Band bending-induced polarity switching in heterojunctions for self-validated aptasensor toward fg-level...

Although bias-regulated photocurrent polarity switching has been preliminarily explored for self-verifying photoelectrochemical (PEC) sensing, achieving stable bipolar photoresponses with a clearly defined interfacial charge-transfer mechanism remains challenging. Herein, a P-N covalently bridged red phosphorus (RP)/g-C₃N₄ heterojunction is fabricated as a self-verifying PEC aptasensing platform for chloramphenicol detection. The interfacial P-N covalent bonding strengthens electronic communication between RP and g-C₃N₄, promotes photogenerated charge separation, and stabilizes the heterointerface during repeated bias modulation. The resulting sensor exhibits reversible anodic and cathodic photocurrent outputs, with a polarity transition potential of approximately -0.1 V. Mechanistic investigations reveal that the polarity switching is governed by bias-induced band bending, which reconstructs the interfacial energy alignment and reverses the charge-transfer pathway under opposite biases. Owing to this stable bipolar PEC response, the aptasensor enables intrinsic signal cross-validation and achieves chloramphenicol detection over a wide linear range of 10^-13-10^-6 mg/mL, with detection limits of 1.58 × 10^-14 mg/mL (cathodic mode) and 3.05 × 10^-14 mg/mL (anodic mode). This work provides a covalent interfacial engineering strategy for stabilizing polarity-switchable PEC systems and offers mechanistic insight into reliable self-verifying sensing for trace contaminant analysis.