Fluorescent Nanozyme Based on Bimetallic Fe/Co-Doped Carbon Dots for Dual-Mode Detection of Ascorbic Acid and Hydrogen Peroxide

Despite extensive research on nanozymes in analytical sensing, single-mode detection strategies remain constrained by reliability challenges. We developed bimetallic Fe/Co-doped carbon dots nanozymes (FeCo-CDs) for dual-mode (colorimetric/fluorescent) detection of ascorbic acid (AA) and hydrogen peroxide (H2O2). The synergistic Fe/Co codoping strategy generates abundant catalytically active sites, significantly enhancing peroxidase (POD)-like activity while simultaneously amplifying intrinsic fluorescence. The POD-like activity of FeCo-CDs catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) in the presence of H2O2, which subsequently quenches the blue fluorescence of FeCo-CDs due to the inner filter effect (IFE). Upon AA addition, fluorescence recovery and oxTMB reduction synergistically establish a self-validating dual-mode detection platform for H2O2/AA. This system achieves superior sensitivity for AA (limit of detection (LOD): 0.39 μM for colorimetric mode; 0.35 μM for fluorescent mode) and broader detection ranges for H2O2 (colorimetric linear range (LR): 200–1500 μM; fluorescent LR: 60–600 μM), outperforming conventional single-mode approaches. This innovative dual-mode sensing strategy overcomes the limitations of conventional unimodal systems, providing a robust and versatile platform for advanced biosensing applications.