Waveguiding of surface plasmon polaritons by dielectric-loaded metal structures is studied in detail by combining numerical simulations and leakage radiation microscopy. These types of waveguides are first numerically investigated using the effective index model and the differential method. We analyzed systematically the influence of the ridge width and thickness of the waveguide on the properties of the surface plasmon guided modes. In particular we investigated the confinement factor of the modes and their associated propagation lengths. These two parameters can be optimized by adjusting the thickness of the dielectric layer. Waveguides loaded with thick and thin dielectric ridges are then optically characterized by leakage radiation microscopy. The mode propagation distance is measured by direct-space imaging and the propagation constants are evaluated by Fourier imaging and analysis. Good agreements are found between theoretical and experimental data.

Aggregated metal nanoparticles exhibit enhanced localized electromagnetic fields that enable highly sensitive vibrational spectroscopy analysis based on surface-enhanced Raman scattering (SERS). We demonstrate SERS detection of organic analytes adsorbed to optically aggregatedsilver nanoparticles in a microfluidic device. The combination of optical tweezers and microfluidics technologies paves the way for novel lab-on-a-chip based plasmonic chemo/bio sensors and overcomes two important drawbacks of standard SERS sensing schemes; i.e. the renewal of nanofabricated metallic substrates and the difficulty of avoiding uncontrolled aggregation in metal colloids.