Peroxidase-like CuCo–carbon dots for colorimetric/fluorescence detection of ascorbic acid

Abstract

This study reports a sensitive and rapid dual-mode (colorimetric/fluorescence) 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 properties, 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 exhibits a linear detection range of 0.1–30 µmol L⁻¹ with a limit of detection (LOD) of 2.039 µmol L⁻¹, while the fluorescence mode exhibits a linear range of 2–40 µmol L⁻¹ with an LOD of 1.59 µmol L⁻¹. The platform was successfully applied to determine AA in human serum, demonstrating satisfactory analytical performance.