Reusable Self-Powered Electrochromic Sensor Patch Based on Enzymatic Biofuel Cells for On-Site Visualized Monitoring of Lactic Acid

Wearable sensors have broad application potential in motion assessment, health monitoring, and medical diagnosis. However, relying on a specialized instrument for power supply and signal reading makes sensors unsuitable for on-site detection. To solve this problem, a reusable self-powered electrochromic sensor patch based on enzymatic biofuel cells were constructed to realize the on-site visualized monitoring. In this design, hydrophilic agarose hydrogel and SiO₂ hydrophobic film were used to control the collection and elimination of sweat. Lactic acid (LA) served not only as a model analyte, but also as a fuel to convert chemical energy into electrical energy. The generated electrons further reduced the Prussian blue (PB) to Prussian white (PW), accompanied by visible color changes. It could achieve semiquantitative detection by reading color changes with the naked eye or quantitative detection by the output blue value and current signals. In order to reduce costs, the PB color was restored by applying voltage, causing the electrode to change from a faded state to a blue colored state again, thus, achieving the repeated use of the sensor patch. This work established a proof-of-concept for the design of a reusable self-powered electrochromic sensor patch that could provide innovative inspiration for the formation of a general visualized wearable patch.