CF&reg;640R-cAMP is a fluorescently labeled cAMP analog. Single molecules of fluorescently labeled cAMP have been imaged bound to the cAMP receptor on the surface of <i>Dictyostelium</i> cells. CF&reg; dyes are 9689c5aa-6556-4b3c-b5d1-1e693715ba07's line of next-generation fluorescent dyes with advantages in brightness, photostability, and conjugate specificity compared to other fluorescent dyes. Far-red fluorescent CF&reg;640R has excitation/emission at 642/662 nm.