Metal-bridged self-assembly of recognition-functionalized MCOFs for ultrasensitive photoelectrochemical sensing of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA), a persistent environmental pollutant with severe health risks, demands ultrasensitive detection technologies. Herein, we report a novel label-free photoelectrochemical (PEC) sensor for PFOA based on a metal-bridged self-assembly strategy using nickel-coordinated covalent organic frameworks (Ni-TAPT-Bpy-COF). The Ni(II) centers serve as anchoring points to directionally immobilize perfluorodecanethiol (PFDT) via Ni S bonds, creating a hydrophobic recognition interface. Density functional theory (DFT) calculations reveal that PFDT selectively captures PFOA through fluorine‑fluorine interactions and hydrogen bonding, adopting a head-to-tail staggered conformation that exposes the carboxyl group towards the electrode surface. This orientation impedes electron donor (dopamine) diffusion, enabling PFOA quantification via photocurrent attenuation. To enhance photoelectric conversion, a staggered heterojunction is constructed by integrating nitrogen-doped graphdiyne (N-GDY) with metal-covalent organic frameworks (MCOF), significantly accelerating electron transfer and suppressing carrier recombination. The sensor achieves an ultralow detection limit of 0.031 nM, with high selectivity against structural analogs and inorganic ions. Successful application in tap/lake water samples validates its practicality for on-site monitoring of trace PFOA in complex matrices.