MIL-100(Fe) Nanozyme-Powered Dual Mode Detection of Ascorbic Acid

A spectrophotometric method based on nanoenzymes and a smartphone-assisted image colourimetric method has been developed to detect ascorbic acid. A metal-organic frameworks MIL-100(Fe) with nano-enzymatic activity was synthesized through a mild reaction and characterized by infrared spectroscopy, scanning electron microscopy and X-ray polycrystalline diffraction. MIL-100(Fe) acts as a peroxidase-like enzyme to catalyze the generation of hydroxyl radicals from H₂O₂, promoting the oxidative discolouration of 3, 3', 5, 5'-tetramethylbenzidine (TMB), while ascorbic acid can consume the hydroxyl radicals and thus inhibit the oxidation of TMB, which resulted in a noticeable color change in the solution and a significant visible light absorption signal. When MIL-100(Fe) was used for the spectrophotometric detection of ascorbic acid, the linear range was 2~25 µmol/L and the limit of detection was 1.80 µmol/L. The ascorbic acid was further detected by smartphone-assisted image colorimetric, the (G+B)/R value was linearly related to the concentration of ascorbic acid in the range of 2.5~25 µmol/L, and the limit of detection was 1.99 µmol/L.