Catalytic TiO2 with Self-Assembled Monolayer for Highly Sensitive, Selective, and Non-Invasive Monitoring of Sweat L-Cysteine

L-cysteine plays a significant role in numerous physiological processes in the human body health, and monitoring its level has important clinical implications. However, L-cysteine tests are limited to invasive blood drawing and a time-consuming laboratory process, which also fails to give real-time and continuous results. This study introduces a flexible electrochemical sensor based on a self-assembled monolayer (SAM) of 3-mercaptopropyltrimethoxysilane (MPTS) molecular receptor and catalytic titanium oxide-modified carbon cloth (MPTS/TiO 2 /CC). The MPTS and TiO 2 modification serve as the artificial antibody through thiol interactions and the charge transfer layer, respectively, which is further confirmed by density function theory (DFT) calculations. The flexible L-cysteine sensor based on MPTS/TiO 2 /CC shows a wide linear range of up to 500 µ m and an ultra-low limit of detection of 0.046 µ m . A sweat patch consisting of an electrochemical sensing unit, a laser-fabricated microfluidic channel, and a miniaturized electrochemical workstation affords real-time monitoring of L-cysteine detection in dynamic environments and reveals the strong correlation between sweat and blood L-cysteine concentrations. The introduction of molecular receptors and band alignment may offer a general way of designing sensitive, specific electrochemical sensors for point-of-care diagnosis.