Precision 'stubby' gold nanorod synthesis offers hope for biomedicine

Gold nanorods made by the North Carolina State University process are said to be suited to biomedical applications due to their optical properties.

‘This technique should facilitate the economical manufacture of large volumes of gold nanorods,’ said Dr Joseph Tracy, an associate professor of materials science and engineering at NC State and senior author of a paper on the work. ‘And that should be good news for both the science community and the biomedical research and development community.’

The NC State team started with an existing technique, in which gold nanorods are formed by mixing two chemical solutions together. However, the technique converts 30 per cent of the gold into nanorods with the remains dissolved in solution.

To convert the remaining 70 per cent of the gold into nanorods, the researchers added a continuous stream of ascorbic acid to the solution, while constantly stirring the mixture, which pulls the gold out of the solution and deposits it on the existing nanorods.

The researchers also found that the slower they added the ascorbic acid, the ‘stubbier’ the nanorods became, an important outcome as the optical properties of gold nanorods depend on their aspect ratio.

Long, thin gold nanorods absorb light at wavelengths greater than 800 nanometres (in the near infrared spectrum), while shorter, wider gold nanorods absorb light at wavelengths below 700 nanometres (red or dark red).

‘The ability to fine-tune these optical properties will likely be useful for the development of new biomedical applications,’ Tracy said in a statement.

The paper detailing the work, Large-Scale Synthesis of Gold Nanorods through Continuous Secondary Growth, is published online in Chemistry of Materials.

The work was supported by the US National Science Foundation and National Institutes for Health.