The use of dual reductants in gold nanoparticle syntheses

We present novel syntheses of gold nanoparticle colloids using two reducing agents simultaneously as dual reductants. These colloids were characterised by absorption spectroscopy, hydrodynamic distribution data and transmission electron microscope images, and compared to those produced by single reducing agents. The use of tannic acid and sodium borohydride together has resulted in small spherical particles and a brown coloured colloid, and has demonstrated how the size of the reducing/stabilising agent can directly influence the size of the resulting nanoparticles. Further, the simultaneous use of tannic acid and ascorbic acid has given purple/blue and blue/grey shades resulting from quasi-spherical and anisotropic particles respectively. This illustrates how dual reductants can be utilised as a means to control particle shape. Two reducing agents can be used simultaneously to control nanoparticle shape and produce anisotropic nanoparticles without a structure directing agent.