Directionally and Substantially Enhanced Photoelectrochemical Responses by Electrostatic Field of (De)protonated Targets

The ultrasensitive detection of toxic substances in aqueous environments is a critical challenge for environmental monitoring, public health, and sustainable water management. This research reports a hybridized mediation strategy using Au nanoparticles under WO₃ nanosheets to achieve a substantially synergistic enhancement in photoelectrochemical response for detecting herbicides through the combined effects of electrostatic fields and plasmonic near-fields. Beyond optical irradiation, applied potential and near-field effect from Au, another stimulus─a strong electrostatic field induced by the protonation/deprotonation states of herbicide molecules adsorbed on the electrode surface─further accelerates photogenerated carrier separation and transport, thereby suppressing rapid recombination of electron-hole pairs. The ultrahigh sensitivity primarily originates from this electrostatic field effect (25.9-fold enhancement), which significantly surpasses the enhancement by the plasmonic near-field (5.6-fold). This results in a significantly boosted photocurrent responses: deprotonated herbicides on a photoanode under positive potential and protonated herbicides on a photocathode under negative potential. This directionally responsive platform exhibits ultrahigh sensitivity (2.4 pM), excellent selectivity, and superior anti-interference capability across a wide detection range. Additionally, the surface adsorption kinetics of targets provides insights into optimizing electrode materials to mitigate surface accumulation in photocatalytic reactions, facilitating efficient solar-to-chemical energy conversion.