A Water-soluble Near-infrared Fluorescent Probe for Cysteine/ Homocysteine and Its Application in Live Cells and Mice

A near-infrared (NIR) and water-soluble probe was synthesized and studied for the detection of Cys/Hcy in aqueous solution, living cells and mice. The probe was composed of cyanine derivative as the NIR fluorescent reporting unit and pyrimidiny-thioether moiety as the Cys/Hcy responsive unit. Treatment with Cys/Hcy induced the formation of sulfur-substituted products, then intramolecular rearrangement reaction would occur to produce amino-substituted products and resulting in enhanced red fluorescence emissions. It could be applied to sense Cys/Hcy both in solution with the detection limit of 0.17 μM (or 0.32 μM) and in living cells. Cell imaging experiments proved that such a probe exhibited good cell penetration. In addition, the probe could detect Cys/Hcy in live mice with strong turn-on fluorescent response.