Atomically dispersed ruthenium on magnetic layered double hydroxide nanozyme for a multi-mode aptasensor enabling highly sensitive kanamycin detection.

Kanamycin residues in food pose health risks due to their ototoxicity, nephrotoxicity, and antimicrobial resistance promotion. This work reports a multi-mode aptasensor combining atomically dispersed ruthenium-doped magnetic layered double hydroxide (RuSA/MLDH) with exonuclease I-assisted amplification. RuSA/MLDH exhibits DNA-enhanced peroxidase-like activity, catalyzing H2O2-mediated 3,3',5,5'-tetramethylbenzidine oxidation to a blue product with colorimetric and photothermal signals. Kanamycin competitively binds to aptamers, disrupting aptamer-complementary strand hybridization to generate exonuclease I-accessible single-stranded DNA. Subsequent digestion reduces DNA adsorption on RuSA/MLDH, attenuating catalysis and enabling target recycling with signal decrease. This enables kanamycin detection with detection limits of 2.08, 3.85 and 1.33 nM for colorimetric, photothermal, and smartphone-based analysis. The aptasensor demonstrated excellent selectivity and determined kanamycin in honey, milk, and chicken with recoveries of 93%-108%. By integrating a magnetically separable single-atom nanozyme with exonuclease-modulated DNA-nanozyme interactions, this platform offers a sensitive, selective, and user-friendly tool for on-site antibiotic screening in complex foods with cross-validated readouts.