Gold Nanocages: Engineering Their Structure for Biomedical Applications

Abstract

The galvanic replacement reaction between a Ag template and HAuCl4 in an aqueous solution transforms 30–200 nm Ag nanocubes into Au nanoboxes and nanocages (nanoboxes with porous walls). By controlling the molar ratio of Ag to HAuCl4, the extinction peak of resultant structures can be continuously tuned from the blue (400 nm) to the near‐infrared (1200 nm) region of the electromagnetic spectrum. These hollow Au nanostructures are characterized by extraordinarily large cross‐sections for both absorption and scattering. Optical coherence tomography measurements indicate that the 36 nm nanocage has a scattering cross‐section of ∼ 0.8 × 10–15 m2 and an absorption cross‐section of ∼ 7.3 × 10–15 m2. The absorption cross‐section is more than five orders of magnitude larger than those of conventional organic dyes. Exposure of Au nanocages to a camera flash resulted in the melting and conversion of Au nanocages into spherical particles due to photothermal heating. Discrete‐dipole‐approximation calculations suggest that the magnitudes of both scattering and absorption cross‐sections of Au nanocages can be tailored by controlling their dimensions, as well as the thickness and porosity of their walls. This novel class of hollow nanostructures is expected to find use as both a contrast agent for optical imaging in early stage tumor detection and as a therapeutic agent for photothermal cancer treatment.

Gold Nanocages for Biomedical Applications

“…[24] The magnitude of both the scattering and absorption crosssections does, however, depend on the porosity of the nanocages, with both decreasing as the number of holes increase; the SPR peak position does not change with porosity. As these calculations indicate, in addition to being able to finely tune the SPR peak position, the magnitudes of both the absorption and scattering components can be tailored by simply controlling the size and porosity of the nanocages.…”

“…In fact, exposure to a camera flash transforms the Au nanocages (deposited on a carbon-coated TEM grid and surrounded by air) into spherical droplets. [24,31] In biological systems where water offers greater thermal conductivity, the Au nanocages should not melt but rather produce a local temperature rise that can provide a therapeutic effect on cancer cells that are selectively targeted by bioconjugated Au nanocages. Such photothermal therapy is less invasive than chemotherapy or surgery and holds strong promise as a new form of cancer treatment.…”

Vibrational Response of Au−Ag Nanoboxes and Nanocages to Ultrafast Laser-Induced Heating

“…A full description of the synthesis procedure is given in Ref. [31] . Representative transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the particles are shown in Figure 1.…”

“…6 In contrast, the nanocages have truncated corners, which give rise to additional {111} facets. 31 The holes in the nanocages typically develop on the {111} facets. Five different samples were studied: three nanobox samples and two nanocage samples.…”

Environmentally responsive polymeric "intelligent" materials: the ideal components of non-mechanical valves that control flow in microfluidic systems

“…The transverse mode resonance resembles the observed peak for spheres, but the longitudinal mode is considerably red-shifted and depends strongly on the difference in length compared to width. The absorption spectrum can be shifted from the blue to the red by forming elongated wires, tubes, belts, and other more sophisticated structures (stars, rings, cubes, nanoshells and onion-like structures) that incorporate different metals (Aizpurua et al, 2003;Lu et al, 2004;Chen et al, 2005;Halas, 2005;Hirsch et al, 2006). All these shapes have been synthesized to move the absorption peaks across the absorption spectrum and design sensors and molecular labels.…”