Optical Properties of Plasmonic Nanostructures for Bio-Imaging and Bio-Sensing Applications

• Main Author: Kravets, Vira V
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2017
• Subjects: Physics
• ISBN: 9781369768558; 1369768559

Kravets, Vira V. (Ph.D., Physics) Optical properties of plasmonic nanostructures for bio-imaging and bio-sensing applications Dissertation directed by Associate Professor Anatoliy Pinchuk. ABSTRACT This dissertation explores the physics of free electron excitations in gold nanoparticle chains, silver nanoparticle colloids, and thin gold films. Electron excitations in nanostructures (surface plasmons, SP) are responsible for unique optical properties, which are applied in bio-sensing and bio-imaging applications. For gold nanoparticle chains, the effect of SP on resonance light absorption was studied experimentally and theoretically. Mainly, how the spectral position of the absorption peak depends on inter-particle distances. This dependence is used in “molecular rulers”, providing spatial resolution below the Rayleigh limit. The underlying theory is based on particle interaction via scattered dipole fields. Often in literature only the near-field component of the scattered field is considered. Here, I show that middle and far fields should not be neglected for calculation of extinction by particle chains. In silver nanoparticles, SP excitations produce two independent effects: (a) the intrinsic fluorescence of the particles, and (b) the enhancement of a molecule’s fluorescence by a particle’s surface. The mechanism of (a) is deduced by studying how fluorescence depends on particle size. For (b), I show that fluorescence of a dye molecule on the surface of a nanoparticle is enhanced, when compared to that of the free-standing dye. I demonstrate that the dye’s fluorescent quantum yield is dependent on the particle’s size, making labeled silver nanoparticles attractive candidates as bio-imaging agents. Labeled nanoparticles are applied to cell imaging, and their bio-compatibility with two cell lines is evaluated here. Finally, in gold films under attenuated total internal reflection (ATR) conditions, the SP create a propagating wave (SP-polariton, SPP) when coupled with the incident light. Because of the sensitivity of SPPs to the medium adjacent to the gold film surface, they are widely applied in bio-sensing applications. A toolbox for the description of sputter-deposited gold films is presented here: it employs three experimental techniques (ATR, transmittance and atomic force microscopy) in combination with the effective medium theory for double-layered film model. Our findings have allowed for the avoidance of superficial fitting parameters in our model.