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Electroextraction (EE) encompasses a range of sample preparation methods whose effectiveness, selectivity, and efficiency are significantly influenced by the physical-chemical characteristics of analytes, samples, and instrumental conditions. This article explores, for the first time, various strategies aimed at enhancing the extraction efficiency of a recent approach of EE utilizing a paper point (PP) combined with a hollow fiber (HF) (abbreviated as PP-HF-EE) to extract various cationic and anionic model compounds from water samples. The study also explores, experimentally, the impact of agitation, organic filter composition, PP diameter, and PP brand on extraction performance, and proves that all these factors are quite important, especially when digital image analysis is utilized for determination. Furthermore, this work demonstrates the ease and feasibility of simultaneously extracting cations and anions using PP-HF-EE and proposes a straightforward method to enhance analyte concentration on the vertex of the PP through a base-to-vertex focusing. Lastly, it is demonstrated, using capillary electrophoresis coupled to a UV-Vis detector, that for PP-HF-EE, the extraction efficiency and pre-concentration factor are less dependent on other parameters when multiple PPs per sample are utilized, with signal enhancement values of up to 111 and 339 for nortriptyline and haloperidol, respectively. All the findings and strategies presented herein constitute significant contributions that can facilitate future research in method development, particularly in the utilization of PP-HF-EE and similar EE approaches., (© 2024 Wiley‐VCH GmbH.)

Detection of biomarkers is essential for diagnosis and prognosis of diseases for healthcare teams to provide timely appropriate treatments. Reliable, inexpensive, and sensitive devices are desirable to serve this purpose. Paper-based analytical devices (PADs) have gained enormous attention during the past decade as point-of-care devices for biomarker detection due to their simplicity, portability, and biocompatibility. Importantly, the devices highly comply with the WHO "ASSURED" concept (i.e. Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment free, and Deliverable to end-users). Thus, PADs could be sustainably alternative tools for biomarker detection, especially in resources-constraint areas where budget, skillful operators, and health infrastructure are limited. First, this review introduces overviews of biomarkers, their detection and brief history of PADs. Second, description of common fabrication and detection techniques in PADs are provided. Then, it highlights recent state of the art technologies and applications of PADs for various biomarker detection published during 2018 to May 2019. Applications for tumor marker, cardiac and coronary heath disease, and metabolic disorder biomarker detection are tabulated and selected examples are described in details. Finally, it discusses the current challenges, advances, and novel applications of PADs. The review would be valuable for healthcare workers using PADs as cost-effective point-of-care devices for biomarker detection and for researchers working on future developments of the devices., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Bladder cancer is the fourth most common cancer in men, and it is becoming a prevalent malignancy. Most of the regular clinical examinations are prompt evaluations with cystoscopy, renal function testing, which require high-precision instrument, well-trained operators, and high cost. In this study, a microfluidic paper-based analytical device (μPAD) was fabricated to detect nuclear matrix protein 22 (NMP22) and bladder cancer antigen (BTA) from the urine samples. Urine samples were collected from 11 bladder cancer patients and 10 well-beings as experiment and control groups, respectively, to verify the working efficiency of μPAD. A remarkable checkout efficiency of up to 90.91% was found from the results. Meanwhile, this method is feasible for home-based self-detection from urine samples within 10 min for the total process, which provides a new way for quick, economical, and convenient tumor diagnosis, prognosis evaluation, and drug response., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Diffusion of colored dye on water saturated paper substrates has been traditionally exploited with great skill by renowned water color artists. The same physics finds more recent practical applications in paper-based diagnostic devices deploying chemicals that react with a bodily fluid yielding colorimetric signals for disease detection. During spontaneous imbibition through the tortuous pathways of a porous electrolyte saturated paper matrix, a dye molecule undergoes diffusion in a complex network of pores. The advancing front forms a strongly correlated interface that propagates diffusively but with an enhanced effective diffusivity. We measure this effective diffusivity and show that it is several orders of magnitude greater than the free solution diffusivity and has a significant dependence on the solution pH and salt concentration in the background electrolyte. We attribute this to electrically mediated interfacial interactions between the ionic species in the liquid dye and spontaneous surface charges developed at porous interfaces, and introduce a simple theory to explain this phenomenon., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A complete mathematical model for electromigration in paper-based analytical devices is derived, based on differential equations describing the motion of fluids by pressure sources and EOF, the transport of charged chemical species, and the electric potential distribution. The porous medium created by the cellulose fibers is considered like a network of tortuous capillaries and represented by macroscopic parameters following an effective medium approach. The equations are obtained starting from their open-channel counterparts, applying scaling laws and, where necessary, including additional terms. With this approach, effective parameters are derived, describing diffusion, mobility, and conductivity for porous media. While the foundations of these phenomena can be found in previous reports, here, all the contributions are analyzed systematically and provided in a comprehensive way. Moreover, a novel electrophoretically driven dispersive transport mechanism in porous materials is proposed. Results of the numerical implementation of the mathematical model are compared with experimental data, showing good agreement and supporting the validity of the proposed model. Finally, the model succeeds in simulating a challenging case of free-flow electrophoresis in paper, involving capillary flow and electrophoretic transport developed in a 2D geometry., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Microfluidic paper-based analytical devices (μPADs) allow user-friendly and portable chemical determinations, although they provide limited applicability due to insufficient sensitivity. Several approaches have been proposed to address poor sensitivity in μPADs, but they frequently require bulky equipment for power and/or read-outs. Universal serial buses (USB) are an attractive alternative to less portable power sources and are currently available in many common electronic devices. Here, USB-powered μPADs (USB μPADs) are proposed as a fusion of both technologies to improve performance without adding instrumental complexity. Two ITP USB μPADs were developed, both powered by a 5 V potential provided through standard USB ports. The first device was fabricated using the origami approach. Its operation was analyzed experimentally and numerically, yielding a two-order-of-magnitude sample focusing in 15 min. The second ITP USB μPAD is a novel design, which was numerically prototyped with the aim of handling larger sample volumes. The reservoirs were moved away from the ITP channel and capillary action was used to drive the sample and electrolytes to the separation zone, predicting 25-fold sample focusing in 10 min. USB μPADs are expected to be adopted by minimally-trained personnel in sensitive areas like resource-limited settings, the point-of-care and in emergencies., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Exosome quantification is important for estimation of informative messengers (e.g., proteins, lipids, RNA, etc.) involving physiological and pathological effects. This work aimed to develop a simple and rapid distance-based paper portable device using exosome-capture vesicles (polydiacetylene conjugated with antiCD81) for exosome quantification in cell cultures. This novel concept relied on distinct aggregation of exosomes and exosome-capture vesicles leading to different solvent migration. Distances of the migration were used as signal readouts, which could be detected by naked eye. PDA-antiCD81 as exosome-capture vesicles were optimized (e.g., size, reaction ratio, and concentration) and the paper designs were investigated (e.g., diameter of sample reservoir and lamination layer) to enhance the solvent stop-flow effects. Finally, exosome screening on three cell culture samples (COLO1, MDA-MB-231, and HuR-KO1 subclone) was demonstrated. The method could linearly measure exosome concentrations in correlation with solvent migration distances in the range of 10 6 -10 10 particles/mL (R 2  > 0.98) from the cell culture samples. The exosome concentration measurements by the developed device were independently assessed by nanoparticle tracking analysis. Results demonstrated no statistically significant difference (p > 0.05) by t-test. This low-cost and rapid device allows a portable platform for exosome quantification without the requirement of expensive equipment and expertise of operation. The developed device could potentially be useful for quantification of other biomarker-related extracellular vesicles., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Enhancing the sensitivity of colorimetric detection in paper-devices is a quintessential step in achieving frugal diagnosis. Here, we demonstrate an effective way of improving the detection sensitivity of paper-based devices, as mediated by electro-kinetic mechanisms. By directly employing blood plasma, we investigate the electro-kinetic clustering of glucose, a neutral molecule in paper devices. Under the influence of uniform electric field, dispersed glucose gets accumulated in the paper strips. Due to the combination of EOF and electrophoretic migration, we achieve twofold increase in the colour intensity for both normal and diabetic samples. This approach is robust and possesses better sensitivity than conventional colorimetric assays and can be easily extended to other body fluid based diagnosis. These results may turn out to be of profound importance in improving the quality of pathological diagnosis in low-cost paper-based point-of-care devices deployed in resource-limited settings., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this paper we describe the fabrication of novel 3D microfluidic paper-based analytical devices (3D-μPADs) and a 3D microfluidic thread/paper-based analytical device (3D-μTPAD) to detect glucose and BSA through colorimetric assays. The 3D-μPAD and 3D-μTPAD consisted of three (wax, heat pressed wax-printed paper, single-sided tape) and four (hole-punched single-sided tape, blank chromatography circles, heat-pressed wax-printed paper, hole-punched single-sided tape containing trifurcated thread) layers, respectively. The saturation curves for each assay were generated for all platforms. For the glucose assay, a solution of glucose oxidase (GOx), horseradish peroxidase, and potassium iodide was flowed through each platform and, upon contact with glucose, generated a yellow-brown color indicative of the oxidation of iodide to iodine. For the protein assay, BSA was flowed through each device and, upon contact with citrate buffer and tetrabromophenol blue, resulted in a color change from yellow to blue. The devices were dried, scanned, and analyzed yielding a correlation between either yellow intensity and glucose concentration or cyan intensity and BSA concentration. A similar glucose assay, using unknown concentrations of glucose in artificial urine, was conducted and, when compared to the saturation curve, showed good correlation between the theoretical and actual concentrations (percent differences <10%). The development of 3D-μPADs and 3D-μTPADs can further facilitate the use of these platforms for colorimetric bioassays., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper describes enzyme-linked immunosorbent assays (ELISAs) utilizing microfluidic thread/paper-based analytical devices (μTPAD), microfluidic fabric-based analytical devices (μFAD), and microfluidic thread-based analytical devices (μTAD). Here, the quantitative detection of biotinylated goat anti-mouse IgG (system one) and rabbit IgG (system two) antibodies via colorimetric analysis is detailed. In both systems, antibody is spotted on the detection site and subjected to a series of washes, addition of streptavidin-alkaline phosphatase (Strep-ALP) (system 1) or alkaline phosphatase (ALP)-conjugated secondary antibody (system 2), and colorimetric substrate. The devices are scanned and analyzed yielding a correlation between inverse yellow (or purple) intensity. For system one, a linear range of detection at low concentrations of streptavidin-alkaline phosphatase (Strep-ALP) was observed befire the enzyme reached a V max . At higher concentrations of Strep-ALP, saturation is achieved for both the μTPAD and μFAD devices. For system two, the IC 50 values obtained for the non-trifurcated and trifurcated μTADs were determined to be 180.2 fmol/zone and 133.8 fmol/zone, respectively. The IC 50 value was demonstrated to be 1034 fmol/zone and 208.6 fmol/zone for the μTPADs and μFADs, respectively. For all devices the lowest concentration of Strep-ALP or rabbit IgG used in the assay was 3.75 × 10 -4  mg/mL and 0.7 fmol/zone, respectively. The development of this technology should further facilitate the use of these platforms for ELISA to detect and quantitate antibodies., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a microfluidic paper based analytical device implementing ion concentration polarization (ICP) for rapid pre-concentration of Escherichia coli in water. The fabricated device consists of a paper channel with a Nafion ® membrane and in-built micro wire electrodes to supply electric voltage to induce the ICP effect. E. coli cells were stained with SYTO 9 and fluorescence was used as a sensing method. The device achieved high concentration factor up to 2 × 10 5 within minutes. The effect of total ion concentration, on ICP and fluorescence intensity was studied. The reported device and method are suitable and effective for detection of E. coli during ballast water quality monitoring, coastal water quality monitoring where high salinity water is present., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Paper-based microfluidic fuel cells (MFCs) are a potential replacement for traditional FCs and batteries due to their low cost, portability, and simplicity to operate. In MFCs, separate solutions of fuel and oxidant migrate through paper due to capillary action and laminar flow and, upon contact with each other and catalyst, produce electricity. In the present work, we describe an improved microfluidic paper-based direct formate FC (DFFC) employing formate and hydrogen peroxide as the anode fuel and cathode oxidant, respectively. The dimensions of the lateral column, current collectors, and cathode were optimized. A maximum power density of 2.53 mW/cm(2) was achieved with a DFFC of surface area 3.0 cm(2) , steel mesh as current collector, 5% carbon to paint mass ratio for cathode electrode and, 30% hydrogen peroxide. The longevity of the MFC's detailed herein is greater than eight hours with continuous flow of streams. In a series configuration, the MFCs generate sufficient energy to power light-emitting diodes and a handheld calculator., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Filter paper strips were enclosed between two poly(methyl methacrylate) plates to fabricate paper-packed channel microchips under pressure in the presence of far infrared irradiation. After the enclosed paper strip was oxidized by periodate, trypsin was covalently immobilized in them to fabricate microfluidic proteolysis bioreactor. The feasibility and performance of the unique bioreactor were demonstrated by digesting BSA and lysozyme. The results were comparable to those of conventional in-solution proteolysis while the digestion time was significantly reduced to ∼18 s. The suitability of the microfluidic paper-based bioreactors to complex proteins was demonstrated by digesting human serum., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We described a strategy to perform multistep operations on a simple laminated paper-based separation device by using electrokinetic flow to manipulate the fluids. A laminated crossed-channel paper-based separation device was fabricated by cutting a filter paper sheet followed by lamination. Multiple function units including sample loading, sample injection, and electrophoretic separation were integrated on a single paper based analytical device for the first time, by applying potential at different reservoirs for sample, sample waste, buffer, and buffer waste. As a proof-of-concept demonstration, mixed sample solution containing carmine and sunset yellow were loaded in the sampling channel, and then injected into separation channel followed by electrophoretic separation, by adjusting the potentials applied at the four terminals of sampling and separation channel. The effects of buffer pH, buffer concentration, channel width, and separation time on resolution of electrophoretic separation were studied. This strategy may be used to perform multistep operations such as reagent dilution, sample injection, mixing, reaction, and separation on a single microfluidic paper based analytical device, which is very attractive for building micro total analysis systems on microfluidic paper based analytical devices., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Self-pumping porous microfluidic devices have attracted significant interest because of their low cost and broad applicability in point-of-care and low resource settings. One limitation of many of the devices is sensitivity and selectivity for detection. Electrochemistry can provide a sensitive, selective detection method while still using low cost, portable instrumentation as typified by handheld glucometers. Here, the development of electrochemical paper-based analytical devices (ePADs) is reviewed. Given the importance of electrode geometry and composition, fabrication methods are reviewed first. This is followed by a review of example applications demonstrated for ePADs. Finally, major accomplishments and future directions are summarized., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper describes for the first time the fabrication of pencil drawn electrodes (PDE) on paper platforms for capacitively coupled contactless conductivity detection (C(4) D) on electrophoresis microchips. PDE-C(4) D devices were attached on PMMA electrophoresis chips and used for detection of K(+) and Na(+) in human tear samples. PDE-C(4) D devices were produced on office paper and chromatographic paper platforms and their performance were thoroughly investigated using a model mixture containing K(+) , Na(+) , and Li(+) . In comparison with chromatographic paper, PDE-C(4) D fabricated on office paper has exhibited better performance due to its higher electrical conductivity. Furthermore, the detector response was similar to that recorded with electrodes prepared with copper adhesive tape. The fabrication of PDE-C(4) D on office paper has offered great advantages including extremely low cost (< $ 0.004 per unit), reduced fabrication time (< 5 min), and minimal instrumentation (pencil and paper). The proposed electrodes demonstrated excellent analytical performance with good reproducibility. For an inter-PDE comparison (n = 7), the RSD values for migration time, peak area, and separation efficiency were lower than 2.5, 10.5, and 14%, respectively. The LOD's achieved for K(+) , Na(+) , and Li(+) were 4.9, 6.8, and 9.0 μM, respectively. The clinical feasibility of the proposed approach was successfully demonstrated with the quantitative analysis of K(+) and Na(+) in tear samples. The concentration levels found for K(+) and Na(+) were, respectively, 20.8 ± 0.1 mM and 101.2 ± 0.1 mM for sample #1, and 20.4 ± 0.1 mM and 111.4 ± 0.1 mM for sample #2., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We propose here simple electrochemical cells assembled with electrodes pencil drawn on paper for conducting one-spot tests enabling olive oil to be easily distinguished from other vegetable oils. They consist of small circular pads of hydrophilic paper defined by hydrophobic barriers, these last printed by using custom-designed rubber stamps, where working, reference, and counterelectrodes are drawn by pencil leads. These cells were first wetted with a small volume of aqueous electrolyte, avoiding coating of the upper surface of electrodes. A controlled volume of edible oil samples was then applied on top of the moist cell. The results found proved that these devices can be adopted as effective platforms suitable for the detection of electroactive compounds present in edible oils. In fact, they allow voltammetric profiles to be recorded not only for the oxidation of water soluble species (ortho-diphenols, as well as some monophenols and polyphenols) present in olive oils, but also for electroactive hydrophobic components (e.g., α-tocopherol) present in sunflower oils, which were chosen as model of seed oils. The whole of collected findings pointed out that simple one-spot tests performed by these devices enable olive oils to be easily distinguished from other edible oils on the basis of their clearly different voltammetric profiles. A satisfactory interdevice reproducibility (±13%) was estimated by applying strictly similar extra virgin olive oil samples onto seven different cells carefully prepared by the same procedure. An operating mechanism able to account for the detection of also electroactive hydrophobic compounds present in oils is proposed., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We describe the first direct formate fuel cell on a paper microfluidic platform. In traditional membrane-less microfluidic fuel cells (MFCs), external pumping consumes power produced by the fuel cell in order to maintain co-laminar flow of the anode stream and oxidant stream to prevent mixing. However, in paper microfluidics, capillary action drives flow while minimizing stream mixing. In this work, we demonstrate a paper MFC that uses formate and hydrogen peroxide as the anode fuel and cathode oxidant, respectively. Using these materials we achieve a maximum power density of nearly 2.5 mW/mg Pd. In a series configuration, our MFC achieves an open circuit voltage just over 1 V, and in a parallel configuration, short circuit of 20 mA absolute current. We also demonstrate that the MFC does not require continuous flow of fuel and oxidant to produce power. We found that we can pre-saturate the materials on the paper, stop the electrolyte flow, and still produce approximately 0.5 V for 15 min. This type of paper MFC has potential applications in point-of-care diagnostic devices and other electrochemical sensors., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this paper, an alkaline nickel oxide hydroxide/zinc (NiOOH/Zn) battery featuring a cellulose matrix separator between electrodes is presented. The metallic electrodes and the paper separator are inserted in a layer-by-layer assembly that provides mechanical stability to the system resulting in a lightweight and easy-to-use device. The battery was optimized for the amount of NiOOH-ink used at the cathode (11.1 mg/cm 2 ) and thickness of the paper membrane separating the electrodes (360 μm). The battery was able to function using a small volume (75 μL) of 1.5 M potassium hydroxide (KOH) producing a maximum voltage, current density, and power density of 1.35 ± 0.05 V, 10.62 ± 0.57 mA/cm², and 0.56 ± 0.01 mW/cm², respectively. The system displayed a maximum current of 23.9 mA and a maximum power of 1.26 mW. Moreover, four batteries connected in series were able to power a small flameless candle for approximately 22 min. This work has potential in fulfilling the demands for short-term and lightweight power supplies., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper presents a novel paper-based analytical device based on the colorimetric paper assays through its light reflectance. The device is portable, low cost (<20 dollars), and lightweight (only 176 g) that is available to assess the cost-effectiveness and appropriateness of the original health care or on-site detection information. Based on the light reflectance principle, the signal can be obtained directly, stably and user-friendly in our device. We demonstrated the utility and broad applicability of this technique with measurements of different biological and pollution target samples (BSA, glucose, Fe, and nitrite). Moreover, the real samples of Fe (II) and nitrite in the local tap water were successfully analyzed, and compared with the standard UV absorption method, the quantitative results showed good performance, reproducibility, and reliability. This device could provide quantitative information very conveniently and show great potential to broad fields of resource-limited analysis, medical diagnostics, and on-site environmental detection., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This work reports an investigation for the analysis of different paper samples using CE with laser-induced detection. Papers from four different manufactures (white-copy paper) and four different paper sources (white and recycled-copy papers, adhesive yellow paper notes and restaurant serviettes) were pulverized by scratching with a surgical scalpel prior to their derivatization with a fluorescent labeling agent, 8-aminopyrene-1,3,6-trisulfonic acid. Methodological conditions were evaluated, specifically the derivatization conditions with the aim to achieve the best S/N signals and the separation conditions in order to obtain optimum values of sensitivity and reproducibility. The best conditions, in terms of fastest, and easiest sample preparation procedure, minimal sample consumption, as well as the use of the simplest and fastest CE-procedure for obtaining the best analytical parameters, were applied to the analysis of the different paper samples. The registered electropherograms were pretreated (normalized and aligned) and subjected to multivariate analysis (principal component analysis). A successful discrimination among paper samples without entanglements was achieved. To the best of our knowledge, this work presents the first approach to achieve a successful differentiation among visually similar white-copy paper samples produced by different manufactures and paper from different paper sources through their direct analysis by CE-LIF and subsequent comparative study of the complete cellulose electropherogram by chemometric tools., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Three-dimensional (3D) paper-based microfluidics, which is featured with high performance and speedy determination, promise to carry out multistep sample pretreatment and orderly chemical reaction, which have been used for medical diagnosis, cell culture, environment determination, and so on with broad market prospect. However, there are some drawbacks in the existing fabrication methods for 3D paper-based microfluidics, such as, cumbersome and time-consuming device assembly; expensive and difficult process for manufacture; contamination caused by organic reagents from their fabrication process. Here, we present a simple printing-bookbinding method for mass fabricating 3D paper-based microfluidics. This approach involves two main steps: (i) wax-printing, (ii) bookbinding. We tested the delivery capability, diffusion rate, homogeneity and demonstrated the applicability of the device to chemical analysis by nitrite colorimetric assays. The described method is rapid (<30 s), cheap, easy to manipulate, and compatible with the flat stitching method that is common in a print house, making itself an ideal scheme for large-scale production of 3D paper-based microfluidics., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, a fast, low-cost, and facile spray method was proposed. This method deposits highly sensitive surface-enhanced Raman scattering (SERS) silver nanoparticles (AgNPs) on the paper-microfluidic scheme. The procedures for substrate preparation were studied including different strategies to synthesize AgNPs and the optimization of spray cycles. In addition, the morphologies of the different kinds of paper substrates were characterized by SEM and investigated by their SERS signals. The established method was found to be favorable for obtaining good sensitivity and reproducible results. The RSDs of Raman intensity of randomly analyzing 20 spots on the same paper or different filter papers depositing AgNPs are both below 15%. The SERS enhancement factor is approximately 2 × 10(7) . The whole fabrication is very rapid, robust, and does not require specific instruments. Furthermore, the total cost for 1000 pieces of chip is less than $20. These advantages demonstrated the potential for growing SERS applications in the area of environmental monitoring, food safety, and bioanalysis in the future., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Developing paper-based electrophoretic methods involve dealing with significant uncertainty levels when compared to their capillary counterparts. Critical information for developing these kinds of methods are the electrophoretic mobility of background electrolytes and samples. This work presents the design and characterization of a device for measuring the electrophoretic mobilities of dyes in porous media. The device was developed with the aim of validating a previously presented model and also proposing a protocol for the straightforward determination of electrophoretic mobilities in porous media when open-channel values are already known. Whatman #1 paper was used as a model substrate as far as it is the most common porous medium substrate for paper-based electrophoresis. The device was designed using a numerical simulation-assisted approach, utilizing OpenFOAM® and specific solvers for capillary transport and electromigration, namely porousMicroTransport and electroMicroTransport, respectively. The electrophoretic mobilities of five dyes were analyzed experimentally with the proposed device. To establish appropriate comparative values at different pHs, experiments in fused silica capillaries were also performed. An effective parameter model for describing the electrophoretic behavior of dyes in porous media, that is, the constriction factor, was found consistent with previous reports for the Whatman #1 paper. This consistency was found after considering (via direct measurements) the chromatographic effect of the medium over each dye. Consequently, the recorded values hold significant worth due to their potential for direct application in designing new experiments or devices in Whatman #1 paper. With the validation of the model through the experiments with the proposed device, those researchers interested on developing electrophoretic methods in porous substrates can make use of the open-channel electrophoretic mobilities reported in the literature, or in the well-known software databases, and correct them for the media of interest just by performing two simple characterization steps., (© 2023 Wiley‐VCH GmbH.)

Protein electrophoresis and immunoblotting are indispensable analytical tools for the characterization of proteins and posttranslational modifications in complex sample matrices. Owing to the lack of automation, commonly employed slab-gel systems suffer from high time demand, significant sample/antibody consumption, and limited reproducibility. To overcome these limitations, we developed a paper-based open microfluidic platform for electrophoretic protein separation and subsequent transfer to protein-binding membranes for immunoprobing. Electrophoresis microstructures were digitally printed into cellulose acetate membranes that provide mechanical stability while maintaining full accessibility of the microstructures for consecutive immunological analysis. As a proof-of-concept, we demonstrate separation of fluorescently labeled marker proteins in a wide molecular weight range (15-120 kDa) within only 15 min, reducing the time demand for the entire workflow (from sample preparation to immunoassay) to approximately one hour. Sample consumption was reduced 10- to 150-fold compared to slab-gel systems, owing to system miniaturization. Moreover, we successfully applied the paper-based approach to complex samples such as crude bacterial cell extracts. We envisage that this platform will find its use in protein analysis workflows for scarce and precious samples, providing a unique opportunity to extract profound immunological information from limited sample amounts in a fast fashion with minimal hands-on time., (© 2021 The Authors. Electrophoresis published by Wiley-VCH GmbH.)

Droplet-based microfluidics is a modular platform in high-throughput single-cell and small sample analyses. However, this droplet microfluidic system was widely fabricated using soft lithography or glass capillaries, which is expensive and technically demanding for various applications, limiting use in resource-poor settings. Besides, the variation in droplet size is also restricted due to the limitations on the operating forces that the paper-based platform is able to withstand. Herein, we develop a fully integrated paper-based droplet microfluidic platform for conducting droplet generation and cell encapsulation in independent aqueous droplets dispersed in a carrier oil by incorporating electric fields. Through imposing an electric field, the droplet size would decrease with increasing the electric field and smaller droplets can be produced at high applied voltage. The droplet diameter can be adjusted by the ratio of inner and outer flow velocities as well as the applied electric field. We also demonstrated the proof of concept encapsulation application of our paper device by encapsulating yeast cells under an electric field. Using a simple wax printing method, carbon electrodes can be integrated on the paper. The integrated paper-based microfluidic platform can be fabricated easily and conducted outside of centralized laboratories. This microfluidic system shows great potential in drug and cell investigations by encapsulating cells in resource-limited environments., (© 2021 Wiley-VCH GmbH.)

Here we present a simple and low-cost production method to generate paper-based microfluidic devices with wax for portable bioassay. The wax patterning method we introduced here included three different ways: (i) painting with a wax pen, (ii) printing with an inkjet printer followed by painting with a wax pen, (iii) printing by a wax printer directly. The whole process was easy to operate and could be finished within 5-10 min without the use of a clean room, UV lamp, organic solvent, etc. Horse radish peroxidase, BSA and glucose assays were conducted to verify the performance of wax-patterned paper.

Neurotransmitters play key roles in cell-to-cell communication. These chemical messengers are involved in many functional processes, including growth, reproduction, memory, and behavior. In this communication, we describe a novel microfluidic paper-based analytical device (μPAD) to detect acetylcholinesterase (AChE) activity and inhibitor screening through a colorimetric analysis. The μPAD is easily fabricated via a wax printing process whereby wax is deposited onto the surface of chromatographic paper, and heated to create a hydrophobic barrier. Separate solutions of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and samples containing AChE and acetylthiocholine iodide (ATC) (or cysteine, Cys), respectively, are directly spotted onto the μPAD. DTNB and AChE/ATC (or Cys) flow towards each other where a reaction occurs to form the yellow colored 2-nitro-5-thiobenzoic acid anion (TNB 2- ). The device is dried, scanned, and analyzed yielding a linear range of average inverse yellow intensities versus substrate concentration. An IC 50 value (0.045 nM) with a known inhibitor, neostigmine bromide (NB), is obtained on the device. μPADs are low cost and easy to fabricate and have great potential to quantify neurotransmitter activity., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An easy-to-do paper-based solid-phase microextraction (p-SPME) was developed for determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in urine sample by CE-LIF. Small piece of filter paper was used as a solid phase to extract 8-OHdG from urine sample. Its primary mechanism is based on the hydrogen-bonding interaction between 8-OHdG and cellulose molecules. The effects of the pH of the sample solution, extraction time, and temperature on the peak area of the analyte were investigated in order to obtain the optimal p-SPME conditions. Comparing with the untreated sample, the p-SPME can significantly reduce the interference to the separation of 8-OHdG by CE-LIF. Meanwhile, the p-SPEM can provide more than three times concentrated effect. The developed method was evaluated according to an FDA guideline for biological analysis. The precisions (RSD%, n = 5) of the peak area and migration time of the analyte at three different concentrations were within 3.02-5.82% and 0.92-1.58%, respectively. The limit of identification of the method is about 5 nM according to the significant difference between two sets of the samples with and without spiking the standard (Student's t-test, p < 0.05). Good linearity was obtained in the range of 10-1000 nM (R 2 >0.99) based on the standard addition. The recoveries at three different concentrations were within 99.8-103.5%. The results of the real sample analysis are consistent with those reported in our previous paper (Electrophoresis 2014, 35, 1873-1879)., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

One of the most cited limitations of biochemical detection is its poor sensitivity, owing to the relatively high complexity of micro-samples. Moreover, some samples cannot be easily self-replicated and their abundance cannot be increased through traditional technologies. Therefore, the preconcentration of low-abundance samples is a key requirement for microfluidic biological analysis. In recent years, the ion-concentration polarization phenomenon has aroused widespread interest in the application of microfluidic technology. In addition, paper-based materials are readily available, easy to modify, and exhibit good hydrophilicity. The study of the ion-concentration polarization preconcentration of micro-samples in paper-based microfluidic chips is of considerable significance. In this review, we discuss the development and applications of ion-concentration polarization paper-based preconcentrator in the past 5 years, with emphasis on key progresses in chip fabrication and performance optimization under different conditions. The current needs and development prospects in this field have also been discussed., (© 2021 Wiley-VCH GmbH.)

A new tool for the solution of electromigrative separations in paper-based microfluidics devices is presented. The implementation is based on a recently published complete mathematical model for describing these types of separations, and was developed on top of the open-source toolbox electroMicroTransport, based on OpenFOAM ® , inheriting all its features as native 3D problem handling, support for parallel computation, and a GNU GPL license. The presented tool includes full support for paper-based electromigrative separations (including EOF and the novel mechanical and electrical dispersion effects), compatibility with a well-recognized electrolyte database, and a novel algorithm for computing and controlling the electric current in arbitrary geometries. Additionally, the installation on any operating system is available due to its novel installation option in the form of a Docker image. A validation example with data from literature is included, and two extra application examples are provided, including a 2D free-flow IEF problem, which demonstrates the capabilities of the toolbox for dealing with computational and physicochemical modeling challenges simultaneously. This tool will enable efficient and reliable numerical prototypes of paper-based electrophoretic devices to accompany the contemporary fast growth in paper-based microfluidics., (© 2021 Wiley-VCH GmbH.)

A novel method for electroosmotic flow (EOF) measurement on paper substrates is presented; it is based on dynamic mass measurements by simply using an analytical balance. This technique provides a more reliable alternative to other EOF measurement methods on porous media. The proposed method is used to increase the amount and quality of the available information about physical parameters that characterize fluid flow on microfluidic paper-based analytical devices (μPADs). Measurements were performed on some of the most frequently used materials for μPADs, i.e., Whatman #1 , S&S, and Muntktell 00A filter paper. Obtained experimental results are consistent with the few previously reported data, either experimental or numerical, characterizing EOF in paper substrates. Moreover, a thorough analysis is presented for the quantification of the different effects that affect the measurements such as Joule effect and evaporation. Experimental results enabled, for the first time, to establish well-defined electroosmotic characteristics for the three substrates in terms of the magnitude of EOF as funtion of pH, enabling researchers to make a rational choice of the substrate depending on the electrophoretic technique to be implemented. The measurement method can be described as robust, reliable, and affordable enough for being adopted by researchers and companies devoted to electrophoretic μPADs and related technologies., (© 2021 Wiley-VCH GmbH.)

Bare gold nanoparticles selectively enhance the Raman signal of beta-agnonists in swine hair extract at 780 nm, which enables analysis of beta-agonists in swine hair extract without chemical labeling, purification, or separation. The analysis is multiplexable and the LOD of beta-agonists is around ng/mL in the assistance of microfluidic paper., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A simple procedure for preparing inexpensive paper-based three-electrode electrochemical cells is described here. They consist of small circular pads of hydrophilic paper defined by hydrophobic barriers printed on paper with wax-based ink. The back face of these pads is insulated by thermally laminating a polyethylene layer and working, reference and counter electrodes are drawn on paper by using commercial pencil leads. At last, a controlled volume of sample containing a supporting electrolyte was laid to soak in paper channels. Their performance was evaluated by assaying these devices as both simple cells suitable for recording voltammograms on static samples and low-cost detectors for flowing systems. Voltammetric tests, conducted by using potassium hexacyanoferrate(II) as model prototype, were also exploited for identifying the brand and softness of graphite sticks enabling paper to be marked with lines displaying the best conductivity. By taking advantage of the satisfactory information thus gained, pencil drawn electrodes were tested as amperometric detectors for the separation of ascorbic acid and sunset yellow, which were chosen as prototype electroactive analytes because they are frequently present concomitantly in several food matrices, such as soft drinks and fruit juices. This separation was performed by planar thin layer chromatography conducted on microfluidic paper-based devices prepared by patterning on filter paper two longitudinal hydrophobic barriers, once again printed with wax-based ink. Factors affecting both separation and electrochemical detection were examined and optimised, with best performance achieved by using a 20 mM acetate running buffer (pH 4.5) and by applying a detection potential of 0.9 V. Under these optimum conditions, the target analytes could be separated and detected within 6 min. The recorded peaks were well separated and characterized by good repeatability and fairly good sensitivity, thus proving that this approach is indeed suitable for rapidly assembling inexpensive and reliable electrochemical detectors for flow analysis systems., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We describe a paper microfluidic-based enzyme catalyzed double microreactor assay using fluorescent detection. Here, solutions of lactate dehydrogenase (LDH) and diaphorase (DI) were directly spotted onto the microfluidic paper-based analytical device (μPAD). Samples containing lactic acid, resazurin, and nicotinamide adenine dinucleotide oxidized form (NAD(+) ), potassium chloride (KCl), and BSA, in MES buffer were separately spotted onto the μPAD and MES buffer flowed through the device. A cascade reaction occurs upon the sample spot overlapping with LDH to form pyruvate and nicotinamide adenine dinucleotide reduced form (NADH). Subsequently, NADH is used in the conversion of resazurin to fluorescent resorufin by DI. The μPAD avoids the need of surface functionalization or enzyme immobilization steps. These microreactor devices are low cost and easy to fabricate and effect reaction based solely on buffer capillary action., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper describes the fabrication of and data collection from two microfluidic devices: a microfluidic thread/paper based analytical device (μTPAD) and 3D microfluidic paper-based analytical device (μPAD). Flowing solutions of glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI), through each device, on contact with glucose, generated a calibration curve for each platform. The resultant yellow-brown color from the reaction indicates oxidation of iodide to iodine. The devices were dried, scanned, and analyzed yielding a correlation between yellow intensity and glucose concentration. A similar procedure, using an unknown concentration of glucose in artificial urine, is conducted and compared to the calibration curve to obtain the unknown value. Studies to quantify glucose in artificial urine showed good correlation between the theoretical and actual concentrations, as percent differences were ≤13.0%. An ANN was trained on the four-channel CMYK color data from 54 μTPAD and 160 μPAD analysis sites and Pearson correlation coefficients of R = 0.96491 and 0.9739, respectively, were obtained. The ANN was able to correctly classify 94.4% (51 of 54 samples) and 91.2% (146 of 160 samples) of the μTPAD and μPAD analysis sites, respectively. The development of this technology combined with ANN should further facilitate the use of these platforms for colorimetric analysis of other analytes., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The interest in low-cost microfluidic platforms as well as emerging microfabrication techniques has increased considerably over the last years. Toner- and paper-based techniques have appeared as two of the most promising platforms for the production of disposable devices for on-chip applications. This review focuses on recent advances in the fabrication techniques and in the analytical/bioanalytical applications of toner and paper-based devices. The discussion is divided in two parts dealing with (i) toner and (ii) paper devices. Examples of miniaturized devices fabricated by using direct-printing or toner transfer masking in polyester-toner, glass, PDMS as well as conductive platforms as recordable compact disks and printed circuit board are presented. The construction and the use of paper-based devices for off-site diagnosis and bioassays are also described to cover this emerging platform for low-cost diagnostics.

A method utilizing paper microfluidics coupled with gold nanoparticles and two anticocaine aptamers has been developed to detect seized cocaine samples. The ready-to-use format involves the use of a paper strip that produces a color change resulting from the salt-induced aggregation of gold nanoparticles producing a visible color change indicating the presence of the drug. This format is specific for the detection of cocaine. The visual LOD for the method was 2.5 μg and the camera based LOD was 2.36 μg. The operation of the device is easy and rapid, and does not require extensive training or instrumentation. All of the materials utilized in the device are safe and environmental friendly. This device should prove a useful tool for the screening of forensic samples., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nonfluorescing protein bands can be detected by the fluorescence optics of the commercial gel electrophoresis apparatus with automated scanning of the migration path (HPGE-1000, LabIntelligence, Belmont CA), taking advantage of the decrease of emission from a fluorescent paper placed below the gel by the absorbance of proteins ("fluorescence reduction"). That decrease of fluorescence gives rise to an inverted protein peak. Nonfluorescent colorless proteins appear to reduce the intensity of light emitted from the fluorescent paper due to absorbance of incident and emitted light. When the absorbance spectrum only slightly overlaps with the excitation and emission spectra of the fluorescent paper, that reduction is weak, and detection sensitivity in that application is consequently only 1/30 of that of fluorescent proteins. By contrast, when the protein is colored so that its absorbance spectrum overlaps widely with the excitation and emission spectra of the fluorescent paper, the sensitivity of "fluorescence reduction" equals 1/4 to 1/5 of that obtained for fluorescent proteins. Bands detected by "fluorescence reduction" provide a quantitative measure of protein load and mobility. The area of the inverted bands is proportional to protein loads up to 16 microg/lane of the gel tray. A theory of "fluorescence reduction" is presented which accounts for the existence of a linear relationship between band area and load.

A novel microfluidic thread/paper-based analytical device (μTPAD) to detect glucose through a colorimetric assay is described. The μTPAD was fabricated from nylon thread trifurcated into three channels terminating at analysis sites comprised of circular zones of chromatography paper, which have previously been spotted with glucose of different concentrations. A solution of glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) is transported via capillary action to the analysis sites where a yellow-brown color is observed indicating oxidation of iodide to iodine. The device was then dried, scanned, and analyzed yielding a correlation between yellow intensity and glucose concentrations. Both a flat platform constructed mainly of tape, and a cone platform constructed from tape and polyvinyl chloride, are described. Studies to quantitate glucose in artificial urine showed good correlation using the μTPAD., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Clenbuterol (CL), as a feed additive, has been banned in many countries due to its potential threat to human health. In detection of CL, a fast, low-cost technique with high accuracy and specificity would be ideal for its administrative on-field inspections. Among the attempts to pursue a reliable detection tool of CL, a technique that combines surface enhanced Raman spectroscopy (SERS) and immunoassay, is close to meet the requirements as above. However, multiple steps of interactions between CL analyte, antibody, and antigen are involved in this method, and under conventional setup, the operation of SERS/immunoassay were unwieldy. In this paper, to facilitate a more manageable sample manipulation for SERS-immunoassay measurement, a 3D paper chip was suggested. A switch-on-chip multilayered (abbreviated as SoCM-) microfluidic paper-based analysis device (μPad) was fabricated to provide operators with manual switches on the interactions between different microfluids. Besides, on a detection slip we made on the main body of our SoCM-μPad, antigen was anchored in pattern. With this architecture, multistep interactions between the CL analyte in swine hair extract and the SERS probe-modified antibody and antigen, were managed for on-chip SERS-immunoassay detection. This would be very attractive for fast, cheap, accurate, and on-site specific detection of CL from real samples., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper reports for the first time the use of colored toner to produce polyester toner (PT) ME devices. Colored PT devices were designed in drawing software and printed on a polyester film using a color laser printer with 3600 dpi resolution. The colored toner is composed of a copolymer mixture (styrene and acrylate), wax, silicon dioxide, and pigments. The presence of silica in the toner composition has enhanced the EOF magnitude and improved the analytical performance. For a pH range between 2 and 12, the EOF measured on a magenta PT chip, for example, ranged from 3.8 to 5.8 (× 10(-4) cm(2) V(-1) s(-1) ). Typical separations of inorganic cations (K(+) , Na(+) , and Li(+) ) were used as model system to investigate the analytical feasibility of the proposed devices. The repeatability for the migration times of all analytes exhibited RSD values lower than 1% (n = 10). The separation efficiencies found on colored PT devices ranged from 10 000 to 49 000 plates/m, which means between 7 and 23% of the maximum theoretical efficiency on this microfluidic platform (1.85 × 10(5) plates/m). The improvements achieved on the proposed devices are associated with the small additional amount of silica on the toner composition as well as the printing of channels with smoother surfaces and better uniformity when compared to the conventional PT chips printed with monochromatic laser printers., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel drug-screening system, consisting of paper spray-MS (PS-MS) and a CE-ESI-MS method was developed. This system can be easily switched either to PS-MS for rapidly screening samples or to the traditional CE-ESI-MS method for separation and to obtain detailed mass spectral information, while sharing the same mass spectrometer. In the former case, when a sharp (15°-tip) chromatography paper was used, the optimized distance from the paper tip to the mass inlet was 7.7 mm, whereas the optimized distance for the CE-ESI tip was ∼13.5 mm. Using 4-chloroamphetamine as a model compound, the LODs for PS-MS and CE-ESI-MS were determined to ∼0.1 and 0.25 ppm, respectively. Comparisons of results obtained using PS-MS and CE-ESI-MS and the experimental conditions are described., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The use of two-dimensional gel electrophoresis as a tool for the investigation of human bronchoalveolar lavage fluid (BALF) has been hampered by technical difficulties. In the last decade attempts have been made to establish a two-dimensional (2-D) protein map of BALF samples, resulting in the identification of a number of proteins present in BALF. In this study, we report an improved sample handling and separation protocol for investigation of human BALF proteins. The sample has been analyzed by employing a number of strategies, including the 'paper bridge' sample application method in combination with narrow range immobilized pH gradient (IPG) DryStrips, followed by comparison to the corresponding plasma map. Using peptide mass fingerprinting, we have identified 49 proteins in the narrow pH range 4.5-5.2 from an individual healthy BALF sample. Furthermore, we identified 17 BALF proteins, not detected in plasma. Twelve of these proteins have, to our knowledge, not previously been described in the BALF 2-D map. The mapping of BALF proteins with inclusion of those at low concentration increases the possibility to subsequently screen patient material for disease markers.

This paper describes the use of aluminum and zinc as anodic materials for a battery employing nickel (II) oxide (NiO) as cathode. Comparison of both materials resulted in the development of a compact, cost effective, and easy to use primary NiO/Al battery employing an alkaline electrolyte. The system features electrodes composed of powder forms of the active materials on modified paper substrates that are contained in a simple multilayer design utilizing thin laminated plastic materials to provide structure and flexibility to the battery as well as a paper separator. Various concentrations of potassium hydroxide (KOH) electrolyte were examined and maximum performance was observed at 6 M KOH. A maximum current density and power density of 1.94 mA/cm 2 and 1 mW/cm 2 , respectively was achieved. This user-friendly device was able to produce a maximum capacity of 2.33 mAh/g when 2 mA/g was applied. This work demonstrates the viability of a paper-based battery featuring powder electrodes as a possible power source for microelectronic devices., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Fabric-based microfluidic fuel cells (MFCs) serve as a novel, cost-efficient alternative to traditional FCs and batteries, since fluids naturally travel across fabric via capillary action, eliminating the need for an external pump and lowering production and operation costs. Building on previous research with Y-shaped paper-based MFCs, fabric-based MFCs mitigate fragility and durability issues caused by long periods of fuel immersion. In this study, we describe a microfluidic fabric-based direct formate fuel cell, with 5 M potassium formate and 30% hydrogen peroxide as the anode fuel and cathode oxidant, respectively. Using a two-strip, stacked design, the optimized parameters include the type of encasement, the barrier, and the fabric type. Surface contact of the fabric and laminate sheet expedited flow and respective chemical reactions. The maximum current (22.83 mA/cm 2 ) and power (4.40 mW/cm 2 ) densities achieved with a 65% cotton/35% polyester blend material are a respective 8.7% and 32% higher than previous studies with Y-shaped paper-based MFCs. In series configuration, the MFCs generate sufficient energy to power a handheld calculator, a thermometer, and a spectrum of light-emitting diodes., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this paper, a microfluidic thread-based analytical device (μTAD) to assess the activity of acetylcholinesterase (AChE) via colorimetric analylsis is described. Fabrication of the device consists of two platforms, both with a nylon thread trifurcated into three channels terminating at open analysis sites at the end of the thread. 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) was spotted and dried on the analysis sites. Acetylthiocholine iodide (ATC) (or cysteine, Cys) is transported through an inlet channel of the nylon thread by capillary action due to the hydrophilic nature of nylon. AChE is transported through the other inlet channel and mixes with the ATC (or Cys) as they travel up to the analysis sites. As the solution reaches the analysis sites, an intense yellow color change occurs indicating the reaction of the thiol with DTNB to produce the yellow anion TNB 2- . The sites are then dried, scanned, yielding a linear range of inverse yellow mean intensity versus substrate concentration. An IC 50 value (1.74 nM) with a known inhibitor, neostigmine bromide (NB), is obtained on the device. The multiplex design enables triplicate data collection in a device that is easy to use. μTADs have great potential to be employed in a myriad of tests including point-of-care diagnostic devices for resource-challenged settings., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)