Controlled synthesis of gold nanorings with structural defects assisted by elastic induction of mixed surfactants

Abstract

Controlled synthesis of gold nanorings was realized by reducing chloroauric acid in aqueous mixed solutions of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). It is revealed that the gold nanowires are induced to fabricate the gold nanorings with an average diameter of ~300 nm. The synthesis of the nanowires and the formation of the nanorings can be achieved in one step. A variety of gold nanostructures, such as short nanowires, nanorings, nanostars with a number of soft protuberances and nanopolyhedra, could be readily obtained by simply changing the CTAB/SDS molar ratio. Both the "structural defects" and the "elastic induction", which are closely related to the mixed bilayers (CTAB/SDS), are indispensable for the final formation of the gold nanorings. Four surfactants with similar structures were also used to further verify the formation mechanism.

One-Step Controlled Synthesis of Size-Tunable Toroidal Gold Particles for Biochemical Sensing

“…34 The size transition of SDS:CTAB templates from nanoscale to micrometer-scale and the binary capping effect upon temperature change may exert a subtle impact on the overall capping process, resulting in a difference in the gold growth direction and increasing the diversity of the gold structures that are grown. 9,27,32 Additionally, we found that vigorous mechanical stirring is critical to ensure the complete closure of the gold loop. Experiments carried out in static conditions (no magnetic stirring) revealed a majority of unclosed toroidal structures (Figure S6).…”

“…Although two-dimensional (2D) metal nanoring arrays produced by lithography-based processes enable great control over the periodic arrangement of the nanoring, the underlying support greatly reduces the effective surface area compared to freely floating nanorings, resulting in limited applications for biomedical research. Lithographic techniques also usually suffer from a complicated, time-consuming fabrication process with low yield and a dependence on expensive facilities. , Wet chemistry provides a direct and facile approach for nanoring synthesis. , Jiang et al reported an ultrasonic irradiation assisted aqueous synthesis of gold nanorings which had a reduced reaction time and a stable reaction condition ascribed to the Ostwald ripening process . However, since the gold nanorings were produced from oxidizing a silver nanotemplate, additional purification steps were needed to remove the AgCl impurity.…”

“…CTAB is known to have a preferentially higher adsorption rate and coverage density on Au(100) and Au(110) surfaces, which results in greater growth of gold structures along the [111] direction . The introduction of the counterionic surfactant SDS into the CTAB capping system exerts control over the growth direction of the gold structure and has previously been shown to lead to the formation of various gold structures. ,, However, to the best of our knowledge, a SDS:CTAB capping system for size-tunable controlled synthesis of toroidal-shape gold particles has not been explored previously. This reaction can be accomplished in one single step in 30 min of reaction time compared to the hours needed for previous protocols. ,, The resulting gold nanorings obtain very high purity as confirmed by energy-dispersive X-ray spectroscopy (EDS) elemental mapping, and its size can be tuned by simply elevating the reactant temperature.…”

“…25,26 Although two-dimensional (2D) metal nanoring arrays produced by lithography-based processes enable great control over the periodic arrangement of the nanoring, the underlying support greatly reduces the effective surface area compared to freely floating nanorings, resulting in limited applications for biomedical research. Lithographic techniques also usually suffer from a complicated, time-consuming fabrication process with low yield 27 and a dependence on expensive facilities. 15,16 Wet chemistry provides a direct and facile approach for nanoring synthesis.…”

“…31 The introduction of the counterionic surfactant SDS into the CTAB capping system exerts control over the growth direction of the gold structure and has previously been shown to lead to the formation of various gold structures. 9,27,32 However, to the best of our knowledge, a SDS:CTAB capping system for sizetunable controlled synthesis of toroidal-shape gold particles has not been explored previously. This reaction can be accomplished in one single step in 30 min of reaction time compared to the hours needed for previous protocols.…”