Novel silver nanostructures for bioanalytical applications

Silver nanoparticles are of great interest to many researchers due to their unique optical properties. These optical properties are governed by the collective oscillations of conduction electrons, termed plasmon resonances, which are affected by the size, shape, and dielectric environment of the particle. Excitation of surface plasmons create enhanced local electric fields which extend from the surface of the nanoparticles. These enhanced fields are responsible for phenomena such as enhanced fluorescence, photonics, photocatalysis, and surface-enhanced Raman scattering (SERS).; This dissertation focuses on applications utilizing the enhanced field surrounding silver nanoparticles as well as modulating the plasmon resonance of particles in nanostructures for various analytical applications. Fabrication and characterization of nanostructures to be used for applications such as SERS spectroscopy and spectroelectrochemical studies will be discussed.; The effect of the applied potential on the cooperative plasmon mode in 2D coupled arrays of silver nanoparticles was studied using a spectroelectrochemical approach. Spectral changes were observed and presented as difference spectra measured between applied potentials and the potential of zero charge (PZC) for silver. The changes were interpreted as potential-induced changes of the local dielectric environment around the nanoparticles due to reorganization of the electric double layer.; Silver nanoparticles were also used to fabricate sandwich SERS substrates (3S) utilizing coupling between continuous metal films and plasmonic particles. The effect of excitation wavelength and nanoparticle size on SERS spectra of poly(vinylpyridine) was studied to determine the optimum conditions for the strongest SERS signal. Raman enhancement resulted from the plasmon coupling of silver nanoparticles to the underlying continuous film as well as the lateral plasmon coupling between the silver nanoparticles. The 3S configuration was used to obtain SERS spectra of dipicolinic acid (DPA), a chemical signature for Bacillus anthracis.; The mirror 3S were then used to monitor the kinetics of Bacillus subtilis endospore germination. The sandwich configuration of the substrates allowed for the sensitive detection of germination in samples that contained only several hundreds of endospores. Germination at varying concentrations of L-alanine and different temperatures was studied. The germination of endospores was monitored by the appearance and growth of Raman peaks characteristic for DPA.