Gold Nanomaterials at Work in Biomedicine *

Gold is a precious metal with a characteristic bright and beautiful hue known as the golden yellow color. When processed into sub-100 nm structures, Au shows a unique host of new properties distinct from bulk Au. In the fourth century, Au flakes were introduced into glass to craft the famous Lycurgus Cup, which can display complementary green or red color depending on how it is exposed to light. In addition to the aforementioned optical properties, Au also has a variety of inherent attributes that make its nanostructures an attractive platform for biomedical applications. Gold has a substantial history in both biomedicine and biological studies. The first report on the use of Au compounds to treat arthritis appeared in 1934. Gold clusters refer to molecular species containing a few to several hundred Au atoms, with their dimensions below a critical size for electronic energy quantization. Conventional Au nanoparticles refer to polycrystalline nanostructures with a poorly defined, quasi-spherical shape.