Fabrication of a gel particle array in a microfluidic device for bioassays of protein and glucose in human urine samples

Unveiling the state of the art: a systematic review and meta-analysis of paper-based microfluidic devices

Introduction

This systematic review and meta-analysis present a comprehensive evaluation of paper-based microfluidic devices, focusing on their applications in immunoassays. These devices are emerging as innovative solutions to democratize access to diagnostic technologies, especially in resource-limited settings. Our review consolidates findings from diverse studies to outline advancements in paper-based microfluidic technology, including design intricacies and operational efficacy. Key advantages such as low cost, portability, and ease of use are highlighted.

Materials and Methods

The review categorizes literature based on the design and operational nuances of these diagnostic tools, exploring various methodologies, fabrication techniques, detection methods, and applications, particularly in protein science. The meta-analysis extends to the diverse applications of these technologies, providing a framework for classifying and stratifying their uses in diagnostics.

Results and discussion

Notable findings include a critical analysis of performance metrics, such as sensitivity and specificity. The review addresses challenges, including the need for further validation and optimization for broader clinical applications. A critical discussion on the validation processes, including cross-validation and rigorous control testing, is provided to ensure the robustness of microfluidic devices. This study offers novel insights into the computational strategies underpinning these technologies and serves as a comprehensive roadmap for future research, potentially broadening the impact across the protein science universe.

Point-of-care testing for lysine concentration in swine serum via blue-emissive carbon dot-entrapped microfluidic chip

Lysine is one of the essential amino acids and plays a vital role in the growth, development and health of pigs. Blood lysine concentration is a direct indication of lysine status; however, current methods can not satisfy the demands for rapid and on-site lysine concentration measurement of swine serum. Here, we developed blue-emissive nitrogen-doped carbon dots as a fluorescence probe for the determination of lysine with high fluorescence quantum yield, stability, sensitivity and specificity. The carbon dots were entrapped within hydrogel microstructures to fabricate microfluidic chips for rapid assay for lysine quantification. We further developed an imaging attachment to integrate the microfluidic chip and a smartphone into a portable point-of-care testing platform. This platform requires only 3 μL sample and has a linear detection range of 25 to 300 μmol/L with a limit of detection less than 16 μmol/L, which covers the normal range of lysine concentration in swine serum. We tested lysine concentration in swine serum using this platform with high accuracy, low sample consumption, and within 3 min. Together, these results may provide a rapid and portable platform for dynamic monitoring of swine lysine status and contribute to precise feed formula modulation with low-protein diet strategy.

Hydrogel Paper-Based Analytical Devices: Separation-Free In Situ Assay of Small-Molecule Targets in Whole Blood

While colorimetric-based assays are very convenient to determine biomarkers in point-of-care testing (POCT), they often suffer from pretreatment procedures for separation of plasma or serum from whole blood samples. Here, we report a simple colorimetric paper-based analytical device (c-PAD) that is capable of performing sample-to-answer analysis by directly dropping the whole blood sample on paper. This is accomplished by utilizing sodium alginate hydrogel, which exhibits a nanometer-scale porous structure to effectively prevent the passage of large red blood cells and hemoglobin molecules, to encapsulate enzymes and chromogenic reagents. As the small targets in the blood sample enter the sensing region to trigger a chromogenic reaction, the resulting color signal is recorded by a smartphone. The interference from the red blood to the color signal can be completely avoided without the requirement of any separation process. The analytical performance of the method is evaluated by assaying glucose in real blood samples. The results show that rapid and accurate analysis can be achieved with the limit of detection as low as 0.12 mM. In addition, simultaneous detection of different targets (glucose, cholesterol, and triglycerides) in whole blood can be achieved by fabricating c-PAD with multiple sensing regions. Owing to its several essential advantages including an extremely simple procedure for fabrication, sample-to-answer analysis without tedious pretreatment, and capability to perform high-throughput analysis, the proposed c-PAD will be of great value in POCT applications of whole blood samples.

Three-Dimensional Paper-Based Microfluidic Analysis Device for Simultaneous Detection of Multiple Biomarkers with a Smartphone

Paper-based microfluidic analysis devices (μPADs) have attracted attention as a cost-effective platform for point-of-care testing (POCT), food safety, and environmental monitoring. Recently, three-dimensional (3D)-μPADs have been developed to improve the performance of μPADs. For accurate diagnosis of diseases, however, 3D-μPADs need to be developed to simultaneously detect multiple biomarkers. Here, we report a 3D-μPADs platform for the detection of multiple biomarkers that can be analyzed and diagnosed with a smartphone. The 3D-μPADs were fabricated using a 3D digital light processing printer and consisted of a sample reservoir (300 µL) connected to 24 detection zones (of 4 mm in diameter) through eight microchannels (of 2 mm in width). With the smartphone application, eight different biomarkers related to various diseases were detectable in concentrations ranging from normal to abnormal conditions: glucose (0–20 mmol/L), cholesterol (0–10 mmol/L), albumin (0–7 g/dL), alkaline phosphatase (0–800 U/L), creatinine (0–500 µmol/L), aspartate aminotransferase (0–800 U/L), alanine aminotransferase (0–1000 U/L), and urea nitrogen (0–7.2 mmol/L). These results suggest that 3D-µPADs can be used as a POCT platform for simultaneous detection of multiple biomarkers.

Single-step design of hydrogel-based microfluidic assays for rapid diagnostics

For the first time we demonstrate a microfluidic platform for the preparation of biosensing hydrogels by in situ polymerization of polyethyleneglycol diacrylate (PEG-DA) in a single step. Capillary pressure barriers enable the precise formation of gel microstructures for fast molecule diffusion. Parallel arrangement of these finger structures allows for macroscopic and standard equipment readout methods. The analyte automatically fills the space in between the gel fingers by the hydrophilic nature of the gel. Introducing the functional structures in the chip fabrication allows for rapid assay customization by making surface treatment, gel curing mask alignment and washing steps obsolete. Simple handling and functionality are illustrated by assays for matrix metalloproteinase, an important factor in chronic wound healing. Assays for total protein concentration and cell counts are presented, demonstrating the possibilities for a wide range of fast and simple diagnostics.