Electron–Ion Coupling for Nanostructured Photocathode in Ion-Assisted Photoelectrochemical Microfluidic Biosensing Platform

and CuO exhibits broad visible-light absorption and an adjustable photogenerated carrier separation potential. Based on this, we demonstrate that rapid ion adsorption in copper hexacyanoferrate (CuFe HCF)-modified cathode materials in the liquid phase can significantly enhance electron coupling efficiency. Precise modulation of the electron-ion receptor characteristics of the cathode materials enables targeted optimization of the coupling process, thereby improving the separation and transport efficiency of photogenerated charge carriers in the ion-assisted photoelectrochemical (IAPEC) system for the target recognition response. Furthermore, the incorporation of a microfluidic system physically isolates the automatic sampling recognition zone from the photoelectrochemical detection zone, fully exposing the active sites of the photoelectrochemical cathode material for detection. The IAPEC biosensing achieves highly efficient detection of the marine pollutant okadaic acid toxin, featuring a low detection limit of 23.1 pg/mL and a broad linear range of 0.1-200 ng/mL. This dual-engineering strategy not only overcomes the long-standing limitations of standard PEC systems but also establishes a foundational framework for designing efficient biosensors for marine environmental monitoring.