Shedding Light on the Growth of Gold Nanoshells

Abstract

Nanostructured particles containing noble metals can have highly tunable localized surface plasmon resonances and are therefore of particular interest for numerous applications. Nanoshells comprising a dielectric core and gold or silver shell are a widely researched systems because of the strong dependence of their optical properties on the ratio of core diameter to shell thickness. Although seeded-growth procedures have been developed to produce these particles, the many reported studies show significant variation in the nanoshell morphologies and hence optical properties. In order to establish processes that reproducibly synthesize nanoshells with high optical quality, it is necessary to develop techniques that monitor changes at the core particle surface during shell growth. For that purpose, we have carried out in situ nonlinear second-harmonic scattering (SHS) and linear vis-NIR extinction spectroscopy simultaneously during the seeded growth of gold nanoshells on silica core particles. Our SHS measurements show a striking variation in the nonlinear optical properties of the growing gold nanoshells. In comparison with linear optical measurements and with scanning electron microscopy (SEM) images made of gold nanoshells produced with varying shell completenesses, the SHS signal was observed to reach a peak intensity at a stage prior to shell closure. We attribute this high sensitivity of the SHS signal to the incomplete nanoshell surface morphology to the generation and subsequent degeneration of regions of electric field enhancement at gaps between isolated gold islands, which grow and coalesce. This conclusion is corroborated by finite-difference time-domain simulations of incomplete nanoshells. We suggest that the in situ analytical approach demonstrated here offers significant promise for future activities regarding the in-process optimization of the morphology and optical properties of metal nanoshells and other nanostructured plasmonic particles.

Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

“…With the original reaction rate, gold nanoshell formation was completed at the outlet and the growth process could not be traced. The TEM images in Figure S9 (Supporting Information) demonstrate that as the reaction time increases, gold islands gradually grow and merge with each other, which agrees with the in situ measurements of second‐harmonic light scattering . This result along with the XRD measurement in Figure E suggests that the structure of gold nanoshells is multicrystalline formed through the fusion of AuNP seeds.…”

Nonlinear plasmonic imaging techniques and their biological applications

“…Because SHG can point out defects that linear responses cannot, it is attractive in some specific nanoparticle geometries such as the nonlinear optical characterization of gold nanotips by incident beams with azimuthal and radial polarizations [135]. Based on the structural sensitivity, SHG is capable to provide useful information during the chemical synthesis of plasmonic nanoparticles [136][137][138][139]. From the same principle but in a completely different context, SHG emission from plasmonic nanoparticles also finds application in laser beam characterization, which is a crucial parameter for laser microscopy and imaging [33,140].…”

Comparative hyperthermia effects of silica–gold nanoshells with different surface coverage of gold clusters on epithelial tumor cells

“…[1][2][3][4] Hybrid nanoshells with tailored optical properties possess the highly tunable plasmon resonance of collective oscillations of free electrons across the visible into the near-infrared (NIR) region, where optical transmittance in the tissue is optimized. Tunable optical properties of nanoshells conjugated with targeting moieties or antibodies can provide noninvasive optical diagnosis and therapeutic payloads such as hyperthermia cancer therapy, photothermal-triggered drug release, and bio-imaging with cell targeting.…”

“…12,13 Nanomicelles with Au shells are designed to be multifunctional drug-delivery vehicles and to combine bio-imaging, targeting, and light-triggered drug release. 14 Since the first report 1 regarding seed-mediated fabrication of silica-gold nanoshell (SGNS) nearly two decades ago, numerous studies [2][3][4][5][6]8,[13][14][15] have focused on the fabrication of SGNS exhibiting robust structural integrity and the tunable optical resonance by simply adjusting the core-shell ratio across the metal interface, and there have been many attempts to utilize the strong NIR absorption of SGNS as a phototriggered hyperthermia agent on the morbidity of tumor cells. However, there have been concerns regarding the potential human carcinogenicity of silica core materials.…”