Photoelectrochemical biosensors: New insights into promising photoelectrodes and signal amplification strategies

The photoelectrochemical (PEC) process is a promising low-cost approach to convert chemical energy to electricity under light illumination and applied potential. PEC biosensing has attracted huge attention because of its ability to detect biomolecules through the photocurrent generated from biomolecule oxidation. However, important factors in the mechanism of PEC biosensing, particularly photoexcited (charge) carrier generation and separation at nano-bio interfaces, are not well explored. Therefore, with the objective of emphasising the implications of photoexcited (charge) carrier transport, here we review recent efforts indicating the significance of electrode design to enhance the performance of PEC biosensor with semiconductor photocatalytic materials. Besides enzymatic PEC biosensors, the underlying beneficial mechanism of direct oxidisation of biomolecules onto a wide range of semiconductor photocatalyst surfaces by the photogenerated holes is briefly discussed. This review is primarily divided into three parts: materials, signal amplification, and promising device architectures, based on recent advances in PEC biosensors. In addition, this review outlines the strategies used to detect a wide range of bioanalytes. After a summary of PEC sensing architectures, the review concludes with an outlook and the current challenges in fabricating solar-light-driven and self-powered biosensors using nanostructured photocatalytic semiconductors. The PEC biosensing schemes presented in this review provide unambiguous operating guidelines of this subject to facilitate our understanding of the compatibility between semiconductor photocatalysts and bioanalytes.