In this study, we investigate the geometrical parameters that control the sensitivity of the plasmon resonance wavelength of a silica-gold nanoshell to changes in its dielectric environment. It was found that the magnitude of the SPR frequency shift upon a change in refractive index of the embedding medium depends primarily C, on total nanoparticle size and less sensitively on the core/shell ratio. Immobilized nanoshells on a glass substrate showed a 25% decrease in magnitude of the SPR shifts; however, sensitivities as large as Deltalambda /Deltan = 555.4 nm/RIU were obtained for this geometry.