<p> A portable dual-mode biosensor has been developed for rapid and on-site detection of carbendazim (CBZ) based on an Au-Pt bimetallic alloy-modified CeO₂ nanozymes (AuPt@CeO₂). The nanozyme exhibits pH-switchable dual enzymatic behaviors: oxidase-like under acidic regimes and glucose oxidase-like (GOx-like) in neutral to mildly alkaline milieus. Notably, this nanozyme demonstrates a pronounced glucose oxidase-like (OXD) activity, which is approximately sixfold higher than that of Au NPs, 1.8 times that of Pt NPs, and twice that of either Au@CeO₂ or Pt@CeO₂. Density functional theory (DFT) calculations reveal that the alloy structure underlies its superior catalytic activity. In contrast to H₂O₂-dependent peroxidase-like (POD-like) systems (e.g., 3,3’,5,5’-tetramethylbenzidine (TMB) oxidation), the O₂-mediated oxidase-like (OXD-like) activity offers superior operational simplicity and reliability for point-of-care testing (POCT). By integrating the AuPt@CeO₂ nanozymes with a portable glucose meter (PGM) platform, a robust biosensing system was constructed. Through nanozyme-catalyzed amplified transduction, the system achieves ultrasensitive detection of CBZ, with limits of detection (LOD) as low as 0.332 ng/mL for PGM and 0.188 ng/mL for colorimetric mode. This work presents a dual-mode strategy driven by pH-switchable multi-nanozyme activities without exogenous H₂O₂, facilitating point-of-care monitoring in environmental and food safety applications.</p> Graphical abstract <p></p>