Novel Bi2+xWO6 p–n Homojunction Nanostructure: Preparation, Characterization, and Application for a Self-Powered Cathodic Photoelectrochemical Immunosensor

Synthesizing novel cathodic photoactive materials with high photoelectrochemical (PEC) performance is urgently important for the development of photocathodic sensors. Herein, a novel photocathode material, Bi self-doped Bi2WO6 (i.e., Bi2+xWO6) p–n homojunction, is prepared via a simple ethylene glycol-assisted solvothermal reduction for the first time. Compared with pristine Bi2WO6, Bi2+xWO6 possesses a narrower band gap and higher light harvesting ability. Among the synthesized materials, Bi2.1WO6 exhibits the highest photocurrent response, which is 23 times that of pure Bi2WO6 because of the synergistic effect of doped Bi and the p–n homojunction. The open circuit potential, "V-shaped" Mott–Schottky plot, linear sweep voltammetry curve, and transient photocurrent demonstrate the p–n homojunction characteristics of the material well. By using the Bi2+xWO6 p–n homojunction as the photocathode for sensing and the plasmonic WO3/Au composite as the photoanode for signal amplification, a new self-powered membraneless PEC immunosensor is established for a highly sensitive detection of human epididymal protein 4. This study offers a new idea for designing novel photocatalysts with satisfactory performance, and the Bi2+xWO6 p–n homojunction is expected to act as a promising PEC platform for developing various self-powered biosensors.