Fabrication and Tailoring Plasmonic Properties of Two Dimensional Assemblies of Metal Nanostructures towards Engineering Novel Plasmonic Sensors

Electromagnetic mechanism of enhancement, proposed to elucidate surface enhanced Raman scattering (SERS) and Surface enhanced fluorescence (SEF), was justified by studying distance dependent enhancement of SERS and SEF using 2D self-assembled spheroidal silver nanoparticles containing probe molecules. Spacer layer between the metal surface and the probe was created by layer-by-layer deposition of oppositely charged polyelectrolytes. A decreasing trend in SERS enhancement factor and an increasing trend in SEF enhancement factor with increasing separation distance were observed, which corroborate with proposed electromagnetic mechanism of SERS and SEF. In order to fabricate effective SERS substrates by exploiting hot spots, supported 2D assemblies of silver nanocubes (NCs) with controlled interparticles distance were fabricated using LB technique. Interparticles distance in such substrates was tailored by incorporation of NCs in phospholipid monolayers in Langmuir trough and optimizing lateral surface pressure during the film transfer onto a solid surface. However, to develop plasmonic sensors with high refractive index sensitivity (RIS), investigation was performed to optimize RIS of supported and colloidal silver NCs. The size of the NCs, RI of supporting dielectric substrate, and the monolayer surface pressure were used as variables in refractive index sensing optimization. It was found that high refractive index dielectric substrates, a passive molecular spacer and large angles of incidence facilitate the detection of plasmonic response of supported 2D assemblies of nanocubes. Furthermore, a simple and robust strategy was demonstrated for assembling silver NCs into 2D hierarchical structures (uniform rounded islands, branched-parallel chains) on LB films exploiting phase behaviors of multi-components lipid mixtures in Langmuir films.;The density of the building blocks, size and shape of the resulting patterns can be controlled by tailoring the lateral surface pressure, lipid composition of the Langmuir film. Finally, integration of nanoscale coating on optical fiber with noble metal was performed to engineer fiber surface plasmon sensors. The method of electroless deposition of gold was found an effective route to generate continuous film on fiber surface pre-coated with gold nanoparticles as a precursor layer. The thickness of the gold film required to support SPR was self-optimized using a Tilted Fiber Bragg Grating sensor. The resulting fiber with gold coating of optimized thickness showed potential to develop infrared surface plasmon sensor.