Development of a smartphone-integrated microfluidic paper-based optosensing platform coupled with molecular imprinting technique for in-situ determination of histamine in canned tuna

We reported the development of a smartphone-integrated microfluidic paper-based optosensing platform for in-situ detection and quantification of histamine in canned tuna. Molecularly imprinted polymers were synthesized via precipitation polymerization and utilized as dispersive solid phase extraction sorbent to selectively extract histamine from canned tuna. Carbon quantum dots functioning as a fluorescent probe were synthesized and introduced onto the microzones of the microfluidic paper device. This facilitated a noticeable fluorescence color change from dark red to vivid blue upon the addition of histamine. The change in fluorescence on the paper device was converted into specific RGB values using a portable UV light box combined with a smartphone. This assay achieved the limit of detection of 14.04 mg/kg with the linear range from 20 to 100 mg/kg of histamine in canned tuna. The entire molecular imprinting-microfluidic optosensing test could be completed in 45 min including sample preparation.

The use of biological fluids in microfluidic paper-based analytical devices (μPADs): Recent advances, challenges and future perspectives

The use of microfluidic paper-based analytical devices (μPADs) for aiding medical diagnosis is a growing trend in the literature mainly due to their low cost, easy use, simple manufacturing, and great potential for application in low-resource settings. Many important biomarkers (proteins, ions, lipids, hormones, DNA, RNA, drugs, whole cells, and more) and biofluids are available for precise detection and diagnosis. We have reviewed the advances μPADs in medical diagnostics have achieved in the last few years, focusing on the most common human biofluids (whole blood/plasma, sweat, urine, tears, and saliva). The challenges of detecting specific biomarkers in each sample are discussed, along with innovative techniques that overcome such limitations. Finally, the difficulties of commercializing μPADs are considered, and future trends are presented, including wearable devices and integrating multiple steps in a single platform.

A novel approach to low-cost, rapid and simultaneous colorimetric detection of multiple analytes using 3D printed microfluidic channels

This research paper presents an inventive technique to swiftly create microfluidic channels on distinct membrane papers, enabling colorimetric drug detection. Using a modified DIY RepRap 3D printer with a syringe pump, microfluidic channels (µPADs) are crafted on a flexible nylon-based substrate. This allows simultaneous detection of four common drugs with a single reagent. An optimized blend of polydimethylsiloxane (PDMS) dissolved in hexane is used to create hydrophobic channels on various filter papers. The PDMS-hexane mixture infiltrates the paper's pores, forming hydrophobic barriers that confine liquids within the channels. These barriers are cured on the printer's hot plate, controlling channel width and preventing spreading. Capillary action drives fluid along these paths without spreading. This novel approach provides a versatile solution for rapid microfluidic channel creation on membrane papers. The DIY RepRap 3D printer integration offers precise control and faster curing. The PDMS-hexane solution accurately forms hydrophobic barriers, containing liquids within desired channels. The resulting microfluidic system holds potential for portable, cost-effective drug detection and various sensing applications.

Flow control by circular cavities in lateral flow porous membranes

This research explores the flow penetration in porous media by virtue of capillary action and geometric control of the liquid imbibition rate in microfluidic paper-based analytical devices (μPADs) having applications in food quality management, medical diagnostics, and environmental monitoring. We examine changes in flow resistance and membrane geometry, aiming to understand factors influencing capillary penetration rates for various practical applications. We conducted experiments and simulations using lateral porous membranes and altered the flow resistance by changing the liquids or the paper channel geometry by adding cavities. From experiments, it was revealed that by creating a circular cavity in the paper channel, the penetration rate was sufficiently altered. Moreover, increasing the cavity size and type of liquid (w.r.t. viscosity) also caused a decrease in the flow rate. Imbibition rates were also influenced by the position of the cavities in the paper channel. The maximum delay for water was almost 2 times with a 16 mm circular cavity located at 3 cm from strip bottom edge. Overall, we attained a maximum delay in the case of castor oil which was almost 85 times slower than water and 3.7 times slower than olive oil. A good agreement was observed with CFD analysis. We believe that this research would help in developing advance techniques to enhance the flow control strategies in μPADs and indicators.

Atomically Dispersed Manganese on Graphene Nanosheets as Biocompatible Nanozyme for Glutathione Detection in Liver Tissue Lysate Using Microfluidic Paper-based Analytical Devices

Recently, single atom catalysts (SACs) featuring M-Nx (M = metal) active sites on carbon support have drawn considerable attention due to their promising enzyme-like catalytic properties. However, typical synthesis methods of SACs often involve energy-intensive carbonization processes. Herein, we report a facile one-pot, low-temperature, wet impregnation method to fully utilize M-N4 sites of manganese phthalocyanine (MnPc) by decorating molecular MnPc over the sheets of graphene nanoplatelets (GNP). The synthesized MnPc@GNP exhibits remarkable peroxidase-mimic catalytic activity toward the oxidation of chromogenic 3,3',5,5'-tetramethylbenzidine (TMB) substrate owing to the efficient utilization of atomically dispersed Mn and the high surface-to-volume ratio of the porous catalyst. A nanozyme-based colorimetric sensing probe is developed to detect important biomarker glutathione (GSH) within only 5 min in solution phase based on the ability of GSH to effectively inhibit the TMB oxidation. The high sensitivity and selectivity of the developed colorimetric assay enable us to quantitatively determine GSH concentration in different biological fluids. This work, for the first time, reports a rapid MnPc@GNP nanozyme-based colorimetric assay in the solid substrate by fabricating microfluidic paper-based analytical devices (μPADs). GSH is successfully detected on the fabricated μPADs coated with only 6.0 μg of nanozyme containing 1.6 nmol of Mn in the linear range of 0.5-10 μM with a limit of detection of 1.23 μM. This work also demonstrates the quantitative detection of GSH in mice liver tissue lysate using μPADs, which paves the way to develop μPADs for point-of-care testing.

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.

Digital Quantification Method for Sensitive Point-of-Care Detection of Salivary Uric Acid Using Smartphone-Assisted μPADs

Uric acid (UA) is an important biomarker for many diseases. A sensitive point-of-care (POC) testing platform is designed for the digital quantification of salivary UA based on a colorimetric reaction on an easy-to-build smartphone-assisted microfluidic paper-based analytical device (SμPAD). UA levels are quantified according to the color intensity of Prussian blue on the SμPAD with the aid of a MATLAB code or a smartphone APP. A color correction method is specifically applied to exclude the light effect. Together with the engineering design of SμPADs, the background calibration function with the APP increases the UA sensitivity by 100-fold to reach 0.1 ppm with a linear range of 0.1-200 ppm. The assay time is less than 10 min. SμPADs demonstrate a correlation of 0.97 with a commercial UA kit for the detection of salivary UA in clinical samples. SμPADs provide a sensitive, fast, affordable, and reliable tool for the noninvasive POC quantification of salivary UA for early diagnosis of abnormal UA level-associated health conditions.

Leveraging Arylboronic Acid - Cellulose Binding as a Versatile and Scalable Approach to Hydrophobic Patterning

Paper-based analytical devices, or μPADs, have proven to be valuable bioanalytical tools for a broad range of applications. New methods for μPAD fabrication are needed, however, to facilitate their mass production at a competitive cost. To address this need, we report the use of a boronic acid-containing siloxane polymer (BorSilOx) for patterning hydrophobic barriers for μPADs. This material functions by covalently binding to hydroxyl groups in the paper substrate. It is compatible with inkjet printing or roll-to-roll (stamping) processes, as demonstrated here using three different deposition methods. BorSilOx is able to render a broad range of cellulosic materials (from paper towels to wood) hydrophobic, with contact angle measurements demonstrating superhydrophobicity in many cases. We further demonstrate the utility of the polymer in μPADs via assays for pH and glucose.

Rapid segmentation and sensitive analysis of CRP with paper-based microfluidic device using machine learning

Microfluidic paper-based analytical devices (μPADs) have been widely used in point-of-care testing owing to their simple operation, low volume of the sample required, and the lack of the need for an external force. To obtain accurate semi-quantitative or quantitative results, μPADs need to respond to the challenges posed by differences in reaction conditions. In this paper, multi-layer μPADs are fabricated by the imprinting method for the colorimetric detection of C-reactive protein (CRP). Different lighting conditions and shooting angles of scenes are simulated in image acquisition, and the detection-related performance of μPADs is improved by using a machine learning algorithm. The You Only Look Once (YOLO) model is used to identify the areas of reaction in μPADs. This model can observe an image only once to predict the objects present in it and their locations. The YOLO model trained in this study was able to identify all the reaction areas quickly without incurring any error. These reaction areas were categorized by classification algorithms to determine the risk level of CRP concentration. Multi-layer perceptron, convolutional neural network, and residual network algorithms were used for the classification tasks, where the latter yielded the highest accuracy of 96%. It has a promising application prospect in fast recognition and analysis of μPADs.

Sensory materials for microfluidic paper based analytical devices - A review

The microfluidic paper-based analytical devices (μPADs) have grown-up swiftly over the decade due to its low cost, simple fabrication procedure, resource-limitedness, non-toxicity and their environmentally benign nature. The μPADs, also identified as point-of-care devices or health care devices have successfully applied in several fields such as diagnostics, biological, food safety, environmental, electrochemical and most importantly colorimetric/fluorimetric sensors, owing to the attractive passive motions of analyte without any external forces. In recent years, a large number of colorimetric and fluorimetric probes have been reported that can selectively recognize the analytes in μPADs. However, there is no organized review on its structure-activity relationship. In this review, we have focused to summarize the colorimetric and fluorimetric probes utilized in μPADs. This review discuss about the relationships between the structure and functions of various probes as signaling units of the efficient μPADs. The probes including nanomaterials, nanozymes, polymers and organic molecules, their structural activity with regard to sensing performances along with their limit of detection are also discussed. This review is expected to assist readers for better understanding of the sensing mechanisms of various chemo and bio-probes utilized in μPADs, as well as promote their advancement in the field. On the other hand, this review also helps the researchers for enhancement of μPADs and paves way for synergistic application of existing molecular probes as an effective diagnostic tool for the worldwide pandemic novel corona virus COVID-19.

μOPTO: A microfluidic paper-based optoelectronic tongue as presumptive tests for the discrimination of alkaloid drugs for forensic purposes

Natural and synthetic alkaloids are widely used for several applications, ranging from clinical purposes to criminal activities. Presumptive color tests are considered a leading tool to reveal on-scene substance identification via rapid chemical reactions that result in visual color changes. Colorimetric tests are popular due to their inherent simplicity, low cost, promptitude and portability; however, in many cases the results of such tests may not be predictable, partly because of the interference from similar species. In this proof-of-concept study, we present a paper-based microfluidic optoelectronic tongue - the so-called μOPTO - comprised of 6 indicators in lieu of one specific test and capable of discriminating 8 different alkaloid drugs (i.e. scopolamine, atropine, cocaine, morphine, ephedrine, caffeine, dipyrone and alprazolam) used for recreational, criminal and medical purposes. The wax printing method was employed to fabricate the microfluidic analytical device with six circular spots for reagent accommodation connected to a centered spot to enable simultaneous reactions with one sample injection. Digital images were obtained using an ordinary flatbed scanner, and the RGB information from before and after sample exposure was extracted using appropriate software. The color changes related to each spot were used to build differential maps with a unique fingerprint for each drug. The chemometric tools (i.e. PCA and HCA) showed suitable discrimination of all studied alkaloids in different quantities. To demonstrate a practical application, different alcoholic beverages spiked with scopolamine - a famous substance that causes drug abuse - were analyzed using the optoelectronic tongue. The results showed that small quantities of the drug were identified in different beverages, demonstrating that our device has the potential to be used in situ to prevent ingestion of contaminated samples.

Electrochemical paper-based microfluidic device for on-line isolation of proteins and direct detection of lead in urine

In this work, we developed a microfluidic paper-based analytical device (μPAD) for the on-line isolation of proteins and the electrochemical detection of lead ions (Pb(II)) in urine samples. The patterned filter paper was prepared through the direct printing of microchannel patterns on filter paper using an office laser printer. The paper was modified with protein precipitant and was then coupled with a detachable three-electrode system. Experimental parameters, namely, modification reagents, microchannel length and width, deposition potential, and deposition time, were optimized. Then, the maximum protein concentration under which the device can function was obtained as 300 mg L^-1. The linear range was 10-500 μg L^-1 with a detection limit of 9 μg L^-1. The effectiveness of this device was demonstrated through the quantification of Pb(II) in urine samples and the results agreed with those of atomic absorption spectrometry (AAS).

Polychlorinated biphenyl detection in organic solvents with paper-based analytical devices

Sample pretreatment process is usually performed before real sample detection. Extraction is one of the most prevalent pretreatment methods. Due to the unequal solubility in two liquid phases, target is extracted (usually from water to organic phase) and further detected with laboratory instruments. Although the analytical instruments have high sensitivity and selectivity, they are relatively expensive and require skilful hands, which is restricted to laboratory use. Here, paper-based analytical devices (μPADs) for measuring samples extracted with organic solvents were tested. The μPADs were employed as a filter for buffer exchange, allowing the transfer of targets from organic solvent to water-based buffer, which could be specifically detected by water-based assays. As an example, polychlorinated biphenyls (PCBs) in n-hexane were detected with aptamer and gold nanoparticles (AuNPs) on μPADs within 30 min. The result of colour change can be recognized from 70.0 ng/L with a low loading amount (0.5 μL). Instead of laboratory instrumental analysis with relative high cost, this assay showed the promising utility of μPADs for target detection after sample pretreatment, which could be utilized as a general platform for inexpensive onsite detection.

Detecting Chemical Hazards in Foods Using Microfluidic Paper-Based Analytical Devices (μPADs): The Real-World Application

Food safety remains one of the most important issues in most countries and the detection of food hazards plays a key role in the systematic approach to ensuring food safety. Rapid, easy-to-use and low-cost analytical tools are required to detect chemical hazards in foods. As a promising candidate, microfluidic paper-based analytical devices (μPADs) have been rarely applied to real food samples for testing chemical hazards, although numerous papers have been published in this field in the last decade. This review discusses the current status and concerns of the μPAD applications in the detection of chemical hazards in foods from the perspective of food scientists, mainly for an audience with a background in mechanical and chemical engineering who may have interests in exploring the potential of μPAD to address real-world food safety issues.

Fabrication and Operation of Paper-Based Analytical Devices

This review focuses on the fabrication techniques and operational components of microfluidic paper-based analytical devices (μPADs). Being low-cost, user-friendly, fast, and simple, μPADs have seen explosive growth in the literature in the last decade. Many different materials and technologies have been employed to fabricate μPADs for various applications, including those that employ patterning, the creation of physical boundaries, and three-dimensional structures. In addition to fabrication techniques, flow control and other operational components in μPADs are of great interest. These components enable μPADs to control flow rates, direct flow paths via valves, sequentially deliver reagents automatically, and display test results, all of which will make μPADs more suitable for point-of-care applications.

Advances in Microfluidic Paper-Based Analytical Devices for Food and Water Analysis

Food and water contamination cause safety and health concerns to both animals and humans. Conventional methods for monitoring food and water contamination are often laborious and require highly skilled technicians to perform the measurements, making the quest for developing simpler and cost-effective techniques for rapid monitoring incessant. Since the pioneering works of Whitesides' group from 2007, interest has been strong in the development and application of microfluidic paper-based analytical devices (μPADs) for food and water analysis, which allow easy, rapid and cost-effective point-of-need screening of the targets. This paper reviews recently reported μPADs that incorporate different detection methods such as colorimetric, electrochemical, fluorescence, chemiluminescence, and electrochemiluminescence techniques for food and water analysis.