CF™640R hydrazide is a far red fluorescent dye with a hydrazide group. CF™640R is much brighter than Cy®5 and at least as bright as Alexa Fluor® 647 when excited at 633 or 635 nm. However, the most important advantage of CF™640R is its exceptional photostability. CF™640R is far more photostable than the cyanine-based dyes Cy®5 and Alexa Fluor® 647. It is also more photostable than Atto 647N, a dye that has been extensively used in single molecule-based imaging. CF™640R is also extremely water-soluble and pH-insensitive. These properties make CF™640R a much better alternative to Cy®5, Alexa Fluor® 647 and other spectrally similar dyes. Our CF™ dye hydrazides are bright, extremely water-soluble and nontoxic. These properties make the dyes excellent fixable polar tracers for neurons, or for gap junction studies. The dyes can be introduced into cells by microinjection. Hydrazides also can be used for labeling aldehyde or ketone groups, such as carbohydrate molecules after peroxidation with periodate. However, for this application we recommend using CF™ dye aminooxy forms, which are more reactive toward these groups than hydrazide forms.Compatible with the NucleoCounter® NC-3000™.