Mechanism Exploration of the Photoelectrochemical Immunoassay for the Integration of Radical Generation with Self-Quenching

Photoelectrochemical (PEC) sensing mechanisms based on enzyme-catalyzed strategies primarily achieve the quantitative analysis of biomolecules through the enhancement or attenuation of photocurrent signals. However, there are still no reports that delve into the principles of photocurrent signaling conversion in the reaction between photoactive materials and the biomolecules. In this work, we demonstrated that indium oxysulfide InOS-0.5 heterojunction has excellent peroxidase activity to catalyze the reaction of H₂O₂-generated hydroxyl radicals (^•OH) with the self-generated electrons, thereby resulting in synergistic quenching of the photocurrent signal. Based on the above principles, we coupled InOS-0.5 with a sandwich-type immunoassay to introduce H₂O₂ production catalyzed by glucose oxidase for the development of a PEC immunosensing platform. H₂O₂ reacted with InOS-0.5 to produce ^•OH with strong oxidizing properties, thus quenching the photogenerated electrons and realizing the PEC detection of the carcinoembryonic antigen (CEA, as a model analyte). The photocurrent intensity decreases with the logarithmic increase in CEA concentration (0.02-50 ng mL^-1), with a remarkable limit of detection of 8.9 pg mL^-1 (S/N = 3). This study further investigates the mechanism of hydrogen peroxide-induced photocurrent quenching, providing deeper insights into the mechanisms of electron-hole transport in hollow porous semiconductor materials and paving the way for the development of efficient PEC sensors.