Gold Nanocages Engineering Their Structure for Biomedical Appications

Gold Nanocages: Engineering Their Structure for Biomedical Appications Xia et al. , University of Washington Andrew van Bommel February 28 th, 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 • Ag. NO 3 is reduced by ethylene glycolnanocrystal seeds • More Ag atoms are added to the seeds as Ag. NO 3 is constantly reduced • Cubes: – Preferential addition to {111} – Sharp corners produces

Conversion into Au nanocages • HAu. Cl 4 reduced by Ag nanostructures: 3 Ag + Au. Cl- Au + 3 Ag+ + 4 Cl- • 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 HAu. Cl 4: • 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