Method of permanent fluorescent assay

This invention relates to a method for a permanent fluorescent assay, and in particular, toward a fluorescent peroxidase-based assay utilizing a soluble p-hydroxyphenyl-containing substrate which forms an insoluble product through peroxidase activity. A method for performing a peroxidase-based assay by reacting a peroxidase enzyme with a soluble organic p-hydroxyphenyl-containing compound having the formula: wherein Q is a linear or branched 1-12 heteroatom alkyl wherein the heteroatoms are selected from C, N, O, and S, wherein the bonds connecting the heteroatom alkyl chain are single or double, wherein any carbon atom in the heteroatom alkyl chain optionally includes a substituent selected from -OH, -COOH, -NH, and -SH, and wherein R is selected from -OH, -COOH, -NH, and -CH; and converting the soluble organic p-hydroxyphenyl-containing compound into a stable insoluble product which becomes highly fluorescent after illumination, upon excitation.