Optical Properties of Noncontinuous Gold Shell Engineered on Silica Mesosphere

The optical properties of individual noncontinuous shells with different gold coverage are investigated by the single-particle dark field scattering measurements and single-particle surface-enhanced Raman scattering (SERS) measurements at different excitation wavelengths. By controlling the growth of gold seeds, multi-metallic nanogaps/crevices with different optical responses are assembled on silica mesospheres forming noncontinuous shells that can be confirmed through the transmission electron microscope images. We find the surface plasmon resonance of single shell red-shifts from 510 to 680 nm with the increase of gold coverage. At the excitation of 532 and 785 nm, the best enhancements about 2.0 x 10(5) and 1.1 x 10(7) are obtained on spheres with similar to 60 and 83 % gold coverage, respectively. The weak polarization-dependent SERS indicates that the enhancement is from the multi-gaps on single noncontinuous shell. This optical tunable and SERS active noncontinuous gold shell can be applied in biosensing, ultra trace detection, and molecule analysis needing multi-wavelengths excitation.