The excitation peak of Alexa fluor 680 is 679 nm and the maximum emission is 702 nm, which is similar to cy5.5. Alexa fluor 680 can be well distinguished from other red fluorescent groups, such as Texas Red, R-phycoerythrin, Alexa fluor 594 and Alexa fluor 647. It is an ideal three color and four color labeling dye.