Allophycocyanin (APC) is a phycobiliprotein isolated from Spirulina sp., a blue-green alga. Like other phycobiliproteins, APC is fluorescent, with an extremely high absorptivity and a high quantum efficiency. It is a protein which can be easily linked to antibodies and other proteins by conventional protein cross-linking techniques without altering its spectral characteristics. Its strong absorption at 633 nm and 647 nm makes the tandem one of the best fluorophores used with a red laser in flow cytometry applications.

APC-iFluor 700 is spectrally similar to Alexa Fluor® 700 tandem. It is a popular color used in flow cytometry with a primary absorption peak is at 651 nm with emission peak at ~710 nm.

For an example antibody conjugation protocol, please see here.