CF™405S BCN, an alternative to fluorescently labeled DIBO and DBCO, reacts with azide to form 1,2,3-triazole by copper free 1,3-dipolar Huisgen cycloaddition. This copper free bioorthogonal reaction allows staining the surface of live cells or having concerns about native protein function loss with copper in cell extracts. CF™405S has 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 CF™405S dye results in much brighter signal than that using Alexa Fluor® 405.