thumb|solutions of gold nanoparticles of various sizes. the size difference causes the difference in colors.  colloidal gold is a suspension (or colloid) of submicrometre-size particles of gold in a fluid, usually water. the liquid is usually either an intense red colour (for particles less than 100&nbsp;nm) or blue/purple (for larger particles).bernhard wessling, conductive polymer / solvent systems: solutions or dispersions?, 1996 (on-line here)university of wisconsinâmadison: making and conjugating colloidal metals. due to the unique optical, electronic, and molecular-recognition properties of gold nanoparticles, they are the subject of substantial research, with applications in a wide variety of areas, including electron microscopy, electronics, nanotechnology,paul mulvaney, university of melbourne, the beauty and elegance of nanocrystals, use since roman timesc. n. ramachandra rao, giridhar u. kulkarni, p. john thomasa, peter p. edwards, metal nanoparticles and their assemblies, chem. soc. rev., 2000, 29, 27â35. (on-line here; mentions cassius and kunchel) and materials science. properties and applications of colloidal gold nanoparticles strongly depend upon their size and shape. for example, rodlike particles have both transverse and longitudinal absorption peak, and anisotropy of the shape affects their self-assembly. ==history==  thumb|the newe iewell of health, 1576, trans. george baker. known, or at least used (perhaps proceeding by accident without much understanding of the process) since ancient times, the synthesis of colloida
Colloids Gold Nanoparticles