Colloidal gold is a colloid, or suspension of particles of gold in a liquid, usually water. Its color is normally either a deep red or a dirty goldish color, the latter being the color of the suspension of larger particles. While it has existed since ancient times, new applications for this substance have great potential impact in many fields.
The suspension of gold particles dates back as far as the ancient Roman times when it was used to stain glass, producing vivid colors, their intensity and hue determined by the concentration of gold utilized and the size of the particles. It is also noted in throughout history and across cultures for its use in elixirs and potions. In general, gold has always been maintained to be of great value, not only as a means of monetary exchange, but also for its health benefits and therapeutic value.
The synthesis of colloidal gold can be done in several ways, some of the techniques developed include those by Turkevich, Brust/Schiffrin and Perrault/Chan. Most methods involve the formulation of a reduction of chloroauric acid which, when rapidly stirred and upon the addition of a reducing agent, creates a supersatured solution within which the neutralized gold atoms precipitates in the form of sub-nanometer particles. To these the remaining gold atoms attach resulting in particles that are remarkable uniform in size. Other methods include sonolysis and laser ablation.
There is a significant amount of research being done within many scientific fields of the substance and its potential use in electronics, nanotechnology, electron microscopy, and other applications. In the same way that the Romans and the Egyptians found that gold was well tolerated by the body and valuable for both spiritual and medicinal purposes, modern scientists are taking this several steps farther and its use may lead to breakthroughs in these fields.
Of note is the extensive and interesting research being done examining colloid gold’s potential in medical applications. These include its use as a pain reliever and even as a possible cure, in conjuction with other methods, of Alzheimer’s disease. Other applications include its use as a drug carrier via nanosized particles, as a way to target and detect tumors using SERS, and the use of gold nanorods as photothermal converters of near infrared light to ablate cancers and other targets within the human body.