Laser-etched grooves for rapid fluid delivery for a paper-based chemiresistive biosensor

The use of biological fluids in microfluidic paper-based analytical devices (μPADs): Recent advances, challenges and future perspectives

The use of microfluidic paper-based analytical devices (μPADs) for aiding medical diagnosis is a growing trend in the literature mainly due to their low cost, easy use, simple manufacturing, and great potential for application in low-resource settings. Many important biomarkers (proteins, ions, lipids, hormones, DNA, RNA, drugs, whole cells, and more) and biofluids are available for precise detection and diagnosis. We have reviewed the advances μPADs in medical diagnostics have achieved in the last few years, focusing on the most common human biofluids (whole blood/plasma, sweat, urine, tears, and saliva). The challenges of detecting specific biomarkers in each sample are discussed, along with innovative techniques that overcome such limitations. Finally, the difficulties of commercializing μPADs are considered, and future trends are presented, including wearable devices and integrating multiple steps in a single platform.

Development of the viscosity biosensor for the detection of DNase I based on the flow distance on the paper with DNA mucus

Deoxyribonuclease I (DNase I) is a biomarker which has important applications in various biological processes. Thus, it is highly important to develop a user-friendly method for the detection of DNase I. Here, we present a paper-based distance sensor for the rapid detection of DNase I based on changes in the viscosity of DNA mucus. The viscosity of DNA mucus varies with different concentrations of DNase I, showing different water flow lengths on the pH test papers, this makes the quantification of DNase I possible. This method has a wide linear range (0.01-10 U/mL), excellent sensitivity, remarkable specificity and excellent reproducibility. The detection limit reaches 0.003 U/mL. Additionally, it can be well applied to detection of DNase I inhibitors, assay of DNase I in human serum and quality evaluation of nucleic acid scavengers. In general, this study offers a brief, convenient, label-free, and economical method to construct paper-based distance sensors using DNA mucus, which is very promising in the detection of DNase I in various applications.

On-site screening method for bioavailability assessment of the organophosphorus pesticide, methyl parathion, and its primary metabolite in soils by paper strip biosensor

An important public concern worldwide is soil pollution caused by organophosphorus pesticides and their primary metabolites. To protect the public's health, screening these pollutants on-site and determining their soil bioavailability is important, but doing so is still challenging. This work improved the already-existing organophosphorus pesticide hydrolase (mpd) and transcriptional activator (pobR), and it first designed and constructed a novel biosensor (Escherichia coli BL21/pNP-LacZ) that can precisely detect methyl parathion (MP) and its primary metabolite p-nitrophenol with low background value. To create a paper strip biosensor, E. coli BL21/pNP-LacZ was fixed to filter paper using bio-gel alginate and sensitizer polymyxin B. According to the calibrations of the paper strip biosensor for soil extracts and standard curve, the color intensity of the paper strip biosensor collected by the mobile app may be used to compute the concentration of MP and p-nitrophenol. This method's detection limits were 5.41 µg/kg for p-nitrophenol and 9.57 µg/kg for MP. The detection of p-nitrophenol and MP in laboratory and field soil samples confirmed this procedure. Paper strip biosensor on-site allows for the semi-quantitative measurement of p-nitrophenol and MP levels in soils in a simple, inexpensive, and portable method.

Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

A Nitrocellulose Paper-Based Multi-Well Plate for Point-of-Care ELISA

Low-cost diagnostic tools for point-of-care immunoassays, such as the paper-based enzyme-linked immunoassay (ELISA), have become increasingly important, especially so in the recent COVID-19 pandemic. ELISA is the gold-standard antibody/antigen sensing method. This paper reports an easy-to-fabricate nitrocellulose (NC) paper plate, coupled with a desktop scanner for ELISA, which provides a higher protein immobilization efficiency than the conventional cellulose paper-based ELISA platforms. The experiments were performed using spiked samples for the direct ELISA of rabbit IgG with a limit of detection (LOD) of 1.016 μg/mL, in a measurement range of 10 ng/mL to 1 mg/mL, and for the sandwich ELISA of sperm protein (SP-10) with an LOD of 88.8 ng/mL, in a measurement range of 1 ng/mL to 100 μg/mL. The described fabrication method, based on laser-cutting, is a highly flexible one-step laser micromachining process, which enables the rapid production of low-cost NC paper-based multi-well plates with different sizes for the ELISA measurements.

Sustainable materials and COVID-19 detection biosensor: A brief review

COVID-19 is the current global problem. Billions of infected cases due to the pandemic cause an emergency requirement to contain the pandemic. A basic concept to manage the outbreak is an early diagnosis and prompt treatment. To diagnose COVID-19, the new biosensors become new interventions that are hopeful to help effective diagnosis. In clinical material science, the issues on materials of COVID-19 detection biosensor is very interesting. In this brief review, the authors summarize and discuss on sustainable materials and COVID-19 detection biosensor. The paper, cellulose and graphene - based materials are specifically focused and biosensors for RNA sensing, antigenic determination and immune response detection are covered in this short article.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.