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.