Abstract: Methods are herein described which reduce the non-specific light scattering background from polymeric microspheres in aqueous suspension to a level where individual metal or metal-like plasmonic nanoparticles that have been chemically bound to the surface of individual polymeric microspheres can be imaged by high resolution optics and enumerated by image analysis software. The non-specific light scattering background is reduced by employing aqueous-miscible solvents to remove residual water at the microsphere surfaces and resuspending the microspheres in a fluid having a refractive index substantially similar to the refractive index of polymeric microspheres. Embodiments of the method disclosed herein enable sensitive quantitative assays for ligand receptor binding, antigen antibody binding and nucleic acid hybridization binding. The embodiments disclosed herein further may employ polystyrene microspheres and gold plasmonic nanoparticles.