Visual detection of vitamin C in fruits and vegetables using UiO-66 loaded Ce-MnO2 mimetic oxidase

A nanocomposite (UiO-66/Ce-MnO2) was fabricated by combining UiO-66 with cerium-doped manganese dioxide (Ce-MnO2) for colorimetric detecting vitamin C (Vc). Compared with traditional artificial enzymes, the as-synthesized UiO-66/Ce-MnO2 were simple to prepare and did not require the participation of other active substances. The doping of cerium increased the oxygen vacancies and the UiO-66 as a carrier improved the dispersibility. The formation of superoxide anion (O2-) and the inside Ce4+/Ce3+ and Mn4+/Mn3+ redox couples of UiO-66/Ce-MnO2 endowed UiO-66/Ce-MnO2 with a high catalytic capability, which could catalytically oxidize 3, 3', 5, 5'-tetramethylbenzidine (TMB) into oxidation state TMB (oxTMB) without H2O2, accompanying with color change and a prominent peak at 652 nm in UV-vis spectra. Based on the inhibitory effects of Vc on catalytic oxidation of TMB, detection of Vc can be achieved, exhibiting a linear relationship in the concentration of 1.13-17.01 μmol L-1 with a low detection limit of 65.82 nmol L-1. This system can also be detected by smartphone, the linear detection range is 12.47-22.67 μmol L-1. Vc contents in fruits and vegetables detected by the sensor were in good agreement with the 2, 4-Dinitrophenylhydrazine colorimetry method (P > 0.05), indicating a reliable sensor for Vc detection.