Coupled plasmonic nanostructures for improved biological sensing applications

Plasmonics, a sub-field of nanophotonics, has attracted amazing interests in recent years due to its promise of revolutionary impacts on nanotechnologies, medicine, and our daily lives. In short, plasmonics guides, confines, localizes, and enhances electromagnetic waves to a small area to enable novel applications such as plasmonic waveguides, sub-wavelength diffraction lithography and imaging, higher photovoltaic efficiency, sub-wavelength lasers, and biological sensing. The first part of this dissertation will introduce the general concepts of plasmonics and its applications in biological sensing, starting from Maxell's equations and the Drude model of metal. In the second part, it will delve into the specifics of designing, simulating, fabricating, and characterizing nanostructures that show improved performance characteristics over previous published results. Plasmonic coupling of propagating surface plasmon polaritons and localized plasmons is utilized to fabricate three-dimensional mushroom-like metallodielectric array for improved surface plasmon resonance biological sensing over conventional nanohole array. It is used to determine the hydrophilicity of a surface by monitoring the shift in resonant wavelength. In addition, the fabricated structure is used to detect specific binding events between biotinylated-bovine serum albumin and streptavidin protein and demonstrates an improved limit of detection. The real- time control and manipulation of nanoparticles in a biocompatible aqueous solution is demonstrated in a multilayer micro/nanofluidic chip platform by using voltage control. This will have future applications to control and position nanoparticles and biomolecules to an area of maximum field enhancement to co-localize the analyte with the plasmonic nanostructure for maximal enhancement efficiency. Finally, the intra-particle plasmonic coupling of a nanotorch structure is utilized for surface enhanced Raman scattering detection to yield high enhancement factor and better than 80\% Raman signal uniformity due to the fabrication of controllable rim opening of the nanotorch and the deterministic orientation of the structure. The common theme of this dissertation is coupled plasmonic nanostructures for improved biological sensing application