Design of Mn-Car multivalent laccase mimics through self-assembled coordination and its application for ultrasensitive colorimetric detection of kanamycin in food

Kanamycin (KAN) can generate a serious threat to human health due to its tendency to accumulate in food. Current colorimetric strategy for KAN detection still faces some challenges, and nanozyme-based colorimetry is an ideal alternative approach. Herein, a non‑copper-based multivalent laccase mimic named Mn-Car is first synthesized through a self-assembly of manganese ions and the endogenous biomolecule carnosine, which is further used to develop a novel colorimetric method for ultrasensitive and selective detection of KAN. The laccase-like catalytic center is formed through the multidentate chelation bonds between manganese ions and imidazolium groups of histidine as well as carboxyl groups of β-alanine in carnosine. The multivalent oxidation states of manganese dynamically regulate electron transfer pathways through synergistic coordination. The unique Mn-Car architecture drives the efficient generation of superoxide radicals (O 2 · − ) and semiquinone radicals (SQ· − ). Leveraging the excellent laccase-like activity of Mn-Car , a highly sensitive colorimetric method for KAN detection is developed. Mn-Car forms polydentate chelation with the amino and hydroxyl groups in KAN, which can trigger multi-step cascade oxidation reactions that disrupt the structural core of Mn-Car and lead to reduced colorimetric signals. The colorimetric method achieves a limit of detection (LOD) of 0.102 μM and is successfully applied for on-site detection of KAN in water samples and honey, providing a novel platform for antibiotic residue analysis.