as CdS in our previous work.11,12 Another more important strategy is to modulate its property by chemical doping and modification.13 Doping carbon nanomaterials with heteroatoms (e.g., P-doped graphite layer, B-doped CNTs, B (S or I)-doped graphene, N-doped graphene) can effectively tune their intrinsic properties, including electronic characteristics, surface and local chemical features.14-16 Among them, the N atom, possessing a comparable atomic size and five valence electrons for bonding with carbon atoms, has been widely used for chemical doping in carbon-based nanomaterials. Nitrogen-doped GQDs (NGQDs) have been investigated in many fields due to their extraordinary physical and chemical properties such as electrocatalytic activity, tunable luminescence and biocompatibility.17-19 For instance, utilizing NGQDs as the metal-free oxygen reduction reaction (ORR) catalysts in fuel cells, Li et al demonstrated that NGQDs exhibited a better electrocatalytic activity comparable to that of a commercially available Pt/C catalyst for ORR.3 Recently, Ju and Chen have developed a simple strategy to prepare NGQDs and constructed a fluorescent sensing platform for Fe3+ detection with a wide concentration range, indicating the promise for future applications of NGQDs in the field of analysis.20 Nevertheless, as innovative electrode materials, NGQDs-based electrochemical sensors have scarcely been reported and thus, it’s necessary to develop new ways to prepare NGQDs and expand the applications of the NGQDs in

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 5 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

the electroanalytical field. Pentachlorophenol (PCP), commonly used as a wood preservative, pesticide, and fungicide, is the most acutely toxic of all chlorophenol congeners, which has been listed on the black list of priority pollutants and persistent organic pollutants (POPs) by the US Environmental Protection Agency.21,22 Classified as a group 2B environmental carcinogen by International Agency for Research on Cancer, it needs to be monitored due to its adverse effects on human health and the environment.23 Furthermore, the United States Environmental Protection Agency maximum contaminant level is 9.85 ng/mL PCP for potable water. Extensive works have been carried out on the trace and ultra-trace detection of PCP in the last decade. So far, various PCP detection and measurement methods have been explored, including capillary electrophoresis,24 high performance liquid chromatography (HPLC),25 fluorescence detection,26 chemiluminescence detection (CL)27 and so on. To our best knowledge, as a newly powerful potential detection method, the ECL sensor has attracted much more attention due to their great advantages such as miniaturization, inexpensive instrumentation, excellent detection sensitivity and high selectivity.28 As a result, it is of great necessity to develop ECL-based sensors for the detection of PCP. Graphene oxide (GO) has been widely used as two-dimensional support materials due to its large surface area, oxygen functional groups, and relatively good stability for sensing analysis.29,30 Herein, employing GO as the immobilization support for NGQDs obtained by the combination of thermal and hydrothermal treatment, GO decorated with NGQDs (NGQDs-GO) were successfully prepared.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 6 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Based on the excellent ECL performance of the resulting NGQDs-GO, a novel ultrasensitive PCP detection assay was constructed. The attractive response performances of the proposed method and potential merits are presented in details.

Experimental Reagents Graphite was purchased from Qingdao Tianhe Graphite Co., Ltd. GO was synthesized from graphite powder by the modified Hummers’s method.31 The nitrogen-doped graphene (NG) was synthesized as described in our previous work.32 K2S2O8 was obtained from Sinopharm Chemical Reagent Co., Ltd. PCP, benzo(a)pyrene(BaP),

3-monochlorophenol(3-CP),

2-amino-anthracene(Ant),

2,

4-dichlorophenol(2,4-DCP), fluorene(Flu), 1,3,5-trichlorobenzene(1,3,5-TCP) were purchased from Sigama Aldrich. Phosphate buffered solution (PBS, 0.1 M) of various pH values were prepared by mixing stock standard solutions of NaH2PO4 and Na2HPO4, and the pH was adjusted with 0.1 M H3PO4 or NaOH solution. Chitosan (95 % deacetylation) and other chemicals were of analytical grade and used without further purification. Doubly distilled water was used throughout the work. Apparatus The transmission electron microscopy (TEM) image was obtained with a JEOL 2100 transmission electron microscope (JEOL, Japan) operated at 200 kV. The UV-vis spectra were measured on a Perkin-Elmer Lambda 18 UV-vis-NIR spectrometer (USA). All fluorescence (FL) spectra were acquired by Hitachi F-4500 FL

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 7 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

spectrophotometer (Tokyo, Japan). The X-ray photoelectron spectroscopy (XPS) data were recorded on an Escalab-MKII spectrometer with Mo Kα x-ray as excitation source. All ECL signals were recorded by a Model MPI-A ECL analyzer system with a photomultiplier tube (PMT) biased at 800 V, and the potential was 0 V to −1.8 V in the ECL process. The ECL spectrum was obtained by collecting the ECL peak intensity during the cyclic potential sweep with a series of optical filters at 400, 420, 440, 460, 480 and 500 nm from Omega Optical Inc, USA. All ECL curves were recorded by a conventional three-electrode system where glassy carbon electrode (GCE, 3 mm in diameter) was used as working electrode, Ag/AgCl (saturated KCl solution) as reference electrode and platinum wire as counter electrode, respectively. Preparation of NGQDs and NGQDs-GO nanocomposites The NG (25 mg) was oxidized in concentrated H2SO4 (10 mL) and HNO3 (30 mL) for 24 h under mild ultrasonication (500 W, 40 kHz); after filtration and water washing to neutral, the product (NGO) was dried in a vacuum at 60 oC and then re-dispersed in 20 mL of ultrapure water. The pH of solution was tuned to 8.0 with NaOH. The suspension was transferred to a poly(tetrafluoroethylene) (Teflon)-lined autoclave (25 mL) and heated at 200 oC for 10 h. After cooling to room temperature, the resulting black suspension was filtered through a 0.22-µm microporous membrane and a brown filter solution was separated. The brown filtrate was dialyzed in a dialysis bag (retained molecular weight: 3500 Da) for 12 h, and the resultant NGQDs showed blue photoluminescence under UV light (365 nm).

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 8 of 29 View Article Online

DOI: 10.1039/C4AN01752H

The NGQDs-GO nanocomposites were prepared by physical adsorption. Briefly, the GO was dissolved in double distilled water to form a 0.9 mg/mL GO solution and then, 1 mL NGQDs (0.5 mg/mL) and 1 mL of above-mentioned GO solution were mixed under stirring for 1 h to form NGQDs-GO solution for the use. Fabrication of the modified electrodes Prior to its coating, the GCE was firstly polished with sand paper followed by 1.0, 0.3, and 0.05 mm alumina slurry, respectively, and then sonicated in water to remove any residues. The modified electrode was prepared by a simple casting method as follows: initially, the pretreated GCE was modified by dropping 6 µL aforementioned NGQDs-GO nanocomposites solution and drying, then 6 µL chitosan solution (CHIT) was coated on the NGQDs-GO modified GCE (denoted as NGQDs-GO/CHIT/GCE). As a comparison, similar procedures were used to fabricate the CHIT/GCE, GO/CHIT/GCE and NGQDs/CHIT/GCE, respectively. Results and discussion Characterization The NGQDs were synthesized from NG by the hydrothermal approach described in the experimental section and confirmed by XPS characterizations after analyzing the elemental composition and nitrogen bonding configurations. The full-scan XPS spectrum of the NGQDs was shown in Fig. 1A. Obviously, three elements (C, N, O) were detected with peaks at ~285.9 eV (C 1s), ~400.5 eV (N 1s), and ~532.3 eV (O 1s) respectively, which was in accordance with previous results on N-containing carbon-based materials.15,33 Fig. 1B presented the C1s high-resolution XPS spectra of

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 9 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

as-prepared NGQDs; the components of the C1s spectrum of NGQDs located at 284.8, 285.9, 287.2 and 289.1 eV, representing sp2-sp2C, N-sp2C, N-sp3C and C-O type bonds, respectively.33 To further determine the N configurations existing in the NGQDs, the N 1s spectrum was also analyzed (Fig. 1C). The N 1s peak at 400.5 eV can be deconvoluted into three peaks centered at 398.5, 399.7 and 400.5 eV, corresponding to pyridinic (398.5 eV), amino (399.7 eV) and pyrrolic nitrogen (400.5 eV), respectively.32,34-36 In addition, the high-resolution O 1s spectrum of the NGQDs (Fig. 1D) further confirmed the presence of O-rich groups, which may be infered that the nitric acid-treatment introduces a large amount of oxygenated functional groups.13 It is worth noting that the presence of these oxygenated functional groups make the NGQDs soluble in water and very stable. These results indicated that the NGQDs were prepared successfully. The morphology and structure of NGQDs and NGQDs-GO nanocomposites were investigated by TEM. From Fig. 2A and B, it’s noted that the NGQDs with a size of about 10 nm were attached on the surface of GO sheets with relatively uniform distribution. Compared with Fig. 2A, the layer structure of GO is present as can be seen from the Fig. 2B. The UV-visible absorption was further used to characterize the obtained nanocomposites. As shown in Fig. 2C, the prepared NGQDs and NGQDs-GO in solution displayed similar UV-visible absorption bands centered at 220 nm and 320 nm with a clear blue shift, which is assigned to the π→π* transition of aromatic sp2 domains.37 Furthermore, Fig. 1C showed the corresponding emission spectra of the NGQDs. A strong peak at 418 nm was observed and the ECL spectrum

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 10 of 29 View Article Online

DOI: 10.1039/C4AN01752H

of NGQDs with the maximum wavelength at 442 nm, which is red-shifted (24 nm) compared with the NGQDs PL spectrum excited at 345 nm, suggesting the negligible surface defect of the NGQDs and the surface states have been passivated.9 When the excitation wavelength was changed from 340 to 480 nm, the photoluminescence (PL) peak shifted to longer wavelengths and its intensity decreases rapidly, with the strongest peak excited at the absorption band in Fig. 2D. Apparently, the broad and excitation-dependent emission of NGQDs resemble that of most GQDs, which reflects effects from both sp2 of different size and different emission sites of each sp2 clusters.37,38 Herein, all characterization methods could prove the existence of GO in nanocomposites. ECL behaviors and mechanism of the NGQDs-GO nanocomposites The obtained NGQDs-GO nanocomposites were studied in PBS without and with K2S2O8 as coreactant. The ECL behaviors (Fig. 3A) revealed that the NGQDs-GO/CHIT/GCE produced only a very weak cathodic ECL signal in the absence of coreactant while a strong ECL light emission was observable when the coreactant was present. These results indicate that the ECL comes from the reaction between NGQDs and S2O82−. By referencing the proposed GQDs model,9 the possible ECL detection mechanism is elucidated as below: NGQDs + ne− → nNGQDs•− S2O82− + e− → S2O8•2− S2O8•2− → SO42− + SO4•− NGQDs•− + SO4•− → NGQDs* + SO42−

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 11 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

NGQDs* → NGQDs + hv Furthermore, ECL emission measurements were carried out with CV in 0.1 M PBS (pH = 8.0) containing 100 mM K2S2O8. As shown in Fig. 3B, in the presence of coreactant S2O82−, the ECL emission of the NGQDs-GO/CHIT/GCE (curve d) was much higher than that of the CHIT/GCE (curve a), NGQDs/CHIT/GCE (curve b), and GO/CHIT/GCE (curve c), suggesting that the NGQDs-GO could enhance the ECL signal of the system, effectively. Moreover, it should be highlighted that the ECL intensity from NGQDs-GO/CHIT/GCE was 3.8-fold higher than that observed from NGQDs/CHIT/GCE, indicating that GO not only acted as an immobilization platform for NGQDs, but also served as a good ECL signal amplifier, which would greatly enhance the sensitivity of ECL detection.39 According to previous studies, it may be attributed to that the GO containing oxygen functional groups could create more active sites and the porous structure of the GO-CHIT composite can facilitate the diffusion of coreactant K2S2O8 into the membrane, resulting in the occurrence of ECL signal both at the interface and in the inside of porous film.8 Besides, it can be seen that the ECL onset potential of the NGQDs-GO/CHIT/GCE was 200 mV more positive than that of NGQDs/CHIT/GCE. Fig. 4 showed that the ECL emission was stable under continuous cyclic scans of 10 cycles, demonstrating the ECL emission was high repeatable and the obtained NGQDs-GO sensor was acceptable stability for ECL detection. Optimization of the ECL detection conditions The pH of the test solutions is a crucial factor influencing the ECL reaction of

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 12 of 29 View Article Online

DOI: 10.1039/C4AN01752H

QDs. The change of the ECL signal with the pH of test solutions under a constant concentration of PCP was investigated. As depicted in Fig. 5A, the ECL intensity increases with the increase of in pH (5.0 ~ 8.0) and then drops at higher pH. Possible reason might be stated that when pH was too low, the proton was easy to be reduced to hydrogen at the applied potential, which might inhibit the reduction of S2O82−; while in basic solutions, SO4•− was scavenged by OH-, resulting in a decrease in the ECL intensity.40 Therefore, pH 8.0 was selected in following experiments. Additionally, we discovered that the ECL emission intensity was dependent on the concentration of coreactant. Fig. 5B showed the ECL intensity increased with the increasing S2O82 - concentration from 20 mM to 180 mM and increased to a maximum value at 100 mM. Thus, the ECL detection was performed in PBS (pH = 8.0) containing 100 mM K2S2O8 throughout the experiment. Detection of PCP As shown in Fig. 6A, the ECL intensity decreased gradually with the increasing concentration of PCP, which indicated that the obtained ECL sensor could be utilized for the determination of PCP. The ECL signal decreased linearly with increasing the concentration of PCP ranging from 0.1 to 10 pg/mL with a limit of detection (LOD) of 0.03 pg/mL (S/N = 3) (Fig. 6B). The achieved LOD was much lower than those published in previous reports.41-44 It's worth noting that the LOD was even lower than that of CdS/GQDs in our earlier work.12 The PCP-resulted quenching of the ECL intensity can be elucidated as below: The ECL emission herein was originated from the formation of excited-state NGQDs* via electron transfer annihilation of NGQDs•−

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 13 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

and SO4•− radicals. When PCP was added, it would be absorbed onto the NGQDs-GO surface and be oxidized to produce the chloranil. And then the quenching effect would be happened due to the energy-transfer process, which reduced the production of excited NGQDs* and results in a decrease in ECL,9,12 which was similar to CQDs.41 Interference determination and reproducibility In order to investigate the selectivity of the sensor, interferences of polycyclic aromatic hydrocarbons (Flu, BaP, Ant) and analogs of PCP (3-CP, 2,4-DCP, 1,3,5-CP) on the ECL responses were studied. The results were listed in Table 1. When these analogs of PCP were added, no obvious decrease of ECL intensity was found, suggesting these compounds showed little interference in the detection of PCP. The possible reason might be that: (1) compared with PCP, the analogs of PCP were difficultly oxidized by NGQDs* due to their more stable chemical properties, and (2) the adsorption capacity of NGQDs to different materials was different.41 The reproducibility of the sensor was examined by measuring the ECL responses in 0.1 M PBS (pH 8.0) with 2 pg/mL PCP. In a series of five electrodes prepared in the same way as the manuscript shown, a relative standard deviation (RSD) of 4.6 % was obtained, implying the reliability of this method. We also conducted five measurements using a single electrode were made in 0.1 M PBS (pH=8.0) with 2 pg/mL PCP with RSD of 2.2 %. These results demonstrated this sensor has excellent reproducibility. Analytical application of the sensor in real samples To evaluate the analytical reliability and application potential of the proposed

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 14 of 29 View Article Online

DOI: 10.1039/C4AN01752H

method, real water samples were analyzed using standard addition method. All the water samples were filtered by 0.22 µm cellulose membranes before measurement, and then the solutions were tested using the proposed method and gas chromatograph-mass spectrometer (GC/MS), respectively. The results were shown in Table 2. The percentage recovery assays obtained satisfactory recoveries of 97.00 ∼ 98.32 %. The concentration of PCP measured by the ECL system was higher than the GC results, which was likely due to the interferents existing in river water leading to a positive deviation. All these results indicated that the proposed method could be applied for analysis of real samples. Conclusions In summary, the NGQDs-GO nanocomposites were fabricated via the physical method and applied in the ECL detection of PCP based on the PCP-resulted quenching of the ECL signal. The novel ECL sensor exhibited the supersensitive and selective towards to the detection of PCP through a multistage NGQDs ECL signal amplification.

More

importantly,

NGQDs-GO

nanocomposites

show

more

outstanding ECL performances compared with the NGQDs. Further, the ECL sensor exhibits well in PCP-selective sensing with a wide linear relationship and a low detection. The application of this ECL sensor in real sample analysis showed satisfactory results. Besides, the present sensor has many advantages such as avoiding complicated experiment design, regenerability and low toxicity and thus, it could be a promising method for the emergency and routine monitoring of PCP in real water samples.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 15 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Acknowledgements The present work was supported by the National Natural Science Foundation of China (Nos. 21175061, 21375050 and 21405062), China Postdoctoral Science Foundation (no. 2014M551507), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (No. PAPD-2014-37), Qing Lan Project and Key Laboratory of Modern Agriculture Equipment and Technology (No. NZ201109).

References 1 X. Sun, Z. Liu, K. Welsher, J. T. Robinson, A. Goodwin and S. Zaric, Nano Res., 2008, 1, 203-212. 2 Y. Q. Dong, G. L. Li, N. N. Zhou, R. X. Wang, Y. W. Chi and G. N. Chen, Anal Chem., 2012, 84, 8378-8382. 3 Y. Li, Y. Zhao, H. Cheng, Y. Hu, G. Shi, L. Dai and L. Qu, J. Am. Chem. Soc., 2012, 134, 15-18. 4 X. Yan, X. Cui, B. Li and L. Li, Nano Lett., 2010, 10, 1869-1873. 5 Z. P. Zhang, J. Zhang, N. Chen and L. T. Qu, Energy Environ Sci., 2012, 5, 8869-8890. 6 D. Y. Pan, J. C. Zhang, Z. Li and M. H. Wu, Adv. Mater., 2010, 22, 734-738. 7 L. L. Li, G. H. Wu, G. H. Yang, J. Peng, J. Zhao and J. J. Zhu, Nanoscale, 2013, 5, 4015-4039.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 16 of 29 View Article Online

DOI: 10.1039/C4AN01752H

8 T. Wang, S. Y. Zhang, C. J. Mao, J. M. Song, H. L. Niu, B. K. Jin and Y. P. Tian, Biosens. Bioelectron., 2012, 31, 369-375. 9 L. L. Li, J. Ji, R. Fei, C. Z. Wang, Q. Lu, J. R. Zhang, L. P. Jiang and J. J. Zhu, Adv. Funct. Mater., 2012, 22, 2971-2979. 10 J. J. Lu, M. Yan, L. Ge, S. G. Ge, S. W. Wang, J. X. Yan and J. H. Yu, Biosens. Bioelectron., 2013, 47, 271-277. 11 D. Tang, J. Liu, X. Y. Wu, R. H. Liu, X. Han, Y. Z. Han, H. Huang, Y. Liu, and Z. H. Kang, ACS Appl. Mater. Interfaces, 2014, 6, 7918-7925. 12 Q. L, J. R. Cai, K. Wang, J. Huan, J. Q, H. P. Mao and G. B. Zhu, Analyst, 2014, 139, 2912-2918. 13 Y. Liu and P. Y. Wu, ACS Appl. Mater. Interfaces, 2013, 5, 3362-3369. 14 H. T. Liu, Y. Q. Liu and D. B. Zhu, J. Mater. Chem., 2011, 21, 3335-3345. 15 K. P. Gong, F. Du, Z. H. Xia, M. Durstock and L. M. Dai, Science, 2009, 323, 760-764. 16 Z. T. Fan, Y. C. Li, X. H. Li, L. Z. Fan, S. X. Zhou, D. C. Fang and S. H. Yang, Carbon, 2014, 70, 149-156. 17 Q. Liu, B. Guo, Z. Rao, B. Zhang, and J. R. Gong, Nano Lett., 2013, 13, 2436-2441. 18 Y. Dong, H. P. Yang, H. B. Guo, C. Shao, J. Chi, Y. Li, C. M. T. Yu, Angew. Chem. Int. Ed., 2013, 52, 7800-7804. 19 L. B. Tang, R. B. Ji, X. M. Li, K. S. Teng and S. P. Lau, J. Mater. Chem. C, 2013, 1, 4908-4915.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 17 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

20 J. Ju and W. Chen, Biosens. Bioelectron., 2014, 58, 219-225. 21 W. Y. Shiu, K. C. Ma, D. Varhanickova and D. Mackay, Chemosphere, 1994, 29, 1155-1224. 22 L. H. Keith and W. A. Telliard, Environ. Sci. Technol., 1979, 13, 416-423. 23 Y. Ding and C. D. Garcia, Analyst, 2006, 131, 208-214. 24 Y. R. Wang and H. W. Chen, J. Chromatogr., A, 2005, 1080, 192-198. 25 M. Thomassin, E. Cavalli, Y. Guillaume and C. Guinchard, J. Pharm. Biomed. Anal., 1997, 15, 831-838. 26 W. J. Dong, J. P. Song, C. Dong and M. M. F. Choi, Chin. Chem. Lett., 2010, 21, 346-348. 27 A. Ogawa, H. Arai, H. Tanizawa, T. Miyahara and T. Toyo'o ka, Anal. Chim. Acta, 1999, 383, 221-230. 28 J. P. Lei and H. X. Ju, Trends Anal. Chem., 2011, 30, 1351-1359. 29 D. Du, L. M. Wang, Y. Y. Shao, J. Wang, M. H. Engelhard and Y. H. Lin, Anal. Chem., 2011, 83, 746-752. 30 S. J. He, B. Song, D. Li, C. F. Zhu, W. P. Qi, Y. Q. Wen, L. H. Wang, S. P. Song, H. P. Fang and C. H. Fan, Adv. Funct. Mater., 2010, 20, 453-459. 31 S. Gilje, S. Han, M. S. Wang, K. L. Wang and R. B. Kaner, Nano Lett., 2007, 7, 3394-3397. 32 D. Jiang, Q. Liu, K. Wang, J. Qian, X. Y. Dong, Z. T. Yang, X. J. Du and B. J. Qiu, Biosens. Bioelectron., 2014, 54, 273-278. 33 K. J. Zhang, P. X. Han, L. Gu, L. X. Zhang, Z. H. Liu, Q. S. Kong, C. J. Zhang, S.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 18 of 29 View Article Online

DOI: 10.1039/C4AN01752H

M. Dong, Z. Y. Zhang, J. H. Yao, H. X. Xu, G. L. Cui , and L. Q. Chen, ACS Appl. Mater. Interfaces 2012, 4, 658-664. 34 D. Wei, Y. Liu, Y. Wang, H. Zhang, L. Huang and G. Yu, Nano Lett., 2009, 9, 1752-1758. 35 H. M. Jeong, J. W. Lee, W. H. Shin, Y. J. Choi, H. J. Shin, J. K. Kang and J. W. Choi, Nano Lett., 2011, 11, 2472-2477. 36 A. L. M. Reddy, A. Srivastava, S. R. Gowda, H. Gullapalli, M. Dubey and P. M. Ajayan, ACS Nano., 2010, 4, 6337-6342. 37 D. Pan, J. Zhang, Z. Li and M. Wu, Adv. Mater., 2010, 22, 734-738. 38 Y. Q. Dong, J. W. Shao, C. Q. Chen, H. Li, R. X Wang, Y. W. Chi, X. M. Lin and G.N. Chen, Carbon, 2012, 50, 4738-4743. 39 Y. Wang, J. Lu, L. H. Tang, H. X. Chang and J. H Li, Anal. Chem., 2009, 81, 9710-9715. 40 W. Yao, L. Wang, H. Wang and X. Zhang, Electrochim. Acta, 2008, 54, 733-737. 41 S. L. Yang, J. S. Liang, S. L. Luo, C. B. Liu and Y. H. Tang, Anal. Chem., 2013, 85, 7720-7725. 42 Q. Kang, L. X. Yang, Y. F. Chen, S. L. Luo, L. F. Wen, Q. Y. Cai and S. Z. Yao, Anal. Chem., 2010, 82, 9749-9754. 43 J. Zou, J. A. Ma, Y. X. Zhang, L. Li, J. Z. Jiang and J. F. Chen, Analytical Letters, 2013, 46, 1108-1116. 44 J. S. Liang, S. L. Yang, S. L. Luo, C. B. Liu, Y. H. Tang, Microchim. Acta, 2014, 181, 759-765.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 19 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Figure captions

Scheme 1 Schematic showing the ECL detection of PCP with NGQDs-GO/GCE in S2O82



solution.

Fig. 1 (A) Full-scan XPS spectrum of the NGQDs; (B) The C1s XPS spectrum; (C) The N1s XPS spectrum; (D) The O1s XPS spectrum.

Fig. 2 TEM of (A) NGQDs and (B) NGQDs-GO; (C) UV-vis absorption of the NGQDs and NGQDs-GO dispersed in water and PL (at 345nm excitation) and ECL spectra of the NGQDs; Inset: Photograph of the NGQDs aqueous solution taken under the visible light and a 365 nm UV lamp. (D) PL spectra of the NGQDs at different excitation wavelengths.

Fig. 3 (A) ECL curves of NGQDs-GO/CHIT /GCE in 0.1 M PBS (pH = 8.0) in the absence (a) and presence (b) of 100 mM K2S2O8; (B) ECL-potential curves of (a) CHIT/GCE,

(b)

GO/CHIT/GCE,

(c)

NGQDs/CHIT/GCE

and

(d)

NGQDs-GO/CHIT/GCE in 0.1 M PBS (pH = 8.0) containing 100 mM S2O82-.

Fig. 4 ECL emission from NGQDs-GO/CHIT with 100 mM S2O82- under continuous cyclic scans for 10 cycles.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 20 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Fig. 5 Influences of (A) pH and (B) the concentrations of S2O82



on the ECL

intensity.

- Fig. 6 ECL intensity response of NGQDs-GO/CHIT in 100 mM S2O82 solution (pH

= 8.0) at different concentrations of PCP (pg/mL): (a) 0.1, (b) 1, (c) 10, (d) 100, (e) 2000 and (f) 10 000; the inset plot is the calibration curve for PCP determination.

Table 1 Interferences in PCP detection.

Table 2 Results of recovery tests for PCP detection in river water.

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 21 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Scheme 1

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 22 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Fig. 1

B

O 1s

N 1s

300 600 900 Binding energy (eV)

390

280

D

N 1s

285 290 295 Binding energy (eV)

O 1s

Intensity (a.u.)

C

1200

395 400 405 410 Binding energy (eV)

415 525

530 535 540 Binding energy (eV)

Analyst Accepted Manuscript

C 1s

0

C1s

Intensity (a.u.)

Intensity (a.u.)

A

Intensity (a.u.)

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 23 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

0.6 PL ECL

0.2

0.0

NGQDs

Intensity (a.u.)

0.4

340 nm 360 nm 380 nm 400 nm 420 nm 440 nm 460 nm 480 nm

D PL Intensity (a.u.)

C

NGQDs-GO

200

300 400 500 Wavelength (nm)

600

360

420 480 540 Wavelength (nm)

600

Analyst Accepted Manuscript

Fig. 2

Absorption

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 24 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Fig. 3

12.0k

9.0k 6.0k

b

B

30 28

ECL Intensity (a.u.)

ECL Intebsity ( a.u.)

A

26 24 22 0

10 20 Time ( s)

30

3.0k

a

0.0 0

10

20 Time (s)

30

40

d

9.0k 6.0k 3.0k

c

0.0

b a -2.0

-1.5 -1.0 -0.5 Potential (V)

0.0

Analyst Accepted Manuscript

12.0k ECL Intensity (a.u.)

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 25 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Fig. 4 12.0k 9.0k 6.0k 3.0k 0.0 0

100

200 Time (s)

300

Analyst Accepted Manuscript

ECL Intensity (a.u.)

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 26 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Fig. 5 12.0k

12.0k A

B

9.0k 6.0k 3.0k 5

6

7

8 pH

9

10

11

9.0k

6.0k

3.0k 0

50

100 150 K2S2O8 (mM)

200

Analyst Accepted Manuscript

ECL Intensity (a.u.)

ECL Intensity ( a.u.)

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 27 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Fig. 6 10.0k

12.0k b

c d e

6.0k 3.0k 0.0 Time (s)

f

8.0k

6.0k

4.0k -1.2

0.0

1.2 2.4 lg C

3.6

Analyst Accepted Manuscript

9.0k

B

A a

ECL Intensity (a.u.)

ECL Intensity (a.u.)

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analyst

Page 28 of 29 View Article Online

DOI: 10.1039/C4AN01752H

Table 1

Interferences in PCP detection. Substance

Concentration

∆I/I

Blank

/

0.00 % -10

Flu

6.0×10

BaP

9.5×10

Ant

7.0×10

3-CP

5.0×10

2,4-DCP

6.0×10

1,3,5-CP

7.5×10

PCP

1.0×10

Mixed Interferences

4.1×10

-10

-10

-10

-10

-10

-10

-9

4.88 % 6.22 % 5.31 % 2.15 % 2.66 % 3.56 % 74.18 % 19.24 %

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 29 of 29

Analyst View Article Online

DOI: 10.1039/C4AN01752H

Table 2

Results of recovery tests for PCP detection in river water. Added

Found

GC/MS

Recovery

RSD (%)

(pg/L)

(pg/L)

(pg/L)

(%)

(n = 3)

0

39.6 ± 0.2

37.8 ± 0.2

/

3.58

10

48.2 ± 0.1

45.7 ± 0.3

97.18

4.22

20

58.6 ± 0.2

56.6 ± 0.2

98.32

6.65

30

67.5 ± 0.3

66.4 ± 0.1

97.00

5.22

Sample

River water

Analyst Accepted Manuscript

Published on 10 December 2014. Downloaded by University of California - San Francisco on 17/12/2014 08:44:54.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fabrication of graphene oxide decorated with nitrogen-doped graphene quantum dots and its enhanced electrochemiluminescence for ultrasensitive detection of pentachlorophenol.

Nitrogen-doped graphene quantum dots (NGQDs), as a new class of quantum dots, have potential applications in fuel cells and optoelectronics fields due...
2MB Sizes 2 Downloads 7 Views