Paper-based Flexible Devices for Energy Harvesting, Conversion and Storage Applications: A Review

A paper-based microfluidic sensor array combining molecular imprinting technology and carbon quantum dots for the discrimination of nitrophenol isomers.

Microfluidic paper-based analytical devices (microPADs) are emerging as simple-to-use, low-cost point-of-care testing platforms. Such devices are mostly fabricated at present by creating hydrophobic barriers using wax or photoresist patterning on porous paper sheets. Even though devices fabricated using these methods are used and tested with a wide variety of analytes, still they pose many serious practical limitations for low-cost automated mass fabrication for their widespread applicability. We present an affordable and simple two-step process - cut and heat (CH-microPADs) - for the selective fabrication of hydrophilic channels and reservoirs on a wide variety of porous media such as tissue/printing/filter paper and cloth types, such as cotton and polyester, by a lamination process. The technique presents many advantages as compared to existing commonly used methods. The devices possess excellent mechanical strength against bending, folding and twisting, making them virtually unbreakable. They are structurally flexible and show good chemical resistance to various solvents, acids and bases, presenting widespread applicability in areas such as clinical diagnostics, biological sensing applications, food processing, and the chemical industry. Fabricated paper media 96 well-plate CH-microPAD configurations were tested for cell culture applications using mice embryonic fibroblasts and detection of proteins and enzymes using ELISA. With a simple two-step process and minimal human intervention, the technique presents a promising step towards mass fabrication of inexpensive disposable diagnostic devices for both resource-limited and developed regions.

Rapid and inexpensive process to fabricate paper based microfluidic devices using a cut and heat plastic lamination process.

The focus on precise medicine enhances the need for timely diagnosis and frequent monitoring of chronic diseases. Moreover, the recent pandemic of severe acute respiratory syndrome coronavirus 2 poses a great demand for rapid detection and surveillance of viral infections. The detection of protein biomarkers and antigens in the saliva allows rapid identification of diseases or disease changes in scenarios where and when the test response at the point of care is mandated. While traditional methods of protein testing fail to provide the desired fast results, electrochemical biosensors based on nanomaterials hold perfect characteristics for the detection of biomarkers in point‐of‐care settings. The recent advances in electrochemical sensors for salivary protein detection are critically reviewed in this work, with emphasis on the role of nanomaterials to boost the biosensor analytical performance and increase the reliability of the test in human saliva samples. Furthermore, this work identifies the critical factors for further modernization of the nanomaterial‐based electrochemical sensors, envisaging the development and implementation of next‐generation sample‐in‐answer‐out systems.

Advances in Electrochemical Biosensors Based on Nanomaterials for Protein Biomarker Detection in Saliva

Mycotoxins are secondary metabolic products of fungi. They are poisonous, carcinogenic, and mutagenic in nature and pose a serious health threat to both humans and animals, causing severe illnesses and even death. Rapid, simple and low-cost methods of detection of mycotoxins are of immense importance and in great demand in the food and beverage industry, as well as in agriculture and environmental monitoring, and, for this purpose, lateral flow immunochromatographic strips (ICSTs) have been widely used in food safety and environmental monitoring. The literature to date describing the development of ICSTs for the detection of different types of mycotoxins using different nanomaterials, nanoparticle size, and replicates was reviewed in an attempt to identify the most important determinants of the limit of detection (LOD). It is found that the particle size and type of materials contribute significantly to determining the LOD. The nanoparticle sizes used in most studies have been in the range 15–45 nm and gold nanoparticle-based ICSTs have been shown to exhibit the lowest LOD. Perspectives for potential future development to reduce the LODs of ICSTs are also discussed.

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Limits of Detection of Mycotoxins by Laminar Flow Strips: A Review

Paper-based microfluidic analytical devices (μPADs) have shown great potential in the field of analysis due to their advantages of rapid analysis, environmental friendliness and the ability to realize the flow of fluid without external power. Saliva is an emerging biofluid which is used in diseases diagnostic and screening for the easy collection and the reflection of the physiological state. This review focuses on the fabrication methods for two-dimensional (2D) and three-dimensional (3D) μPADs and their applications on the saliva analysis. In the first part, the flow mechanism in μPADs is discussed. The second part mainly introduces the fabrication methods for the μPADs and compares the different methods. The third part presents the application of μPADs in the detection of biomarkers such as nitrite, glucose, and thiocyanate in saliva. Finally, the research directions of saliva analysis are discussed in the conclusion. There have been a lot of researches on μPADs, but the fabrication methods and applications need to be further studied to meet the commercial needs.

Hongyu Chen

Papers

Fabrication for paper-based microfluidic analytical devices and saliva analysis application