Paper-based Microfluidic System Research Articles

Wearable electrochemical device based on butterfly-like paper-based microfluidics for pH and Na+ monitoring in sweat

A wearable potentiometric device is reported based on an innovative butterfly-like paper-based microfluidic system, allowing for continuous monitoring of pH and Na+ levels in sweat during physical activity. Specifically, the use of the butterfly-like configuration avoids evaporation phenomena and memory effects, enabling precise and timely biomarker determination in sweat. Two ad hoc modified screen-printed electrodes were embedded in the butterfly-like paper-based microfluidics, and the sensing device was further integrated with a portable and miniaturized potentiostat, leveraging Bluetooth technology for efficient data transmission. First, the paper-based microfluidic configuration was tested for optimal fluidic management to obtain optimized performance of the device. Subsequently, the two electrodes were individually tested to detect the two biomarkers, namely pH and Na+. The results demonstrated highly promising near-Nernstian (0.056 ± 0.002 V/dec) and super-Nernstian (− 0.080 ± 0.003 V/pH) responses, for Na+ and pH detection, respectively. Additionally, several important parameters such as storage stability, interferents, and memory effect by hysteresis study were also investigated. Finally, the butterfly-like paper-based microfluidic wearable device was tested for Na+ and pH monitoring during the physical activity of three volunteers engaged in different exercises, obtaining a good correlation between Na+ increase and dehydration phenomena. Furthermore, one volunteer was tested through a cardiopulmonary test, demonstrating a correlation between sodium Na+ increase and the energetic effort by the volunteer. Our wearable device highlights the high potential to enable early evaluation of dehydration and open up new opportunities in sports activity monitoring.Graphical abstract

Generalized predictive analysis of reactions in paper devices via graph neural networks

Microfluidic technology facilitates high-throughput generation of time series data for biological and medical studies. Deep learning enables accurate, predictive analysis and proactive decision-making based on autonomous recognition of intricate pattern hidden in series. In this work, we first devised a paper-based microfluidic system for portable nucleic acid amplification test with economic energy consumption. Then, we employed Graph Neural Network (GNN), distinguished by its non-Euclidean data structure tailored for deep learning, with spatio-temporal attention mechanism to perform near-sensor predictive analysis of the on-chip reaction. Our findings demonstrated that the novel GNN model can provide accurate predictions of positive outcomes at the early stages of the reaction using less than one-third of the total reaction time. Then, the deep learning model trained by on-chip data was subsequently applied to more than 900 clinical plots. Generalization of the GNN model was successfully validated across different detection methods, diverse types of datasets and time series with variable length. Accuracy, sensitivity and specificity of the predictive approach were 96.5 %, 94.3 % and 99.0 % by utilizing the early half of reaction information. Finally, we compared the GNN model with various deep learning models. Despite differences in the prediction of negative samples among various models were minute, GNN obviously offered overall superior performance. This work ignites a cutting-edge application of deep learning in point-of-care and near-sensor tests. By harnessing the power of body area networks and edge/fog computing, our approach unlocks promising possibilities in diverse fields like healthcare and instrument science.

Paper-based microfluidic system and chiroptical functionalized gold nano-oval for colorimetric detection of L-Tryptophan

“The development and deployment of a practical and portable technology for on-site chiral identification of enantiomers hold immense significance in the fields of medical and biological sciences. Among the essential amino acids, Tryptophan (Trp) plays a crucial role in human metabolism and serves as a diagnostic marker for various metabolic disorders. In this study, we introduce an innovative approach that combines an enantio-selective ZIF-8-His MOF-MIPs packed-bed centrifugal microfluidic system with an enantioselective colorimetric sensor probe. This system is further integrated with smartphone-based on-site data recording. The basis of this colorimetric sensor's operation lies in the controlled morphology and surface passivation of gold nano-ovals (Au–NOs) through DL-Alanine. To confirm the successful synthesis of the chiral recognition elements, we employed various characterization techniques, including FE-SEM, TEM, FTIR, CD, UV–Vis, zeta potential, DLS, and XRD. Our focus was on optimizing operational parameters for the effective separation and determination of L-chiral tryptophan on-site. The sensor exhibited two linear ranges for L-Trp detection: 0–5.42 and 5.42–80.47 mM, with a detection limit of 0.5 mM. The integrated system possesses advantages such as ease of availability, preparation, high stability, desirable selectivity even in the presence of similar biomolecules, and rapid detection capabilities. Furthermore, our method demonstrated successful enantioselective sensing of L-Trp in various biological samples, including human blood plasma, urine, milk, and bovine serum albumin (BSA), yielding promising results. The integrated microfluidic platform follows a "sample-in and answer-out" approach, making it highly applicable in healthcare, environmental monitoring, food safety analysis, and point-of-care testing. The chiral recognition pretreatment assay and self-contained, automated colorimetric detection on the microfluidic disc represent a promising avenue for cutting-edge research in these domains”.

A paper-based aptamer-sandwich assay for detection of HNP 1 as a biomarker for periprosthetic joint infections on an integrated microfluidic platform

BackgroundTotal joint arthroplasty (TJA) has significantly improved the quality of life for millions suffering from end-stage arthritis. However, periprosthetic joint infections (PJI) remain a serious complication, necessitating extensive interventions and prolonged antimicrobial treatments. The aging population is expected to lead to a rise in TJA cases, subsequently increasing the incidence of PJI, particularly in the elderly who face higher mortality rates. Current diagnostic methods for suspected PJI, such as radiographs and biochemical markers like CRP and ESR, exhibit limited sensitivity. Therefore, there is a critical need for a specific synovial fluid biomarker assay to enhance PJI diagnosis using specific SF-based assay. ResultsThis study introduces a novel microfluidic chip with a paper-based aptamer-sandwich assay for the quantitative detection of HNP 1, a crucial PJI biomarker, in synovial fluid. The assay leverages the advantages of aptamers over antibodies, demonstrating high selectivity and affinity for target molecules. The integration of a nitrocellulose (NC) membrane onto the microfluidic platform represents a significant advancement, reducing background signals and simplifying the assay procedure without intricate procedure and pre-treatment. The NC membrane-based microfluidic device offers rapid, cost-effective, and highly sensitive detection of HNP 1, with a limit of detection of 0.5 mg L−1. The microfluidic device demonstrates exceptional performance, detecting up to four clinical samples in approximately 42 min on a single chip with 100 % accuracy, as confirmed by analysis of 12 clinical samples and comparison with “gold-standard”. Moreover, the assay exhibits a wide dynamic range of 0.5–100 mg L-1, underscoring its potential as a powerful tool for PJI diagnosis in clinical settings. SignificanceThis work introduces a paper-based microfluidic system tailored for rapid HNP 1 detection using synovial fluid near joint region (and not serum via blood) for better diagnosis. The innovative paper-based aptamer-sandwich assay yields results within 42-min. Significantly, it boasts a wide dynamic range, detecting levels from an impressive 0.5 mg L-1, crucial in the 2.6 mg L-1 threshold region. This heightened sensitivity and expansive detection capability establish our assay as a leader in PJI diagnostics, promising unmatched precision and efficiency in clinical applications.

Amperometric Measurements by a Novel Aerosol Jet Printed Flexible Sensor for Wearable Applications

In the last years, increasing interest has been addressed on wearable devices for the continuous monitoring of biochemical profiles of patients and athletes. Among various markers, lactate represents one of the most interesting to deepen the knowledge on fatigue processes, in combination with traditional electromyographic features. In this work, we propose a new, low-cost, rapid, and flexible electrochemical amperometric lactate carbon biosensor fabricated by the novel technique of aerosol jet printing (AJP). The developed biosensors were combined with a paper-based microfluidic system and a chitosan-based stable functionalization to allow a long-term continuous monitoring of human daily activities. The sensor performances were evaluated by static and dynamic electrochemical tests in buffered media. The limit of detection is 11 ± 2 mM for the static setup and of 15 ± 6 mM for the dynamic setup, while sensitivity is 0.02 and 0.04 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> /mM, respectively, with single sigma standard deviation lower than 8%. Increasing and decreasing concentration steps of lactate induces comparable response times below 30 s. These results obtained in vitro under controlled laboratory conditions represent a promising starting point to pursue with ex-vivo and in vivo validation for the future development of stand-alone wearable patches for noninvasive lactate measurements.

Testing of Beeswax Printing Technology in the Design of a Paper-Based Microfluidic System

Testing of Beeswax Printing Technology in the Design of a Paper-Based Microfluidic System

Development of a Paper-Based Microfluidic System for a Continuous High-Flow-Rate Fluid Manipulation.

The current study describes the development of a disposable paper-based microfluidic system, which unlike its predecessors that are only capable of processing a small amount of fluid, can continuously process the fluid at a high flow rate of up to 1.5 mL/min. The fabrication procedure was clean-room-free and robust, involving the use of a CO2 laser to engrave the microchannels on a paper substrate, followed by alkenyl ketene dimer treatment to hydrophobize the paper and lamination. The microchannel down to a minimum depth of ∼80 μm with an average roughness of ∼8 μm was engraved on the substrate. As a proof of concept, the applicability of this system to enrich the microparticles based on the inertial focusing mechanism was tested. This new generation of paper-based microfluidic system can be potentially used for the diagnostic applications where the analyte is low in quantity and processing a large volume of fluid sample is required.

Improved performance of a paper-based glucose fuel cell by capillary induced flow

This work describes the use of a capillary quasi-steady flow to improve the power and current output of a paper-based enzymatic glucose/O2 fuel cell. Anode and cathode of the fuel cell are made with screen-printed carbon electrodes properly functionalized with enzyme-based inks. The electrodes have been placed at both sides of a paper strip. The strip is connected to a paper-based microfluidic system that allows establishing capillary flow. Quasi-steady flows with different flow rates have been generated by modifying the paper materials that constitute the adsorbent pad of the system. The polarization curves of the fuel cell at physiological glucose concentration (5 mM, pH 7.4) show that convective mass transport generated by the capillary flow allows mitigating cathode current limitations and improves the overall fuel cell performance. Four different flow rates ranging from 0.22 ± 0.01 μL/s to 2.68 ± 0.30 μL/s were investigated obtaining an increase in the fuel cell power output up to 56%.

A paper-based microfluidic Dot-ELISA system with smartphone for the detection of influenza A

An automated, portable, and integrated paper-based microfluidic system has been developed for influenza A detection with smartphone at point-of-care (POC) settings. The low-cost paper-based microfluidic chip consists of a reagent storage and reaction modules. The storage module, which consists of a couple of reagent chambers with dispensation channels, is responsible for reagent storage and release. The reaction module consists of an absorbent pad and a nitrocellulose (NC) membrane which is functionalized with specific monoclonal antibodies on a test and control spots for immunoassay detection. Microfluidic Dot-ELISA is performed when the dispensed reagent flows through the NC membrane at a controllable speed and reaches the absorbent pad because of the gravity and capillary force without active pumping. A smartphone is used to capture image from the NC membrane with its own camera and process the image with an intelligent algorithm of custom application software which is developed with Java. With a smartphone, the detection result can be displayed and transmitted to other medical agencies if necessary. Experimental results show that, compared with the traditional methods, more convenient and efficient influenza A detection can be achieved with the developed paper-based POC microfluidic chip with the assistance of smartphone.

Paper-based microfluidic system for tear electrolyte analysis.

The analysis of tear constituents at point-of-care settings has a potential for early diagnosis of ocular disorders such as dry eye disease, low-cost screening, and surveillance of at-risk subjects. However, current minimally-invasive rapid tear analysis systems for point-of-care settings have been limited to assessment of osmolarity or inflammatory markers and cannot differentiate between dry eye subclassifications. Here, we demonstrate a portable microfluidic system that allows quantitative analysis of electrolytes in the tear fluid that is suited for point-of-care settings. The microfluidic system consists of a capillary tube for sample collection, a reservoir for sample dilution, and a paper-based microfluidic device for electrolyte analysis. The sensing regions are functionalized with fluorescent crown ethers, o-acetanisidide, and seminaphtorhodafluor that are sensitive to mono- and divalent electrolytes, and their fluorescence outputs are measured with a smartphone readout device. The measured sensitivity values of Na+, K+, Ca2+ ions and pH in artificial tear fluid were matched with the known ion concentrations within the physiological range. The microfluidic system was tested with samples having different ionic concentrations, demonstrating the feasibility for the detection of early-stage dry eye, differential diagnosis of dry eye sub-types, and their severity staging.

An Acoustothermal Heater for Paper Microfluidics towards Point-of-care Glucose Detection

We report the first observation of acoustothermal heating of wet papers under high frequency vibrations. The proposed heating method utilizes acoustic absorption of cellulose fiber, which exhibits viscoelastic properties. The surface acoustic waves propagate on the piezoelectric substrate and refract into a wet paper strip on the substrate. The refracted longitudinal waves deliver acoustic energy into the wet paper by vibration damping in the form of heat. Acoustothermal heating was discovered to be frequency-dependent and to reach local maxima at certain frequencies. Based on this finding, we developed a paper-based microfluidic heating system for point-of-care glucose detection.

Practical electricity generation from a paper based biofuel cell powered by glucose in ubiquitous liquids

This paper introduces a novel enzymatic fuel cell design that employs cellulose paper-based quasi-2D microfluidic system to supply biofuel to the enzymatic layer. The state of the art nanoarchitectural design, employing carbon nanotube-based papers for the bioelectrodes, allows a single cell to maintain 400mV for 16days of continuous operation in glucose solution and reach 1mA of current output. Stacks of cells connected in series show successful performance using glucose in Gatorade® resulting in stack-cell potential of 1.8V, employed to power a digital clock for 36h, continuously. These designs open the possibility for obtaining enzymatic fuel cells that can run small portable devices on easily available ubiquitous liquids while addressing environmental concerns that are prevalent in traditional fuel cells.

Three-Dimensional Paper-Based Microfluidic Device for Assays of Protein and Glucose in Urine

The first step in curing a disease is being able to detect the disease effectively. Paper-based microfluidic devices are biodegradable and can make diagnosing diseases cost-effective and easy in almost all environments. We created a three-dimesnional (3D) paper device using wax printing fabrication technique and basic principles of origami. This design allows for a versatile fabrication technique over previously reported patterning of SU-8 photoresist on chromatography paper by employing a readily available wax printer. The design also utilizes multiple colorimetric assays that can accommodate one or more analytes including urine, blood, and saliva. In this case to demonstrate the functionality of the 3D paper-based microfluidic system, a urinalysis of protein and glucose assays is conducted. The amounts of glucose and protein introduced to the device are found to be proportional to the color change of each assay. This color change was quantified by use of Adobe Photoshop. Urine samples from participants with no pre-existing health conditions and one person with diabetes were collected and compared against synthetic urine samples with predetermined glucose and protein levels. Utilizing this method, we were able to confirm that both protein and glucose levels were in fact within healthy ranges for healthy participants. For the participant with diabetes, glucose was found to be above the healthy range while the protein level was in the healthy range.

Acoustically-driven microcentrifugation

A microcentrifugation technique is demonstrated in which symmetry breaking of a planar surface acoustic wave (SAW) propagating along a piezoelectric substrate can generate rotational acoustic streaming in a nanoliter drop. The azimuthal flow is rapid, with linear velocities of several cm/s - such fast azimuthal streaming, shown to be chaotic beyond a threshold power, can be used to generate intense micromixing within the drop. Indeed, we show that the rate and yield of a variety of distinct chemical and biochemical reaction classes far exceed that obtained using ultrasonic or microwave-assisted mixing, and with considerably lower power. Further, samples can be atomised from a cheap paper-based microfluidic system, thus demonstrating the potential for direct interfacing with mass spectrometry following chemical synthesis. The microcentrifugation effect can also be exploited for particle manipulation and sorting. This is demonstrated for bioparticle concentration for rapid and sensitive pathogen detection or the separation of red blood cells from plasma for miniaturized diagnostic applications. In addition, it is also possible to separate two different particle species by size by exploiting the unique size-dependent scaling between the acoustic and drag forces acting on the particle.

A perspective on paper-based microfluidics: Current status and future trends.

"Paper-based microfluidics" or "lab on paper," as a burgeoning research field with its beginning in 2007, provides a novel system for fluid handling and fluid analysis for a variety of applications including health diagnostics, environmental monitoring as well as food quality testing. The reasons why paper becomes an attractive substrate for making microfluidic systems include: (1) it is a ubiquitous and extremely cheap cellulosic material; (2) it is compatible with many chemical/biochemical/medical applications; and (3) it transports liquids using capillary forces without the assistance of external forces. By building microfluidic channels on paper, liquid flow is confined within the channels, and therefore, liquid flow can be guided in a controlled manner. A variety of 2D and even 3D microfluidic channels have been created on paper, which are able to transport liquids in the predesigned pathways on paper. At the current stage of its development, paper-based microfluidic system is claimed to be low-cost, easy-to-use, disposable, and equipment-free, and therefore, is a rising technology particularly relevant to improving the healthcare and disease screening in the developing world, especially for those areas with no- or low-infrastructure and limited trained medical and health professionals. The research in paper-based microfluidics is experiencing a period of explosion; most published works have focused on: (1) inventing low-cost and simple fabrication techniques for paper-based microfluidic devices; and (2) exploring new applications of paper-based microfluidics by incorporating efficient detection methods. This paper aims to review both the fabrication techniques and applications of paper-based microfluidics reported to date. This paper also attempts to convey to the readers, from the authors' point of view the current limitations of paper-based microfluidics which require further research, and a few perspective directions this new analytical system may take in its development.