Colorimetric Detection of Ascorbic Acid and Total Antioxidant Capacity Based on CoNi Bimetallic Metal Organic Framework

Abstract

A bimetallic CoNi metal–organic framework (CoNi-MOF) was fabricated through a room-temperature co-precipitation approach. Leveraging the synergistic interplay between cobalt and nickel, the bimetallic framework demonstrated markedly enhanced oxidase-mimicking activity relative to its single-metal counterparts, enabling it to catalyse the oxidation of the chromogenic probe 3,3′,5,5′-tetramethylbenzidine (TMB) and generate a distinct colour response. This chromogenic process was strongly suppressed upon introduction of ascorbic acid (AA). Accordingly, a colourimetric assay for AA quantification was developed. The sensing system displayed a linear response to AA spanning 1–16 μmol/L, with a detection limit of 0.34 μmol/L (S/N = 3), alongside excellent specificity and prolonged shelf-life. Its practical utility was validated through the determination of total antioxidant capacity (TAC) in fresh fruit specimens and commercially available beverages. Recovery tests on spiked passion fruit samples yielded values between 98.17 % and 101.30 %, with relative standard deviations (RSDs) remaining under 7 %. Without addition of H₂O₂, this detection system was simple to operate and low in cost, which provided a new analytical method for food quality monitoring and antioxidant capacity evaluation, and expanded new horizons for application of bimetallic MOF nanozymes in sensing analysis.