Dye-sensitized NiO photocathode based on cyclometalated iridium(III) complex with enhanced photocurrent for photoelectrochemical immunoassay

This work reports a novel [(C6)2Ir(dcbpy)]+ complex-sensitized NiO photocathode system and its first application for cathodic photoelectrochemical (PEC) immunoassay. The photocathode system was fabricated by hydrothermal and electrodeposition of hierarchical microspheres NiO film on the ITO electrode, followed by grafting photosensitizer [(C6)2Ir(dcbpy)]+ complex (C6 = Coumarin-6, dcbpy = 2,2′-bipyridyl-4,4′-dicarboxylate) through the condensation reaction of the –COOH group and NiO, and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV−vis absorption spectra. The Ir(III) complex-sensitized NiO photocathode was demonstrated to possess favorable PEC characteristics with relatively strong, stable and reproducible PEC response under visible light illumination with dissolved oxygen in the electrolyte as electron acceptor. A possible mechanism for this sensitized system was speculated according to the value of HOMO and LUMO for [(C6)2Ir(dcbpy)]+. A simple PEC immunoassay based on the as-prepared photocathode system displayed high sensitivity as well as excellent selectivity for the determination of prostate-specific antigen (PSA). The present work demonstrated a promising future to iridium complex-sensitized NiO photocathode for PEC bioanalysis.