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. Allophycocyanin is the least stable among the major phycobiliproteins, susceptible to dissociation at low concentrations including concentrations at which some assays are performed. CL-APC is chemically cross-linked between α and  subunits, and is much more stable than APC. The crosslinked allophycocyanin has improved stability in aqueous solution. Our APC-iFluor 750 Tandem is an excellent replacement to APC-Cy7 and APC-Alexa Fluor 750 Tandem due to their similar spectral properties. Our APC-iFluor 750 Tandem is more photostable than APC-Cy7 Tandem.