A cyanine-based fluorescent sensor for detecting endogenous zinc ions in live cells and organisms

The highly sensitive and selective, cyanine-based Zn2+ fluorescent sensor CTMPA was designed, prepared and utilized to monitor endogenous zinc ions in live cells and organisms. Upon addition of Zn2+ to solutions of CTMPA, an observable blue to light red color change occurs that can be monitored by using UV–vis spectroscopy. Concomitantly, a remarkably hypsochromic shift (ca.140 nm) in the emission maximum of CTMPA takes place from 730 nm to 590 nm. The observations indicate that association of the probe with Zn2+ leads to shortening of the conjugated, π-electron system in the cyanine dye, the phenomenon likely responsible for the large hypsochromic shift observed in emission spectra. Since CTMPA has meritorious features, including a large spectral shift induced by Zn2+, a low fluorescence background and a high sensitivity toward Zn2+, CTMPA was employed to monitor endogeneous zinc ions released during apoptosis and trace intact Zn2+ during zebrafish development. Owing to its low background and high sensitivity, CTMPA serves as the first probe for fluorescence detection of neuromasts in zebrafish. The results obtained from experiments using live cells and organisms suggest that CTMPA will be a highly useful probe in zinc biology studies. The effort has demonstrated that a strategy, which relies on changes in the π-electron conjugation length of cyanine molecules promoted by guest coordination, has great potential for the creation of cyanine-based probes.