Cu-Fe@C dual-mode sensing platform: ratiometric electrochemistry combined with pre-incubation-activated colorimetry for self-calibrated detection of ascorbic acid

Construction of an electrochemical/colorimetric dual-mode sensing platform. • Ratiometric electrochemical method using methylene blue as an internal reference. • Pre-incubation strategy to activate the peroxidase-like activity of Cu-Fe@C. Ascorbic acid (AA) is an essential biomarker involved in numerous physiological processes, accurate and reliable detection remains a challenge. Herein, we constructed a novel dual-mode sensing platform integrating ratiometric electrochemical detection with pre-incubation-activated colorimetric sensing based on Cu-Fe@C (where ‘@C’ denotes the carbon matrix derived from the carbonization of the copper‑iron metal-organic framework, Cu-Fe-MOF) for self-calibrated AA detection. In the electrochemical mode, Cu-Fe@C exhibited excellent electrocatalytic activity toward AA oxidation, while methylene blue (MB) loaded on mesoporous carbon spheres (MCS) provided a stable internal reference peak at −0.2 V, enabling ratiometric analysis with a linear range of 2.0–720.0 μmol·L −1 and a detection limit of 0.67 μmol·L −1 (S/N = 3). In the colorimetric mode, pre-incubation with AA reduced Fe 3+ and Cu 2+ in Cu-Fe@C to Fe 2+ and Cu + , activating its Fenton-like activity to catalyze the H 2 O 2 -TMB (3,3′,5,5′-tetramethylbenzidine) system, producing a color response with a linear range of 1.0–79.0 μmol·L −1 and a detection limit of 0.33 μmol·L −1 (S/N = 3). The dual-mode configuration provides built-in cross-validation between two independent detection channels, substantially enhancing detection reliability. The sensor was successfully applied to AA determination in green tea and orange juice samples with recoveries of 93.5%–104.8%, demonstrating its practical utility for real-sample analysis. Scheme 1. Illustration of the principle of a dual-mode sensing platform for ascorbic acid based on Cu-Fe@C: ratiometric electrochemical detection and pre-incubation-activated colorimetric detection. Download: Download high-res image (139KB) Download: Download full-size image