Wenqiang Lai

Flower-like Fe₃S₄ nanosheets were synthesized via a one-step solvothermal method and employed as peroxidase-mimicking nanozymes in a colorimetric immunoassay for the sensitive detection of carcinoembryonic antigen (CEA). Comprehensive structural and chemical characterizations confirmed the successful synthesis and surface modification of the Fe₃S₄ nanosheets, enabling efficient antibody conjugation. The nanozymes demonstrated significant peroxidase-mimicking behavior by facilitating the hydrogen peroxide (H₂O₂)-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), where hydroxyl radicals (•OH) were confirmed to be the dominant reactive intermediates. Kinetic studies revealed low Michaelis-Menten constants for both TMB and H₂O₂, indicating high substrate affinity and excellent catalytic efficiency. Under optimized conditions, the developed immunoassay showed a linear response in the CEA concentration range 0.05-50 ng/mL, with a detection limit of 82 pg/mL, which is well below the commonly used clinical cutoff for CEA (5.0 ng/mL). The assay exhibited good reproducibility (RSD = 4.2%), retained 93% of its activity after one week of storage, and showed strong agreement with commercial ELISA kits in clinical serum samples. The novelty of this work lies in the application-oriented design of flower-like Fe₃S₄ nanosheets via a simple one-step solvothermal route, delivering a sensitive and practical colorimetric immunoassay with robust stability and reproducibility. Taken together, these results establish a robust and cost-effective nanozyme platform with promising potential for clinical diagnostics and point-of-care tumor biomarker detection. Graphical abstract

A facile visual and photothermal sensing platform that employs the peroxidase-like activity of chrysanthemum-like Fe–Co LDH for highly sensitive detection of H ₂ O ₂ and glucose.