Spring Expanding-like Polarity Reversal in Photoelectrochemical Biosensing

Although polarity-reversal photoelectrochemical (PEC) analysis can effectively eliminate false-positive and negative signals caused by interferents, achieving high sensitivity and accuracy is still a challenge. Hence, a spring expanding-like polarity reversal strategy with bipolar signal synergistic amplification is first proposed to help build a high-performance PEC analysis system. In this study, l-cysteine (l-cys) is discovered to not only act as a polarity regulator to elaborately reverse photocurrent via its covalent bond to Cu and Bi but also provide a relatively stable electron donor to effectively consume the photogenerated holes compared with commonly used H₂O₂ and ascorbic acid. More importantly, the amino and electron-rich functional acridine groups in the dye acriflavine endow an electrochemical activity to accelerate electron transfer between the electrode and solution, thus enabling bipolar synergistic signal amplification for acquiring an extremely enlarged photocurrent variation that is of great significance to overcome the rigorous signal prereversal depression and reversal amplification in traditional polarity-reversal systems. Accordingly, the PEC biosensor with the proposed spring expanding-like polarity reversal strategy exhibits excellent sensitivity and accuracy, reflecting ultralow detection limits of 0.04 fM toward lead ions (Pb²⁺) and good anti-interference ability in the detection of natural water samples. This work provides an avenue for exploring a new polarity reversal strategy for accomplishing high-performance PEC bioanalysis, expected to be widely applied in environmental monitoring, clinical diagnosis, and food supervision.