Ultrasensitive cathode photoelectrochemical immunoassay based on TiO2 photoanode-enhanced 3D Cu2O nanowire array photocathode and signal amplification by biocatalytic precipitation

Highlights: • A promising new cathode photoelectrochemical immunoassay was developed. • TiO₂ photoanode-enhanced 3D Cu₂O nanowire array photocathode could evidently enhance photocurrent response. • Horseradish peroxidase-induced biocatalytic precipitation could remarkably decrease photocurrent detection signal. • This cathode photoelectrochemical protocol exhibited both good anti-interference capability and ultrahigh sensitivity. - Abstract: Cathode photoelectrochemical immunoassay usually shows better anti-interference capacity toward real samples than anode photoelectrochemical immunoassay. However, its poor photocurrent response has greatly restricted the detection sensitivity. Herein, a promising ultrasensitive cathode photoelectrochemical immunoassay was developed based on TiO₂ photoanode-enhanced 3D Cu₂O nanowire array (NWA) photocathode, and coupled with signal amplification by horseradish peroxidase (HRP)-induced biocatalytic precipitation (BCP). Carcinoembryonic antigen (CEA, Ag) was used as a detection model, TiO₂ nanoparticle-modified indium tin oxide (ITO) electrode served as the photoanode, and Cu₂O NWAs grown in situ on Cu mesh was both the photocathode and photoelectrochemical matrix to immobilize the capture CEA antibodies (Ab₁). The signal CEA antibodies (Ab₂) were labeled with HRP to form Ab₂-HRP bioconjugates, and employed as signal amplifiers when the specific immunoreaction occurred. The developed photoanode-enhanced cathode photoelectrochemical immunoassay has good anti-interference capability, outstanding photocurrent response, and high sensitivity for target Ag detection, which was attributed to the synergistic effects of the 3D nanostructure of Cu₂O NWA photocathode, the introduction of TiO₂ photoanode as counter electrode, and the signal amplification of Ab₂-HRP bioconjugate-induced BCP. The developed cathode photoelectrochemical immunoassay showed a low limit of detection (0.037 pg mL^-1) with a wide linear range (from 0.1 pg mL^-1 to 50 ng mL^-1) for CEA detection.