ZnO/Cu₂O heterojunction integrated fiber-optic biosensor for remote detection of cysteine

Indium tin oxide, semiconductor nanomaterial ZnO, and Cu₂O were first loaded on the surface of the optical fiber to form an optical fiber probe. Large-volume macroscopic spatial light is replaced by an optical fiber path, and remote light injection is implemented. Based on the optical fiber probe, a photoelectrochemical biosensor was constructed and remote detection of cysteine was realized. In this tiny device, the optical fiber probe not only acts as a working electrode to react with the analyte but also directs the light exactly where it is needed. Simultaneously, the electrochemical behavior of cysteine on the surface of the working electrode is dominated by diffusion-control, which provides strong support for quantitative detection. Then, under the bias potential of 0 V, the linear range of the fiber-optic-based cysteine biosensor was 0.01∼1 μM, the regression coefficient (R²) value was 0.9943. In spiked synthetic urine, the detection of cysteine was also realized by the integrated biosensor. Moreover, benefiting from the low optical fiber loss, the new structure also possesses a unique remote detection function. This work confirms that photoelectrochemical biosensors can be integrated via optical fibers and retain comparable sensing performance. Based on this property, different materials can also be loaded on the surface of the optical fiber for remote detection of other analytes. It is expected to facilitate the research on fiber-optic-based integrated biosensors and show application prospects in diverse fields such as biochemical analysis and disease diagnosis.