Microfluidic Paper-based Analytical Devices Research Articles

Paper Microfluidic Device with a Horizontal Motion Valve and a Localized Delay for Automatic Control of a Multistep Assay.

A microfluidic paper-based analytical device (μPAD) is a cost-effective platform to implement assays, especially for point-of-care testing. Developing μPADs with fluidic control is important to implement multistep assays and provide high sensitivities. However, current localized delays in μPADs made of sucrose have a limited ability to decrease the flow rate. In addition, existing μPADs for automatic multistep assays are limited by their need for auxiliary instruments, their false activation, or their unavoidable tradeoff between available fluid volumes and temporal differences between steps. Here, a novel μPAD composed of a localized dissolvable delay and a horizontal motion mechanical valve for use as an automatic multistep assay is reported. A mixture of fructose and sucrose was used in the localized dissolvable delay and it provided an effective decrease in the flow rate to ensure adequate sensitivity in an assay. The dissolvable delay effectively doubled the flow time. A mechanical valve using a horizontal movement was developed to automatically implement a multistep process. Two-step and four-step processes were enabled with the μPAD. Cardiac troponin I (cTnI), a gold-standard biomarker for myocardial infarction, was used as a model analyte to show the performance of the developed μPAD in an assay. The designed μPAD, with the simple-to-make localized dissolvable delay and the robust mechanical valve, provides the potential to automatically implement high-performance multistep assays toward a versatile platform for point-of-care diagnostics.

Simple biodegradable plastic screen-printing for microfluidic paper-based analytical devices

Abstract The goal of using microfluidic paper-based analytical devices (μPADs) in remote areas has prompted the development of uncomplicated, affordable, and environmentally-friendly fabrication methods. Here, screen-printed biodegradable polycaprolactone (PCL) as a simple, low-cost, and non-toxic alternative approach to create μPADs was introduced. No need for a heating step contributed to low PCL dispersion resulting in high resolution hydrophobic barriers. The proposed method achieved a narrowest hydrophilic channel and hydrophobic edge of 510 ± 40 μm and 490 ± 30 μm, respectively. The method was used to generate several designs for Cr3+ and Cl− detections. For Cr3+ analysis, silver nanoparticles were used as the colorimetric probe to selectively measure Cr3+ using a spot format that achieved a limit of detection (LOD) of 15.0 μg L-1 and a linear working range of 50.0–1000.0 μg L-1. For Cl- determination, the distance-based pattern using traditional precipitation titration was utilized to resolve the coffee ring effect from colorimetric detection. The method gave an LOD and a linear range for Cl- detection of 10.0 mg L-1 and 10.0–500.0 mg L -1, respectively. Finally, the μPADs were applied for Cl- analysis in instant noodle seasonings and the results significantly agreed with those using the traditional titration at 95 % confidence.

Fabrication of Miniaturized Microfluidic Paper-Based Analytical Devices for Sandwich Enzyme-Linked Immunosorbent Assays using INKJET Printing

Main application of microfluidic paper-based analytical devices (µPADs) is for low-cost and portable assays. In order to reduce the cost, miniaturization seems to be an effective way to save reagents, samples, materials, etc. Present study demonstrates that mini-µPADs based on nitrocellulose membrane with only 2 main channels can perform sandwich enzyme-linked immunosorbent assays (ELISA) for quantitative determination of human chorionic gonadotropin (hCG). Moreover, the width and the length of these devices are only about 4.0 and 33.4 mm, respectively. Inkjet printing technology, having the advantages of simple and material-saving process, was used to create hydrophobic barrier. Colorimetric signals from ELISA captured by digital camera and measured by ImageJ software shows that these µPADs can quantitative determine of hCG in the range from 5 to 10 000 ng/mL. Furthermore, duration for each tests is only about 5 min. The success in fabricating miniaturized µPADs shows the potentials to reduce the size of µPADs as well as the amount of needed samples, time and reagents. For all these reasons, this miniaturization concept can be applied to many further applications of analytical biochemical assays.

Recent Advances of Hepatitis B Detection towards Paper-Based Analytical Devices.

Hepatitis B virus (HBV) still remains a major global public health problem. One-half to one-third of the total HBV infected people died due to late detection of HBV. Serological antigen and viral HBV detections can help in the diagnosis, referral, and treatment of HBV. Available methods for HBV detection mostly used bulky instruments. Miniaturization of devices for HBV detection has been started by narrowing down the size of the devices. Several methods have also been proposed to increase the selectivity and sensitivity of the miniaturized methods, such as sandwich recognition of the biomarkers and the use of nano- to micro-sized materials. This review presents recent HBV detections in the last two decades from laboratory-based instruments towards microfluidic paper-based analytical devices (µPADs) for point-of-care testing (POCT) purposes. Early and routine analysis to detect HBV as early as possible could be achieved by POCT, especially for areas with limited access to a central laboratory and/or medical facilities.

Metabolic biomarker modeling for predicting clinical diagnoses through microfluidic paper-based analytical devices

The development of microfluidic devices for point-of-care (POC) testing has been widely applied for food quality control, environmental monitoring, and clinical diagnoses. Regarding the latter, microfluidic paper-based analytical devices (µPADs) have a great potential in developing portable and disposable platforms for fast disease-relevant biomarker detection in remote areas. In this work, k-nearest neighbors (k-NN) classifiers were applied to demonstrate the reliability of using chemical data obtained from µPADs for diagnosis of diseases like diabetes mellitus and hyperuricemia. Predictors based on glucose, lactate, and uric acid biomarkers were evaluated to reach this goal. Healthy adults were differentiated from the diagnosed patients with a perfect success rate. Metabolic disorders were suitably predicted with 95.0% overall accuracy. This model also showed sensitivities and specificities in the ranges 75–100% and 93–100%, respectively, indicating that the classification protocol is robust. The k-NN modeling proved the potential of the µPADs to be applied in telemedicine for reliable off-site diagnoses.

A Three-Dimensional Paper-Based Isoelectric Focusing Device for Direct Analysis of Proteins in Physiological Samples.

On-site protein analysis is crucial for disease diagnosis in community and family medicine in which microfluidic paper-based analytical devices (μPADs) have attracted growing attention. However, the practical applications of μPADs in protein analysis for physiological samples with high complexity is still limited. Herein, we developed a three-dimensional (3D) paper-based isoelectric focusing (IEF) platform, which is composed of power supply, reservoirs, and separation channel and made by the origami and stacking method, to simultaneously separate and enrich proteins in both low-salt and high-salt samples. Under the optimized experimental conditions, standard proteins (bovine hemoglobin (BHb) and phycocyanin (Phy)) were separated within 18 min under a 36 V power supply and obtained a 10-fold enrichment using the 3D paper-based IEF platform. Then, the capability of the 3D paper-based IEF platform for direct pretreatment of high-salt samples using a 12 V battery as power supply was measured through separating three standard proteins in saline (0.9% NaCl) with separation resolution (SR) > 1.29. Through further coupling with colorimetric and lateral flow strip measurements, the 3D paper-based IEF platform was applied to directly pretreat and quantitatively analyze microalbuminuria and C-reactive proteins in clinical urine and serum samples with analytical results with relative deviations of <8.4% and < 13.1%, respectively, to the clinical test results. This work proposes a new strategy to minimize the difficulty of directly processing high-salt samples with the traditional IEF system and provides a versatile, miniaturized, and low voltage demand analytical platform for on-site analysis of proteins in physiological samples.

On-site microfluidic paper- based titration device for rapid semi-quantitative vitamin C content in beverages

A rapid, simple and on-site redox titration of vitamin C was accomplished using a novel microfluidic paper-based analytical device. The analysis was based on the combination of traditional redox titration and a microfluidic paper-based titration. The device was designed to have one sample zone connected to a titrant zone where ten different concentrations of iodine (titrant) were filled in each well. The top part of the device was a detection zone where the starch solution (indicator) was added. Vitamin C was added into a sample zone and then flowed to the titrant zone where the vitamin C was oxidized by the iodine. The excess iodine reacted with the starch indicator and endpoint of titration was reached when the blue-black product was observed by the naked eye in the detection zone. The proposed method for vitamin C detection showed the working range between 2.5 and 1,000 mg/L. The limit of detection was 2.5 mg/L. Time for an assay was only 3 sec. The developed paper-based device was applied to detect vitamin C in the real sample of beverage and the results corresponded to those obtained from traditional redox titration. The developed assay proved to be less reagent consumption compared to the traditional one. It is a truly portable device with no glassware and skilled personnel to require.

Hemp-Based Microfluidics.

Hemp is a sustainable, recyclable, and high-yield annual crop that can be used to produce textiles, plastics, composites, concrete, fibers, biofuels, bionutrients, and paper. The integration of microfluidic paper-based analytical devices (µPADs) with hemp paper can improve the environmental friendliness and high-throughputness of µPADs. However, there is a lack of sufficient scientific studies exploring the functionality, pros, and cons of hemp as a substrate for µPADs. Herein, we used a desktop pen plotter and commercial markers to pattern hydrophobic barriers on hemp paper, in a single step, in order to characterize the ability of markers to form water-resistant patterns on hemp. In addition, since a higher resolution results in densely packed, cost-effective devices with a minimized need for costly reagents, we examined the smallest and thinnest water-resistant patterns plottable on hemp-based papers. Furthermore, the wicking speed and distance of fluids with different viscosities on Whatman No. 1 and hemp papers were compared. Additionally, the wettability of hemp and Whatman grade 1 paper was compared by measuring their contact angles. Besides, the effects of various channel sizes, as well as the number of branches, on the wicking distance of the channeled hemp paper was studied. The governing equations for the wicking distance on channels with laser-cut and hydrophobic side boundaries are presented and were evaluated with our experimental data, elucidating the applicability of the modified Washburn equation for modeling the wicking distance of fluids on hemp paper-based microfluidic devices. Finally, we validated hemp paper as a substrate for the detection and analysis of the potassium concentration in artificial urine.

Handheld and ‘Turnkey’ 3D printed paper-microfluidic viscometer with on-board microcontroller for smartphone based biosensing applications

Herein, Microfluidic Paper-based Analytical Devices (μPAD) strips, also called microstrips, have been fabricated using a fused-deposition modeling (FDM) based 3D printer. A polycaprolactone (PCL) filament on a chromatography paper was harnessed to create hydrophobic boundaries of a microchannel. A pair of screen-printed electrodes, with known separation, were integrated on the microchannel to measure the time taken for fluid automatically. A mini electronic sub-system, amenable to connect with an android smartphone, consists of an easily programmable microcontroller, Bluetooth module and voltage booster circuit. The pluggable-and-playable disposable microstrip was utilized to measure the viscosity of various biological samples with an accuracy of >92% with respect to a benchtop viscometer. In particular, the protein denaturation of Bovine Serum Albumin (BSA) and Lysozyme, and viscosity variation of human saliva have been observed. With a competency to measure the viscosity between 0.5 cP to 10 cP, platform cost of <US$ 8 and a cost-per-test of less than US$ 0.02, the present device has a strong potential to be employed as a personalized gadget for various viscosity dependent measurements.

Point-of-care diagnostics for infectious diseases: From methods to devices.

The current widespread of COVID-19 all over the world, which is caused by SARS-CoV-2 virus, has again emphasized the importance of development of point-of-care (POC) diagnostics for timely prevention and control of the pandemic. Compared with labor- and time-consuming traditional diagnostic methods, POC diagnostics exhibit several advantages such as faster diagnostic speed, better sensitivity and specificity, lower cost, higher efficiency and ability of on-site detection. To achieve POC diagnostics, developing POC detection methods and correlated POC devices is the key and should be given top priority. The fast development of microfluidics, micro electro-mechanical systems (MEMS) technology, nanotechnology and materials science, have benefited the production of a series of portable, miniaturized, low cost and highly integrated POC devices for POC diagnostics of various infectious diseases. In this review, various POC detection methods for the diagnosis of infectious diseases, including electrochemical biosensors, fluorescence biosensors, surface-enhanced Raman scattering (SERS)-based biosensors, colorimetric biosensors, chemiluminiscence biosensors, surface plasmon resonance (SPR)-based biosensors, and magnetic biosensors, were first summarized. Then, recent progresses in the development of POC devices including lab-on-a-chip (LOC) devices, lab-on-a-disc (LOAD) devices, microfluidic paper-based analytical devices (μPADs), lateral flow devices, miniaturized PCR devices, and isothermal nucleic acid amplification (INAA) devices, were systematically discussed. Finally, the challenges and future perspectives for the design and development of POC detection methods and correlated devices were presented. The ultimate goal of this review is to provide new insights and directions for the future development of POC diagnostics for the management of infectious diseases and contribute to the prevention and control of infectious pandemics like COVID-19.

Precise electroosmotic flow measurements on paper substrates

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 relatedtechnologies.

In situ synthesis of fluorescent silicon nanodots for determination of total carbohydrates in a paper microfluidic device combined with laser prepared graphene heater

We report a simple, rapid, low-resource and one-step method for formation of fluorescent silicon nanodots (SNDs) in a microfluidic paper-based analytical device (μPAD) incorporated in a reusable, portable and flexible heater for determination of total carbohydrates. The synthesis of SNDs is based on the redox reaction between (3-aminopropyl) triethoxysilane (APTS) reagent and carbohydrates, which act as a reducer. The graphene-based heater was fabricated by laser ablation of Kapton polyimide. Thereby, the developed system heat the μPAD during the synthesis of SNDs at 80 °C for 30 min. The blue emitting SNDs formed have an emission peak wavelength at 475 nm. We used a digital camera and smartphone for the quantitative analysis of total carbohydrates expressed such as index of glucose or fructose with grey scale value as the analytical parameter. Under the optimal conditions, the method has a low detection limit (0.80 μM for glucose and 0.51 μM for fructose, respectively), and a linear response (10–200 μM for glucose and 10–100 μM for fructose). The method has been applied to the determination of glucose in biological fluids (serum and urine samples). In addition, determination of total carbohydrates in commercial juices and teas have been carried out.

Programmable microfluidic flow for automatic multistep digital assay in a single-sheet 3-dimensional paper-based microfluidic device

A single-sheet 3-dimensional paper-based microfluidic analytical device (3D-μPAD) has a user-friendly compact format that eliminates any potential for user alignment error compared to the stacking and folding format. However, achieving sophisticated analysis is still a challenge because forming a complex 3D microfluidic network sufficient for performing analysis in a single sheet of paper is difficult. Here, we present the first report of automatic multistep digital analysis in a single-sheet 3D-μPAD created by controlling the penetration of different wax inks into paper. Simple printing of different wax inks with different spreading properties produces different dimension microchannels in paper. This controllable change in the dimensions of the microchannels results in different flow rates of fluid in each microchannel. Based on the spatial resolution of the microchannels, our strategy enables programming of microfluidic flow through manipulation of the fluidic time delay. This approach creates 3D-μPADs capable of sequential fluid delivery and multistep biochemical reactions with single loading of a sample solution. The methodology can be further expanded to combination with digital assays to measure the concentration of a target analyte by simply counting the number of colored bars at a fixed time. It does not require any external instruments to analyze the measurement of the target analyte concentration. The significance of this work lies in the promising potential for automatic multistep digital assays in a low-cost and easy-to-use paper-based format that can be integrated with a roll-to-roll process for commercial-scale manufacturing.

Sensitive fluorometric determination of gold in geological samples using fire assay pre-concentration coupled with microfluidic paper-based analytical device

The present study was conducted to develop a simple, low-cost and sensitive micro fluidic paper-based analytical device (µPAD) for analysis of gold in geological samples. This µPAD was fabricated employing eyeliner pencil method. It consists of different zones, including detection, pH adjustment, reaction and elution. We injected 29 µL elution solution in the center of µPAD, direct Au3+, after adjusting pH, to make it react with rhodamine B. The formation of RB-Au3+ complex led to quench of rhodamine B fluorescence. The image of each detection zone was captured using a cell phone camera under a UV lamp, and luminosity intensity was subsequently measured with Photoshop software. Various parameters were studied in order to achieve the most efficient performance of the paper sensor. Under the optimized condition, a wide linear range (1–40 mg L−1, R2 = 0.996) was obtained with detection limit of 0.15 mg L−1. Ultimately, the developed µPAD was applied for the determination of gold in ore samples. The obtained results were in good agreement with those obtained from standard method. The combination of fire assay and µPAD in the determination of gold in geological samples improved the detection limit based on enrichment factor of 75.

Enhanced selectivity and sensitivity for colorimetric determination of glyphosate using Mn–ZnS quantum dot embedded molecularly imprinted polymers combined with a 3D-microfluidic paper-based analytical device

We report a novel three-dimensional microfluidic paper-based analytical device (3D-μPAD) with colorimetric detection, using Mn–ZnS quantum dot embedded molecularly imprinted polymer (Mn–ZnS QD-MIP), for selective glyphosate determination in whole grain samples. Detection is based on the catalytic activity of Mn–ZnS QD-MIP in the H2O2 oxidation of ABTS. Glyphosate imprinted polymer is successfully synthesized on the Mn–ZnS QD surface using a poly (N-isopropylacrylamide) (NIPAM) and N, N′-Methylenebisacrylamide (MBA) as the functional monomers. The catalytic activity depends on binding or non-binding of glyphosate molecules on the synthetic recognition sites of the Mn–ZnS QD-MIP. Glyphosate selectively binds to the cavities embedded on the Mn–ZnS QD surface, and subsequently turns-off or inhibits the ABTS oxidation and color change to light green. The change of reaction color from dark green to light green depends on the concentration of glyphosate. We report, for the first time, using the relatively new penguard enamel colour to create a hydrophobic barrier. The foldable 3D-μPAD comprises three layers (top/center/bottom), named as the detection zone, immobilized Mn–ZnS QD-MIP disc, and sample loading. Assay on the 3D-μPAD can determine glyphosate by ImageJ detection, over an operating range of 0.005–50 μg mL−1 and with a detection limit of 0.002 μg mL−1. Our 3D-μPAD exhibits high accuracy, with a 0.4% (intra-day) and 0.7% (inter-day) relative difference from the certified CRM value. Moreover, the fabricated 3D-μPAD provides good reproducibility (1.7% RSD for ten devices). The developed 3D-μPAD was successfully applied to determine the glyphosate concentration in whole grain samples and shows great promise as an alternative highly selective and sensitive colorimetric method. The 3D-μPAD is well suited to food-quality control and onsite environmental-monitoring applications, without sophisticated instrumentation.

Simultaneous analysis of multiple adulterants in milk using microfluidic paper-based analytical devices.

This study reports the simultaneous colorimetric detection of urea, H2O2, and pH in milk samples using microfluidic paper-based analytical devices (μPADs) fabricated through a craft cutter printer. Paper-based devices were designed to contain three detection zones interconnected to a sampling zone by microfluidic channels. Colorimetric analysis was performed using images digitalized through an office scanner. The volumes of chromogenic and sample solutions were optimized, and the best colorimetric performance was achieved by adding 0.5 and 10 μL into detection and sampling zones, respectively. Simultaneous assays were then carried out, and the recorded responses revealed a linear behavior in the concentration ranges from 0-30.0 mmol L-1, 0-10.0 mmol L-1 and 6.0-9.0 for urea, H2O2 and pH, respectively. The limit of detection values obtained for urea and H2O2 were 2.4 mmol L-1 and 0.1 mmol L-1, respectively. For pH measurements, colorimetric assay allowed the monitoring of solution pH with a resolution of 0.25 units. The use of μPADs to detect target adulterants exhibited suitable reproducibility (RSD ≤ 6.0%), accuracy (91-102%) and no cross-reaction occurrence. When compared to reference techniques, colorimetric assays did not reveal a significant difference at a confidence level of 95%. As a proof-of-concept, the feasibility of the proposed approach was successfully demonstrated through the analysis of potential adulterants in sixteen milk samples, which were tested without any pretreatment requirement. Based on the achievements, μPADs in conjunction with colorimetric measurements emerge as a powerful tool for rapid screening of potential adulterants in milk.

Recent advances in lab-on-paper diagnostic devices using blood samples.

Lab-on-paper, or microfluidic paper-based analytical devices (μPADs), use paper as a substrate material, and are patterned with a system of microchannels, reaction zones and sensing elements to perform analysis and detection. The sample transfer in such devices is performed by capillary action. As a result, external driving forces are not required, and hence the size and cost of the device are significantly reduced. Lab-on-paper devices have thus attracted significant attention for point-of-care medical diagnostic purposes in recent years, particularly in less-developed regions of the world lacking medical resources and infrastructures. This review discusses the major advances in lab-on-paper technology for blood analysis and diagnosis in the past five years. The review focuses particularly on the many clinical applications of lab-on-paper devices, including diabetes diagnosis, acute myocardial infarction (AMI) detection, kidney function diagnosis, liver function diagnosis, cholesterol and triglyceride (TG) analysis, sickle-cell disease (SCD) and phenylketonuria (PKU) analysis, virus analysis, C-reactive protein (CRP) analysis, blood ion analysis, cancer factor analysis, and drug analysis. The review commences by introducing the basic transmission principles, fabrication methods, structural characteristics, detection techniques, and sample pretreatment process of modern lab-on-paper devices. A comprehensive review of the most recent applications of lab-on-paper devices to the diagnosis of common human diseases using blood samples is then presented. The review concludes with a brief summary of the main challenges and opportunities facing the lab-on-paper technology field in the coming years.

An electricity- and instrument-free infectious disease sensor based on a 3D origami paper-based analytical device.

Infectious diseases cause millions of deaths annually in the developing world. Recently, microfluidic paper-based analytical devices (μPADs) have been developed to diagnose such diseases, as these tests are low cost, biocompatible, and simple to fabricate. However, current μPADs are difficult to use in resource-limited areas due to their reliance on external instrumentation to measure and analyze the test results. In this work, we propose an electricity and external instrumentation-free μPAD sensor based on the colorimetric enzyme-linked immunosorbent assay (ELISA) for the diagnosis of infectious disease (3D-tPADs). Designed based on the principle of origami, the proposed μPAD enables the sequential steps of the colorimetric ELISA test to be completed in just ∼10 min. In addition, in order to obtain an accurate ELISA result without using any instrument, we have integrated an electricity-free "timer" within the μPAD that can be controlled by the buffer viscosity and fluid path volume to indicate the appropriate times for washing and color development steps, which can avoid false positive or false negative results caused by an extended or shortened amount of washing and development times. Due to the low background noise and high positive signal intensity of the μPAD, positive and negative detection results can be distinguished by just the naked eye. Furthermore, the ELISA result can be semi-quantified by comparing the results shown on the μPAD with a color chart diagram with a detection limit of HIV type 1(HIV-1) p24 antigen as low as 0.03 ng mL-1. These results demonstrate the proposed sensor can perform infectious disease diagnosis without external instrumentation or electricity, extending the application of the μPAD test for on-site detection and use in resource-limited settings.

The colorimetric and microfluidic paper-based detection of cysteine and homocysteine using 1,5-diphenylcarbazide-capped silver nanoparticles.

We have prepared a microfluidic paper-based analytical device (μPAD) for the determination of cysteine and homocysteine based on 1,5-diphenylcarbazide-capped silver nanoparticles. The μPAD was developed to identify and quantify the levels of cysteine and homocysteine. The proposed μPAD enabled the detection of cysteine and homocysteine using a colorimetric reaction based on modified silver nanoparticles. The color of the modified AgNPs in the test zone immediately changed after the addition of cysteine and homocysteine. Based on this change, the quantification of these two amino acids was achieved using an RGB color model and ImageJ software. Under optimized conditions, the proposed device enabled the determination of cysteine in the 0.20–20.0 μM concentration range with a limit of detection (LOD) of 0.16 μM. In addition, the LOD of homocysteine was calculated to be 0.25 μM with a linear range of 0.50–20.0 μM. In this work, we focused on the use of the μPAD for the analysis of a series of human urine samples.

A multilayer microfluidic paper coupled with an electrochemical platform developed for sample separation and detection of dopamine

A new construction of a multilayer electrochemical microfluidic paper-based analytical device using a single drop of the sample solution was performed for highly selective detection of dopamine in the presence of ascorbic acid interference.