Bismuth sulfide (Bi2S3) is considered an attractive photo-active material due to its improved photo-electric conversion efficiency, but its instability caused by photocorrosion restricts its potential application for photoelectrochemical (PEC) sensors. Here, carbon-coated Bi2S3 nanorods (Bi2S3@C NRs) with a highly sufficient and stable photocurrent response were prepared via a simple solvothermal method, and served as a novel photoactive material. A label-free PEC aptasensor based on Bi2S3@C NRs was constructed for the highly sensitive and selective detection of ampicillin (AMP) using an aptamer as the biorecognition element. When the target AMP molecules were captured by the aptamers, the formed aptamer–protein complex with poor electron conductivity prevented electron transfer, and resulted in a decrease in photocurrent. Under the optimal conditions, the developed PEC aptasensor possessed an excellent linear range (0.1–5.0 pg mL−1) with a low detection limit of 50.1 fg mL−1. This work not only provides a new avenue for the design of efficient photoactive materials, but also expands the application of PEC sensors in the field of environmental analysis.
