Metallic Nanoparticles for Biomedical Applications
47
singly twinned seeds, and surface activation of bipyramids can produce beam-like
structures. Multiply twinned seeds can grow into decahedron and icosahedron, while
plate-like seed gives a hexagonal or triangular plate. The reason behind the formation
of producing different shapes with the same seed is the different capping ability
introduced by the polymer or ionic species present in the synthesis [59]. It has been
found that La-Mer nucleation, followed by the Ostwald ripening mechanism, help
to modify polydispersed particles into monodispersed [58]. By this, the lamellar
structure can be generated and get adsorbed on the surface of a metal crystal plane.
Then metal starts to grow in between layers into a 2D structure [57, 60].
Anisotropic Au NPs are found to have enormous applications in the biomedical
field mainly due to its multiple plasmonic behaviours, and it can be tuned to the
near-infrared region simply by varying the reaction concentration, seed parameters
and seed to reagent ratio [61]. The shape evolution of Au NPs with a seeded growth
method has been studied by Langille et al. [62]. They fabricated ten different shapes
of Au nanostructures successfully and investigated the effect of reducing agents,
halides, and the presence of additives on the shape evolution of Au NPs using a
seeded growth method. Figure 9a–c shows how the concentration of weak reducing
agent ascorbic acid can control the shape. Increasing the concentration of reducing
agent increases the rate of gold ion reduction. Hence, it is preferred for the kinetically
favourable growth of particle morphology. {111} faceted octahedra were formed with
0.5 mM ascorbic acid, while {100} faceted cubes were evolved with 2 mM ascorbic
acid. Further increase in ascorbic acid concentration (10 mM) leads to the formation
of ill-formed trisoctahedra with high index facets. Hence, the overall trend is that
increased concentration of reducing agent leads to the formation of higher energy
Fig. 9 Shape controlled synthesis of Au NPs using seed-mediated growth method under controlled
pH environment; SEM images of NPs synthesized using various concentrations of reducing agent,
10 mM CTA-Br and a 0.5 b 2 and c 10 mM of ascorbic acid, d schematic representation of the effect
of halide on seeded growth of Au NPs. Effect of halide in the presence of silver ions; SEM images
of synthesized particles with 40 mM CTA-Cl, 10 μM AgNO 3 and e 0, f 10, g 20 and h 50 μM
NaBr. Reprinted with permission from [62]. Copyright (2012) American Chemical Society
47
singly twinned seeds, and surface activation of bipyramids can produce beam-like
structures. Multiply twinned seeds can grow into decahedron and icosahedron, while
plate-like seed gives a hexagonal or triangular plate. The reason behind the formation
of producing different shapes with the same seed is the different capping ability
introduced by the polymer or ionic species present in the synthesis [59]. It has been
found that La-Mer nucleation, followed by the Ostwald ripening mechanism, help
to modify polydispersed particles into monodispersed [58]. By this, the lamellar
structure can be generated and get adsorbed on the surface of a metal crystal plane.
Then metal starts to grow in between layers into a 2D structure [57, 60].
Anisotropic Au NPs are found to have enormous applications in the biomedical
field mainly due to its multiple plasmonic behaviours, and it can be tuned to the
near-infrared region simply by varying the reaction concentration, seed parameters
and seed to reagent ratio [61]. The shape evolution of Au NPs with a seeded growth
method has been studied by Langille et al. [62]. They fabricated ten different shapes
of Au nanostructures successfully and investigated the effect of reducing agents,
halides, and the presence of additives on the shape evolution of Au NPs using a
seeded growth method. Figure 9a–c shows how the concentration of weak reducing
agent ascorbic acid can control the shape. Increasing the concentration of reducing
agent increases the rate of gold ion reduction. Hence, it is preferred for the kinetically
favourable growth of particle morphology. {111} faceted octahedra were formed with
0.5 mM ascorbic acid, while {100} faceted cubes were evolved with 2 mM ascorbic
acid. Further increase in ascorbic acid concentration (10 mM) leads to the formation
of ill-formed trisoctahedra with high index facets. Hence, the overall trend is that
increased concentration of reducing agent leads to the formation of higher energy
Fig. 9 Shape controlled synthesis of Au NPs using seed-mediated growth method under controlled
pH environment; SEM images of NPs synthesized using various concentrations of reducing agent,
10 mM CTA-Br and a 0.5 b 2 and c 10 mM of ascorbic acid, d schematic representation of the effect
of halide on seeded growth of Au NPs. Effect of halide in the presence of silver ions; SEM images
of synthesized particles with 40 mM CTA-Cl, 10 μM AgNO 3 and e 0, f 10, g 20 and h 50 μM
NaBr. Reprinted with permission from [62]. Copyright (2012) American Chemical Society