Recent advances of colorimetric sensors based on laccase-mimicking nanozymes

Natural laccase exhibits poor stability, high cost, strict storage requirements and weak recyclability, which greatly limits its utility in colorimetric sensing and catalytic remediation. Laccase-mimicking nanozymes circumvent these shortcomings. Copper derivatives replicate laccase Cu(I)/Cu(II) redox via tailored coordination, whereas Ag-, Mn-, Ce-, Co-, Pt- and Fe-based nanozymes realize comparable phenolic oxidation using multivalent metal redox pairs and oxygen vacancies modulated by heterostructures and ligands. This review outlines recent advances in nanozyme-based colorimetric sensors. We categorize laccase-mimicking nanozymes into predominant Cu-based variants (amino acid-, peptide-, nucleotide-, MOF-, copper oxide- and bimetal-doped Cu hybrids) and complementary Ag-, Mn-, Ce-, Co-, Pt- and Fe-based analogues, and detail their synthesis, catalytic pathways and structural optimization. Two categories of colorimetric sensing mechanisms are summarized: catalytic signal mechanisms (direct catalytic activation, inhibition and activity-enhancement-based sensing) and target-recognition mechanisms (aptamer-mediated and molecular imprinting-based recognition). We review their reported applications in environmental monitoring, food safety screening and biomedical biomarker quantification targeting phenols, pesticides, heavy metals, mycotoxins, antibiotics and catecholamines. Notably, most existing work remains laboratory-based proof-of-concept research, lacking validated field and clinical practical implementations. We also identify key limitations, including inadequate matrix stability, narrow substrate specificity, intricate synthesis and low single-target throughput. Prospective strategies are proposed, covering biomimetic active-site engineering, machine learning-aided sensor arrays, multimodal signal transduction, scalable low-cost fabrication and smartphone-coupled portable detectors.