A hydroxyquinolone compound formulated as a fluorescent dye for protein detection, assay, quantitation, etc. The hydroxyquinolone compound may be modified, for example, by adding or removing sulfate groups, changing hydrocarbon chain lengths, etc. to result in more desirable properties such as enhanced binding to basic proteins, enhanced solubility, etc. The dye has enhanced sensitivity over commercially available protein stains, and may be used to stain proteins in solution, proteins separated on gels, proteins transferred to solid supports, etc. Methods of using the dyes are also disclosed.