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Colloidal gold is a sol or colloidal suspension of submicrometre-size nanoparticles of gold in a fluid, usually water. The liquid is usually either an intense red colour (for particles less than 100 nm) or blue/purple (for larger particles).〔Bernhard Wessling, ''Conductive Polymer / Solvent Systems: Solutions or Dispersions?'', 1996 ((on-line here) )〕〔University of Wisconsin–Madison: (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 times )〕〔C. N. Ramachandra Rao, Giridhar U. Kulkarni, P. John Thomasa, Peter P. Edwards, ''Metal nanoparticles and their assemblies'', Chem. Soc. Rev., 2000, 29, 27–35. ((on-line here; mentions Cassius and Kunchel ))〕 and materials science. The properties of colloidal gold nanoparticles, and thus their applications, depend strongly 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== Known, or at least used (perhaps proceeding by accident without much understanding of the process) since ancient times, the synthesis of colloidal gold was crucial to the 4th-century Lycurgus Cup, which changes colour depending on the direction of the light. Later it was used as a method of staining glass. A so-called Elixir of Life, a potion made from gold, was discussed, if not actually manufactured, in ancient times. In the 16th century, the alchemist Paracelsus claimed to have created a potion called ''Aurum Potabile'' (Latin: potable gold). In ''The newe iewell of health'', 1576, translator George Baker promoted the use and preparation of potable gold, along with other "most excellent secretes of phisicke and philosophie". In the 17th century, the glass-colouring process was refined by Andreus Cassius and Johann Kunckel, allowing them to produce a striking deep-ruby colored form of glass. In 1842, John Herschel invented a photographic process called chrysotype (from the Greek χρῡσός meaning "gold") that used colloidal gold to record images on paper. Modern scientific evaluation of colloidal gold did not begin until Michael Faraday's work of the 1850s.〔V. R. Reddy, "Gold Nanoparticles: Synthesis and Applications" 2006, 1791, and references therein〕〔Michael Faraday, ''Philosophical Transactions of the Royal Society'', London, 1857〕 Paracelsus' work is known to have inspired Faraday to prepare the first pure sample of colloidal gold, which he called 'activated gold', in 1857. He used phosphorus to reduce a solution of gold chloride. For a long time, the composition of the Cassius ruby-gold was unclear. Several chemists suspected it to be a gold tin compound, due to its preparation. Faraday was the first to recognize that the color was actually due to the minute size of the gold particles. In 1898, Richard Adolf Zsigmondy prepared the first colloidal gold in diluted solution. Apart from Zsigmondy, Theodor Svedberg, who invented ultracentrifugation, and Gustav Mie, who provided the theory for scattering and absorption by spherical particles, were also interested in understanding synthesis and properties of colloidal gold.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Colloidal gold」の詳細全文を読む スポンサード リンク
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