Transcript Slide 1

Gold Nanocages: Engineering
Their Structure for Biomedical
Appications
Xia et al., University of Washington
Andrew van Bommel
February 28th, 2006
Introduction
• For biomedical applications, the body is highly
transparent to near-IR light, 800-1200 nm
• Sperical Au particles show extinction at 520650 nm
• Au particles can be shifted to the near-IR
region:
Note: extinction =
scattering + absorption
– Aggregation of spherical Au nanoparticles
– Elongation of Au nanoparticles into nanorods
– Emptying the interiors of spherical nanoparticles to
form hollow nanostructures
Blue-Shift
• Surface Plasmon Resonance (SPR)- free
electrons in the Au nanoparticles collectively
oscillate and scatter/absorb the incident
electromagnetic wave
• A composite spherical particle consisting of a
metallic shell and a dielectric core could give
rise to SPR modes with their wavelengths
variable over a broad range
Synthesis of Ag nanocubes
• AgNO3 is reduced by ethylene glycolnanocrystal seeds
• More Ag atoms are added to the seeds as
AgNO3 is constantly reduced
• Cubes:
– Preferential addition to {111}
– Sharp corners produces
Conversion into Au nanocages
• HAuCl4 reduced by Ag nanostructures:
3Ag + AuCl-  Au + 3Ag+ + 4Cl-
• Au atoms evolve a thin shell around each Ag
nanocube template
• By controlling the concentration of reagents,
hollow Au nanocages can be obtained with
controlled dimensions
Mechanism
i) Initiation of replacement by
selective pitting of the Ag
nanocubes
ii) Formation of nanobox made of a
Au/Ag alloy
iii)Generation of pores through a
dealloying process (Ag selectively
oxidized)
iv)Ag nanotube template is dissolved
Optical Characterization
• UV-vis-NIR spectra: increasing the amount of
HAuCl4:
• Peak broadening due to variations in wall
thickness
Applications
• Photothermal effectselective attachment to
cancer cells with localized
heating
• Can add functionalities to
target cancer cells for
photothermal therapy or
diagnosis