Low-cost fabrication of a paper-based microfluidic using a folded pattern paper

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

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.

Rapid integration of screen-printed electrodes into thermoplastic organ-on-a-chip devices for real-time monitoring of trans-endothelial electrical resistance

Trans-endothelial electrical resistance (TEER) is one of the most widely used indicators to quantify the barrier integrity of endothelial layers. Over the last decade, the integration of TEER sensors into organ-on-a-chip (OOC) platforms has gained increasing interest for its efficient and effective measurement of TEER in OOCs. To date, microfabricated electrodes or direct insertion of wires has been used to integrate TEER sensors into OOCs, with each method having advantages and disadvantages. In this study, we developed a TEER-SPE chip consisting of carbon-based screen-printed electrodes (SPEs) embedded in a poly(methyl methacrylate) (PMMA)-based multi-layered microfluidic device with a porous poly(ethylene terephthalate) membrane in-between. As proof of concept, we demonstrated the successful cultures of hCMEC/D3 cells and the formation of confluent monolayers in the TEER-SPE chip and obtained TEER measurements for 4 days. Additionally, the TEER-SPE chip could detect changes in the barrier integrity due to shear stress or an inflammatory cytokine (i.e., tumor necrosis factor-α). The novel approach enables a low-cost and facile fabrication of carbon-based SPEs on PMMA substrates and the subsequent assembly of PMMA layers for rapid prototyping. Being cost-effective and cleanroom-free, our method lowers the existing logistical and technical barriers presenting itself as another step forward to the broader adoption of OOCs with TEER measurement capability.

Recent Trends of Microfluidics in Food Science and Technology: Fabrications and Applications

The development of novel materials with microstructures is now a trend in food science and technology. These microscale materials may be applied across all steps in food manufacturing, from raw materials to the final food products, as well as in the packaging, transport, and storage processes. Microfluidics is an advanced technology for controlling fluids in a microscale channel (1~100 μm), which integrates engineering, physics, chemistry, nanotechnology, etc. This technology allows unit operations to occur in devices that are closer in size to the expected structural elements. Therefore, microfluidics is considered a promising technology to develop micro/nanostructures for delivery purposes to improve the quality and safety of foods. This review concentrates on the recent developments of microfluidic systems and their novel applications in food science and technology, including microfibers/films via microfluidic spinning technology for food packaging, droplet microfluidics for food micro-/nanoemulsifications and encapsulations, etc.

Paper-Based Enzymatic Electrochemical Sensors for Glucose Determination

The general objective of Analytical Chemistry, nowadays, is to obtain best-quality information in the shortest time to contribute to the resolution of real problems. In this regard, electrochemical biosensors are interesting alternatives to conventional methods thanks to their great characteristics, both those intrinsically analytical (precision, sensitivity, selectivity, etc.) and those more related to productivity (simplicity, low costs, and fast response, among others). For many years, the scientific community has made continuous progress in improving glucose biosensors, being this analyte the most important in the biosensor market, due to the large amount of people who suffer from diabetes mellitus. The sensitivity of the electrochemical techniques combined with the selectivity of the enzymatic methodologies have positioned electrochemical enzymatic sensors as the first option. This review, focusing on the electrochemical determination of glucose using paper-based analytical devices, shows recent approaches in the use of paper as a substrate for low-cost biosensing. General considerations on the principles of enzymatic detection and the design of paper-based analytical devices are given. Finally, the use of paper in enzymatic electrochemical biosensors for glucose detection, including analytical characteristics of the methodologies reported in relevant articles over the last years, is also covered.

Smartphone-based paper microfluidic competitive immunoassay for the detection of α-amanitin from mushrooms

α-Amanitin is often considered the most poisonous mushroom toxin produced by various mushroom species, which are hard to identify from edible, non-toxic mushrooms. Conventional detection methods require expensive and bulky equipment or fail to meet high analytical sensitivity. We developed a smartphone-based fluorescence microscope platform to detect α-amanitin from dry mushroom tissues. Antibody-nanoparticle conjugates were captured by immobilized antigen-hapten conjugates while competing with the free analytes in the sample. Captured fluorescent nanoparticles were excited at 460 nm and imaged at 500 nm. The pixel numbers of such nanoparticles in the test zone were counted, showing a decreasing trend with increasing analyte concentration. The detection method exhibited a low detection limit (1 pg/mL), high specificity, and selectivity, allowing us to utilize a simple rinsing for toxin extraction and avoiding the need for high-speed centrifugation. In addition, this assay's short response time and portable features enable field detection of α-amanitin from amanitin-producing mushrooms.

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.

Latex-Based Paper Devices with Super Solvent Resistance for On-the-Spot Detection of Metanil Yellow in Food Samples

The following paper presents a construct for a paper-based device which utilizes latex as the hydrophobic material for the fabrication of its hydrophobic barrier, which was deposited onto the cellulose surface either by free-hand or stenciled drawing. This method demands the least amount of expertise and time from its use, enabling a simple and rapid fabrication experience. Several properties of the hydrophobic material were characterized, such as the hydro head and penetration rate, with the aim of assessing its robustness and stability. The presented hydrophobic barriers fabricated using this approach have a barrier width of 4 mm, a coating thickness of 208 µm, and a hydrophilic resolution of 446.5 µm. This fabrication modality boasts an excellent solvent resistance with regard to the hydrophobic barrier. These devices were employed for on-the-spot detection of Metanil Yellow, a banned food adulterant often used in curcumin and pigeon peas, within successful limits of detection (LOD) of 0.5% (w/w) and 0.25% (w/w), respectively. These results indicate the great potential this fabricated hydrophobic device has in numerous paper-based applications and other closely related domains, such as diagnostics and sensing, signalling its capacity to become commonplace in both industrial and domestic settings.

Paper-based microfluidic devices for food adulterants: Cost-effective technological monitoring systems

Analytical sciences have witnessed emergent techniques for efficient clinical and industrial food adulterants detection. In this review, the contributions made by the paper-based devices are highlighted for efficient and rapid detection of food adulterants and additives, which is the need of the hour and how different categories of techniques have been developed in the past decade for upgrading the performance for point-of-care testing. A simple strategy with an arrangement for detecting specific adulterants followed by the addition of samples to obtain well-defined qualitative or quantitative signals for confirming the presence of target species. The paper-based microfluidics-based technology advances and prospects for food adulterant detection are discussed given the high-demand from the food sectors and serve as a valued technology for food researchers working in interdisciplinary technological frontiers.

Enhancement of the Detection Performance of Paper-Based Analytical Devices by Nanomaterials

Paper-based analytical devices (PADs), including lateral flow assays (LFAs), dipstick assays and microfluidic PADs (μPADs), have a great impact on the healthcare realm and environmental monitoring. This is especially evident in developing countries because PADs-based point-of-care testing (POCT) enables to rapidly determine various (bio)chemical analytes in a miniaturized, cost-effective and user-friendly manner. Low sensitivity and poor specificity are the main bottlenecks associated with PADs, which limit the entry of PADs into the real-life applications. The application of nanomaterials in PADs is showing great improvement in their detection performance in terms of sensitivity, selectivity and accuracy since the nanomaterials have unique physicochemical properties. In this review, the research progress on the nanomaterial-based PADs is summarized by highlighting representative recent publications. We mainly focus on the detection principles, the sensing mechanisms of how they work and applications in disease diagnosis, environmental monitoring and food safety management. In addition, the limitations and challenges associated with the development of nanomaterial-based PADs are discussed, and further directions in this research field are proposed.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.

A Perovskite-Based Paper Microfluidic Sensor for Haloalkane Assays

Detection of haloalkanes is of great industrial and scientific importance because some haloalkanes are found serious biological and atmospheric issues. The development of a flexible, wearable sensing device for haloalkane assays is highly desired. Here, we develop a paper-based microfluidic sensor to achieve low-cost, high-throughput, and convenient detection of haloalkanes using perovskite nanocrystals as a nanoprobe through anion exchanging. We demonstrate that the CsPbX₃ (X = Cl, Br, or I) nanocrystals are selectively and sensitively in response to haloalkanes (CH₂Cl₂, CH₂Br₂), and their concentrations can be determined as a function of photoluminescence spectral shifts of perovskite nanocrystals. In particular, an addition of nucleophilic trialkyl phosphines (TOP) or a UV-photon-induced electron transfer from CsPbX₃ nanocrystals is responsible for achieving fast sensing of haloalkanes. We further fabricate a paper-based multichannel microfluidic sensor to implement fast colorimetric assays of CH₂Cl₂ and CH₂Br₂. We also demonstrate a direct experimental observation on chemical kinetics of anion exchanging in lead-halide perovskite nanocrystals using a slow solvent diffusion strategy. Our studies may offer an opportunity to develop flexible, wearable microfluidic sensors for haloalkane sensing, and advance the in-depth fundamental understanding of the physical origin of anion-exchanged nanocrystals.

Negligible-cost microfluidic device fabrication using 3D-printed interconnecting channel scaffolds

This paper reports a novel, negligible-cost and open-source process for the rapid prototyping of complex microfluidic devices in polydimethylsiloxane (PDMS) using 3D-printed interconnecting microchannel scaffolds. These single-extrusion scaffolds are designed with interconnecting ends and used to quickly configure complex microfluidic systems before being embedded in PDMS to produce an imprint of the microfluidic configuration. The scaffolds are printed using common Material Extrusion (MEX) 3D printers and the limits, cost & reliability of the process are evaluated. The limits of standard MEX 3D-printing with off-the-shelf printer modifications is shown to achieve a minimum channel cross-section of 100×100 μm. The paper also lays out a protocol for the rapid fabrication of low-cost microfluidic channel moulds from the thermoplastic 3D-printed scaffolds, allowing the manufacture of customisable microfluidic systems without specialist equipment. The morphology of the resulting PDMS microchannels fabricated with the method are characterised and, when applied directly to glass, without plasma surface treatment, are shown to efficiently operate within the typical working pressures of commercial microfluidic devices. The technique is further validated through the demonstration of 2 common microfluidic devices; a fluid-mixer demonstrating the effective interconnecting scaffold design, and a microsphere droplet generator. The minimal cost of manufacture means that a 5000-piece physical library of mix-and-match channel scaffolds (100 μm scale) can be printed for ~$0.50 and made available to researchers and educators who lack access to appropriate technology. This simple yet innovative approach dramatically lowers the threshold for research and education into microfluidics and will make possible the rapid prototyping of point-of-care lab-on-a-chip diagnostic technology that is truly affordable the world over.

Origami-Inspired Approaches for Biomedical Applications

Modern day biomedical applications require progressions that combine advanced technology with the conformability of naturally occurring, complex biosystems. These advancements yield conformational interactions between the biomedical devices and the biological organisms' structures. Biomedical applications that adapt origami-inspired approaches have accrued aspired advances. Along with application-specific advantages, the most pertinent advances provided by origami-inspired strategies include voluminous structures with the ability to conform to biosystems, shape-shifting from two-dimensional (2D) to three-dimensional (3D) structures, and biocompatibility. Throughout this paper, the exploration of new studies, primarily within the past decade, with origami-based applications of biomedical devices, including their theories, experimental results, and plans for future testing are reviewed. This mini-review contains examples that aid the advancement of biomedical applications and hold promising future discoveries. The origami-inspired applications discussed within this paper are tissue scaffolds, drug delivery approaches, stents and catheters, implants, microfluidic devices, biosensors, and origami usage in surgery.

Foldable paper-based analytical device for membraneless gas-separation and determination of iodate based on fluorescence quenching of gold nanoclusters

A new design of a paper-based analytical device (PAD) for membraneless gas-separation with subsequent determination of iodate is presented. The rectangular PAD was invented as the folded pattern, where two circular reservoirs: the donor reservoir and the acceptor reservoir were situated in "a single paper" for convenient use. The hydrophobic barrier of each reservoir was easily fabricated by painting with a permanent marker. The PAD was demonstrated for the quantitative analysis of iodate, based on the fluorescence quenching of the bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs). The BSA-AuNCs were fast prepared by a microwave-assisted approach. The nanoclusters solution was applied into the acceptor reservoir, while the sample, iodide and sulfuric acid were sequentially aliquoted into the donor reservoir. After folding the PAD, the donor and the acceptor were mounted together via a two-sided mounting tape. The headspace between the two reservoirs allows membraneless gas-separation of free iodine from the donor to diffuse into the acceptor. Etching of gold core of the nanoclusters in the acceptor resulted in quenching of the red emission, was monitored by two methods, i.e. "fluorometric detection" (λ_ex: 490 nm, λ_em: 630 nm) and "image capture" of the acceptor under the UV irradiation by a smart phone's camera. Two calibrations were plotted accordingly to their detections and good linearities (r² ˃ 0.98) were observed from 0.005 to 0.1 mmol L^-1 iodate. High accuracy (mean recovery: 95.1 (±4.6) %) and high precision (RSD < 3%) were obtained. The lower limits of detection were 0.005 mmol L^-1 (with fluorometric detection) and 0.01 mmol L^-1 (with image capture). The method was effectively applied for the measurement of iodate in iodized salts and fish sauces without prior sample pre-treatment.

PMAA-CeO2 nanoparticle-based paper microfluidic device with customized image processing software for antioxidant assay

Despite recent advancements in the field of microfluidic paper-based analytical devices (μPADs), a key challenge remains in developing a simple and efficient μPAD with customized imaging capabilities for antioxidant assays. In the present study, we report a facile approach for μPAD fabrication through the application of transparent nail paint leading to creation of hydrophobic barriers and well-defined channels. The resultant μPADs were then characterized through scanning electron microscopy and contact angle measurements. The resolution and functional features of the fabricated μPAD were amenable to the intended assay. The μPAD's impregnated poly(methacrylic acid) (PMAA)-coated cerium oxide (CeO₂) nanoparticles oxidized the 3,3',5,5'-tetramethylbenzidine (TMB) leading to the formation of a blue-colored charge-transfer complex. The addition of different antioxidant standard solutions resulted in a reduction in the blue color in a dose-dependent manner which could be observed visually. The color intensity of the PMAA-CeO₂ nanoparticle@TMB oxidation product was inversely proportional to the antioxidant concentration and was measured using customized in-house MATLAB-based image processing software. Importantly, PMAA-CeO₂ nanoparticle-based μPADs demonstrated good analytical characteristics and were able to be stored for long periods without any loss of activity. Moreover, potential interferents did not pose any threat to the colorimetric signal read-out for determination of antioxidant activity. The developed method was further applied for the assessment of antioxidant activity in a variety of tea samples and performed satisfactorily in comparison with a commonly used antioxidant detection method. Collectively, the developed μPAD-based platform holds great potential as a low-cost, convenient, portable and reliable method for pursuing various on-site antioxidant assays. Graphical Abstract.

Ready-to-use, functionalized paper test strip used with a smartphone for the simultaneous on-site detection of free chlorine, hydrogen sulfide and formaldehyde in wastewater

The simultaneous detection of free chlorine, hydrogen sulfide and formaldehyde in wastewater samples was performed. In this report, we designed and fabricated functionalized paper test strips featuring detection zones that use 3-aminopropyltriethoxysilane (APTES) for the immobilization of chromogenic substrates to detect free chlorine, hydrogen sulfide and formaldehyde. After multiple chromogenic reactions, red, blue and purple colors were obtained on the detection zones and analyzed using a smartphone. Under optimum conditions, the paper test strips showed 1.7, 1.8 and 1.7 orders of magnitude for free chlorine, hydrogen sulfide and formaldehyde, respectively. This sensitivity is caused by the formation of homogeneous complexes on detection zones resulting from the chromogenic reagents immobilized on the detection zone via APTES. Through this strategy, free chlorine, hydrogen sulfide and formaldehyde analysis was achieved within 5 min with detection limits of 0.08, 0.14 and 0.13 mg L^-1, respectively. The developed paper test strip was able to selective detection of free chlorine, hydrogen sulfide and formaldehyde even in the presence of common interfering agents therefore, the test strip was highly selective. In a further demonstration, the developed functionalized paper test strip was successfully used for simultaneous detection of free chlorine, hydrogen sulfide and formaldehyde in wastewater in the field and exhibited with high precision and accuracy in detecting free chlorine, hydrogen sulfide and formaldehyde in wastewater samples. Compared to other methods, this assay was advantageous in terms of its low detection limit, time savings, good stability and highly portable format, which facilitates rapid on-site environmental monitoring with a smartphone.

Advances in Paper-Based Analytical Devices

Microfluidic paper-based analytical devices (μPADs) are the newest generation of lab-on-a-chip devices and have made significant strides in both our understanding of fundamental behavior and performance characteristics and expansion of their applications. μPADs have become useful analytical techniques for environmental analysis in addition to their more common application as medical point-of-care devices. Although the most common method for device fabrication is wax printing, numerous other techniques exist and have helped address factors ranging from solvent compatibility to improved device function. This review highlights recent reports of fabrication and design, modes of detection, and broad applications of μPADs. Such advances have enabled μPADs to be used in field and laboratory studies to address critical needs in fast, cheaper measurement technologies.

Smartphone-imaged multilayered paper-based analytical device for colorimetric analysis of carcinoembryonic antigen

Paper-based immunoassays are effective methods that employ microfluidic paper-based analytical devices (μPADs) for the rapid, simple, and accurate quantification of analytes in point-of-care diagnosis. In this study, we developed a wax-printed multilayered μPAD for the colorimetric detection of carcinoembryonic antigen (CEA), where the device contained a movable and rotatable detection layer to allow the μPAD to switch the state of the sample solutions, i.e., flowing or storing in the sensing zones. A smartphone with a custom-developed program served as an automated colorimetric reader to capture and analyze images from the μPAD, before calculating and displaying the test results. After optimizing the crucial conditions for the assay, the proposed method exhibited a wide linear dynamic range from 0.5 to 70 ng/mL, with a low CEA detection limit of 0.015 ng/mL. The clinical performance of this method was successfully validated using 50 positive and 40 negative human serum samples, thereby demonstrating the high sensitivity of 98.0% and specificity of 97.5% in the detection of CEA. The proposed method is greatly simplified compared with the cumbersome steps required for traditional immunoassays, but without any loss of accuracy and stability, as well as reducing the time needed to detect CEA. Complex and bulky instruments are replaced with a smartphone. The proposed detection platform could potentially be applied in point-of-care testing. Graphical abstract.

Fabrication of paper-based microfluidic device by recycling foamed plastic and the application for multiplexed measurement of biomarkers

Microfluidic paper-based analytical devices (μPADs) are emerging as effective analytical platforms for point-of-care assays in resource-limited areas. Simple and cost-effective fabrication method still remains challenging on μPADs. A simple and cost-effective method for fabricating paper-based devices was presented in this work by using of dipping strategy with the recycled polystyrene in chloroform as the hydrophobic reagent. Adhesive tape was employed as mask to transfer the hydrophilic channel pattern to the paper substrate. With the single-sided adhesive tape stuck on the hydrophilic parts of the paper surface, the paper-based device was immersed in chloroform solution with dissolving recycling polystyrene for several seconds. Then the hydrophilic pattern can be achieved and all the other parts on the paper surface were hydrophobic. The adhesive tape was torn off from the hydrophilic parts. The highest contact angle value of 114° of the hydrophobic part was acquired with this simple fabrication method. By using of the sandwich-type immunoreactions and luminol-H₂O₂p-iodophenol (PIP) chemiluminescence(CL) system, three cancer biomarkers were simultaneously detected in human serum samples on μPADs with the linear range of 0.05-80.0 ng·mL^-1 for carcinoembryonic antigen (CEA), 5.0-80.0 ng·mL^-1 for alpha-fetal protein (AFP) and 1.0-50.0 ng·mL^-1 for prostate-specific antigen (PSA). The fabricating strategy with recycling polystyrene and adhesive tape provides a versatile platform for prototyping of μPADs in both developed and resource constrained region.

New Single-Layered Paper-Based Microfluidic Devices for the Analysis of Nitrite and Glucose Built via Deposition of Adhesive Tape

A simple, low-cost technique has been developed for the rapid fabrication of single-layered paper-based microfluidic devices (μPADs). This technique, for the first time, made use of the deposition of patterned adhesive tape into the filter paper to construct hydrophobic barriers, with the help of toluene. Unlike other reported multi-layered μPADs that merely made use of adhesive tape as a separate layer for sealing or fluid flow controlling, the patterned adhesive tape was simultaneously dissolved and penetrated into the filter paper, which resulted in the successful transfer of the pattern from the tape to the filter paper. To demonstrate the effectiveness of this approach, nitrite and glucose were individually measured; detection limits as low as 0.015 ± 0.004 mM and 0.022 ± 0.006 mM were reported for nitrite and glucose, respectively. Multiplexed analysis of both analytes was also carried out with respective detection limits of 0.048 ± 0.005 mM and 0.025 ± 0.006 mM for nitrite and glucose. The application of the method was demonstrated by measuring nitrite and glucose in spiked artificial urine samples and satisfied recovery results were obtained.

Fabrication, Flow Control, and Applications of Microfluidic Paper-Based Analytical Devices

Paper-based microfluidic devices have advanced significantly in recent years as they are affordable, automated with capillary action, portable, and biodegradable diagnostic platforms for a variety of health, environmental, and food quality applications. In terms of commercialization, however, paper-based microfluidics still have to overcome significant challenges to become an authentic point-of-care testing format with the advanced capabilities of analyte purification, multiplex analysis, quantification, and detection with high sensitivity and selectivity. Moreover, fluid flow manipulation for multistep integration, which involves valving and flow velocity control, is also a critical parameter to achieve high-performance devices. Considering these limitations, the aim of this review is to (i) comprehensively analyze the fabrication techniques of microfluidic paper-based analytical devices, (ii) provide a theoretical background and various methods for fluid flow manipulation, and iii) highlight the recent detection techniques developed for various applications, including their advantages and disadvantages.