Novel Bi_2+xWO₆ p–n Homojunction Nanostructure: Preparation, Characterization, and Application for a Self-Powered Cathodic Photoelectrochemical Immunosensor

Abstract

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+x WO6) p–n homojunction, is prepared via a simple ethylene glycol-assisted solvothermal reduction for the first time. Compared with pristine Bi2WO6, Bi2+x WO6 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+x WO6 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+x WO6 p–n homojunction is expected to act as a promising PEC platform for developing various self-powered biosensors.

Redox-induced electricity for energy scavenging and self-powered sensors

“…Thereby, many photoelectrochemical redox reactions are initiated by solar irradiance. Many sensors based on redox-based photoelectrochemical energy scavenging devices have been fabricated such as glucose sensors, 136,137 aptasensors, [138][139][140][141] immunusensors, 142 and photodetectors. 143 A hematite (Fe 2 O 3 ) nanorod-based self-powered photoelectrochemical glucose sensor was fabricated, showing excellent sensitivity and selectivity with extended stable operation.…”

“…140,141 A PEC immunosensor to detect human epididymal protein 4 (HE4) was fabricated using a novel photocathode Bi-doped W 2 O 6 p-n homojunction and WO 3 /Au as the photoanode to sense and amplify the signal, respectively. 142 A schematic of the structure of the immunosensor with its operation principle is presented in Fig. 14c photocurrent.…”

“…Thus, the sensor delivered excellent sensitivity with few interferences for detection, having a sensing limit of 77.8 fg mL À1 in the concentration range of 0.001 to 100 ng mL À1 . 142 A novel ultraviolet (UV) photodetector by a self-powered PEC sensor was introduced, where the counter electrode based on Ga 2 O 3 was redesigned to enhance the device performance. 143 The improvement in the design of the new UV detector compared to the traditional one is illustrated in Fig.…”

Novel Anti-Interference Strategy for a Self-Powered Sensor: Mediator-Free and Biospecific Photocathode Interface

“…18,19 For instance, Zhang et al constructed an AAassisted photocathode PFC, in which AA was added into the anodic chamber as the electron donor to guarantee the output power; 16 Zeng et al used H 2 O 2 as a hole capture reagent for the photoanode and an electron acceptor for the photocathode to establish a photoelectrochemical immunosensor, which improved the signal response. 20 However, the introduction of redox mediators was not a good choice for the application of the sensor due to the drawback of non-negligible toxicity and limited stability. 21 For example, it was difficult to maintain the long-term stable state for these mediators, resulting in a lower voltage output due to the thermodynamic reasons.…”

“…Therefore, the photocathode had good anti-interference ability and was not affected by the reducing substances in the electrolyte. , It must be acknowledged that the photocathode cannot produce higher photocurrent response than the photoanode, resulting in a lower sensitivity than the photoanode self-powered sensor. Therefore, some electron donors or acceptors, such as AA or H 2 O 2 , were often injected into the electrolyte to improve the signal and stabilize the response. , For instance, Zhang et al constructed an AA-assisted photocathode PFC, in which AA was added into the anodic chamber as the electron donor to guarantee the output power; Zeng et al used H 2 O 2 as a hole capture reagent for the photoanode and an electron acceptor for the photocathode to establish a photoelectrochemical immunosensor, which improved the signal response . However, the introduction of redox mediators was not a good choice for the application of the sensor due to the drawback of non-negligible toxicity and limited stability .…”