Structure-optimized Au@Pt nanozymes enable robust dual-signal ELISA for on-site screening of ractopamine in swine products

Ractopamine (RAC), a banned β-adrenergic agonist, poses severe risks to human health, necessitating rapid and ultrasensitive detection methods. This work presents a novel dual-mode immunoassay utilizing peroxidase-mimicking Au@Pt core-shell nanozymes for the colorimetric and photothermal detection of RAC. The optimized one-step synthesized Au@Pt nanoparticles (Au/Pt = 1:1) exhibited exceptional peroxidase-like activity (27.32 U/mg). After conjugation with monoclonal antibodies, the nanozymes served as immunoprobes in a one-step enzyme-linked immunosorbent assay (ELISA). The enhanced catalysis was elucidated by reactive oxygen species trapping, confirming hydroxyl radicals and singlet oxygen as key intermediates. The assay demonstrated outstanding sensitivity, with limits of detection at 5.32 pg/mL (colorimetric) and 1.03 pg/mL (photothermal), a significant improvement over conventional ELISA. Practical applicability was confirmed in spiked pork and pig urine, achieving recoveries of 86.0–113.0% (coefficient of variation<14.3%), offering a robust platform for on-site screening.