Fluorescent/Colorimetric Probe for the Detection of Cr(Ⅵ) Based on Mil-101(Fe)-Nh2 with Peroxidase-Like Activity

Abstract

In the present research, Fe-based metal-organic frameworks (MIL-101(Fe)-NH2) nanoparticles were synthesized by simple solvothermal methods and used to assay Cr(Ⅵ). The MIL-101(Fe)-NH2 performs dual functions: the 2-aminoterephthalic acid (NH2-BDC) ligand endows a strong fluorescence emission at 428 nm, and the Fe metal nodes are able to facilitate the oxidation of 3,3′,5,5′- tetramethylbenzidine (TMB) directly, resulting in the generation of blue-green-colored oxidized-TMB (ox-TMB). Our research results show that reducing agents such as ascorbic acid (AA) can collapse the structures of MIL-101(Fe)-NH2 because of the reduction of Fe3+ by AA, resulting in release of NH2-BDC. When there is Cr(Ⅵ) present, the fluorescence intensity MIL-101(Fe)-NH2 +AA system can decrease due to the competitive reduction of Fe3+ and Cr(Ⅵ)，and the oxidation of TMB by MIL-101(Fe)-NH2 can be significantly accelerated due to Cr(Ⅵ)-boosted the electron transfer rates of Fe3+ and Fe2+. Therefore, a fluorescent/colorimetric dual-mode platform was developed for Cr(Ⅵ) with an extensive linear range (7.5-750 μg/L and 13.3-1000 μg/L) as well as a tiny detection limit (0.99 μg/L and 1.98 μg/L). These properties make the MIL-101(Fe)-NH2 a potential fluorescent and colorimetric sensor for selectively detecting Cr(Ⅵ).

Keywords: MIL-101(Fe)-NH2, chromium(Ⅵ), fluorescent/colorimetric dual-mode sensor, peroxidase-like activity