Seeded growth of gold nanorods: the effect of sulfur-containing quenching agents

Herein we present a study on the efficacy of selected sulfur-containing species as growth quenchers andmetal ion scavengers in the framework of gold nanorod (GNR) synthesis. The here utilized seeded growth method is the referenceGNRsynthesis approach.However,GNRs synthesized according to it are prone to morphological changesuponaging,promotedbythepresenceofunreacted metal ions in the stock suspension. This, in turn, leads to optical property changes. Sodium sulfide is an efficient GNR growth quencher and metal ion scavenger, because sulfide ion has a strong affinity towards noble metals used for the GNRs’ synthesis. Moving from these considerations, different sulfur-containing moleculeswere selected and their interaction with GNR surface was investigated: sulfate, sulfite, thiourea, and dodecyl sulfate were chosen for their difference in terms of net charge, size, and hydrophobicity. We initially assessed the best synthesis conditions in terms of reaction time, seed amount, silver concentration, and quencher amount. Consequently, the quencher/scavenger was varied. Thiourea, sulfite, and sulfate ions all showeda feeble, yet non-negligible, interaction with metals. Although sodium sulfide turned out to be the most efficient quencher/scavenger, also dodecyl sulfate showed evidences of adsorption on theGNRsurface, probablypromptedbyhydrophobic interactions.These findings are expected to contribute as a background for further advancements in the perfection of GNR synthetic approaches specifically in terms of post-synthesis treatments.