Colorimetric detection of kasugamycin via silver oxide nanoparticles with intrinsic laccase activity.

While nanozyme-based inhibition assays are gaining momentum, they have remained predominantly limited to structurally compatible phenolic antibiotic targets. In this study, we report the first colorimetric sensor for kasugamycin (KAS)-a highly hydrophilic, non-phenolic aminoglycoside antibiotic that has traditionally eluded optical detection due to its challenging physicochemical profile. Here, we engineered silver oxide nanoparticles (Ag₂O NPs) to function as a robust laccase mimic. Critically, we exploit their catalytic behavior to develop an unprecedented inhibition-based sensing mechanism for KAS. The sensor operates via strong and selective adsorption of KAS onto the nanozyme surface, leading to quantitative suppression of catalytic activity. This enables ultrasensitive detection with a limit of 2.8 nM, even in complex food matrices. Our approach marks a conceptual shift in nanozyme-based sensing-from phenol-centric paradigms to the detection of non-phenolic analytes-establishing a broadly applicable strategy for identifying otherwise elusive antibiotic residues.