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 Bi 2 WO 6 ( i.e., Bi 2+ x WO 6 ) p–n homojunction, is prepared via a simple ethylene glycol-assisted solvothermal reduction for the first time. Compared with pristine Bi 2 WO 6, Bi 2+ x WO 6 possesses a narrower band gap and higher light harvesting ability. Among the synthesized materials, Bi 2.1 WO 6 exhibits the highest photocurrent response, which is 23 times that of pure Bi 2 WO 6 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 Bi 2+ x WO 6 p–n homojunction as the photocathode for sensing and the plasmonic WO 3 /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 Bi 2+ x WO 6 p–n homojunction is expected to act as a promising PEC platform for developing various self-powered biosensors.