A ratiometric, turn-on fluorosensor for specific detection of Zn2+ ions

A potentially active fluorescent chemosensor (E)-2-(((2-(1H-benzo[d]imidazol-2-yl)phenyl)imino)methyl)-5-(diethylamino)phenol (BMDP) is developed by the condensation of 2-(2-aminophenyl)-1H-benzimidazole and 4-(diethylamino)salicylaldehyde. It shows an exceptional ratiometric fluorescence behavior when exposed to Zn²⁺ ions and the photoluminescence color is changed from blue to cyan under the exposure of a 365 nm UV light which is also strongly evident from the color chromaticity diagram. The exceptional ratiometric fluorescence behavior in the presence of Zn²⁺ ions is found to be due to the chelation-enhanced fluorescence (CHEF). The 1:1 stoichiometry of BMDP and Zn²⁺ ions in Zn²⁺ ions chelated BMDP complex is confirmed through Job’s plot analysis. Remarkably, Cd²⁺ does not interfere with the selective ratiometric fluorescence behavior induced by Zn²⁺ ions. The lowest detection limit and quantification limit are estimated to be 28 nM and 92 nM respectively. The cyan fluorescence of the Zn²⁺ ions chelated BMDP complex is interestingly reversed to the original BMDP in the presence of ethylenediamine tetraacetic acid (EDTA). At the molecular level, this can be thought of as a complimentary “INHIBIT” logic gate. Furthermore, it is possible to utilize the probe for on-site identification in test strips with improved Zn²⁺ ions selectivity. We have also used a smartphone-based method to demonstrate the usefulness of BMDP for the immediate quantification and detection of Zn²⁺ ions. In light of this, probe BMDP is a trustworthy fluorescence probe for on-site monitoring that can accurately identify Zn²⁺ ions even when some other metals and anions compete.