Gold nanorods with varying aspect ratios have been utilized in recent years for a wide range of applications
including vaccines, surface enhanced Raman spectroscopy (SERS) substrates, and as medicinal therapeutic
agents. The surfactant-directed seed mediated approach is an aqueous based protocol that
produces monodisperse nanorods with controlled aspect ratios. However, an inherent problem with this
approach is poor efficiency of gold conversion from HAuCl4 into nanorods. In fact only 15% of gold is
converted, motivating the need for alternate synthetic protocols in order to make the process more scalable
and efficient as gold nanorods progress toward commercial applications. In the current study, we
have significantly improved this conversion by growing rods in several iterations of supernatant solutions
that were previously discarded as waste. Inductively coupled plasma mass spectrometry (ICP-MS) data
indicates 14% gold conversion per nanorod solution with a total recovery of 75%. Gold nanorods prepared
in consecutive supernatant solutions generally have slightly increased aspect ratios and maintain
stability and monodispersity as measured by UV–vis and TEM. The increased nanorod yield minimizes
gold waste and results in a greener synthetic approach.