Plasmon resonance of gold nanoshells: Sensitivity to the local dielectric environment

摘要

The sensitivity of the gold nanoshell localized plasmon resonance (LPR) to the local dielectric environment is studied in terms of a multilayered sphere with a silica core, gold nanoshell, and two dielectric modeling the primary functionalization of gold surface and the secondary binding of target biomolecules. The adsorption-induced changes in the extinction and scattering spectra are analyzed by the dipolar Rayleigh approximation and multilayered Mie codes for gold shell diameters 20-160 nm and (gold shell thickness)/(gold shell diameter) ratios 0.025-0.75. The dependence of the LPR extinction and scattering spectral shifts on the conjugate structure can be well described by an analytical expression derived in the dipole approximation. Our analysis predicts greater sensitivity of nanoshell's LPR to the local dielectric environment as compared to the solid gold spheres, whereas the absolute changes in spectral maxima are less than those for the equivolume spheres. By contrast, the differential extinction and scattering spectra of gold nanoshells can be used as a sensitive tool for optical monitoring of biomolecular binding onto nanoshell surface. The maximal local-environment sensitivity has been found for the gold (shell/radius) ratios within the range 0.2-0.4.