NIR-induced label-free subcutaneous PEC biosensor UC@Cu2O@TiO2 for detection of L-cysteine
Conventional photoelectrochemical (PEC) biosensors based on ZnO and TiO2 face challenges in applications in vivo due to the poor penetration of excitation light through the skin. To address this limitation, we designed a novel near-infrared (NIR)-driven FTO@UC@Cu2O@TiO2 heterojunction biosensor for subcutaneous L-cysteine detection. NIR light penetrates the skin and excites the upconversion material (called UC for short, NaYF4:Er, Yb), which emits visible light at 540 nm. This emission activates the Cu2O semiconductor to generate photocurrent. The Cu2O@TiO2 heterojunction facilitates charge carrier separation and suppresses electron-hole recombination. The biosensor demonstrates stable, sensitive, and reproducible detection of L-cysteine over a range of 10 μM to 10 pM, with a detection limit of 5.2 pM. Notably, it also enables subcutaneous detection covering a range from 10 μM to 100 pM, with a detection limit of 74 pM. These results provide a promising strategy for real-time in situ monitoring of L-cysteine in clinical applications.
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