Gold nanoparticles can be synthesized and stabilized by peptides, proteins, DNA and chemical/biological polymers. The reducing reagents could be either inorganic such as sodium/potassium borohydrate, hydrazine and salts of tartarate, or organic ones like, sodium citrate, ascorbic acid and amino acids capable of being oxidized. Various reagents serve as stabilizing agent to make the nanoparticles formed to be stabile for further use. These include the polymers such as different kind of polyethyleneglycol, polyvinyl alcohol, polyvinyl pyrilidon and the surfactant viz, sodium dodycel sulfate, tween 80, triton and carbohydrates like chitosane.

Chemical reduction

Chemical reduction technique employing L-Tryptophane as reducing agent can be used to synthesis gold nanoparticles. In this method, solutions of HAuCl4.3H2O, L-Tryptophane and polyethyleneglycol 1000 are prepared. Gold nanoparticle synthesis is done by Turkevich method. In this method, HAuCl4.3H2O is heated to its boiling on a magnetite stirrer, to which, reducing agent is injected. Heating is continued till the color of the solution changed from colorless to pink/red. Few milliliter of polyethyleneglycol 1000 at room temperature is added to the above solution. The formed gold nanoparticles are stable and the diameter of the nanoparticles can range from 10-25 nm. While synthesizing gold nanoparticles, reduction of anions is important and this is brought about by tryptophane. Such gold nanoparticles have promising application in nanomedicine, nanobiotechnology and other related fields.