Metal-organic framework-derived FeCoZn-NC-1.5-800 as a dual-enzyme mimic for L-cysteine detection

A trimetallic (Fe, Co, and Zn) nanozyme embedded within an N-doped carbon matrix (FeCoZn-NC-1.5-800) was engineered via the coordination-controlled pyrolysis of a Fe ion-doped core-shell ZIF-8@ZIF-67 (ZIF-8@ZIF-67-Fe-1.5) precursor, which exhibited dual oxidase/peroxidase-mimicking activities. The bifunctional catalyst oxidized 3,3',5,5'-tetramethylbenzidine (TMB) to form blue oxidized TMB (oxTMB) without exogenous H₂O₂. However, the added L-cysteine (L-Cys) acted as a potent inhibitor, quenching oxTMB formation via thiol-mediated electron transfer, leading to a significant decrease in absorbance and the fading of the blue colour to colourless. Consequently, an H₂O₂-independent colorimetric biosensor was developed with a wide linear range (5-50 μM), a low detection limit (0.569 μM, 3σ), good selectivity and anti-interference ability. This study establishes a paradigm for transition metal nanozyme design, offering clinical translation potential in point-of-care thiol monitoring and biocatalytic system development.