Multienzyme-like nanozymes-powered smartphone biosensor for on-site multicolor visual detection of aminoglycosides

Aminoglycosides (AGs) are widely used for the prevention and treatment of infectious diseases due to their bactericidal and bacteriostatic properties. However, the residues of AGs in milk have become a common concern in the food safety field due to the misuse of AGs, which has led to their over-accumulation in foods of animal origin. In this study, AGs regulate dual enzyme-mimicking activities (peroxidase-/catalase-like) of multienzyme nanozymes (AuNPs) were investigated, and the underlying activity regulation mechanisms were elucidated. In combination with the etching of gold nanorods (AuNRs), two multicolor visual biosensors were established using kanamycin (KAN) and tobramycin (TOB) as model analytes. Under neutral conditions, KAN enhanced the peroxidase-like activity of AuNPs and catalyzed the generation of more TMB²⁺-etched AuNRs. Under alkaline conditions, TOB enhanced the catalase-like activity of AuNPs, reducing H₂O₂ residue and decreasing the extent of AuNRs etching. AuNRs served as signal transducers, exhibiting a linear correlation between their longitudinal surface plasmon resonance (LSPR) peak shift and AGs concentration. The distinct colorimetric changes accompanying the LSPR shift enabled the development of a multicolor visual sensing platform with enhanced visual discrimination. To enable portable analysis, smartphone technology was integrated into biosensors, achieving a low detection limit (0.464 nmol/L for KAN, 0.07 μmol/L for TOB) that is 100-fold lower than maximum residue limits. The biosensors demonstrate superior performance in the rapid, visual, and cost-effective detection of AGs in milk samples.