A gold-platinum nanozyme-based immunochromatographic strip for rapid detection of ofloxacin in chicken and fish

Ofloxacin (OFL), a third-generation quinolone antibiotic, has been reported to cause adverse multisystem reactions in humans after residual ingestion. The aim of this study was to develop a gold core-platinum shell nanozymes (Au@Pt NPs) via a layer-by-layer seed growth method for the rapid detection of OFL. The synthesized Au@Pt NPs, with a 25 nm gold core and 6 platinum shells, exhibited robust peroxidase-like activity. Kinetic analysis revealed a Michaelis constant (Km) of 0.41 ± 0.04, a catalytic constant (Kcat) of 1.41 × 10 5 , and a catalytic efficiency (Kcat/Km) of 3.40 × 10 5 . An indirect competitive Enzyme-linked immunosorbent assay (ic-ELISA) and an immunochromatographic strip were developed based on these nanozymes. The ic-ELISA demonstrated a linear range of 0.2–7.35 ng/mL, an IC 50 of 0.96 ng/mL, and a limit of detection (LOD, IC 10 ) of 0.03 ng/mL. The immunochromatographic strip exhibited a detection range of 0.060–4.512 ng/mL, an IC 50 of 0.521 ng/mL, and an LOD of 0.017 ng/mL, with a detection time of 5–7 min. Applied to real samples, the method achieved recoveries of 86.48 %-116.96 % in fish and 73.90 %-123.37 % in chicken, with relative standard deviations (RSDs) below 20 %. Therefore, this Au@Pt NP-based immunoassay demonstrated a rapid, sensitive, and specific method for screening antibiotic residues in food.