Development of p-Si-Photocathode PEC Biosensors Based on Surface Antireflection Effect of Photonic

It is generally believed that the sensing signal amplification mechanism of photoelectrochemical (PEC) biosensors developed based on photocathode materials lies in the changes in surface impedance caused by target substances. In this study, a PEC aptamer biosensor based on a p-Si/BaSnO3(BSO)/Pt–Au photocathode is fabricated, the heterojunction structure constructed by BSO and silicon can synergistically enhance the photoelectric response and protection capability of the device. The research reveals that its signal amplification mechanism stems from the fact that the adsorption concentration of the detected target substance alters the antireflection capability of the photocathode surface, thereby inducing a linear change in the photocurrent. This is distinct from the signal amplification mechanism of many conventional photocathode-based PEC biosensors. Based on this principle, the sensor achieves ultrasensitive detection of 5-hydroxytryptamine (5-HT), a key marker of depression. The experimental results demonstrate that the PEC biosensor exhibits a linear detection range of 1 × 10–14 to 1 × 10–10 g/mL, with a limit of detection (LOD) of 2.1 × 10–15 g/mL and a resolution of ΔI = 39.78 μA/cm2. Meanwhile, techniques such as ultraviolet–visible/near-infrared (UV–vis/NIR) diffuse reflection spectroscopy, time-resolved photoluminescence (TRPL) spectroscopy and incident photon-to-current efficiency (IPCE) measurement confirm that the anomalous mechanism, where the photocathode current of the PEC biosensor increases linearly with the concentration of the detected target substance, is indeed attributed to the linear enhancement of the antireflection capability of the photoelectrode surface. This innovative signal amplification mechanism not only expands the design concepts of PEC sensing but also provides a new technical pathway for the development of high-sensitivity PEC biosensors.