3D Microfluidic Devices in a Single Piece of Paper for the Simultaneous Determination of Nitrite and Thiocyanate

Unveiling the potential of the capillary-driven microfluidic paper-based device integrated with smartphone-based for simultaneously colorimetric salivary ethanol and △9-tetrahydrocannabinol analysis

Monitoring various biomarkers in saliva samples emerges as a dynamic and non-invasive method. However, the high viscosity of saliva presents a distinct challenge when integrating paper-based platforms for on-site analysis. In addressing this challenge, we introduced the capillary-driven microfluidic paper-based analytical devices (μCD-PAD) designed for user-friendly and simultaneous detection of ethanol and tetrahydrocannabinol (THC) in saliva without a sample preparation step. Employing a colorimetric approach, we quantified both analytes. Synthetic salivas of varying viscosity flowed seamlessly to the detection zone without needing a sample preparation step, and no impact on colorimetric detection due to viscosity was observed (RSD <5 %). Within 10 min after the solution reached the detection zone, the device produced a homogeneous color signal, easily analyzed by a smartphone camera. To extend the application for determination to cover a legal limit concentration of ethanol and concentration of salivary THC even 24 h after marijuana consumption, the detection time of 30 min was optimized. Moreover, a saliva sample containing both analytes was used to demonstrate the capability of the developed device to detect ethanol and THC simultaneously. No cross-talk between ethanol and THC occurred and showed recovery in the 98-102 % for ethanol and 95-105 % for THC with acceptable accuracy. This developed device exhibits excellent potential for forensic applications, providing a user-friendly, cost-effective, and real-time screening tool for detecting ethanol and THC in saliva.

Saliva Analysis Based on Microfluidics: Focusing the Wide Spectrum of Target Analyte

Saliva is one of the most critical human body fluids that can reflect the state of the human body. The detection of saliva is of great significance for disease diagnosis and health monitoring. Microfluidics, characterized by microscale size and high integration, is an ideal platform for the development of rapid and low-cost disease diagnostic techniques and devices. Microfluidic-based saliva testing methods have aroused considerable interest due to the increasing need for noninvasive testing and frequent or long-term testing. This review briefly described the significance of saliva analysis and generally classified the targets in saliva detection into pathogenic microorganisms, inorganic substances, and organic substances. By using this classification as a benchmark, the state-of-the-art research results on microfluidic detection of various substances in saliva were summarized. This work also put forward the challenges and future development directions of microfluidic detection methods for saliva.

Application of Paper-Based Microfluidic Analytical Devices (µPAD) in Forensic and Clinical Toxicology: A Review

The need for providing rapid and, possibly, on-the-spot analytical results in the case of intoxication has prompted researchers to develop rapid, sensitive, and cost-effective methods and analytical devices suitable for use in nonspecialized laboratories and at the point of need (PON). In recent years, the technology of paper-based microfluidic analytical devices (μPADs) has undergone rapid development and now provides a feasible, low-cost alternative to traditional rapid tests for detecting harmful compounds. In fact, µPADs have been developed to detect toxic molecules (arsenic, cyanide, ethanol, and nitrite), drugs, and drugs of abuse (benzodiazepines, cathinones, cocaine, fentanyl, ketamine, MDMA, morphine, synthetic cannabinoids, tetrahydrocannabinol, and xylazine), and also psychoactive substances used for drug-facilitated crimes (flunitrazepam, gamma-hydroxybutyric acid (GHB), ketamine, metamizole, midazolam, and scopolamine). The present report critically evaluates the recent developments in paper-based devices, particularly in detection methods, and how these new analytical tools have been tested in forensic and clinical toxicology, also including future perspectives on their application, such as multisensing paper-based devices, microfluidic paper-based separation, and wearable paper-based sensors.

Recent Advances In the development of enzymatic paper-based microfluidic biosensors

Using microfluidic paper-based analytical devices has attracted considerable attention in recent years. This is mainly due to their low cost, availability, portability, simple design, high selectivity, and sensitivity. Owing to their specific substrates and catalytic functions, enzymes are the most commonly used bioactive agents in μPADs. Enzymatic μPADs are various in design, fabrication, and detection methods. This paper provides a comprehensive review of the development of enzymatic μPADs by considering the methods of detection and fabrication. Particularly, techniques for mass production of these enzymatic μPADs for use in different fields such as medicine, environment, agriculture, and food industries are critically discussed. This paper aims to provide a critical review of μPADs and discuss different fabrication methods as the central parts of the μPADs production categorized into printable and non-printable methods. In addition, state-of-the-art technologies such as fully printed enzymatic μPADs for rapid, low-cost, and mass production and improvement have been considered.

Simultaneous Cross-type Detection of Water Quality Indexes via a Smartphone-App Integrated Microfluidic Paper-Based Platform

Water quality guarantee in remote areas necessitates the development of portable, sensitive, fast, cost-effective, and easy-to-use water quality detection methods. The current work reports on a microfluidic paper-based analytical device (μPAD) integrated with a smartphone app for the simultaneous detection of cross-type water quality parameters including pH, Cu(II), Ni(II), Fe(III), and nitrite. The shapes, baking time, amount, and ratios of reaction reagent mixtures of wax μPAD were optimized to improve the color uniformity and intensity effectively. An easy-to-use smartphone app was established for recording, analyzing, and directly reading the colorimetric signals and target concentrations on μPAD. The results showed that under the optimum conditions, the current analytical platform has reached the detection limits of 0.4, 1.9, 2.9, and 1.1 ppm for nitrite, Cu(II), Ni(II), and Fe(III), respectively, and the liner ranges are 2.3-90 ppm (nitrite), 3.8-400 ppm (Cu(II)), 2.9-1000 ppm (Ni(II)), 2.8-500 ppm (Fe(III)), and 5-9 (pH). The proposed portable smartphone-app integrated μPAD detection system was successfully applied to real industrial wastewater and river water quality monitoring. The proposed method has great potential for field water quality detection.

3D printed hydrophobic barriers in a paper-based biosensor for point-of-care detection of dengue virus serotypes

Paper-based biosensor is one of the most commonly used platforms for point-of-care testing (POCT). Among these platforms, microfluidic paper-based analytical devices (μPADs) have the most versatile designs due to the different hydrophobic barrier patterns and layers of the devices. In addition, μPADs can also be used in combination with other biosensor platforms to improve the performance of the device. Simple and convenient methods for fabricating low-cost and design-adjustable hydrophobic barriers on paper are one of the most challenging aspects for creating μPADs. This work demonstrated a simple technique for using the common polylactic acid (PLA) filament and wax filament to create hydrophobic barriers on paper for μPADs using a commercialized 3D printer. As a proof of concept, the papers with 3D printed PLA barrier were used in combination with a fluidic chip in a prototype biosensor, in which the barrier paper housed four cell-free reactions and the fluidic chip achieved sample delivery to the reactions in the device. Our designed prototype was capable of discriminating dengue virus serotypes based on small nucleotide sequence differences. The proposed combination of 3D-printed barrier paper and fluidic chip provides a versatile platform for rapid prototyping of POCT with possible compatibility with various detection systems.

Semi-quantitative analysis of nickel: counting-based μPADs built via hand drawing and yellow oily double-sided adhesive tape

Counting-based μPADs were fabricated by hand drawing and yellow oily double-sided adhesive tape, and then successfully applied for the semi-quantitative analysis of nickel.

Aqueous Two-Phase System–Ion Chromatography for Determination of Thiocyanate in Raw Milk

Thiocyanate could effectively inhibit bacteria in milk and extend the shelf life of milk. However, excessive addition will lead to health risks. Therefore, the determination of thiocyanate in raw milk has received a lot of attention, but the determination could be interfered with by other components in raw milk and the pre-treatment of raw milk is complex. In this study, a new pretreatment method combined with ion chromatography (IC) for rapid and sensitive determination of thiocyanate is proposed. An acetonitrile/(NH4)2SO4 aqueous two-phase system (ATPS) was developed for the separation and enrichment of thiocyanate in raw milk. Response surface methodology was performed to optimize the extraction conditions and an efficient pretreatment were obtained using ATPS composed of 42% acetonitrile (w/w) and 16% (NH4)2SO4 (w/w), with the pH 4.7, and the recovery of thiocyanate reached 107.24 ± 0.5%, and the enrichment ratio was 10.74 ± 0.03. IC was used to establish a thiocyanate enrichment method. The linear range was from 0.05 to 15 mg/L and R2 = 0.998, the limit of detection (LOD) was 0.2 μg/L, the limit of quantification (LQD) was 0.6 μg/L. Hence, it is feasible to combine ATPS with IC for the enrichment and determination of thiocyanate in raw milk.

A colorimetric paper-based optode sensor for highly sensitive and selective determination of thiocyanate in urine sample using cobalt porphyrin derivative

In this work, a highly sensitive colorimetric paper-based optode for the determination of thiocyanate in urine samples was developed for the first time. The cocktail solution of the optode was composed of 5,10,15,20-tetrakis(4-octyloxyphenyl)porphyrin cobalt(II) complex (L), tridodecylmethylammonium chloride (TDMACl), 2-nitrophenyl octyl ether, and polyvinyl chloride as an ionophore, an ion exchanger, a plasticizer, and a polymer, respectively. The paper-based optode responded to thiocyanate by increasing the blue component in the RGB index and a visible change, with the naked-eye, of the optode color from pink to green was observed. From the central composite design, the optimized conditions that yielded the highest sensitivity were 4.70 mmol/kg TDMACl and 13.75 mmol/kg L. The developed optode sensor was highly selective and responded to thiocyanate over other anions, with a working range of 0.001-5 mM and with a coefficient of determination (R²) of 0.9915. The limits of detection using naked-eye and camera were determined to be 50.0 μM and 1.26 μM, respectively. In addition, the LOD and LOQ estimated from the standard deviation of the blank were 0.65 and 1.87 μM, respectively. Furthermore, this sensor was successfully applied to the detection of thiocyanate in urine samples from non-smokers and smokers. The results were in good agreement with the standard ion chromatography (IC) technique. This developed paper-based optode sensor was simple, low-cost, portable, and easy to use as a sensing device without any complicated instrument.

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

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