Advanced Signal-Amplification Strategies for Paper-Based Analytical Devices: A Comprehensive Review

Exploring the diagnostic landscape: Portable aptasensors in point-of-care testing

Aptamers, discovered in the 1990s, have marked a significant milestone in the fields of therapeutics and diagnostics. This review provides a comprehensive survey of aptamers, focusing on their diagnostic applications. It especially encapsulates a decade of aptamer, encompassing research, patents, and market trends. The unique properties and inherent stability of aptamers are discussed, highlighting their potential for various clinical applications. It goes on to introduce biosensor design, emphasizing the advantages of aptamers over antibodies as conventional molecular recognition interface. The operation and design of aptasensors are examined, with a focus on single- and dual-site binding configurations and their respective recognition modes. Paper-based sensors are highlighted as cost-effective, user-friendly alternatives that are gaining widespread adoption, particularly in point-of-care platforms.

Ag-coated Au nanostar-based Lateral Flow Immunoassay for Highly Sensitive Influenza A virus antibody Detection in Colorimetric and Surface-Enhanced Raman Scattering (SERS) modes

Antibody testing for virus aids diagnosis, promotes vaccination and development, and evaluates antibody treatment efficacy. Hence, it is essential to examine and monitor antibody levels for accurate disease diagnosis and prevention. Lateral Flow Immunoassay (LFIA) is a technique that is known for its simplicity and speed, making it a popular choice for immediate detection. Noble metal nanoparticles are extensively employed in LFIA due to their exceptional colorimetric and Raman properties, which are a result of the LSPR effect. Au nanostars (Au NSs) have excellent SERS properties due to multiple sharp branches and more "hot spots" on the surface, while Ag nanoparticles (Ag NPs) have higher extinction coefficient and better refractive index sensitivity. The electromagnetic field strength on the surface of Ag-Au bimetallic nanomaterial is greatly enhanced, which further enhances the SERS intensity. In this work, we created a core-shell nanoparticle by combining Au NS as the core and Ag as the shell (Au NSMBA@Ag). We then inserted a Raman reporter molecule between the core and shell. Using this, we developed an LFIA platform that can detect influenza A virus antibodies in both colorimetric and Raman modes. The detection limit in colorimetric mode was 0.1 ng/mL, while in Raman mode it was 8.0 pg/mL, making it approximately 12 times more sensitive than the colorimetric mode. Furthermore, the method has shown excellent specificity, stability, and resistance to interference. Hence, this method can be applied to various fields such as environmental monitoring, clinical diagnosis, and food safety, showing great potential for future applications.

Multi-dimensional microfluidic paper-based analytical devices (μPADs) for noninvasive testing: A review of structural design and applications

The rapid emergence of microfluidic paper-based devices as point-of-care testing (POCT) tools for early disease diagnosis and health monitoring, particularly in resource-limited areas, holds immense potential for enhancing healthcare accessibility. Leveraging the numerous advantages of paper, such as capillary-driven flow, porous structure, hydrophilic functional groups, biodegradability, cost-effectiveness, and flexibility, it has become a pivotal choice for microfluidic substrates. The repertoire of microfluidic paper-based devices includes one-dimensional lateral flow assays (1D LFAs), two-dimensional microfluidic paper-based analytical devices (2D μPADs), and three-dimensional (3D) μPADs. In this comprehensive review, we provide and examine crucial information related to paper substrates, design strategies, and detection methods in multi-dimensional microfluidic paper-based devices. We also investigate potential applications of microfluidic paper-based devices for detecting viruses, metabolites and hormones in non-invasive samples such as human saliva, sweat and urine. Additionally, we delve into capillary-driven flow alternative theoretical models of fluids within the paper to provide guidance. Finally, we critically examine the potential for future developments and address challenges for multi-dimensional microfluidic paper-based devices in advancing noninvasive early diagnosis and health monitoring. This article showcases their transformative impact on healthcare, paving the way for enhanced medical services worldwide.

Tuning Hydrophobicity of Paper Substrates for Effective Colorimetric detection of Glucose and Nucleic acids

This study investigated the colorimetric response of standard glucose, serum glucose, and nucleic acid assays on various paper surfaces with different wettability, including hydrophilic, hydrophobic, and nearly superhydrophobic surfaces. Water contact angles (WCA) formed by water droplets on each surface were measured using ImageJ software. The hydrophilic surface showed no contact angle, while the hydrophobic and nearly superhydrophobic surfaces exhibited contact angles of 115.667° and 133.933°, respectively. The colorimetric sensitivity of the standard glucose assay was analyzed on these surfaces, revealing enhanced sensitivity on the nearly superhydrophobic surface due to the high molecular crowding effect owing to its non-wetting behavior and eventually confined reaction product at the sample loading zone. The hydrophobic nature of the surface restricts the spreading and diffusion of the reaction product, leading to a controlled and localized concentration of the assay product leading to moderate colorimetric intensity. On the other hand, the hydrophilic surface showed the least enhancement in colorimetric sensitivity; this is attributed to the high wettability of the hydrophilic surface causing the reaction product to spread extensively, resulting in a larger area of dispersion and consequently a lower colorimetric intensity. The measured limit of detection (LOD) for nucleic acid on nearly superhydrophobic surfaces was found to be 16.15 ng/µL, which was almost four-fold lower than on hydrophilic surfaces (60.08 ng/µL). Additionally, the LODs of standard glucose and clinical serum samples were two-fold lower on nearly superhydrophobic surfaces compared to hydrophilic surfaces. Our findings clearly highlight the promising potential of utilizing superhydrophobic surfaces to significantly enhance colorimetric sensitivity in paper-based diagnostic applications. This innovative approach holds promise for advancing point-of-care diagnostics and improving disease detection in resource-limited settings.

Fluorescence-Based Portable Assays for Detection of Biological and Chemical Analytes

Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.

Paper-based analytical device coupled with Bi-MOF: Electric field amplification and fluorescence sensing of glyphosate

Glyphosate, a potent herbicide wildly used in the world, involves potential hazards to human health by accumulating in the food chain. Due to its absence of chromophores and fluorophores, the rapid visual detection of glyphosate has always been difficult. Herein, a paper-based geometric field amplification device visualized by the amino-functionalized bismuth-based metal-organic framework (NH₂-Bi-MOF) was constructed for sensitive fluorescence determination of glyphosate. Fluorescence of the synthesized NH₂-Bi-MOF was immediately enhanced by interaction with glyphosate. The field amplification of glyphosate was implemented by coordinating the electric field and the electroosmotic flow, which was orchestrated by the geometric configuration of paper channel and the concentration of polyvinyl pyrrolidone, respectively. Under the optimal conditions, the developed method exhibited a linear range of 0.80-200 μmol L^-1 with about 12500-fold signal enhancement achieved by just 100 s electric field amplification. It was applied to soil and water with recoveries between 95.7% and 105.6%, holding great prospects in on-site analysis of hazardous anions for environment safety.

A Plasmonic Fluor-Lightened Microneedle Array Enables Ultrasensitive Multitarget Whole Blood Diagnosis of Anemia in A Paper Origami-Based Device

This work reports a portable, origami-type paper device with a plasmonic fluor-labeled microneedle sensing module for the multiplexed quantification of anemia biomarkers in whole blood. Sequential steps, including serum separation, target enrichment, and multiplexed readout by a gel imager, are rapidly accomplished with the flexible and highly integrated device. The microneedle array enabled efficient sampling of trace targets from ng mL^-1 to pg mL^-1 level. Combined with the plasmonic fluor label, the signal is improved by ≈7.6 folds compared with the flat substrate-based assay. The device is applied to simultaneously quantify hemoglobin (Hb), ferritin, folic acid (FA), and vitamin B₁₂ (VB₁₂ ), which are four anemia biomarkers distributed in different environments with different concentration ranges. Featured by the small sample volume (150 µL), short assay time (20 min), low cost (2 $), robust stability, and user-friendliness, the device is promising for the rapid and accurate diagnosis of anemia in real practice.

Research progress on detection techniques for point-of-care testing of foodborne pathogens

The global burden of foodborne disease is enormous and foodborne pathogens are the leading cause of human illnesses. The detection of foodborne pathogenic bacteria has become a research hotspot in recent years. Rapid detection methods based on immunoassay, molecular biology, microfluidic chip, metabolism, biosensor, and mass spectrometry have developed rapidly and become the main methods for the detection of foodborne pathogens. This study reviewed a variety of rapid detection methods in recent years. The research advances are introduced based on the above technical methods for the rapid detection of foodborne pathogenic bacteria. The study also discusses the limitations of existing methods and their advantages and future development direction, to form an overall understanding of the detection methods, and for point-of-care testing (POCT) applications to accurately and rapidly diagnose and control diseases.

Microfluidic Paper-based Device for Medicinal Diagnosis

BACKGROUND

The demand for point-of-care testing (POCT) devices has rapidly grown since they offer immediate test results with ease of use, makingthem suitable for home self-testing patients and caretakers. However, the POCT development has faced the challenges of increased cost and limited resources. Therefore, the paper substrate as a low-cost material has been employed to develop a cost-effective POCT device, known as "Microfluidic paper-based analytical devices (μPADs)". This device is gaining attention as a promising tool for medicinal diagnostic applications owing to its unique features of simple fabrication, low cost, enabling manipulation flow (capillarydriven flow), the ability to store reagents, and accommodating multistep assay requirements.

OBJECTIVE

This review comprehensively examines the fabrication methods and device designs (2D/3D configuration) and their advantages and disadvantages, focusing on updated μPADs applications for motif identification.

METHODS

The evolution of paper-based devices, starting from the traditional devices of dipstick and lateral flow assay (LFA) with μPADs, has been described. Patterned structure fabrication of each technique has been compared among the equipment used, benefits, and drawbacks. Microfluidic device designs, including 2D and 3D configurations, have been introduced as well as their modifications. Various designs of μPADs have been integrated with many powerful detection methods such as colorimetry, electrochemistry, fluorescence, chemiluminescence, electrochemiluminescence, and SER-based sensors for medicinal diagnosis applications.

CONCLUSION

The μPADs potential to deal with commercialization in terms of the state-of-the-art of μPADs in medicinal diagnosis has been discussed. A great prototype, which is currently in a reallife application breakthrough, has been updated.