Water soluble and efficient amino acid Schiff base receptor for reversible fluorescence turn-on detection of Zn2+ ions: Quantum chemical calculations and detection of bacteria

An amino acid Schiff base (R) capable of recognizing Zn2+ ions selectively and sensitively in an aqueous medium was prepared and characterized. Upon addition of Zn2+ ions, the receptor exhibits fluorescence intensity enhancements (similar to 40 fold) at 460 nm (quantum yield, Phi = 0.05 for R and Phi = 0.18 for R-Zn2+) and can be detected by naked eye under UV light The receptor can recognize the Zn2+ (1.04 x 10(-8) M) selectively for other metal ions in the pH range of 7.5-11. The Zn2+ chelation with R decreases the loss of energy through non-radiative transition and leads to fluorescence enhancement. The binding mode of the receptor with Zn2+ was investigated by H-1 NMR titration and further validated by ESI-MS. The elemental color mapping and SEM/EDS analysis were also used to study the binding of R with Zn2+. Density functional theory calculations were carried out to understand the binding mechanism. The receptor was applied as a microbial sensor for Escherichia coli and Staphylococcus aureus. (C) 2015 Elsevier B.V. All rights reserved.