Paper-based Analytical Devices Research Articles

Nanomaterial-based optical- and electrochemical-biosensors for urine glucose detection: A comprehensive review

Urine glucose detection is an important diagnostic tool for screening and early diagnosis of diabetes mellitus. Detection of urine glucose has many advantages over blood glucose, such as non-invasive, easy-to-detect, simple sampling and being well accepted by patients. Therefore, it is commonly used to monitor diabetes progression, assist in therapeutic intervention as well as in point-of-care testing (POCT). In recent years, with the development of material science, electrochemistry and miniaturization technology, novel applications of natural enzymes, nanozymes as well as nanomaterials, such as metal (Au, Pt, Ni, Co, etc.), alloy, grapheme, in the analysis of urine glucose level have been increasing sharply. In particular, different types of nanozymes-based biosensors, inspired by natural enzymes, have been developed with improved characteristics of being low-cost, stable, and mass-produced. On the other hand, making use of portable devices, such as smartphones and microfluidic paper-based analytical devices, has facilitated on site accurate urine glucose monitoring in real time. All these rapid advancements in nanotechnologies and devices have contributed greatly to the development of cost effective, highly sensitive, user friendly urine glucose biosensors. This review summarizes the most recent improvements in two major types of urine glucose biosensors: the optical- and electrochemical-biosensors. We also discuss the limitations, challenges and perspectives of these biosensors. Finally, we propose future research directions, development trends and potential clinical applications of nanomaterial-based biosensors developed for urine glucose detection.

A novel polymer-based nitrocellulose platform for implementing a multiplexed microfluidic paper-based enzyme-linked immunosorbent assay

Nitrocellulose (NC) membranes, as porous paper-like substrates with high protein-binding capabilities, are very popular in the field of point-of-care immunoassays. However, generating robust hydrophobic structures in NC membranes to fabricate microfluidic paper-based analytical devices (μPADs) remains a great challenge. At present, the main method relies on an expensive wax printer. In addition, NC membranes very easy to adhere during the printing process due to electrostatic adsorption. Herein, we developed a facile, fast and low-cost strategy to fabricate μPADs in NC membranes by screen-printing polyurethane acrylate (PUA) as a barrier material for defining flow channels and reaction zones. Moreover, hydrophobic barriers based on UV-curable PUA can resist various surfactant solutions and organic solvents that are generally used in immunoassays and biochemical reactions. To validate the feasibility of this PUA-based NC membrane for immunoassays in point-of-care testing (POCT), we further designed and assembled a rotational paper-based analytical device for implementing a multiplexed enzyme-linked immunosorbent assay (ELISA) in a simple manner. Using the proposed device under the optimal conditions, alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA) could be identified, with limits of detection of 136 pg/mL and 174 pg/mL, respectively, which are below the threshold values of these two cancer biomarkers for clinical diagnosis. We believe that this reliable device provides a promising platform for the diagnosis of disease based on ELISA or other related bioassays in limited settings or remote regions.

Progress toward a Simplified UTI Diagnostic: Pump-Free Magnetophoresis for E. coli Detection.

Urinary tract infections (UTIs) are one of the most common infections across the world and can lead to serious complications such as sepsis if not treated in a timely manner. Uropathogenic Escherichia coli account for 75% of all UTIs. Early diagnosis is crucial to help control UTIs, but current culturing methods are expensive and time-consuming and lack sensitivity. The existing point-of-care methods fall short because they rely on indirect detection from elevated nitrates in urine rather than detecting the actual bacteria causing the infection. Magnetophoresis is a powerful method used to separate and/or isolate cells of interest from complex matrices for analysis. However, magnetophoresis typically requires complex and expensive instrumentation to control flow in microfluidic devices. Coupling magnetophoresis with microfluidic paper-based analytical devices (μPADs) enables pump-free flow control and simple and low-cost operation. Early magnetophoresis μPADs showed detection limits competitive with traditional methods but higher than targets for clinical use. Here, we demonstrate magnetophoresis using hybrid μPADs that rely on capillary action in hydrophilic polyethylene terephthalate channels combined with paper pumps. We were able to detect E. coli with a calculated limit of detection of 2.40 × 102 colony-forming units per mL.

Electrochemical paper-based analytical devices containing magnetite nanoparticles for the determination of vitamins B2 and B6

Disposable electrochemical paper-based analytical devices were developed from a conductive ink using graphite powder, automotive varnish and magnetite nanoparticles. The addition of magnetite nanoparticles in the conductive ink improved the sensitivity of the analytical devices. The devices were applied in the quantification of vitamins B2 (VB2) and B6 (VB6) in commercial dietary supplements. The characterization of the analytical devices was carried out by microscopy and electrochemical techniques. Square wave voltammetry (SWV) was used to study the electrochemical behavior of the vitamins and the experimental parameters were optimized (pH, supporting electrolyte and SWV parameters). The calibration plot for VB2 (−484 mV vs. graphite) was obtained in Britton-Robinson buffer (pH 2.0) in the range of 2.0 to 20.0 μmol L−1 with a detection limit of 0.25 µmol L−1. Similarly, for the VB6 (+675 mV vs. graphite), the calibration plot was obtained in McIlvaine buffer (pH 4.0) in the range of 0.2 to 2.0 mmol L−1 with a detection limit of 29.5 µmol L−1. The analytical devices were employed to determine VB2 and VB6 levels in B-complex supplements (capsules and sublingual liquid) and the results were compared with those provided by fluorescence spectrometry. The statistical analysis showed no considerable difference in terms of the precision and accuracy of the data obtained by both methods.

A study of Factors Affecting the Decision Making of Paper-based Analytical Device Utilization for HPV Type 16 Detection among Medical Technologists in Thailand

This research aims to determine the factors affecting the decision making of using the paper-based HPV screening test. This is quantitative research; the questionnaire was used to collect the data from 411 medical technologists working in the laboratory nationwide. Data analysis involved descriptive statistics, Exploratory Factor Analysis, and Ordinal logistic regression analysis. The results showed standardization of test kits approved by the Food and Drug Administration and industry standards is the top priority with an average opinion score of 5.0. Consequently, the factor of After-sales service in terms of on-time delivery and user training was prioritized as a score of 4.96 and 4.75, respectively. Meanwhile, the factor that was considered as the least important to decision making of the usage of a paper-based HPV screening test was the test kit that has previously been used in Medical school hospitals with an average score of 3.13. The factors affecting the decision making of using the paper-based HPV screening test consist of 7 factors that were analyzed by Univariable analysis with Ordinal logistic regression analysis. The factor significantly (p-value < 0.05) affect to the decision making of medical technologist who working in laboratory clinic OR = 1.79, 95 %CI: 1.01 - 3.17, p-value = 0.044) were factor of perceived and understood the principle of standard method and factor (OR = 1.82, 95 %CI: 1.13 - 2.91, p-value = 0.013) and after-sales service (OR = 0.43, 95 %CI: 0.23 - 0.78, p-value = 0.006).
 HIGHLIGHTS
 
 The top priority for medical device development and commercialization is the standardization of test kits to meet the requirement of the Food and Drug Administration approval and industry standard
 With the limited health facilities and budget in middle-income country, a paper-based medical device can enhance a level of access to medical screening and treatment
 Exploratory Factor Analysis and Ordinal logistic regression analysis are conducted to determine the factors affecting the decision making of using the paper-based HPV screening test
 The factor significantly affects to the decision making of medical technologist were factor of perceived and understood the principle of standard method and after-sales service

Improvement strategies on colorimetric performance and practical applications of Paper-based analytical devices

Colorimetric paper-based analytical devices (PADs) have been widely fabricated due to the ease of construction of colorimetric reactions on paper and the high compatibility with low-cost and easy-to-use imaging devices for on-site analysis and results recording. However, the further advance of colorimetric PADs is limited by the detection sensitivity and other intrinsic limitations of paper regarding the color quality. This review summarizes the strategies for improving the colorimetric performances (color intensity and uniformity) of PADs. In particular, the principles of controlling liquid-paper interaction for the color intensity enhancement, developed in printing research, are discussed in relation to PAD designs. The influence of the paper assaying environment to the paper assaying selectivity is discussed through a case study for the first time. Image capture techniques and image process algorithms are related to the accuracy and sensitivity of the colored results, which are carefully introduced. Finally, based on the tendency of improvement of colorimetric PADs for practical applications, we summarized the designs that enhance the portability of colorimetric PADs. It is believed that the new links and opinions provided in this review may be useful to researchers to address the challenges in designing future colorimetric PADs with improved sensitivities for field use.

Silk-fibroin film as enzyme stabilizing material and optical signal transducer for developing alcohol oxidase-based μPAD methanol biosensor

The commercial success of paper-based microfluidic biosensor devices with enzyme as recognition elements may be achieved greatly by improving the enzyme stability, averting the coffee-ring effect on the detection zone, and making it a stand-alone system. We have addressed these issues here by introducing silk-fibroin (SF) film for immobilizing enzymes and chromogenic reagent (ABTS), and wave-design microfluidic channels in the chromatographic paper for developing a hybrid microfluidic paper-based analytical device (μPAD), for methanol detection through peroxidase reaction. The activity of alcohol oxidase (AOx), used as a biorecognition element, could be wholly retained in a non-dissolvable SF film (pore size <3.5 μm) until 40 days of storage at room temperature (RT) by reducing oxygen permeability to the film. Similarly, ABTS in a dissolvable SF film was protected from air-oxidation even up to two months of storage at RT. The detection approach exploited purple color as a high contrast response signal generated from ABTS di-cation formed from the reaction of SF protein with the ABTS radicals generated from the substrate-dependent peroxidase reaction. The wave-designed microfluidic channels could significantly reduce the coffee ring effect in the detection film. The bi-enzyme SF films prepared by co-immobilizing AOx with peroxidase (HRP) offered high sensitivity to the device with a detection limit (LoD) of 1 ± 0.05 mM and a dynamic range of 1 mM–2 M for methanol. The stand-alone hybrid μPAD biosensor for methanol has a high potential for commercial applications.

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).

Microfluidic Paper-Based Blood Plasma Separation Device as a Potential Tool for Timely Detection of Protein Biomarkers.

A current challenge regarding microfluidic paper-based analytical devices (µPAD) for blood plasma separation (BPS) and electrochemical immunodetection of protein biomarkers is how to achieve a µPAD that yields enough plasma to retain the biomarker for affinity biosensing in a functionalized electrode system. This paper describes the development of a BPS µPAD to detect and quantify the S100B biomarker from peripheral whole blood. The device uses NaCl functionalized VF2 filter paper as a sample collection pad, an MF1 filter paper for plasma retention, and an optimized microfluidic channel geometry. An inverted light microscope, scanning electron microscope (SEM), and image processing software were used for visualizing BPS efficiency. A design of experiments (DOE) assessed the device’s efficacy using an S100B ELISA Kit to measure clinically relevant S100B concentrations in plasma. The BPS device obtained 50 μL of plasma from 300 μL of whole blood after 3.5 min. The statistical correlation of S100B concentrations obtained using plasma from standard centrifugation and the BPS device was 0.98. The BPS device provides a simple manufacturing protocol, short fabrication time, and is capable of S100B detection using ELISA, making one step towards the integration of technologies aimed at low-cost POC testing of clinically relevant biomarkers.

Reversible Thermo-Responsive Valve for Microfluidic Paper-Based Analytical Devices.

Fluid control on a paper channel is necessary for analysis with multiple reagents, such as enzyme-linked immunosorbent assay (ELISA) in microfluidic paper-based analytical devices (µPADs). In this study, a thermo-responsive valve was fabricated by polymerizing N-isopropylacrylamide on a PVDF porous membrane by plasma-induced graft polymerization. The polymerized membrane was observed by scanning electron microscopy (SEM), and it was confirmed that more pores were closed at temperatures below 32 °C and more pores were opened at temperatures above 32 °C. Valve permeability tests confirmed that the proposed polymerized membrane was impermeable to water and proteins at temperatures below 32 °C and permeable to water at temperatures above 32 °C. The valve could also be reversibly and repeatedly opened and closed by changing the temperature near 32 °C. These results suggest that plasma-induced graft polymerization may be used to produce thermo-responsive valves that can be opened and closed without subsequent loss of performance. These results indicate that the thermo-responsive valve fabricated by plasma-induced graft polymerization could potentially be applied to ELISA with µPADs.

A paper-based microfluidic sensor array combining molecular imprinting technology and carbon quantum dots for the discrimination of nitrophenol isomers

Paper-based microfluidic analytical devices (μPADs) have recently attracted attention as a rapid test kit owing to their low cost and nonrequirement for external driving pump. However, low accuracy and poor anti-interference ability of μPADs under complex detection condition limit their practical applications. Here, we present a facile way to prepare a novel fluorescence sensor-array μPAD for multi-analyte discrimination based on molecular imprinting technology, and its sensing behavior was studied by using three nitrophenol (NP) isomers (2-, 3-, and 4-NP) as the testing models. Carbon quantum dots (CQDs) emitting blue light were grafted on glass-fiber paper, followed by in-situ modification of three types of molecularly imprinted polymers (MIPs) with 2-, 3-, and 4-NP as template. Each sensing unit on the array showed differential yet cross-reactive binding affinity to NP isomers, resulting in distinct fluorescence quenching efficiency. Thus, precise distinguishment of the three NPs was realized with the MIPs/CQDs/paper-based sensor array. Furthermore, the discrimination ability of the platform was evaluated in mixtures of the NP isomers. Practicability of this apparatus was validated by identification of blind samples and 100% accuracy was achieved. The μPAD has proven to be highly sensitive and accurate, which will serve as an ideal analytical tool in the fields of environment monitoring, disease prognosis, food safety and so on.

Wax-Printed Fluidic Controls for Delaying and Accelerating Fluid Transport on Paper-Based Analytical Devices

In this work, we explore a new method for controlling fluid transport rate on paper-based analytical devices that enables both the delay and the acceleration of fluid flow. The delays were incorporated by wax printing linear patterns of variable width within the flow channel and melted to penetrate the paper. In this manner, the surface tension of the fluid decreases while its contact angle increases, causing a pressure drop along the fluid path that reduces capillary flow. The acceleration of flow was accomplished by overlaying hydrophobic stripes (prepared by wax printing and melting the wax) on the hydrophilic path (top or top–bottom). In this manner, the fluid was repelled from two dimensions (vertical and applicate), increasing the flow rate. The combination of these methods on the same devices could adjust wicking time in intermediate time internals. The method enabled a wide timing of fluid transport, accomplishing a change in wicking times that extended from −41% to +259% compared to open paper channels. As a proof of concept, an enzymatic assay of glucose was used to demonstrate the utility of these fluid control methods in kinetic methods of analysis.

Paper-based multicolor sensor for on-site quantitative detection of 2,4-dichlorophenoxyacetic acid based on alkaline phosphatase-mediated gold nanobipyramids growth and colorimeter-assisted method for quantifying color

On-site quantitative analysis of pesticides is important for food safety. Colorimetric gold nanobipyramids (AuNBPs) sensors are powerful methods for on-site detection. However, a single quantitative method and the instability of AuNBPs in solution limit the practicability of those sensors. Here, a paper-based multicolor AuNBPs sensor involved a colorimeter-assisted method for quantifying color was developed for quantitative detection of 2,4-dichlorophenoxyacetic acid (2,4-D), a common herbicide. The novelty of this study lies in developing a general paper-based quantitative on-site method (PQOM) for colorimetric AuNBPs sensors. Firstly, a paper-based analytical device (PAD) consisting of a nylon membrane, absorbent cotton layers, and two acrylic plates was fabricated to deposit AuNBPs. We demonstrated the PAD could improve the stability of AuNBPs and the detection sensitivity of AuNBPs sensors. Then, a handheld colorimeter was first used to quantify the color change of AuNBPs on the PAD based on the CIELab color space. Finally, as proof of concept, the PQOM was successfully employed to quantify 2,4-D by combining with an alkaline phosphatase-mediated AuNBPs growth method. In this method, 2,4-D specifically inhibited alkaline phosphatase activity to suppress the generation of l-ascorbic acid, thereby mediating AuNBPs growth. The developed sensor exhibited seven 2,4-D concentration-related colors and detected as low as 50 ng mL−1 2,4-D by naked-eye observation and 18 ng mL−1 2,4-D by a colorimeter. It was applied to detect 2,4-D in the spiked rice and apple samples with good recovery rates (91.8–112.0%) and a relative standard deviation (n = 5) < 5%. The success of this study provides a sensing platform for quantifying 2,4-D on site.

Simultaneous enrichment and separation based on ion concentration polarization effect on a paper based analytical device

In this paper, simultaneous enrichment and separation of ions and amphoteric components were successfully demonstrated by using electric field (E) and pH gradient (double gradient) in the ion depletion zone of anion concentration polarization interface established on a paper fluid channel. Experimental results were visualized with colored ions (bright blue and amaranth) and protein probes (phycocyanin and cytochrome C). With optimization, colored phycocyanin and bovine hemoglobin with similar pI as that of albumin and immunoglobulin respectively were well separated in 900 s with 10-fold enrichment effect. Based on the separation and enrichment function of this paper-based analytical device (PAD) and rapid selective staining of human serum albumin (HSA) with bromophenol blue, a rapid colorimetric detection of HSA was implemented with smartphone camera. A limit of detection (LOD) of 5.2 mg·L−1 was achieved in the clinically significant range of 10–300 mg·L−1 (R2 = 0.99). This method was applied to real human urine samples with good agreement (ɑ = 0.01) to clinical detection method (immunoturbidimetry). With the separation and enrichment functions of PAD, both the specificity and sensitivity were enhanced, which provides a solid basis for point-of-care test of microalbuminuria. Therefore, this PAD device is potential for sample pretreatment and detection of target components from complex physiological samples.

Nanocoral-like Polyaniline-Modified Graphene-Based Electrochemical Paper-Based Analytical Device for a Portable Electrochemical Sensor for Xylazine Detection

A portable electrochemical device for xylazine detection is presented for the first time. An electrochemical paper-based analytical device (ePAD) was integrated with a smartphone. The fabrication of the ePAD involved wax printing, low-tack transfer tape, and cutting and screen-printing techniques. Graphene ink was coated on the substrate and modified with nanocoral-like polyaniline, providing an electron transfer medium with a larger effective surface area that promoted charge transfer. The conductive ink on the ePAD presented a thickness of 25.0 ± 0.9 μm for an effective surface area of 0.374 cm2. This sensor was then tested directly on xylazine using differential pulse voltammetry. Two linear responses were obtained: from 0.2 to 5 μg mL–1 and from 5 to 100 μg mL–1. The detection limit was 0.06 μg mL–1. Reproducibility was tested on 10 preparations. The relative standard deviation was less than 5%. The applicability of the sensor was evaluated with beverage samples spiked with trace xylazine. Recoveries ranged from 84 ± 4 to 105 ± 2%. The developed sensor demonstrated excellent accuracy in the detection of trace xylazine. It would be possible to develop the portable system to detect various illicit drugs to aid forensic investigations.

Dip-and-Read, Organic Solvent-Compatible, Paper-Based Analytical Devices Equipped with Chromatographic Separation for Indole Analysis in Shrimp.

We developed an organic solvent-compatible paper-based analytical device (PAD) for the quantitative analysis of indole, which is an indicator of shrimp freshness. Although indole is insoluble in water, ethyl acetate is a suitable solvent to dissolve and extract indole from shrimp. The PADs are fabricated using a cutting method that allows the use of an organic solvent because no hydrophobic barrier is needed to form fluidic channels. Ehrlich's reagent consists of 4-(dimethylamino)benzaldehyde and p-dimethylaminobenzaldehyde and was deposited onto the reaction zone of the PAD followed by lamination to prevent evaporation of the ethyl acetate. Samples are introduced into the PAD via immersion in organic sample solutions. When the PAD is immersed into an indole solution of ethyl acetate in a closed bottle, the sample solution penetrates the channel of the PAD and successively flows into the detection zone to form a hydrophilic colored product. The PADs provide a linear relationship between the logarithm of the indole concentration and the color intensity within a range of 1.0-20 ppm with correlation coefficients of r2 > 0.99. The limits of detection and quantification are 0.36 and 0.71 ppm, respectively. Relative standard deviations for both the intraday (n = 2) and interday (n = 3) precision were less than 2.5%. In the indole analysis of shrimp, the PADs separated the interfering orange-colored astaxanthin in the extract from the colored product of indole via the paper chromatographic principle. We used the PADs to investigate the degradation of shrimp, and the results showed a rapid increase in the indole level after 7 days. High-performance liquid chromatography verified the accuracy of the PADs by showing good agreement with the obtained indole levels.

A Three-Reagent "Green" Paper-Based Analytical Device for Solid-Phase Spectrometric and Colorimetric Determination of Dihydroquercetin.

Microfluidic paper-based analytical devices (µPADs) represent one of the promising green analytical strategies for low-cost and simple determination of various analytes. The actual task is the development of such devices for quantitation of antioxidants, e.g., flavonoids. In this paper, possibilities of a novel three-reagent µPAD including silver nitrate, 4-nitrophenyldiazonium tetrafluoroborate, and iron(III) chloride as reagents are assessed with respect to the determination of dihydroquercetin. It is shown that all the three reagents produce different colorimetric responses that can be detected by a mini-spectrophotometer–monitor calibrator or by a smartphone. The method is applicable to direct measuring high contents of dihydroquercetin (the linearity range is 0.026–1 mg mL−1, and the limit of detection is 7.7 µg mL−1), which is favorable for many dietary supplements. The analysis of a food supplement was possible with the relative standard deviations of 9–26%, which is satisfactory for quantitative and semiquantitative determinations. It was found that plotting a calibration graph in 3D space of the three reagents’ responses allows us to distinguish dihydroquercetin from its close structural analogue, quercetin.

Paper-based microfluidic devices: Fabrication, detection, and significant applications in various fields

Abstract Paper is the most abundant and inexpensive polymeric structure of cellulose available. Paper has micro-porous capillary-like networks which are responsible for flow of solvents instead of pumps or electronic power, making paper an ideally usable tool. Microfluidic paper-based analytical devices use fabricated paper devices on which hydrophilic zones are formed within hydrophobic barriers. Hydrophilic zones act as regions for actual analytical purposes, whereas hydrophobic zones act to demarcate separate zones from one another. Clinically, these devices have been proved to be excellent point-of-care-devices in diagnosis which can bypass use of costly and time-consuming laboratory techniques. In the presented review, the basic principles and components involved in the design of paper-based devices were then summarised in understandable manner. Further, various applications in different fields were also compiled in the form of text under different sections and tables. Paper-based analytical devices may serve as an excellent tool in variety of analytical works as these techniques are simple, rapid, economic, and require less human power or trainings. They have prominent applications in analysis of biological fluids, drugs/metabolites, food stuffs, colorants, biomarkers, and several other fields.

Simultaneous phenotyping of five Rh red blood cell antigens on a paper-based analytical device combined with deep learning for rapid and accurate interpretation

Both the ABO and Rhesus (Rh) blood groups play crucial roles in blood transfusion medicine. Herein, we report a simple and low-cost paper-based analytical device (PAD) for phenotyping red blood cell (RBC) antigens. Using this Rh typing format, 5 Rh antigens on RBCs can be simultaneously detected and macroscopically visualized within 12 min. The proposed Rh phenotyping relies on the presence or absence of hemagglutination in the sample zones after immobilizing the antibodies targeting each Rh antigen. The PAD was optimized in terms of filter paper type, antibodies, and distance of the visualization zone. In this study, the optimal conditions were Whatman filter paper Grade 4; anti-D, –C, -E, -c, and -e antibodies; RBC suspension of 30%; and a visualization zone of 1 cm above the sample zone. The accuracy of simultaneously phenotyping the five Rh RBC antigens in the blood samples (n = 4692) was 99.19%, comparable with the accuracy of the gold-standard tube method used by blood bank laboratories in several regions of Thailand. Furthermore, decision making based on this method can be assisted by deep learning. After implementing a two-stage objective detection algorithm (YOLO v4-tiny) and classification model (DenseNet-201), the ambiguous images (n = 48) were interpreted with 100% accuracy. The PAD integrated with customized-region convolutional neural networks can reduce the interpretation discrepancies in RBC antigen phenotyping in any laboratory.

Low-cost microfluidic electrochemical paper-based device to detect glucose

Continuous monitoring of the level of glucose is essential to maintain the health of a diabetic patient. The use of invasive methods to obtain blood samples to detect glucose is the current method, but such methods may not be preferred by patients. Non-invasive methods such as the determination of glucose based on saliva or sweat can be preferred by patients for continuous monitoring. A low-cost electrochemical microfluidic paper-based analytical device (µPAD) suitable to monitor glucose levels using sweat and saliva is introduced. This device is extremely low-cost due to the use of a paper matrix and varnish for the fabrication of paper. Pseudo-reference stainless steel is used with a working electrode anodized using sodium potassium tartrate tetrahydrate for the development of a three-electrode system. Cyclic voltammetric-based analysis of glucose with µPAD produced a linear response in the working range of 1-10 mmol dm-3 with a limit of detection of 0.058 mol dm-3. The detection of diabetic conditions using saliva and sweat is possible using the device by correlating to the blood glucose levels using prior literature data.