text: Immunogold labeling was first used in 1971 by Faulk and Taylor to identify Salmonella antigens. It was first applied in transmission electron microscopy (TEM) and was especially useful in highlighting proteins found in low densities, such as some cell surface antigens. As the resolution of scanning electron microscopy (SEM) increased, so too did the need for nanoparticle-sized labels such as immunogold. In 1975, Horisberger and coworkers successfully visualised gold nanoparticles with a diameter of less than 30 nm
  and this soon became an established SEM technique.