CF405S streptavidin conjugate is prepared from high quality streptavidin and the fluorescent dye CF405S. CF405S (Ex/Em = 404/431 nm) is a blue fluorescent dye with an absorption peak wavelength that nearly coincides with the 405 nm blue diode laser line. In addition, the emission peak wavelength of the dye well centers within the blue detection window of BD flow cytometers. As a result, flow cytometry analysis using CF405S dye results in much brighter signal than that using Alexa Fluor? 405. We also offer streptavidin conjugated to CF405S (catalog no. 29033), another 405 nm-excitable dye with a longer emission wavelength similar to Pacific Blue?.