Promoted Directional Electron Transfer in Pt-Decorated TiO 2 /Fluorinated Organic Covalent Frameworks for Self-Powered Photoelectrochemical Biosensing

Developing photoactive materials with promoted charge separation and interfacial electron transfer represents an effective avenue for enhancing the performance of self-powered photoelectrochemical biosensors (SPECs). In this work, a TiO 2 /fluorinated covalent organic framework (FCOF) decorated with Pt nanoparticles (TiO 2 /FCOF/Pt) has been developed as photocathode material for SPECs, in which a target-induced dual steric hindrance effect is also integrated as a sensing mechanism. Due to the hot-electron effect, the Pt nanoparticles act as electron sinks for the formation of a directional electron transfer pathway (TiO 2 →FCOF→Pt), which suppresses the electron–hole recombination and thus improves the photoresponsive ability of TiO 2 /FCOF/Pt photocathode. When using CYFRA21-1 as a target analyte, Fe 3 O 4 nanospheres can be immobilized onto the TiO 2 /FCOF/Pt photocathode via sandwich immunoreactions, yielding a steric effect. Meanwhile, the Fe 3 O 4 nanospheres can also mimic peroxidase-like activity and mediate the precipitation reaction, further magnifying the steric hindrance and attenuation in the open circuit voltage of SPECs. Benefiting from the excellent photoresponsive ability and the dual steric hindrance effect, this developed SPECs has realized the analysis of CYFRA21-1 with satisfactory results. This work not only provides a promising tool for the clinical analysis of lung cancer but also offers an effective strategy to improve the directional electron transfer in heterojunction photosystems.