Robert Koch discovered that colloidal gold was an effective treatment for syphilis, tuberculosis and some other infections. But it may be prudent to point out a problem relating mold and CG mentioned by Herbert Freundlich in his Colloid And Capillary Chemistry (3rd ed., 1922, pp 50-507.)
"The phenomenon is often described, both in the case Zsigmondy and Bredig gold sols, of mould forming colonies in them, upon the mycelium of which the gold collects. That this happens with the Bredig sols, which from the start contain no organic compounds, appears curious. If it should prove correct that such colonies of mould appear more easily in a gold sol than in an aqueous solution of the same composition but containing no gold, one might perhaps explain this according to Nathonsohn as follows. Moulds need for their life processes small amounts of organic matter which are obtained from the air. These collect to some extent in the gold sol since they are continually adsorbed by the gold particles, whereby a stronger diffussion gradient of the substances in question is brought about..." Freundlich also mentions that aspergillus oryzae interacts strongly with dilute solutions of gold chloride, reducing it to gold (ibid.) Matthew
