Flexible Biosensors Based on Colorimetry, Fluorescence, and Electrochemistry for Point-of-Care Testing

Abstract

With the outbreak and pandemic of COVID-19, point-of-care testing (POCT) systems have been attracted much attention due to their significant advantages of small batches of samples, user-friendliness, easy-to-use and simple detection. Among them, flexible biosensors show practical significance as their outstanding properties in terms of flexibility, portability, and high efficiency, which provide great convenience for users. To construct highly functional flexible biosensors, abundant kinds of polymers substrates have been modified with sufficient properties to address certain needs. Paper-based biosensors gain considerable attention as well, owing to their foldability, lightweight and adaptability. The other important flexible biosensor employs textiles as substrate materials, which has a promising prospect in the area of intelligent wearable devices. In this feature article, we performed a comprehensive review about the applications of flexible biosensors based on the classification of substrate materials (polymers, paper and textiles), and illustrated the strategies to design effective and artificial sensing platforms, including colorimetry, fluorescence, and electrochemistry. It is demonstrated that flexible biosensors play a prominent role in medical diagnosis, prognosis, and healthcare.

Keywords: flexible biosensor; paper; point-of-care testing; polymer; textile.

FIGURE 1

Schematic diagram of flexible biosensors based on colorimetry, fluorescence, and electrochemistry for point-of-care testing.

FIGURE 2

Biosensors based on polymer substrates. (A) The microfluidic substrate manufactured by PDMS consists of four layers that facilitate the flow of sweat from the skin surface to the top layer containing five assay chambers with pre-embedded colorimetric reagents (Xiao et al., 2019). (B) Exploded view of the complete PDMS-based hybrid battery-free platform (Bandodkar et al., 2019). (C) Electrodes printed on PET flexible substrates, contains working, counter and reference electrodes (Shaikh et al., 2019).

FIGURE 3

Biosensors based on paper and textile substrates. (A) Schematic diagram of a fluorescent paper strip integrated with a portable smartphone platform for monitoring glutathione in human serum (Chu et al., 2020). (B) Specially designed universal paper-based electrochemical sensor (Liu et al., 2019b). (C) Schematic diagram of a zinc oxide nanorod electrochemical sensing electrode integrated with flexible carbon fibers for sweat cortisol detection (Madhu et al., 2020).