Conjugates prepared with the thiol-reactive Alexa Fluor® 555 C5 maleimide are spectrally similar to the Cy3 dye. Total fluorescence of Alexa Fluor® 555 conjugates is higher than that of Cy3 conjugates. Alexa Fluor® 555 dye is also more photostable than the Cy3 dye. With an emission maximum at 702 nm, the Alexa Fluor® 680 dye is well separated from that of other commonly used red fluorophores, such as the tetramethylrhodamine, Texas Red®, R-phycoerythrin (R-PE) and Alexa Fluor® 594 dyes