A. J. Heltzel, Shi, L., and Howell, J. R., “Microsphere Coupler for a Nanowire Waveguide Plasmonic Probe for Molecular Imaging,” Nanotechnology, vol. 22, pp. 045203, 2011.
Highly forward scattering of light by a silica microsphere is predicted by Mie theory. Finite-difference time-domain simulations are used to examine the use of a silica microsphere for coupling light into a ZnO nanowire terminated with a gold nanoparticle (NP) tip, intended for near-field imaging of single molecules immobilized on a gold substrate or gold nanoparticle-labeled cell membranes. The results show that plasmonic coupling at the Au tip is dependent on the incident angle of the excitation. Pre-conditioning the signal with the microsphere amplifies the coupling while reducing background energy levels, significantly boosting the signal-to-noise ratio.