Self-powered Photoelectrochromic Biosensor for Visual Detection Using a Distance-Based Signal Readout

This study presents a self-powered photoelectrochromic biosensor for the visual, direct-reading detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77) based on a distance-based signal readout. The sensor chip integrates a detection zone and an optical channel coated with Prussian blue (PB). In the presence of the target PCB-77, a competitive binding event is triggered that displaces nanozyme-labeled DNA complexes. This reduces the formation of an insulating precipitate on the electrode surface, thereby facilitating the generation and transfer of photogenerated electrons under illumination. The photogenerated electrons reduce PB to Prussian white, creating a bleached zone with a length that can be directly measured. The decoloration length shows a linear relationship with PCB-77 concentration ranging from 4 nM to 5 μM, with a detection limit of 1.14 nM. By translating the electrochemical signal into a measurable distance, this strategy effectively circumvents the subjectivity inherent in traditional colorimetric intensity measurements, offering a robust and portable platform for reliable environmental monitoring.