North Carolina State University researchers have a developed a technique for efficiently producing nanoscale gold rods in large quantities while simultaneously controlling the dimensions of the nanorods and their optical properties. The optical properties of gold nanorods make them desirable for use in biomedical applications ranging from imaging technologies to cancer treatment.
“This technique should facilitate the economical manufacture of large volumes of gold nanorods,” says Dr. Joseph Tracy, an associate professor of materials science and engineering at NC State and senior author of a paper on the work.
Ref: Large-Scale Synthesis of Gold Nanorods through Continuous Secondary Growth. Chemistry of Materials (10 October 2013) | DOI: 10.1021/cm402277y
Gold nanorods (GNRs) exhibit a tunable longitudinal surface plasmon resonance (LSPR) that depends on the GNR aspect ratio (AR). Independently controlling the AR and size of GNRs remains challenging but is important because the scattering intensity strongly depends on the GNR size. Here, we report a secondary (seeded) growth procedure, wherein continuous addition of ascorbic acid (AA) to a stirring solution of GNRs, stabilized by cetyltrimethylammonium bromide (CTAB) and synthesized by a common GNR growth procedure, deposits the remaining (∼70%) of the Au precursor onto the GNRs. The growth phase of GNR synthesis is often performed without stirring, since stirring has been believed to reduce the yield of rod-shaped nanoparticles, but we report that stirring coupled with continuous addition of AA during secondary growth allows improved control over the AR and size of GNRs. After a common primary GNR growth procedure, the LSPR is ∼820 nm, which can be tuned between ∼700 and 880 nm during secondary growth by adjusting the rate of AA addition or adding benzyldimethylhexadecylammonium chloride hydrate (BDAC). This approach for secondary growth can also be used with primary GNRs of different ARs to achieve different LSPRs and can likely be extended to nanoparticles of different shapes and other metals.