ICPBCZin: A red emitting ratiometric fluorescent indicator with nanomolar affinity for Zn super(2) super(+) ions

A new fluorescent Zn super(2) super(+) indicator, namely, ICPBCZin was synthesized and the spectral profile of its free and Zn super(2) super(+) bound forms was studied. The newly synthesized zinc indicator incorporates as chromophore the chromeno [3',2':3,4]pyrido[1,2a] [1,3]benzimidazole moiety and belongs to the dicarboxylate-type of zinc probes. The compound is excited with visible light, exhibits high selectivity for zinc in the presence of calcium and other common biological ions, and its Zn super(2) super(+) dissociation constant is 4.0nM. Fluorescence spectra studies of ICPBCZin indicated a clear shift in its emission wavelength maxima upon Zn super(2) super(+) binding, as it belongs to the class of Photoinduced Charge Transfer (PCT) indicators, along with changes in fluorescence intensity that enable the compound to be used as a ratiometric, visible-excitable Zn super(2) super(+) probe.