Abstract: Disclosed is a method for enhancing the optical signal of precious metal nanoparticles by introducing linker molecules for precious metal nanoparticles to form clusters in a stable colloidal suspension. The formation of clusters according to the present disclosure not only enhances the optical signal, but also can alter the optical spectrum, providing an alternative color for use in visual-based bioassays such as lateral flow immunoassays against the white test paper strips. The formed clusters are capable of passive adsorption of a variety of biomolecules which effectively bind onto the surface, requiring a minimum modification in the bio-assay protocol from that use for standard gold nanoparticles, which is being widely-used in lateral flow immunoassays.

Abstract: In the present invention, a method and assay for the detection of proteases and protease inhibitors using colloidal gold nanoparticles and peptide substrates, which are selectively recognized and cleaved by proteases being assayed, is disclosed. In this assay, the mechanism of signal generation relies on peptide sequence induced aggregation of gold nanoparticles, which are used as signal reporters. The peptide sequences that induce aggregation are either the intact peptide substrates or proteolytic fragments of the intact peptide substrate wherein the proteolytic fragments are produced by the protease being assayed. The present invention provides a novel, simple, sensitive, and inexpensive colloidal gold nanoparticle-based colorimetric assay that allows both visual and quantitative detection of proteases and protease inhibitors.