A visual and sensitive sensor for colorimetric and fluorescent recognition of Fe3+/2+, theoretical calculation and strip applications in wine

Abstract

Total iron ions (Fe3+/2+) are a critical factor influencing wine quality and stability. A novel “turn-on” fluorescent probe (E)-2-((4-(5-methyl-1H-benzo[d]imidazol-2-yl)benzylidene)amino)phenol (probe MBBP) for monitoring Fe3+/2+ in wine was developed. It was designed with benzimidazole as the fluorophore and o-aminophenol as the Fe3+/2+ recognition site, simple and easy to prepare. The probe itself in EtOH/H2O (v: v, 49:1) emitted weak fluorescence and produced strong blue fluorescence after adding Fe3+/2+. The sensing of Fe3+/2+ was performed via the nucleophilic attack of Fe3+/2+ to imine groups of the probe with a 1:1 binding stoichiometry, and the fluorescence enhancement of the sensor was mainly due to the generation of compound 3 with the ICT effect. Results demonstrated that the probe exhibited high selectivity and sensitivity with a lower detection limit of 0.054 nM than previously reported Fe3+/2+ probes. In addition, based on the TD-DFT method and CAM-B3LYP and PBE0 functional theory, the significant changes in the dihedral angle stemmed from the isomerisation and rotation of the C = N bond. Probe MBBP was successfully applied to detect Fe2+/3+ in wine by intelligent software and the rapid detection of Fe3+/2+ using strips was also conducted.