Engineering sub-100 nm multi-layer nanoshells

Abstract

Nanoshells are a novel class of optically tunable nanoparticles that consist of alternatingdielectric and metal layers. They can potentially be used as contrast agents for multi-labelmolecular imaging, provided that the shell thicknesses are tuned to specific ratios.Sub-100 nm multi-layer nanoshells can potentially have improved tissue penetration,generate a strong surface plasmon resonance, and may exhibit absorption peaks inthe visible–near-infrared (NIR) spectrum. Herein we describe the synthesis andcharacterization of bilayered concentric nanoshells with an overall diameter of around 50 nmconsisting of a gold core, a tunable silica spacer layer and an outermost gold shell,which is approximately 16 times smaller than previously described multi-layerednanoparticles. The structured nanoshells were visualized by transmission electronmicroscopy (TEM) at each step of preparation. The absorption spectra of thegold–silica bilayered nanoshells are in good agreement with Mie’s prediction and theirresonance peak position is a function of the relative thickness of silica and gold layers.