A Ratiometric Photoelectrochemical Biosensor Based on Polarity Reversal of Photocurrent Caused by Controllable Surface Defect Engineering

Abstract Ratiometric photoelectrochemical (PEC) biosensors based on polarity reversal of photocurrent can effectively avoid false positive or negative signals. However, the two different sensing interfaces that generate two photocurrent signals with opposite polarities limit the detection accuracy, and the critical voltage cannot be dynamically adjusted based on varying detection conditions. To address the aforementioned issues, this work employs a surface defect engineering strategy to develop a PEC biosensor based on Fe-modified TiO2 nanorods (TiO2–Fe) with rich oxygen vacancies. From a single sensing interface of this sensor, the polarity of photocurrent can be reversed to obtain two signals, attributed to the new charge transfer pathway provided by oxygen vacancies. Furthermore, the critical voltage is modulated by adjusting Fe loading, electrolyte pH and light intensity, and the corresponding mechanism is elucidated based on semiconductor electrode kinetics. This sensor is successfully applied to the evaluation of glucose levels in human serum. It exhibits excellent accuracy for quantitative analysis with spike recoveries ranging from 96.02% to 103.26% and relative standard deviations between 0.61% and 2.53%.