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

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.