Conjugates prepared with the thiol-reactive Alexa Fluor® 568 C_{5 maleimide} are significantly brighter than Lisamine rhodamine B conjugates or even Rhodamine Red™-X conjugates. The red-orange-fluorescent Alexa Fluor® 568 dye is optimally excited by the 568 nm spectral line of the Ar-Kr mixed-gas laser used in many confocal laser-scanning microscopes.