Catalytic TiO ₂ with Self‐Assembled Monolayer for Highly Sensitive, Selective, and Non‐Invasive Monitoring of Sweat L‐Cysteine

Abstract 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.