Circularly Polarized Light as Analytical Dimension in Photoelectrochemical Sensing: A Proof of Concept in Single-Interface Ratiometric Immunoassay

Conventional ratiometric photoelectrochemical (PEC) designs struggle with practical limitations because of rigorous material needs and natural signal fluctuations resulting from complicated processes in dual interface fabrication. In response, we developed a polarization-resolved ratiometric PEC immunosensor on a single interface to overcome these limitations. In detail, the immunosensor was composed of a platform of gradient-etched BiVO 4 /Bi 2 S 3 (BVO-ES) and a pair of chiral photoactive nanoprobes, which were MgFe 2 O 4 @Ag- l -(and d )-cysteine. The BVO-ES platform guaranteed a robust baseline photocurrent with the synergy of bulk and interfacial charge separation. More critically, these chiral photoactive nanoprobes rendered ratiometric detection possible by the fact that they show different quenching efficiencies under left and right circularly polarized light. This differential response directly converted the concentration of analyte NSE into a modulated ratio of two photocurrents, thereby creating a self-calibrated sensing technique without the need for material redesign or modifications of the dual interface. Distinct from conventional ratiometric PEC sensors, this study pioneered the first immunosensing strategy using circularly polarized light to produce a two-signal output. In summary, this work presented a feasible alternative to the conventional ratiometric designs, integrating chiral photonics with a PEC immunoassay, which demonstrated the reliability improvement for practical sensing applications.