Seedless synthesis of gold nanorods in dilute surfactant solutions using hydrophobic polyphenols curcumin and quercetin

The peculiarities of seedless growth of gold nanorods (GNRs) in micellar solutions of cetyltrimethylammonium bromide (CTAB) in the presence of hydrophobic polyphenols – curcumin and quercetin – were studied. The ability of these polyphenols to solubilize in CTAB micelles makes it possible up to 10 times (from 100 to 10 mM) reduce its content in the reaction system. Depending on the concentration, these polyphenols can serve as both reducing agents for metal ions and as hydrophobic additives, promoting the transition of spherical micelles into rod-shaped ones and ensuring the preferential formation of GNRs. Using curcumin as an example, the threshold concentration at which the transition between these two functions of the polyphenol occurs, as well as the concentration ranges of the other components in the reaction system, providing the formation of GNRs with optimal optical characteristics, were determined. The influence of CTAB concentration on the reducing properties of curcumin was discovered for the first time, and an explanation for this effect was proposed. The possibility of controlling the rate of gold ions reduction and the morphology of the resulting nanoparticles by the addition of alkali has been demonstrated. • The use of curcumin or quercetin in Au nanorods synthesis allows reducing the CTAB concentration at least 10 times. • The reducing ability of both polyphenols diminishes with an increase of CTAB concentration. • The reducing ability of both polyphenols depends on the localization their molecules in CTAB micelles. • The addition a small amount of NaOH to the reaction system promotes the nanorods formation.