Photoinduced Electron Transfer Modulation: Toward a Visible-Light-Responsive Photoelectrochemical Platform for Formaldehyde Sensing

Photoelectrochemical (PEC) biosensing has experienced a notable surge in recent years, while the introduction of plasmonic metal precursors with specific recognition functions into the detection interface remains a nascent area of study. Here, a thermally treated zeolitic imidazolate framework-8 (ZIF-8) decorated with zinc oxide nanorods, incorporating silver ions (Ag⁺@ZnO/ZIF-8-T), is constructed for the PEC detection of formaldehyde (HCHO) in biological systems. The ZnO/ZIF-8-T photoanode exhibits an unprecedented ability to harvest visible light, with significantly enhanced photoelectric signals compared to its ZnO and ZnO@ZIF-8 counterparts. Upon exposure to HCHO analytes, the incorporated Ag⁺ ions are <i>in situ</i> transformed into plasmonic Ag nanoparticles sensitized on the ZnO/ZIF-8-T surface, modulating the photoinduced electron injection as revealed by <i>operando</i> transient photovoltage spectroscopy. The proposed PEC platform demonstrates rapid, exclusive, and sensitive HCHO detection with a detection limit of 50 nmol·L^-1. This work introduces a new strategy of employing plasmonic metal ions as recognition nodes to couple analyte specificity with photoinduced charge-transfer modulation, opening new avenues for the design of advanced PEC biosensors.