Au Gold nanopowders have very special local surface plasmon ibration (LSPR) optical properties. When the incident light energy frequency is same as the electrons on the surface of the rice particles, the surface electrons group resonance. LSPR is not only related to materials, but also to the shape, surrounding medium, distance between particles, and symmetry of particles. Different types and sizes of Au nanopowder will have different absorption peaks, while changing the distance between particles, medium, etc. and cause displacement of absorption peak. For DNA or other biomolecules to distance the nanoparticles, for the 20-30nm gold nano powder is the best choice.

Au gold nanopowder with the property of agglomerate leads to the reduction of color. The gold nanopowders are combined with antibodies to establish a micro-agglutination test to detect the corresponding antigen. Like indirect hemagglutination, the agglomerated particles can be directly observed with the naked eye.