Recognition-induced in situ plasmonic modulation of a near-infrared-responsive organic photoelectrochemical transistor for ultrasensitive detection of ampicillin.

Ampicillin (AMP) residues arising from widespread antibiotic use pose increasing concerns for food safety and environmental health, while their trace detection in complex matrices remains challenging. Here, we report a recognition-induced in situ plasmonic modulation strategy integrated with a near-infrared-responsive organic photoelectrochemical transistor (OPECT) for sensitive AMP detection. A Ni6MnO8/UCNPs-based photogate was employed as the near-infrared-responsive transduction interface. Target recognition regulated alkaline phosphatase-mediated generation of ascorbic acid (AA) from ascorbic acid phosphate, and the resulting AA served as an electron donor and reducing agent to promote charge separation and induce the in situ formation of Au NPs. The generated Au NPs modulated the optical absorption and interfacial charge-transfer behavior of the photogate, producing amplified channel-current responses through effective gate-voltage regulation. The proposed OPECT sensor achieved a detection limit of 0.029 pg mL-1 and satisfactory performance in complex food samples. This study provides a promising strategy for antibiotic residue monitoring in complex matrices.