Photocurrent-Polarity-Switch-Enabled Signal “on–off–on” Mode Leveraging the Z-Scheme BiOI NFs/Au NPs/TiO2 NPs Heterojunction and Magnetic Nanozyme Inhibition for Glyphosate Detection in Agricultural Matrices

Critical to sensor performance in real agricultural matrices are high interference resistance and prevention of false-positive/negative signals. To address this, a Z-scheme BiOI nanoflakes (NFs)/Au NPs/TiO2 NPs heterojunction was designed with photocurrent-polarity-switching capability, an inherent feature that could minimize interference from oxidative and reductive species. Subsequently integrated Fe3O4 NPs with catalase-mimicking activity suppressed the photocurrent response to baseline levels, substantially reducing the background noise. In the presence of glyphosate (Gly), the quenching effect was inhibited, leading to a “signal on–off–on” photoelectrochemical (PEC) detection mode. In addition, the inherent magnetism of Fe3O4 NPs enhanced the specificity by facilitating the efficient removal of nonbound interferents and enabling “split-type” PEC detection processes. This approach achieved Gly quantification within a linear range of 0.05–5 mg·L–1, with practical applicability demonstrated in three agricultural matrices. By strategically integrating heterojunction engineering with magnetic nanozyme signaling, this work establishes a PEC sensing paradigm exhibiting exceptional anti-interference capability.