Shape Transformation of Gold Nanoparticles from Octahedron to Cube Depending on in situ Seed-Growth Time

Abstract

Synthesis of shape-controlled metal nanoparticles has been intensively studied due to their shape-dependent material properties. [1][2][3][4][5] In particular, gold nanoparticles have received a great attention due to their usefulness in optical, chemical, and biological applications.3,6-9 Various shapes of gold nanoparticles, such as cubes, octahedrons, rods, and branched multipods have been prepared in a high yield using seed-mediated method which provides better control over the shape and size distribution of the nanoparticles. 10-17In this study, we report on the observation that the particle shape was dependent upon in situ seed-growth time of our one pot synthesis of gold nanoparticles. It was found that the cube yield increased with the increase of the seed-growth time while a short seed-growth time (~15 min) resulted in the formation of high-yield octahedral particles. This can also be regarded as a simple and convenient method of synthesizing octahedral and cubic gold nanoparticles in aqueous solution. Although the synthetic methods using cetyltrimethylammonium bromide (CTAB) and ascorbic acid have been previously reported, the shape control of gold nanoparticles relied on the adjustment of the concentration of reducing agent, gold precursor, activators, or seed particles. In this report, shape of gold nanoparticles was controlled by tuning only one parameter, the in situ seed-growth time, without any variation in reactant concentrations or in the way of a separate seeding.Typically, a 250 μL of 10 mM HAuCl 4 ·3H 2 O solution was added to a 20 mL of 10 mM CTAB aqueous solution. After the solution was gently mixed, 100 μL of 100 mM L-ascorbic acid was added to this solution and mixed thoroughly. The color of the resulting solution changed from yellow to colorless and the mixture was left to stand for 30 min to reduce Au 3+ to Au + sufficiently and then 30 μL of 100 mM NaOH was carefully injected to the bottom of the reaction vessel. The mixtures were left undisturbed for seed particles to form and grow for different periods of time (in situ seedgrowth time). The solutions were then mixed thoroughly after the period of time.As shown in Figure 1, the seed-growth time influenced the shape of gold nanoparticles. It is well-known that the interaction between the faceting tendency of the stabilizing agent and the rate of Au 0 supply to the crystallographic planes is important for the formation of various shapes.14 Generally, the shape control of nanoparticles of an fcc crystal is related to their surface energies associated with different facets which increase in the order of γ {111} < γ {100} < γ {110} .2 However, stabilizing agent can interact selectively with different metal crystal facets and alter their surface energies. In case of CTAB, it prefers the {100} facets to the {111} facets.As described before, gold nanoparticles were synthesized by mixing an aqueous solution of HAuCl 4 , CTAB, and ascorbic acid, followed by the addition of NaOH into the reaction mixture. NaOH was added into the reaction mixtur...

Impact of nanogold morphology on interactions with human serum

“…A modified version of the method detailed by Kim et al was employed to synthesise AuNC. 33 In a typical synthesis 40 mL of 10 mM CTAB was made in a 50 mL tube to which 500 μL of 10 mM HauCl4 was added. The solution was mixed by gentle inversion before 200 μL of 100 mM L-ascorbic acid was added, followed by repeated inversion to mix.…”

Size, shape and surface chemistry of nano-gold dictate its cellular interactions, uptake and toxicity

“…While CTAB is most commonly associated with gold nanorod formation, it can also be used to encourage cubic AuNP formation [157,[160][161][162]. Gold seed particles which are intended for cubic shaped particle growth such as those used by Kim et al, are typically stable, with {111} faces accessible [163].…”

“…Gold seed particles which are intended for cubic shaped particle growth such as those used by Kim et al, are typically stable, with {111} faces accessible [163]. When in the presence of CTAB, which preferentially binds to the {100} face over the {111} face, the {100} faces are effectively "blocked", and growth is encouraged on the {111} face, forming cubes [161]. For this to occur, the synthesis requires elevated levels of a weak reducing agent such as ascorbic acid to be included in the system.…”

“…While there are studies that discuss the synthesis of triangular/prismatic [7,78,135,144,149,277,278] and cubic [41,144,149,157,161,162] AuNPs and their potential for biological use, such particles have been the focus of relatively few biological studies in comparison to spherical nanoparticles. Following spherical AuNPs, the shape that has captured the highest interest of researchers is the gold nanorod, with the relationship between toxicity and nanorod length, or more specifically their aspect ratios, explored by many groups [64,142,260,[279][280][281][282].…”

Hydrothermal synthesis of gold polyhedral nanocrystals by varying surfactant concentration and their LSPR and SERS properties

“…16,27,28 For example, the synthesis of complicated polyhedral NCs, [29][30][31][32][33][34][35] including platonic solids 36 (tetrahedron, cube, octahedron, dodecahedron, and icosahedron) and Archimedean solids 26 (cuboctahedron, truncated cuboctahedron, truncated octahedron and truncated tetrahedron). [37][38][39][40][41][42][43][44] These solids are categorized in terms of the ancient Greek scientists and very mathematical aesthetics and symmetry in geometry. 45 Various synthetic strategies such as polyol reduction, 38 plasmon 46 and photon driven synthesis 47 and seed-assisted growth 1 have been used to achieve the geometry-control of polyhedral Au NCs with the aim to deliberately tailor their plasmonic characteristics.…”