Microfluidic Paper Research Articles

Rapid detection of three mycotoxins in animal feed materials using competitive ELISA-based origami microfluidic paper analytical device (μPAD).

We report the development of a competitive ELISA-based origami microfluidic paper-based analytical device (μPAD) for the detection of mycotoxins in animal feed material. The μPAD was patterned using the wax printing technique with the design of a testing pad in the middle and two absorption pads at the side. Anti-mycotoxin antibodies were effectively immobilized on chitosan-glutaraldehyde-modified sample reservoirs in the μPAD. The determination of zearalenone, deoxynivalenol, and T-2 toxin in corn flour was successfully achieved by performing competitive ELISA on the μPAD in 20min. Colorimetric results were easily distinguished by the naked eye with a detection limit of 1µg/mL for all three mycotoxins. The μPAD integrated with competitive ELISA holds potential for practical applications in thelivestock industry for rapid, sensitive, and cost-effective detection of different mycotoxins in animal feed materials.

Integrated smart analytics of nucleic acid amplification tests via paper microfluidics and deep learning in cloud computing

Pandemics such as COVID-19 have exposed global inequalities in essential health care. Here, we proposed a novel analytics of nucleic acid amplification tests (NAATs) by combining paper microfluidics with deep learning and cloud computing. Real-time amplifications of synthesized SARS-CoV-2 RNA templates were performed in paper devices. Information pertained to on-chip reactions in time-series format were transmitted to cloud server on which deep learning (DL) models were preloaded for data analysis. DL models enable prediction of NAAT results using partly gathered real-time fluorescence data. Using information provided by the G-channel, accurate prediction can be made as early as 9 min, a 78% reduction from the conventional 40 min mark. Reaction dynamics hidden in amplification curves were effectively leveraged. Positive and negative samples can be unbiasedly and automatically distinguished. Practical utility of the approach was validated by cross-platform study using clinical datasets. Predicted clinical accuracy, sensitivity and specificity were 98.6%, 97.6% and 99.1%. Not only the approach reduced the need for the use of bulky apparatus, but also provided intelligent, distributable and robotic insights for NAAT analysis. It set a novel paradigm for analyzing NAATs, and can be combined with the most cutting-edge technologies in fields of biosensor, artificial intelligence and cloud computing to facilitate fundamental and clinical research.

Structural analysis of paper substrate for flexible microfluidics device application

PurposeThe purpose of this paper is to predict a suitable paper substrate which has high capillary pressure with the tendency of subsequent fluid wrenching in onward direction for the fabrication of microfluidics device application.Design/methodology/approachThe experiment has been done on the WhatmanTM grade 1, WhatmanTM chromatography and nitrocellulose paper samples which are made by GE Healthcare Life Sciences. The structural characterization of paper samples for surface properties has been done by scanning electron microscope and ImageJ software. Identification of functional groups on the surface of samples has been done by Fourier transform infrared analysis. A finite elemental analysis has also been performed by using the “Multiphase Flow in Porous Media” module of the COMSOL Multiphysics tool which combines Darcy’s law and Phase Transport in Porous Media interface.FindingsExperimentally, it has been concluded that the paper substrate for flexible microfluidic device application must have large number of internal (intra- and interfiber) pores with fewer void spaces (external pores) that have high capillary pressure to propel the fluid in onward direction with narrow paper fiber channel.Originality/valueSurface structure has a dynamic impact in paper substrate utilization in multiple applications such as paper manufacturing, printing process and microfluidics applications.

Engineered detection zone to enhance color uniformity on paper microfluidics fabricated via Parafilm®-heating-laser-cutting

In this article, we first report a simple fabrication technique to create Parafilm®-laminated microfluidic paper-based analytical devices (µPADs) with a high resolution and then introduce novel engineered detection zones (D-zones) to enhance color uniformity without any chemical modifications. The Parafilm®-heating-laser cutting fabrication method comprises of three steps: 1) flattening a Parafilm® layer on paper, 2) heating in an oven at 90 °C for 30 min, and 3) CO2 laser ablation of the patterns. This method enabled laminated µPADs with a minimum barrier width of 172 ± 15 µm, with resistance to various organic solvents and surfactant solutions. Using this technique, µPADs with two types of engineered D-zones were fabricated. The multi-inlet D-zone had four micro-inlets (<500 µm width), enabling sample entrance into the D-zone from four directions simultaneously towards the center. The segmented D-zone had four segments each with its own micro-inlet allowing for separate reactions to occur in miniaturized segments simultaneously. Using an enzymatic glucose assay for the colorimetric reaction, the multi-inlet and segmented D-zones significantly decreased color gradient from 28.77 ± 1.49 to 12.35 ± 1.18 and 8.95 ± 0.98 %, respectively, compared to the conventional devices. We further used the µPADs with segmented D-zones for the detection of glucose in artificial urine in the clinically relevant range of 2–50 mM, where R2 > 0.99 of the fitted curve showed an excellent correlation between the generated signals and the glucose concentrations. Also, compared to the conventional devices, the engineered D-zones showed improved precision and reproducibility and a better linear range. Finally, spiked real human urine samples were tested, demonstrating the applicability of the engineered devices for real-world applications. Overall, with a simple fabrication method and a novel design for color uniformity, this paper contributes to the advancement of µPADs and paves the way towards commercialization.

Accuracy improvement via novel ratiometry design in distance-based microfluidic paper based analytical device: instrument-free point of care testing.

Developing accurate, precise, instrument-free, and point-of-need microfluidic paper-based devices is highly significant in clinical diagnosis and biomedical analysis. In the present work, a ratiometric distance-based microfluidic paper-based analytical device (R-DB-μPAD), along with a three-dimensional (3D) multifunctional connector (spacer), was designed to improve the accuracy and detection resolution analyses. Specifically, the novel R-DB-μPAD was used for the accurate and precise detection of ascorbic acid (AA) as a model analyte. In this design, two channels were fabricated as detection zones, with a 3D spacer located between the sampling and detection zones to improve the detection resolution by preventing the reagents mixing from overspreading between these zones. Two probes for AA were used: Fe3+ and 1,10-phenanthroline were deposited in the first channel, and oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) was added to the second channel. Accuracy improvement of this ratiometry-based design was achieved by enhancing the linearity range and reducing the volume dependency of the output signal. Moreover, the 3D connector improved the detection resolution by eliminating the systematic errors. Under the optimal conditions, the ratio of the distances of the color bands in the two channels was used to construct an analytical calibration curve in the range from 0.05 to 1.2 mM, with a limit of detection of 16 μM. The proposed R-DB-μPAD combined with the connector was successfully used for the detection of AA in orange juice and vitamin C tablets with satisfactory accuracy and precision. This work opens the door for multiplex analysis of various analytes in different matrices.

Microfluidic paper-based colorimetric quantification of malondialdehyde using silver nanoprism toward on-site biomedical analysis: a new platform for the chemical sensing and biosensing of oxidative stress.

Malondialdehyde (MDA) is a critical product of polyunsaturated adipose acid peroxidation and represents a common biomarker of oxidative stress. The effect of different MDA concentrations on human biofluids reflects pathological changes, which has been seen in diverse types of sickness, such as leukemia, diabetes, cancer, cardiovascular disease, and age-related macular degeneration and liver disease. In this study, different types of silver nanoparticles, including silver nanoprism (AgNPrs), silver nanowires (AgNWs), and silver nanospheres (AgNSs), were synthesized and used for the chemosensing of MDA by colorimetric and spectrophotometric methods. Colorimetric tests were performed to identify malondialdehyde in the solution as well as the one-droplet-based microfluidic paper substrate as a miniaturization device for the monitoring of analytes in human real samples. The analytical quantification of the MDA was done using the UV-Vis method. Also, the utilization of the designed chemosensor for the analysis of MDA in real sample was evaluated in human urine samples. Using the spectrophotometric method, MDA was deformed in the linear range of 0.01192 to 1.192 mM with a low limit of quantification of 0.12 μM. Essential significant features of this study include the first application of AgNPrs with high stability and great optical properties without any reagent as an optical sensing probe of MDA and optimized OD-μPCD toward on-site and on-demand MDA screening in real samples diagnosis and the innovative time/color semi-analytical recognition strategy. Moreover, the prepared OD-μPCD decorated by AgNPrs could be a prized candidate for commercialization due to the benefits of the low-cost materials used, like paper and paraffin, and portability. This innovative process led to uniform hydrophilic micro-channels on the surface of cellulose, without the use of a UV lamp, clean room, and organic solvents. This report could be a pioneering work, inspiring simple and effective on-site semi-analytical recognition devices for harmful substances or illegal drugs, which simply consist of a piece of lightweight paper and one drop of the required reagent.

Point-of-care assay platform for uric acid, urea, and triglycerides with a microfluidic paper device (μPAD) controlled by stimulus-sensitive valves

A microfluidic biosensor paper-based analytical device, or μPAD, was developed as a point-of-care assay platform for the simultaneous determination of three clinically important markers: uric acid, urea, and triglycerides. To achieve a simultaneous determination, thermosensitive valves based on N-isopropylacrylamide polymers controlled the flow of fluid in the μPAD. The evaluation of the analytical characteristics of the μPAD was done using a photographic camera at room temperature.The detection limits were 4.5·10−5, 2.5·10−3, and 1.5·10−3 mg mL−1, for uric acid, urea, and triglycerides, respectively, and the precision expressed as relative standard deviation (% RSD) 3.2, 1.2, and 1.6%. The obtained μPAD devices were validated with real human plasma samples, demonstrating high accuracy and precision. Multiple analyte point-of-care tests such as those developed here have excellent characteristics, being easy to manufacture, cost-effective, easy to use, and highly sensitive.

Threaded 3D microfluidic paper analytical device-based ratiometric fluorescent sensor for background-free and visual detection of organophosphorus pesticides

With the increasing concerns of food safety and environmental protection, it is desirable to develop reliable, effective, and portable sensors for detection of organophosphorus pesticides (OPs). Here, a cascade reaction system integrated with threaded 3D microfluidic paper analytical device (3D μPAD) was firstly developed for background-free and visual detection of OPs in agricultural samples. Butyrylcholinesterase (BChE) hydrolyzed acetylcholine into thiocholine (TCh), which reduced MnO2 nanosheets into Mn2+. With addition of OPs, BChE activity was irreversibly inhibited, and the generation of TCh and the reduction of MnO2 nanosheets were prevented. Then the remaining MnO2 nanosheets oxidized o-phenylenediamine into 2,3-diaminophenazine with yellow-emission fluorescence, which quenched the fluorescence intensity of red-emission carbon dots (RCDs) via inner-filter effect. Based on above mechanism, a ratiometric fluorescent system was established for OPs detection. Threaded 3D μPAD consisted of 4 layers, which allowed to load and/or add reagents to trigger the cascade reaction system for OPs detection. The fluorescent images presented distinguishable color variations from red to yellow with dichlorvos concentrations ranging from 2.5 to 120 μg L−1, and the limit of detection was 1.0 μg L−1. In the practical samples testing, threaded 3D μPAD can eliminate background influence on fluorescent signal for OPs detection. Threaded 3D μPAD integrated with ratiometric sensing platform has merits of accuracy response, facile operation, and background-free detection, which supplies a new alternative approach for on-site pesticide detection.

An origami microfluidic paper device for on-site assessment of urine tampering. First use of Nessler's reagent for the colorimetric determination of creatinine

The relevance of the problem of urine tampering is well-known in forensic toxicology, with sample dilution being the most used method to cheat toxicological controls. Among the criteria to assess urine integrity, the quantification of creatinine probably represents the most popular method. The present paper presents a simple and low-cost analytical device for on-site creatinine determination as first-line screening for urine dilution.The proposed microfluidic devices were designed as a three-dimensional origami pattern. The device included three colorimetric reactions based on picric acid (PA-based reagent), 3,5-dinitrobenzoic acid (DNBA-based reagent), and Nessler's reagent. The last one, to the best of our knowledge, has never been used before for creatinine determination. In order to assure the highest ease and economy of operation, the color detection and data processing were performed using a built-in smartphone camera and the associated software. The optimized device showed a detection limit of 0.02 g/L. The proposed method was used for the qualitative screening for urine dilution of 48 samples, showing a diagnostic sensitivity and specificity for PA-based, DNBA-based and Nessler's reagent of 83.3%–80.0%, 72.2%–70.0%, and 100.0%–93.3% respectively, versus reference enzymatic method adopting a cut-off of 0.2 g/L.In conclusion, the present preliminary study shows that the proposed device could be a useful tool for on-site screening for urine tampering at the time of sample collection for toxicological testing.

3D printed optical sensor for highly sensitive detection of picric acid using perovskite nanocrystals and mechanism of photo-electron transfer

Hand-held, compact and portable sensors for on-site detection of environmental contaminants are in high demand for industry 4.0. Here, we have developed a sensor based on luminescent organic–inorganic metal halide hybrid perovskites nanocrystals (CH3NH3PbBr3) with p-xylylenediamine as an additional capping agent for highly sensitive and selective detection of picric acid (PA), with a good linear range of 1.8 μM–14.3 μM achieving detection of limit (LOD) of 0.3 μM. The electrostatic interaction between PA and the capping ligand of perovskite nanocrystals resulted in significant fluorescence quenching, as revealed by the steady-state and time-resolved spectroscopy. The applicability of the developed sensor for PA detection was validated with a 3D printed device integrating surface mounting device (SMD) and paper microfluidics. This prototype device was successfully applied as a fluorescence turn-off sensor to detect PA, showing great potential for on-site detection. This 3D-printed paper-based microfluidic optical sensor proved very efficient for naked-eye detection of PA with an inbuilt excitation source, avoiding the requirement of expensive and complex instrumentation.

Printed graphene-based electrochemical sensor with integrated paper microfluidics for rapid lidocaine detection in blood

Topical lidocaine patches are commonly used to relieve pain and suffering in various clinical and household settings. Despite its extensive use, excessive skin absorption during numbing or pain reduction procedures can cause systemic toxicity, which can lead to life-threatening conditions. Rapid and reliable monitoring of escalating levels of lidocaine in the blood could help management/prevention of lidocaine overdose and its associated complications. To address this need, here we have developed a disposable point-of-care (POC) diagnostic platform composed of an integrated graphene-based electrochemical sensor with paper-based microfluidics for rapid detection of lidocaine levels in serum and blood samples. The fabrication process takes advantage of advanced, scalable manufacturing techniques, including printing, laser processing, and nondestructive near infrared (NIR) drying. The sensitivity tests of the platform revealed a sensitivity of ∼0.2 μA μM−1 towards lidocaine concentrations in the clinically relevant range (1–100 μM) in both complex matrix fluids of serum and blood with high cross specificity in the presence of the interfering analytes. This proof-of-concept platform could be regarded as the first step toward the development of low-cost and translational POC devices that could help in better pain management and reduce potential side effects or misuse of analgesics.

Microfluidic wearable electrochemical sweat sensors for health monitoring.

Research on remote health monitoring through wearable sensors has attained popularity in recent decades mainly due to aging population and expensive health care services. Microfluidic wearable sweat sensors provide economical, non-invasive mode of sample collection, important physiological information, and continuous tracking of human health. Recent advances in wearable sensors focus on electrochemical monitoring of biomarkers in sweat and can be applicable in various fields like fitness monitoring, nutrition, and medical diagnosis. This review focuses on the evolution of wearable devices from benchtop electrochemical systems to microfluidic-based wearable sensors. Major classification of wearable sensors like skin contact-based and biofluidic-based sensors are discussed. Furthermore, sweat chemistry and related biomarkers are explained in addition to integration of microfluidic systems in wearable sweat sensors. At last, recent advances in wearable electrochemical sweat sensors are discussed, which includes tattoo-based, paper microfluidics, patches, wrist band, and belt-based wearable sensors.

Development of Paper Microfluidics with 3D-Printed PDMS Barriers for Flow Control.

Paper microfluidics has been extensively exploited as a powerful tool for environmental and medical detection applications. Both flow delay and compatibility with either polar or non-polar reagents are indispensable for the automation of detections requiring multiple reaction steps. This article reports the systematic studies of a 3D-printing protocol, characterization, and application of both the partially and fully penetrated polydimethylsiloxane (PDMS) barriers for flexible flow control in paper microfluidics. The physical parameters of PDMS barriers printed using a simple liquid dispenser were found related to the printing pressure, speed, diffusion time after printing, baking temperature, and PDMS viscosity. The capability of PDMS barriers to confine the flow of non-polar solvents was demonstrated using oil flow in both wax- and PDMS-surrounded channels. It was identified that the minimum width of channels to prevent leakage was 470 ± 54 μm, which was as narrow as that fabricated using stamps from lithography. Both the partially penetrated barriers (PPBs) and constriction channels were of the capability to delay flow in paper microfluidics. Additionally, an in silico investigation led to the further understanding that the reduction of channel cross-section resulting from PPBs was the primary reason for flow delay. Our results suggest that increasing the penetration depth of the barriers is more efficient in delaying flow than increasing the PPB length. Finally, devices with four inlet channels and 0-6 PPBs across each channel were successfully applied in flow delay for sequential fluid delivery. These results improve the understanding of the major factors, affecting the 3D PDMS barrier fabrication and the resulting flow control in paper microfluidics, providing practical implications for applications in various fields.

Effects of Relative Humidity and Paper Geometry on the Imbibition Dynamics and Reactions in Lateral Flow Assays

Lateral flow assays and paper microfluidics have the potential to replace benchtop instrumented medical diagnostic systems with instrument-free systems that rely on passive transport of liquid through micro-porous paper substrates. Predicting the imbibition dynamics of liquid through dry paper substrates is mostly modeled through the Lucas-Washburn (LW) equations. However, the LW framework assumes that the fluid front exhibits a sharp boundary between the dry and wet phases across the liquid imbibition interface. Additionally, the relative humidity in the environment results in moisture trapped within the pores of the paper substrates as the paper attains an equilibrium with the ambient air. Here, we apply a two-phase transport framework based on Brooks and Corey's model to capture imbibition dynamics on partially saturated paper substrates. The model is experimentally validated and is then used to predict the liquid-paper imbibition dynamics in simulated environments with 1-70% relative humidity. The model was also used to determine the saturation gradient of liquid along the imbibition interface of the paper substrate. Insights from these studies enabled us to determine the mechanism of the liquid transport in partially saturated porous paper substrates. The model also enabled us to evaluate the optimal paper shapes and relative humidity of the environment that maximize imbibition rates and minimize imbibition front broadening. Finally, we evaluate the effect of moisture content of paper on the rate of paper-based biochemical reaction by amplifying a sequence of the SARS-CoV-2 RNA target via reverse transcriptase loop-mediated isothermal amplification. Taken together, this study provides some important guidelines to academic and applied researchers working in point-of-care diagnostics to develop paper-based testing platforms that are capable of functioning in a robust manner across multiple environmental conditions.

Point-of-need determination of blood typing using a three-dimensional origami microfluidic paper based analytical device

We report a three-dimensional origami paper-based analytical device (3D-µPAD) for ABO and Rh blood type detection using a three-dimensional origami microfluidic technology. A piece of rectangular shaped paper sizing (28.5 × 2) cm was folded into thirteen square layers of 2 cm edge. The first two layers formed the sample zone and distribution zones. Other layers were composed of 4 hydrophilic circle zones, which provide cylindrical channels when the paper layers are folded. Three circle zones on layers from 3 to 8 were pre-deposited with antibodies A, B and D and the reminder circle zone was considered as control. According to the design principle, when blood moves through channels of different antibodies it forms agglutination with those having its complementary blood group antigen. This lowers down the speed of blood movement through the channels. Therefore, the ability of blood movement through each channel was used as the basis of our detection (i.e., counting the number of layers through which blood moved for each channel, separately). The effects of the experimental parameters on the sensor’s performance were investigated by using Placket-Burman and Central Composite Design methods. The device operation was validated by analyzing 67 blood samples. It was found that the if blood had complementary antigens, it moved 3–5 layers in the channels pre-deposited with anti-A or anti-B and 5–7 layer in channels pre-deposited with anti-D. Based on this observation, by single analysis we could determine the blood type of 95 % of samples compared to the gold standard method, which is currently used in blood transfusion labs. Replicate analysis resulted in 100 % accuracy. The device was stable for 14 days before using. However, after using, it was stable for at least 1 year.

Nuclease-propelled target dual-recycling amplification strategy integrated with cascaded sensitization effect of ZnO/CuInS2/Ag2Se photoactive structures for lab-on-paper photoelectrochemical microRNA bioassay

Herein, a new paper-based photoelectrochemical (PEC) biosensor was proposed for microRNA determination based on the cascaded sensitization effect of ZnO/CuInS2/Ag2Se photoactive structures and nuclease-propelled target dual-recycling amplification strategy. Concretely, the paper-based ZnO sensitized with CuInS2 were served as a signal generator and a substrate for immobilizing hairpin DNA (H2). Ag2Se quantum dots (QDs), labeling at the terminal of probe DNA (pDNA), served as the sensitization agents. When target microRNA existed, duplex-specific nuclease activated the first recycling amplification procedure, resulting in the release of numerous converted DNA sequences (cDNA). Afterward, the second target recycling amplification procedure was initiated upon the H2-immobilized electrode was incubated with cDNA and lambda exonuclease, which made massive short DNA fragments free from H2. Consequently, a small quantity of target miRNA-141 was converted into abundant short DNA fragments, which could further hybridize with Ag2Se QDs labelled pDNA, activating the cascaded sensitization effect of ZnO/CuInS2/Ag2Se photoactive structures and giving great signal enhancement. Benefiting from the considerable signal amplification enabled by nuclease-assisted target dual-recycling amplification strategy and cascaded photosensitive structures, the proposed biosensor realized the ultrasensitive detection of miRNA-141 with great accuracy and selectivity, which rendered a prospective paradigm to develop high-performance microfluidic paper analytical devices.

Malaria quantitative POC testing using magnetic particles, a paper microfluidic device and a hand-held fluorescence reader

A point-of-care (POC) device is reported for highly sensitive and selective detection of Plasmodium falciparum lactate dehydrogenase (Pf-LDH), a biomarker of malaria infection, based on a single-step magneto-immunoassay, a single-use microfluidic paper device and a customized hand-held fluorescence reader. The single-step magneto-immunoassay consists in a single 5-min incubation of immuno-modified magnetic particles (c-MAb-MPs), biotinylated detection antibody (bd-MAb), and an enzymatic signal amplifier (Poly-HRP). After on-chip MP concentration and washing, signal generation is achieved by adding a fluorescent enzymatic substrate (QuantaRed). Fluorescence signal is measured using a low-cost customized, portable, and sensible fluorescent detector. The POC affords quantitative Pf-LDH detection in <20 min, with a detection limit of 0.92 ng mL−1 (equivalent to 4.6 parasites μL−1). Furthermore, Pf-LDH quantitation in clinical samples correlates with that provided by the reference ELISA, is more sensitive than a commercial rapid diagnostic test (RDT) and entails little user intervention. These results show that fluorescent paper-based microfluidic devices can be exploited to simplify magneto-immunoassay handling, taking this type of test closer to the requirements of POC testing.

Microfluidic Paper Based Analytical Devices for the Detection of Carbamate Pesticides.

Microfluidic paper-based analytical devices (μ-PADs) are a new technology platform for the development of extremely low-cost sensing applications. In this study, μ-PADs has been developed for quantitative determination of carbamate pesticides. Key experimental parameters including concentration and volume of acetylcholinesterase, acetylthiocholine iodide and 5,5'-dithiobis-(2-nitrobenzoicacid), incubation time and image capturing time were systematically optimized. Under optimal conditions, the method showed wide range of linearity (0.25-16mg/L), repeatability (4%-5% RSD) and intermediate precision (7%-10% RSD). Limit of detection was observed to be 0.4, 0.24 and 0.46mg/L for carbaryl, carbosulfan and furathiocarb, respectively. An acceptable mean recovery (87% to 94%) was observed for the three pesticides at 1mg/L fortification level. The results reveal that the developed method requires minimal reagents, simple and is easy to handle. It can be used for the quantification of carbamate pesticides in resource limited laboratories without the need for the conventional analytical instruments.

A microfluidic paper analytical device using capture aptamers for the detection of PfLDH in blood matrices

BackgroundThe prevalence and death rate arising from malaria infection, and emergence of other diseases showing similar symptoms to malaria require the development of malaria-specific and sensitive devices for its diagnosis. To address this, the design and fabrication of low-cost, rapid, paper-based analytical devices (µPAD) using surface-immobilized aptamers to detect the presence of a recombinant malarial biomarker—Plasmodium falciparum lactate dehydrogenase (rPfLDH)—is reported in this study.MethodsTest zones on paper surfaces were created by covalently immobilizing streptavidin to the paper, subsequently attaching biotinylated aptamers to streptavidin. Aptamers selectively bound rPfLDH. The measurement of captured rPfLDH enzyme activity served as the means of detecting this biomarker. Enzyme activity across three replicate sensors was digitally quantified using the colorimetric Malstat assay.ResultsScreening of several different aptamers reported in the literature showed that aptamers rLDH7 and 2008s immobilized in this manner specifically recognised and captured PfLDH. Using rLDH7, the sensitivity of the µPAD sensor was evaluated and the µPAD sensor was applied for preferential detection of rPfLDH, both in buffered solutions of the protein and in spiked serum and red blood cell lysate samples. In buffered solutions, the test zone of the µPAD sensor exhibited a KD of 24 ± 11 nM and an empirical limit of detection of 17 nM, respectively, a limit similar to commercial antibody-based sensors exposed to rPfLDH. The specific recognition of 133 nM rPfLDH in undiluted serum and blood samples was demonstrated by the µPAD.ConclusionThe reported µPAD demonstrates the potential of integrating aptamers into paper-based malarial rapid diagnostic tests.Graphical The assembly of µPAD sensors using APTEC assay principles for the detection the malarial biomarker, lactate dehydrogenase enzymes from Plasmodium falciparum (PfLDH). The aptamers immobilized at the test zones capture the PfLDH in samples. After washing the unbound sample components from the zones, Malstat assay reagents are added for colour development, proportional to the amount of captured PfLDH.

Detection and discrimination of antibiotics in food samples using a microfluidic paper-based optical tongue.

Antibiotics are used largely in agriculture and animal farming. As a result, antibiotic residues are found in food products as well as pharmaceutical industries and farming wastes. Since consumption of food products contaminated with antibiotic in excessive residuals causes severe environmental risks, our study here aims to detect the residues level of selected antibiotics in milk and egg. For monitoring of the antibiotic residues in various food diaries, low-cost, simple and rapid methods are required. This paper reports fabricating a disposable microfluidic paper-based analytical device for detection and discrimination of 8 antibiotics. This small but efficient device works based on combination of paper microfluidics, sensor array concept (an array of metallochromic complexes, which provides an optical tongue, and chemometrics data analysis. The discrimination is based on differential interaction of the antibiotics with 5 metal-indicator complexes and displacing the chromogenic indicators. This resulted in specific color changes for each antibiotic. The discriminant models obtained by employing linear discriminant analysis could discriminate antibiotics in real samples of milk and egg white and yolk at concentrations of as low as 5.0mgL-1 with 100% accuracy. Also, semi-quantitative analysis was provided to detect trace amounts of the antibiotics (1.0mgL-1).