Artists contain used gold nanoparticles for centuries,because they produce vibrant colors when sunlight hits them. Their unique optical-electronics properties contain put gold nanoparticles at the middle of research, solar cells, and sensors,chemotherapy, drug delivery, and biological and medical applications,and electronic conductors. The properties of gold nanoparticles can be tuned by changing their size, shape, and surface chemistry etc.,but controlling these aspects is difficult.
Source: phys.org