R-Phycoerythrin (R-PE), a fluorescent protein from phycobiliprotein family, is isolated from red algae. SMCC Activated R-PE is chemically modified with SMCC. SMCC reacts with the primary amine on R-PE and introduces maleimide groups to R-PE. These maleimide groups easily react with thiol groups of target protein without the need for any additional activation, resulting in convenient conjugation of R-PE with proteins. R-PE’s primary absorption peak is at 565 nm with secondary peaks at 496 and 545 nm. The broad excitation spectrum provides the advantage for multi-color immunofluorescent staining or cell sorting. R-PE and the closely related BPE are the most intensely fluorescent phycobiliproteins with orange fluorescence. They are significantly brighter and more photostable than conventional organic fluorophores. R-PE conjugates are widely used in applications such as flow cytometry, live cell staining, and immunofluorescent staining.