Synergistic Electric Field-Driven Dual Charge Transfer in Graphitic Carbon Nitride/SnO _2-x Heterojunctions for Enhanced Electrochemiluminescence Biosensing

Despite the promising attributes of graphitic carbon nitride (CN) in electrochemical luminescence (ECL), its practical application is hindered by inherent limitations, such as poor electron transport efficiency, insufficient catalytic active sites, and severe passivation under high potentials, which collectively compromise ECL intensity and stability. To address these challenges, this work proposes a synergistic electric field modulation strategy by constructing Sn²⁺-partially oxidized CN/SnO_2-x (SCN) heterojunctions via a solvothermal method. The incorporation of Sn²⁺/Sn⁴⁺ redox pairs establishes continuous charge transfer pathway, enhancing coreactant (K₂S₂O₈) utilization efficiency and prolonging carrier lifetimes, thereby achieving a nearly 3-fold increase in ECL efficiency. Density functional theory (DFT) calculations reveal that the synergistic interaction between the external and built-in electric fields optimizes directional electron transfer from CN to SnO_2-x, effectively suppressing interfacial passivation at high potentials (-1.8 V). Leveraging this mechanism, a dual-wavelength ECL biosensor was developed for the ultrasensitive detection of carcinoembryonic antigen (CEA), demonstrating high clinical applicability. This study not only provides strategy for modulating multipath charge transfer in heterojunction-based ECL systems but also opens avenues for designing advanced semiconductor hybrids with tailored electronic structures.