CytoTell® Red 650 is a far-red fluorescent cell proliferation indicator developed for monitoring cell division and long-term tracking of live cells by flow cytometry and fluorescence microscopy. As cells divide, the dye is distributed equally between daughter cells, resulting in progressive halving of fluorescence intensity that enables visualization of successive cell generations. CytoTell® Red 650 exhibits peak excitation around 630 nm and peak emission around 660 nm, making it compatible with excitation using the 633 nm red laser line and detection with 660/20 bandpass filters commonly used for APC, Alexa Fluor® 647, and Cy5® channels.

CytoTell® Red 650 was developed for multicolor applications where CFSE and other fluorescein-based proliferation dyes are not suitable due to spectral overlap with GFP or FITC-labeled antibodies. The dye exhibits minimal cytotoxicity and provides spectral separation from fluorescein-based probes for multiparameter cell analysis. Up to 8 generations may be visualized in suitable experimental systems, and the dye can be used for long-term tracking of labeled cells. Two-parameter flow cytometry analysis may improve resolution between successive cell generations, particularly between undivided cells and first-generation daughter cells. CytoTell® Red 650-labeled cells may be fixed and permeabilized for intracellular target analysis using standard formaldehyde-containing fixatives and saponin-based permeabilization buffers.