Peroxidase-Like CuCo-Carbon Dots for Colorimet-ric/Fluorescent Detection of Ascorbic Acid

This study reports a sensitive and rapid dual-mode (colorimetric/fluorescent) sensing platform for the detection of ascorbic acid (AA), which is based on bimetallic copper-cobalt-doped carbon dot nanozymes (CuCo-CQDs, Cu:Co molar ratio = 1:2). The material exhibits strong peroxidase-like catalytic activity and inherent fluorescence, attributed to synergistic effects between copper and cobalt, as well as the presence of catalytically active Cu(I)/Cu(II) redox pairs and Co-N coordination sites. Utilizing the peroxidase-mimetic property, CuCo-CQDs catalyze the oxidation of colorless 3,3′,5,5′tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) in the presence of H2O2. Concurrently, the fluorescence of the nanozymes is quenched via the inner filter effect (IFE) induced by oxTMB. Upon addition of AA, oxTMB is reduced to TMB, resulting in fluorescence recovery. The colorimetric mode shows a linear detection range of 0.1-30 μmol/L with a limit of detection (LOD) of 2.039 μmol/L, while the fluorescence mode provides a linear range of 2-40 μmol/L with an LOD of 1.59 μmol/L. The platform was successfully applied to determine AA in human serum, demonstrating satisfactory analytical performance.