Fluorescent antigen conjugates are provided comprising antigens covalantly bonded to at least one 2,7-dialiphatic substituted-9-phenyl-6-hydroxy-3H-xanthen-3-one, wherein the 1- and 8-positions are unsubstituted. Also provided are novel fluorescent compounds absorbing at wavelengths in excess of 500 nm, having active functionalities for linking to the antigen. Finally, methods are provided for analyzing antigens in serum, whereby serum interference is avoided.
Method for performing fluorescent protein binding assay employing novel alkyl substituted fluorescent compounds and conjugates