**3.1 Paper-based biosensors**

A promising method for efficiently and affordably identifying diseases is provided by paper-based analyzers. Due to their simplicity of use and interpretation, colorimetric paper-based biosensors in particular have promise for point-of-care testing (POCT). These biosensors can deliver improved colorimetric readings by adding nanomaterials thanks to special signal conversion techniques. Studies have examined the development, difficulties, and potential applications of colorimetric paper-based biosensors for pathogen detection. For the study of cortisol in sweat, a unique paperbased microfluidic device has been created. This device produces an immunosensor without the need for reagents by combining filter paper with magnetic beads. Capillary-driven flow is made possible by the microfluidic pattern, which was created using wax printing and laser cutting. Magnetic beads that have been functionalized with a monoclonal antibody enable the precise detection of cortisol. Folding the device allows for the measurement of cortisol levels in the range of 10–140 ng mL−1 by observing the competitive interaction between the target cortisol and tagged cortisol with acetylcholinesterase. A wireless connection module is placed with the device, creating a portable cortisol detection instrument. This paper-based device's dependability has been successfully tested on a volunteer while they were riding [39]. On a disposable paper substrate, a brand-new, low-cost sensor module has been created for the instantaneous detection of uric acid. The sensor uses a capacitive measurement technique and hexagonal ZnO rods on Cu interdigitated electrodes (IDEs). Based on capacitance measurements, the uric acid content is shown on an Arduino Mega Board with an LCD screen. With great sensitivity at lower concentrations, the device shows a linear relationship between uric acid concentration (0.1 mM to 1 mM) and capacitance. By providing early screening of uric acid in actual samples, this proofof-concept demonstrates the potential for clinical applications. A promising development is the creation of this affordable biosensor platform [40].
