A highly selective 'turn-on' fluorescent sensor for Zn2+ based on fluorescein conjugates

A highly selective fluorescent chemosensor was designed, synthesized, and evaluated for Zn2+ recognition based on the photoinduced electron transfer (PET) mechanism. This azofluorescein was comprised of a fluorescein moiety acting as a fluorophore, a linker (-N=N-) and a novel ionophore receptor generated by the coordination of the linker (-N=N-) with phenoxyl and carboxyl functionalities to render a binding pocket for Zn2+ recognition. In the presence of Zn2+, a marked enhanced fluorescence change of 10-fold was observed. Under optimized conditions, a linear relationship between the fluorescence intensity and concentration of Zn2+ was observed with a detection limit of 1.2 mu M. This probe also exhibited selectivity for Zn2+ over other metals ions, especially Cd2+. The binding constant of the Zn2+-azofluorescein complex was determined to be 2.4 x 10(4) M-1. (C) 2016 Elsevier Ltd. All rights reserved.