nanoshells

Nanoshells are a class of core–shell nanoparticles consisting of a dielectric core, typically silica, surrounded by a thin metallic shell, usually gold. By adjusting the core radius and shell thickness, their localized surface plasmon resonance can be tuned across the visible to near-infrared spectrum. This tunability produces strong optical absorption and scattering, with the resonance peak shifting into the biological near-infrared window as geometry is varied, enabling interaction with tissue at clinically relevant wavelengths.

They are generally fabricated in two steps: synthesis of monodisperse silica cores, followed by controlled deposition of a continuous gold shell. The surface of nanoshells can be functionalized with biomolecules or coated with biocompatible polymers such as polyethylene glycol to improve stability, dispersibility, and biocompatibility in physiological environments.

The optical properties of nanoshells make them attractive for biomedical applications. Their strong near-infrared absorption enables photoacoustic and other optical imaging modalities, while the same absorption allows efficient photothermal conversion for targeted tumor ablation. In addition, nanoshells can serve as platforms for drug delivery or as biosensors that detect molecular binding via shifts in plasmon resonance.

In vivo and clinical translation face challenges related to safety and clearance. While gold is generally considered biocompatible, the silica core and surface chemistry influence toxicity and long-term fate. Reproducible manufacturing, biodistribution, immune response, and regulatory considerations are active areas of research.