Editorial
For reprint orders, please contact [email protected]
Paper microfluidics in bioanalysis “...the potential of microfluidics may soon be realized via paper microfluidics and particularly how it relates to bioanalysis, healthcare, medicine and point-of-care (POC) diagnostics.” Keywords: diagnostics • lab-on-a-chip • paper microfluidics
Since the pioneering work by Manz et al. nearly all areas of the chemical, biological, medicinal and agricultural sectors have integrated a microfluidic platform to examine a myriad of molecular species [1] . In fact, applications for microelectromechanical systems (MEMS) have proliferated at a speed reminiscent of the explosive use of microelectronics after the invention of the integrated circuit. Microfluidics is a combination of fluid mechanics, engineering, chemistry, surface science and biology (and frequently microscopy, optics, control systems, electronics and microfabrication) all in one. Research in the field involves integrating many disciplines. Microfluidic lab-on-a-chip technologies represent a new paradigm in laboratory experimentation, providing the benefits of miniaturization, integration, and automation to a myriad of researchbased industries. Microfluidic techniques offer several advantages including speed to analysis, portability, ability to multiplex, and compatibility with other techniques. The number of institute for scientific information (ISI) publications found with ‘microfluidic’ in the title has grown from less than 100 in 1994, to nearly 1000 in 2004, to over 3000 today. These papers are focused on biochemical applications and especially point-of-care (POC) diagnostics, drug discovery and bioterrorism detection. Reasons are simple: microfluidic devices (MDs) are inexpensive and relatively easy to fabricate, are easily maintained requiring little space in a laboratory setting, and require only small sample volumes and reagents. It became quite apparent in the early development of microfluidics that the technology
10.4155/BIO.14.240 © 2014 Future Science Ltd
held great promise in bioanalysis and, in particular, medicine and healthcare. The sheer size of the platforms, albeit not yet in the proportions currently available, small sample volume requirements, low costs due to mass production, fast sampling times, low power consumption, just to name a few, and their potential to supplant instruments of greater dimensions, was enticing to those with longterm vision. The current multiple challenges of an aging population, increasing healthcare costs, the need to bring healthcare to developing countries, and the shift in business models of big pharma from drug-based delivery to preventative and personalized, makes microfluidic diagnostics a leading technology to participate in personalized medicine in the future. Yet, why has the potential of microfluidcs not yet been realized? There are three major reasons why microfluidic diagnostics are yet to have the impact on personalized medicine once dreamt of. The first reason is simple economics and the need for the pharmaceutical industry to continue to sell as much medicine to as many people as possible with little consideration to predictive, personalized, and preemptive medicine. Furthermore, big pharma’s agenda determines trends in funding for biomedical innovation, hence, little has flowed into the biotech sector for personalized approaches. The second reason is due to a technology lag. While great progress has been made in next-generation sequencing platforms, and in proof-of-concept MDs, integrated and foolproof POC devices remain way off into the future.
Bioanalysis (2014) 6(21), 2911–2914
Frank A Gomez Department of Chemistry & Biochemistry California State University, 5151 State University Drive Los Angeles, California, CA 90032–8202, USA Tel.: +1 323 343 2368 Fax: +1 323 343 6490 fgomez2@ calstatela.edu
part of
ISSN 1757-6180
2911
Editorial Gomez The third reason is the inherent problems associated with biology. Science continues to be part black box as all the data in the world cannot unequivocally provide the answer to a patient’s question(s) either at the doctor’s office or in a MD purchased at a local store. The fact that gene mutations do not perfectly predict outcomes is a simple analogy in the molecular biology world. Couple in other technological challenges, regulatory hurdles, commercial and intellectual property concerns, further impede the potential of microfluidics.
“Paper microfluidics may, in fact, be the answer to the three major reasons microfluidics has yet taken the consumer markets by storm.” Fortunately, since the original seminal works of Whitesides et al. [2–9] , the potential of microfluidics may soon be realized via paper microfluidics and particularly how it relates to bioanalysis, healthcare, medicine and POC diagnostics. While on the surface it may appear odd to have returned to such a simple material (paper) given the longstanding emphasis in microfluidics on silicon, glass, ceramic, elastomers, and thermoplastics, the use of paper is actually quite apropos given its simplicity. Paper is a natural platform for microfluidics-based applications mainly due to its availability and low cost, its ability to wick aqueous fluidics allowing for facile transport of fluidics without the use of active pumping, and its historical use as a platform in analytical chemistry (chromatography). Furthermore, paper is thin, available in a variety of thicknesses, lightweight, easy to stack, store, and transport, is compatible with biological samples given its composition (cellulose or blends thereof ), easy to chemically modify for functionalization, typically white thereby amenable for colorimetric tests, and is available in many forms with a diverse range of properties. Paper microfluidics may, in fact, be the answer to the three major reasons microfluidics has yet taken the consumer markets by storm. Furthermore, paper microfluidics is emerging as a multiplexable POC platform that may transcend the capabilities of current assays in settings where resources are limited. The following is a short compilation of the salient works in paper microfluidics over the past year. An inherent problem with paper microfluidics is the intrinsically slow rate of fluid flow in cellulosic channels since flow is driven by capillary action and the distance a liquid travels is proportional to the square root of time. When developing a POC diagnostic device, time is critical, and additional problems that can arise due to solvent evaporation leading
2912
Bioanalysis (2014) 6(21)
to component concentration is not desirable. A recent paper by Renault et al. described a microfluidic paper analytical device (μPAD) utilizing hollow channels as a substitute for cellulose to transport fluids in the development of colorimetric glucose and BSA assays [10] . In this three-layer platform, the top, middle, and bottom layers make up the sample injection, hollowed, and hydrophilic sections, respectively, of the device, thereby resulting in an enhanced flow rate of liquid within the channel by a factor of seven. Hollow μPADs offer reduced analysis times, decreased nonspecific adsorption, do not require external equipment, and have the potential for examination of micron-sized objects within the channels not permissible in cellulose-based platforms. While the focus of paper microfluidics has been on colorimetric detection, recent work has integrated fluorescent, chemiluminescent, electrochemical and electrochemiluminescence (ECL) [11–13] . Mani et al. have developed an inexpensive paper-based ECL device (μPED) fabricated using screen printing of electrodes to detect potential pollutant activity in environmental samples [14] . Specifically, genotoxic equivalents in environmental samples were rapidly measured using as, proof-of-concept, smoke (cigarette), water (treated and untreated sewage) and food samples (chicken extract from charred skin). Here, a pattern was cut out of commercial wax paper then transferred onto filter paper to make hydrophilic channels/spots surrounded by hydrophobic boundaries defined by the wax pattern. The filter paper is screen printed with both carbon working and counter electrodes and a Ag/AgCl reference electrode by use of a stencil fashioned from a plastic transparency paper (film). The advantages of the fabrication include cost (only US$0.80 in materials), time (10 min), and materials (all commercially available.). Little to no specialized technical expertise or equipment is required, scale up is possible with the use of automated instruments, larger heat press, and printer for electrodes, and there is the potential for rapid prototyping for other paper microfluidics applications. The μPED is different from conventional devices that only measure concentrations of individual compounds as it monitors the potential for genotoxicity resulting from the combined pool of toxic chemical that are present in the sample. Microfluidics applications have typically focused on the study and analysis of a single type of biomolecule thereby limiting their use. The ability to do analysis on a variety of proteins, simultaneously, would be relevant to both physicians and patients. Concomitant with this expansion to a multiplexed system would be the required greater sample volumes and
future science group
Paper microfluidics in bioanalysis
increased sample time in addition to technical expertise and higher costs. Malhotra et al. have described a low-cost electrochemical microfluidic array to measure a four-protein panel of four head and neck squamous cell carcinoma (HNSCC) biomarker proteins (interleukin 6 [IL-6], IL-8, vascular endothelial growth factor [VEGF], and VEGF-C in diluted serum) important in the diagnosis of oral cancer [15] . The device consists of an array of nanostructured sensors and labeled beads. A variety of antibodies are attached to the sensor elements, and paramagnetic beads loaded with horseradish peroxidases (HRPs) and secondary antibodies are used to capture proteins from the sample off-line. The work focuses on optimization of the array to allow for simultaneous detection (5−50 fg/ml range) and measurement of the four HNSCC proteins simultaneously and in serum. A formidable goal of paper-based microfluidic diagnostics is the development of a device that does not require an external reader. Lewis et al. utilized time as readout to quantify enzyme analytes where time is measured for a region in the paper device that turns green relative to the assay region [16] . The technique is internally calibrated and compensates for effects of humidity, temperature, and sample viscosity on sample distribution. The assay is sensitive (femtomolar), has short measurement times (15 s to 30 min), is selective, inexpensive, and easy to use. The device is made of stacked layers of wax-patterned papers held together using spray adhesive followed by lamination. The key component of the device is the existence in the one of the layers of bead-bound glucose oxidase which converts d-glucose to product and hydrogen peroxide. The released hydrogen peroxide then encounters an oligomer that is hydrophobic but which will convert to hydrophilic products via a cascade depolymerization reaction. This change in surface character allows the sample to flow through the layers of the device at a rate dependent on the concentration of hydrogen peroxide in the sample which can be correlated to the enzyme analyte. The sample then passes through multiple layers containing the polymer, thereby, redissolving dried green food coloring which is observed in the top of the paper device. Alkaline phosphates and β-galactoside are used as model systems to demonstrate selectivity. Wu et al. were able to demonstrate the development of a paper-based electrochemical immunodevice to detect cancer biomarkers [17] . Here, signal amplification was achieved by use of a graphene film to accelerate electron transfer and silica nanoparticles as a tracing tag for signal antibody labeling using the horseradish peroxidase (HRP)−O-phenylenediamine−hydrogen peroxide electrochemical detection system. A simple,
future science group
Editorial
accurate, and rapid POC assay using a photoresistpatterned microfluidic paper-based analytical device (uPAD) was demonstrated. The device was stable, and yielded reproducible and accurate results thereby demonstrating its efficacy for use in clinical diagnostics. Other recent notable works include the development of paper microfluidic platforms to examine the binding of antibodies via fusion proteins on carbohydrate binding modules [18] , multiplex MDs to diagnosis hepatitis C virus infection [19] , and assays to determine protein and glucose in urine [20] . In the future, paper microfluidics will play a monumental role in the development of individual lab-on-a-chip components in bioanalysis and, in particular, POC diagnostic devices. This simple technology offers new possibilities in a myriad of disciplines due to its practicality and ease of integration into a variety of platforms. As has been detailed, paper microfluidics has great promise in bioanalysis due to its ability to multiplex, sample storage, mixing, and filtration, sample volume control, and ability to analyze an array of samples simultaneously. Forward thinking researchers will see that there are many opportunities for this technology and to expand its capabilities. One area that could broaden the use of paper microfluidics is if statistical methods and computational techniques are used to examine the effect of experimental variables on output response, data classification and signal processing capabilities, as well as the robustness of device output to variations in platform design. Without this optimization, there exists the difficulty in developing technologies that may one day lead to commercialization and products that could serve a useful societal purpose. For the future, it is integral that a balance be struck between scientific invention, innovation, and development and commercialization so as to provide better access and quality of healthcare to people throughout the world through the use of devices developed via paper microfluidic methodologies. Financial & competing interests disclosure The author gratefully acknowledges financial support for this research by grants from the National Science Foundation (EEC-0812348, HRD-0934146, and OISE-0965911). The authors have no other relevant affiliations or financial involvement with an organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
www.future-science.com
2913
Editorial Gomez multiplexed measurement of biomarkers and point-of-care testing. Biomaterials 33(4), 1024–1031 (2012).
References 1
Manz A, Graber N, Widmer HM. Miniaturized total chemical analysis systems: a novel concept for chemical sensing. Sensor Actuat. B Chem. 1, 244–248 (1990).
2
Martinez AW, Phillips ST, Butte MJ, Whitesides GM. Patterned paper as a platform for inexpensive, low-volume, portable bioassays. Angew. Chem. Int. Ed. 46(8), 1318–1320 (2007).
3
Martinez AW, Phillips ST, Carrilho E, Thomas III SW, Sindi H, Whitesides GM. Simple telemedicine for developing regions: camera phones and paper-based microfluidic devices for real-time, off-site diagnosis. Anal. Chem. 80(10), 3699–3707 (2008).
4
5
2914
Bruzewicz DA, Reches M, Whitesides GM. Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper. Anal. Chem. 80(9), 3387–3392 (2008). Martinez AW, Phillips ST, Wiley BJ, Gupta M, Whitesides GM. FLASH: A rapid method for prototyping paper-based microfluidic devices. Lab Chip 8(12), 2146–2150 (2008).
6
Carrilho E, Phillips ST, Vella SJ, Martinez AW, Whitesides GM. Paper microzone plates. Anal. Chem. 81(15), 5990– 5998 (2009).
7
Carrilho E, Martinez AW, Whitesides AW. Understanding wax printing: a simple micropatterning process for paperbased microfluidics. Anal. Chem. 81(16), 7091–7095 (2009).
8
Martinez AW, Phillips ST, Whitesides GM, Carrilho E. Diagnostics for the developing world: microfluidic paperbased analytical devices. Anal. Chem. 82(1), 3–10 (2010).
9
Schilling KM, Lepore AL, Kurian JA, Martinez AW. Fully enclosed microfluidic paper-based analytical devices. Anal. Chem. 84(7), 1579–1585 (2012).
10
Renault C, Li X, Fosdick SE, Crooks RM. Hollow-channel paper analytical devices. Anal. Chem. 85(16), 7976–7979 (2013).
11
Ge L, Yan J, Song X, Yan M, Ge S, Yu J. Three dimensional paper-based electrochemiluminescence Immunodevice for
Bioanalysis (2014) 6(21)
12
Delaney JL, Hogan CF, Tian J, Shen W. Electrogenerated chemiluminescence detection in paper-based microfluidic sensors. Anal. Chem. 83(4), 1300–1306 (2011).
13
Thom NK, Yeung K, Pillion MB, Phillips ST. Fluidic batteries as low-cost sources of power in paper-based microfluidic devices. Lab Chip 12(10), 1768–1770 (2012).
14
Mani V, Kadimisetty K, Malla S, Joshi AA, Rusling JF. Paper-based electrochemiluminescent screening for genotoxic activity in the environment. Environ. Sci. Technol. 47(4), 1937–1944 (2013).
15
Malhotra R, Patel V, Chikkaveeraiah BV et al. Ultrasensitive detection of cancer biomarkers in the clinic. Anal. Chem. 84(14), 6249–6255 (2012).
16
Lewis GG, Robbins JS, Phillips ST. A rapid point-of-care assay platform for quantifying active enzymes to femtomolar levels using measurements of time as the readout. Anal. Chem. 85(21), 10432–10439 (2013).
17
Wu Y, Xue P, Kang Y, Hui KM. Paper-based microfluidic electrochemical immunodevice integrated with nanobioprobes onto graphene film for ultrasensitive multiplexed detection of cancer biomarkers. Anal. Chem. 85(18), 8661–8668 (2013).
18
Rosa AMM, Louro AF, Martins SAM, Inácio J, Azevedo AM, Prazeres DMF. Capture and detection of DNA hybrids on paper via the anchoring of antibodies with fusions of carbohydrate binding modules and ZZ-domains. Anal. Chem. 86(9), 4340–4347 (2014).
19
Mu X, Zhang L, Chang S, Cui W, Zheng Z. Multiplex microfluidic paper-based immunoassay for the diagnosis of hepatitis C virus infection. Anal. Chem. 86(11), 5338–5344 (2014).
20
Sechi D, Greer B, Johnson J, Hashemi N. Three-dimensional paper-based microfluidic device for assays of protein and glucose in urine. Anal. Chem. 85(22), 10733–10737 (2013).
future science group
For reprint orders, please contact [email protected]
Paper microfluidics in bioanalysis “...the potential of microfluidics may soon be realized via paper microfluidics and particularly how it relates to bioanalysis, healthcare, medicine and point-of-care (POC) diagnostics.” Keywords: diagnostics • lab-on-a-chip • paper microfluidics
Since the pioneering work by Manz et al. nearly all areas of the chemical, biological, medicinal and agricultural sectors have integrated a microfluidic platform to examine a myriad of molecular species [1] . In fact, applications for microelectromechanical systems (MEMS) have proliferated at a speed reminiscent of the explosive use of microelectronics after the invention of the integrated circuit. Microfluidics is a combination of fluid mechanics, engineering, chemistry, surface science and biology (and frequently microscopy, optics, control systems, electronics and microfabrication) all in one. Research in the field involves integrating many disciplines. Microfluidic lab-on-a-chip technologies represent a new paradigm in laboratory experimentation, providing the benefits of miniaturization, integration, and automation to a myriad of researchbased industries. Microfluidic techniques offer several advantages including speed to analysis, portability, ability to multiplex, and compatibility with other techniques. The number of institute for scientific information (ISI) publications found with ‘microfluidic’ in the title has grown from less than 100 in 1994, to nearly 1000 in 2004, to over 3000 today. These papers are focused on biochemical applications and especially point-of-care (POC) diagnostics, drug discovery and bioterrorism detection. Reasons are simple: microfluidic devices (MDs) are inexpensive and relatively easy to fabricate, are easily maintained requiring little space in a laboratory setting, and require only small sample volumes and reagents. It became quite apparent in the early development of microfluidics that the technology
10.4155/BIO.14.240 © 2014 Future Science Ltd
held great promise in bioanalysis and, in particular, medicine and healthcare. The sheer size of the platforms, albeit not yet in the proportions currently available, small sample volume requirements, low costs due to mass production, fast sampling times, low power consumption, just to name a few, and their potential to supplant instruments of greater dimensions, was enticing to those with longterm vision. The current multiple challenges of an aging population, increasing healthcare costs, the need to bring healthcare to developing countries, and the shift in business models of big pharma from drug-based delivery to preventative and personalized, makes microfluidic diagnostics a leading technology to participate in personalized medicine in the future. Yet, why has the potential of microfluidcs not yet been realized? There are three major reasons why microfluidic diagnostics are yet to have the impact on personalized medicine once dreamt of. The first reason is simple economics and the need for the pharmaceutical industry to continue to sell as much medicine to as many people as possible with little consideration to predictive, personalized, and preemptive medicine. Furthermore, big pharma’s agenda determines trends in funding for biomedical innovation, hence, little has flowed into the biotech sector for personalized approaches. The second reason is due to a technology lag. While great progress has been made in next-generation sequencing platforms, and in proof-of-concept MDs, integrated and foolproof POC devices remain way off into the future.
Bioanalysis (2014) 6(21), 2911–2914
Frank A Gomez Department of Chemistry & Biochemistry California State University, 5151 State University Drive Los Angeles, California, CA 90032–8202, USA Tel.: +1 323 343 2368 Fax: +1 323 343 6490 fgomez2@ calstatela.edu
part of
ISSN 1757-6180
2911
Editorial Gomez The third reason is the inherent problems associated with biology. Science continues to be part black box as all the data in the world cannot unequivocally provide the answer to a patient’s question(s) either at the doctor’s office or in a MD purchased at a local store. The fact that gene mutations do not perfectly predict outcomes is a simple analogy in the molecular biology world. Couple in other technological challenges, regulatory hurdles, commercial and intellectual property concerns, further impede the potential of microfluidics.
“Paper microfluidics may, in fact, be the answer to the three major reasons microfluidics has yet taken the consumer markets by storm.” Fortunately, since the original seminal works of Whitesides et al. [2–9] , the potential of microfluidics may soon be realized via paper microfluidics and particularly how it relates to bioanalysis, healthcare, medicine and POC diagnostics. While on the surface it may appear odd to have returned to such a simple material (paper) given the longstanding emphasis in microfluidics on silicon, glass, ceramic, elastomers, and thermoplastics, the use of paper is actually quite apropos given its simplicity. Paper is a natural platform for microfluidics-based applications mainly due to its availability and low cost, its ability to wick aqueous fluidics allowing for facile transport of fluidics without the use of active pumping, and its historical use as a platform in analytical chemistry (chromatography). Furthermore, paper is thin, available in a variety of thicknesses, lightweight, easy to stack, store, and transport, is compatible with biological samples given its composition (cellulose or blends thereof ), easy to chemically modify for functionalization, typically white thereby amenable for colorimetric tests, and is available in many forms with a diverse range of properties. Paper microfluidics may, in fact, be the answer to the three major reasons microfluidics has yet taken the consumer markets by storm. Furthermore, paper microfluidics is emerging as a multiplexable POC platform that may transcend the capabilities of current assays in settings where resources are limited. The following is a short compilation of the salient works in paper microfluidics over the past year. An inherent problem with paper microfluidics is the intrinsically slow rate of fluid flow in cellulosic channels since flow is driven by capillary action and the distance a liquid travels is proportional to the square root of time. When developing a POC diagnostic device, time is critical, and additional problems that can arise due to solvent evaporation leading
2912
Bioanalysis (2014) 6(21)
to component concentration is not desirable. A recent paper by Renault et al. described a microfluidic paper analytical device (μPAD) utilizing hollow channels as a substitute for cellulose to transport fluids in the development of colorimetric glucose and BSA assays [10] . In this three-layer platform, the top, middle, and bottom layers make up the sample injection, hollowed, and hydrophilic sections, respectively, of the device, thereby resulting in an enhanced flow rate of liquid within the channel by a factor of seven. Hollow μPADs offer reduced analysis times, decreased nonspecific adsorption, do not require external equipment, and have the potential for examination of micron-sized objects within the channels not permissible in cellulose-based platforms. While the focus of paper microfluidics has been on colorimetric detection, recent work has integrated fluorescent, chemiluminescent, electrochemical and electrochemiluminescence (ECL) [11–13] . Mani et al. have developed an inexpensive paper-based ECL device (μPED) fabricated using screen printing of electrodes to detect potential pollutant activity in environmental samples [14] . Specifically, genotoxic equivalents in environmental samples were rapidly measured using as, proof-of-concept, smoke (cigarette), water (treated and untreated sewage) and food samples (chicken extract from charred skin). Here, a pattern was cut out of commercial wax paper then transferred onto filter paper to make hydrophilic channels/spots surrounded by hydrophobic boundaries defined by the wax pattern. The filter paper is screen printed with both carbon working and counter electrodes and a Ag/AgCl reference electrode by use of a stencil fashioned from a plastic transparency paper (film). The advantages of the fabrication include cost (only US$0.80 in materials), time (10 min), and materials (all commercially available.). Little to no specialized technical expertise or equipment is required, scale up is possible with the use of automated instruments, larger heat press, and printer for electrodes, and there is the potential for rapid prototyping for other paper microfluidics applications. The μPED is different from conventional devices that only measure concentrations of individual compounds as it monitors the potential for genotoxicity resulting from the combined pool of toxic chemical that are present in the sample. Microfluidics applications have typically focused on the study and analysis of a single type of biomolecule thereby limiting their use. The ability to do analysis on a variety of proteins, simultaneously, would be relevant to both physicians and patients. Concomitant with this expansion to a multiplexed system would be the required greater sample volumes and
future science group
Paper microfluidics in bioanalysis
increased sample time in addition to technical expertise and higher costs. Malhotra et al. have described a low-cost electrochemical microfluidic array to measure a four-protein panel of four head and neck squamous cell carcinoma (HNSCC) biomarker proteins (interleukin 6 [IL-6], IL-8, vascular endothelial growth factor [VEGF], and VEGF-C in diluted serum) important in the diagnosis of oral cancer [15] . The device consists of an array of nanostructured sensors and labeled beads. A variety of antibodies are attached to the sensor elements, and paramagnetic beads loaded with horseradish peroxidases (HRPs) and secondary antibodies are used to capture proteins from the sample off-line. The work focuses on optimization of the array to allow for simultaneous detection (5−50 fg/ml range) and measurement of the four HNSCC proteins simultaneously and in serum. A formidable goal of paper-based microfluidic diagnostics is the development of a device that does not require an external reader. Lewis et al. utilized time as readout to quantify enzyme analytes where time is measured for a region in the paper device that turns green relative to the assay region [16] . The technique is internally calibrated and compensates for effects of humidity, temperature, and sample viscosity on sample distribution. The assay is sensitive (femtomolar), has short measurement times (15 s to 30 min), is selective, inexpensive, and easy to use. The device is made of stacked layers of wax-patterned papers held together using spray adhesive followed by lamination. The key component of the device is the existence in the one of the layers of bead-bound glucose oxidase which converts d-glucose to product and hydrogen peroxide. The released hydrogen peroxide then encounters an oligomer that is hydrophobic but which will convert to hydrophilic products via a cascade depolymerization reaction. This change in surface character allows the sample to flow through the layers of the device at a rate dependent on the concentration of hydrogen peroxide in the sample which can be correlated to the enzyme analyte. The sample then passes through multiple layers containing the polymer, thereby, redissolving dried green food coloring which is observed in the top of the paper device. Alkaline phosphates and β-galactoside are used as model systems to demonstrate selectivity. Wu et al. were able to demonstrate the development of a paper-based electrochemical immunodevice to detect cancer biomarkers [17] . Here, signal amplification was achieved by use of a graphene film to accelerate electron transfer and silica nanoparticles as a tracing tag for signal antibody labeling using the horseradish peroxidase (HRP)−O-phenylenediamine−hydrogen peroxide electrochemical detection system. A simple,
future science group
Editorial
accurate, and rapid POC assay using a photoresistpatterned microfluidic paper-based analytical device (uPAD) was demonstrated. The device was stable, and yielded reproducible and accurate results thereby demonstrating its efficacy for use in clinical diagnostics. Other recent notable works include the development of paper microfluidic platforms to examine the binding of antibodies via fusion proteins on carbohydrate binding modules [18] , multiplex MDs to diagnosis hepatitis C virus infection [19] , and assays to determine protein and glucose in urine [20] . In the future, paper microfluidics will play a monumental role in the development of individual lab-on-a-chip components in bioanalysis and, in particular, POC diagnostic devices. This simple technology offers new possibilities in a myriad of disciplines due to its practicality and ease of integration into a variety of platforms. As has been detailed, paper microfluidics has great promise in bioanalysis due to its ability to multiplex, sample storage, mixing, and filtration, sample volume control, and ability to analyze an array of samples simultaneously. Forward thinking researchers will see that there are many opportunities for this technology and to expand its capabilities. One area that could broaden the use of paper microfluidics is if statistical methods and computational techniques are used to examine the effect of experimental variables on output response, data classification and signal processing capabilities, as well as the robustness of device output to variations in platform design. Without this optimization, there exists the difficulty in developing technologies that may one day lead to commercialization and products that could serve a useful societal purpose. For the future, it is integral that a balance be struck between scientific invention, innovation, and development and commercialization so as to provide better access and quality of healthcare to people throughout the world through the use of devices developed via paper microfluidic methodologies. Financial & competing interests disclosure The author gratefully acknowledges financial support for this research by grants from the National Science Foundation (EEC-0812348, HRD-0934146, and OISE-0965911). The authors have no other relevant affiliations or financial involvement with an organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
www.future-science.com
2913
Editorial Gomez multiplexed measurement of biomarkers and point-of-care testing. Biomaterials 33(4), 1024–1031 (2012).
References 1
Manz A, Graber N, Widmer HM. Miniaturized total chemical analysis systems: a novel concept for chemical sensing. Sensor Actuat. B Chem. 1, 244–248 (1990).
2
Martinez AW, Phillips ST, Butte MJ, Whitesides GM. Patterned paper as a platform for inexpensive, low-volume, portable bioassays. Angew. Chem. Int. Ed. 46(8), 1318–1320 (2007).
3
Martinez AW, Phillips ST, Carrilho E, Thomas III SW, Sindi H, Whitesides GM. Simple telemedicine for developing regions: camera phones and paper-based microfluidic devices for real-time, off-site diagnosis. Anal. Chem. 80(10), 3699–3707 (2008).
4
5
2914
Bruzewicz DA, Reches M, Whitesides GM. Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper. Anal. Chem. 80(9), 3387–3392 (2008). Martinez AW, Phillips ST, Wiley BJ, Gupta M, Whitesides GM. FLASH: A rapid method for prototyping paper-based microfluidic devices. Lab Chip 8(12), 2146–2150 (2008).
6
Carrilho E, Phillips ST, Vella SJ, Martinez AW, Whitesides GM. Paper microzone plates. Anal. Chem. 81(15), 5990– 5998 (2009).
7
Carrilho E, Martinez AW, Whitesides AW. Understanding wax printing: a simple micropatterning process for paperbased microfluidics. Anal. Chem. 81(16), 7091–7095 (2009).
8
Martinez AW, Phillips ST, Whitesides GM, Carrilho E. Diagnostics for the developing world: microfluidic paperbased analytical devices. Anal. Chem. 82(1), 3–10 (2010).
9
Schilling KM, Lepore AL, Kurian JA, Martinez AW. Fully enclosed microfluidic paper-based analytical devices. Anal. Chem. 84(7), 1579–1585 (2012).
10
Renault C, Li X, Fosdick SE, Crooks RM. Hollow-channel paper analytical devices. Anal. Chem. 85(16), 7976–7979 (2013).
11
Ge L, Yan J, Song X, Yan M, Ge S, Yu J. Three dimensional paper-based electrochemiluminescence Immunodevice for
Bioanalysis (2014) 6(21)
12
Delaney JL, Hogan CF, Tian J, Shen W. Electrogenerated chemiluminescence detection in paper-based microfluidic sensors. Anal. Chem. 83(4), 1300–1306 (2011).
13
Thom NK, Yeung K, Pillion MB, Phillips ST. Fluidic batteries as low-cost sources of power in paper-based microfluidic devices. Lab Chip 12(10), 1768–1770 (2012).
14
Mani V, Kadimisetty K, Malla S, Joshi AA, Rusling JF. Paper-based electrochemiluminescent screening for genotoxic activity in the environment. Environ. Sci. Technol. 47(4), 1937–1944 (2013).
15
Malhotra R, Patel V, Chikkaveeraiah BV et al. Ultrasensitive detection of cancer biomarkers in the clinic. Anal. Chem. 84(14), 6249–6255 (2012).
16
Lewis GG, Robbins JS, Phillips ST. A rapid point-of-care assay platform for quantifying active enzymes to femtomolar levels using measurements of time as the readout. Anal. Chem. 85(21), 10432–10439 (2013).
17
Wu Y, Xue P, Kang Y, Hui KM. Paper-based microfluidic electrochemical immunodevice integrated with nanobioprobes onto graphene film for ultrasensitive multiplexed detection of cancer biomarkers. Anal. Chem. 85(18), 8661–8668 (2013).
18
Rosa AMM, Louro AF, Martins SAM, Inácio J, Azevedo AM, Prazeres DMF. Capture and detection of DNA hybrids on paper via the anchoring of antibodies with fusions of carbohydrate binding modules and ZZ-domains. Anal. Chem. 86(9), 4340–4347 (2014).
19
Mu X, Zhang L, Chang S, Cui W, Zheng Z. Multiplex microfluidic paper-based immunoassay for the diagnosis of hepatitis C virus infection. Anal. Chem. 86(11), 5338–5344 (2014).
20
Sechi D, Greer B, Johnson J, Hashemi N. Three-dimensional paper-based microfluidic device for assays of protein and glucose in urine. Anal. Chem. 85(22), 10733–10737 (2013).
future science group
