Engineering sub-100 nm multi-layer nanoshells

Nanoshells are a novel class of optically tunable nanoparticles that consist of alternating dielectric and metal layers. They can potentially be used as contrast agents for multi-label molecular 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 in the visible-near-infrared (NIR) spectrum. Herein we describe the synthesis and characterization of bilayered concentric nanoshells with an overall diameter of around 50 nm consisting of a gold core, a tunable silica spacer layer and an outermost gold shell, which is approximately 16 times smaller than previously described multi-layered nanoparticles. The structured nanoshells were visualized by transmission electron microscopy (TEM) at each step of preparation. The absorption spectra of the gold-silica bilayered nanoshells are in good agreement with Mie's prediction and their resonance peak position is a function of the relative thickness of silica and gold layers.