Photoelectrochemical　(PEC)　sensing　has　been　rapidly　evolvinginrecent　years,　while　the　introduction　of　small　molecules　with　specificrecognition　functions　into　the　sensing　interface　remains　a　nascentarea　of　study.　In　this　work,　we　reported　a　PEC　biosensor　for　formaldehyde(FA)　detection　based　on　photoinduced　electron　transfer　(PET)-gatedelectron　injection　between　organic　small　molecules　and　inorganic　semiconductingsubstrates.　Specifically,　an　FA-responsive　probe　(NA-FA-COOH)　andTiO(2)　nanoarrays　were　integrated　to　construct　a　PEC　platform(NFC/TiO2)　via　a　coordination　bond.　NFC　served　simultaneouslyas　a　target-specific　recognition　element　and　a　modulator　of　photoinducedelectron　injection.　Treatment　of　NFC/TiO2　by　FA　would　suppressthe　intramolecular　PET　process,　with　the　quenched　photocurrent　signaldue　to　the　changed　carrier　transfer　pathway,　thus　establishing　thePEC　platform　for　FA　based　on　effective　PET　modulation.　The　proposedPEC　system　exhibited　high　selectivity　and　sensitivity,　with　a　lowdetection　limit　of　0.071　mu　M.　This　study　presents　a　novel　perspectiveon　the　use　of　organic　small　molecules　with　a　PET　effect　for　advancedPEC　bioanalysis.