Gold nanoshells are surface plasmon resonant (SPR) nanoparticles consisting of a nanoscale silica core surrounded by an ultra-thin gold shell. Changing the ratio of the core diameter and the shell thickness tunes the absorption and scattering properties of the nanoshells across the visible and near-IR (NIR) regions of the electromagnetic spectrum. Increasing the size of the silica core, and decreasing the thickness of the gold shell cause the plasmon resonance to shift toward the NIR.
This class of plasmonic nanoparticles has a wide variety of applications, including uses in optical filters, sensing and cancer therapy. For example, one of our most popular nanoshells products has a strong plasmon resonance at 800 nm and the very high absorption in the NIR is the basis for therapies that utilize the localized heating of nanoparticles to eradicate cancer cells. Further tuning of the nanoshell size results in particles that scatter different portions of the spectrum, which can be readily observed using dark field microscopy (see image right). The tunable plasmonic properties make nanoshells of interest for Surface Enhanced Raman Scattering (SERS) applications, or as optical sensors where a shift in color of the nanoshell is indicative of the presence of a target analyte in solution.
Due to the difference in the scattering and absorption properties of the nanoshells, many variants are bichromic: for example, when a solution of 800 nm-resonant nanoshells are viewed in transmission (back lit) the nanoshells solution appears blue, but when viewed with reflected light the same solution can appear a rusty red due to scattering by the particles.
Gold nano shells resonant at 660–980 nm and are available with either polyethylene glycol (PEG) or polyvinylpyrollidone (PVP) capping agents, or in a dried formulation.
Particles with other optical properties, core/shell dimensions, or different surface capping agents are available on request. Contact us for more information about our custom fabrication abilities.
FREQUENTLY ASKED QUESTIONS
The peak resonance wavelength of my nanoshells is not exactly at the wavelength advertised. Are these nanoshells out of specification and will this affect my experiment?
For gold nanoshells, our specification is that the OD at the advertised wavelength is at least 90% of the value of the peak OD. We set it this way to make sure that the particles are functionally equivalent between lots even if the peak wavelength varies slightly from the advertised wavelength. For example, if a gold nanoshell has a peak resonance at 830 nm with an OD of 1.0, the OD value at 800 nm should be at least 0.90.
Gold nanoshells have a relatively broad peak, so even if the peak resonance is shifted from 800 nm they retain most of their absorption and scattering properties across a wide range of wavelengths. This is why nanoshells with peak wavelengths of 750 nm – 850 nm will perform nearly identically to a nanoshell peaked at 800 nm.