Abstract
Catanionic vesicles spontaneously formed by mixing the anionic surfactant bis(2-ethylhexyl) sulfosuccinate sodium salt with the cationic surfactant cetyltrimethylammonium bromide were used as a reducing medium to produce gold clusters, which are embedded and well-ordered into the template phase. The gold clusters can be used as seeds in the growth process that follows by adding ascorbic acid as a mild reducing component. When the ascorbic acid was added very slowly in an ice bath round-edged gold nanoflowers were produced. When the same experiments were performed at room temperature in the presence of Ag+ ions, sharp-edged nanoflowers could be synthesized. The mechanism of nanoparticle formation can be understood to be a non-diffusion-limited Ostwald ripening process of preordered gold nanoparticles embedded in catanionic vesicle fragments. Surface-enhanced Raman scattering experiments show an excellent enhancement factor of 1.7 · 105 for the nanoflowers deposited on a silicon wafer.
Highlights
The size- and shape-dependent optical properties of gold nanoparticles are of special interest in different fields of catalysis [1], photonics [2], sensing [3], and for biomedical uses [4, 5]
The giant vesicles (GVs) in the μm range are surrounded by a shell, similar to the sodium dodecylsulfate (SDS)/ cetyltrimethylammonium bromide (CTAB)-based catanionic vesicles obtained by Tah et al [35]
We have shown by HRTEM and asymmetric flow field flow fractionation (AFFFF) that gold clusters of diameter 2 nm show an absorption maximum at 360 nm [43]
Summary
The size- and shape-dependent optical properties of gold nanoparticles are of special interest in different fields of catalysis [1], photonics [2], sensing [3], and for biomedical uses [4, 5]. Those anisotropic particles leads in surface-enhanced Raman scattering (SERS) to an increased electromagnetic field, which enhances the Raman signal and enables the investigation of catalytic reactions [15,16,17,18]. The more exotic nanostars turned into the focus of the relevant research [20, 21]
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