The invention provides a binding assay reagent comprising a backbone polypeptide comprising glutamic acid residues and lysine residues is proportions such that the backbone polypeptide has a net positive charge, said backbone polypeptide having a molecular mass of ≧ 2.0 x 10⁵ Daltons; an optical dye label covalently bound to the backbone polypeptide, a specific binding molecule covalently bound to the backbone polypeptide, and an enhancing peptide associated with the backbone polypeptide, said enhancing peptide being comprised of a mixture of a) acidic and basic amino acid monomer residues having opposite stereochemical configurations or b) mixtures of homopolymers of acidic amino acids and basic amino acids wherein the homopolymers may be of the same or different stereochemical configurations, and wherein said enhancing peptide is electrically neutral or has a net negative charge. The binding assay reagents exhibit enhanced binding activity over that of the dye labelled polypeptides alone and also enhance the sensitivity of the binding assay by providing increased amounts of optical label.