Date on Master's Thesis/Doctoral Dissertation

8-2010

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Committee Chair

Zamborini, Francis Patrick

Subject

Nanoparticles; Plasmons (Physics)

Abstract

This dissertation describes new procedures for synthesizing and purifying Au and Au/Ag nanoplates directly on surfaces as well as controlled binding of proteins to their surface. It also describes fundamental changes in the optical properties of Au and Au/Ag nanoplates upon interaction with different liquids, proteins, or nanoparticles. Finally, this dissertation describes the highly selective and sensitive label-free detection of proteins in an immunoassay format using the optical properties of Au and Au/Ag nanostructures. A chemical seed-mediated growth procedure allowed the synthesis of Au nanoplates directly on surfaces with an initial 23% yield. Purification by either sonication or adhesive tape led to surfaces coated with ~90% Au nanoplates. Subsequent growth of Ag enabled the synthesis of ~90% Ag-coated Au nanoplates (Au/Ag) directly on the surface. Thiol self-assembly methods allowed select functionalization of the nanoplate terraces or edge sites with human anti-IgG or Au nanoparticles with controlled coverage and binding distance. Characterization of the nanostructures by UV-vis spectroscopy, infrared spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) confirmed the size, shape, composition, and protein or nanoparticle functionalization of the metal nanostructures. The localized surface plasmon resonance (LSPR) band of Au and Au/Ag nanostructures is sensitive to various liquid environments with a global refractive index (RI) sensitivity that follows as Au/Ag nanoplates (650 - 439 nmlRIU) > Au nanoplates (195 nmlRIU) > Au nanospheres (89 nmlRIU). The local LSPR response to protein binding was 2-3 times larger when proteins were bound to the edge sites of nanostructures compared to terrace sites for similar coverages because the plasmon fields are more intense at these sites. The LSPR response increased as the distance between the protein and the metal decreased in fairly good agreement with theory. The LSPR band of the metal nanostructures functionalized with human anti-IgG at the edge sites shifts in the presence of human IgG protein due to a change in the nanostructure environment following the highly selective antibody-antigen interaction with a limit of detection of 1 pg/mL. The sensitivity to human IgG followed the order Au/Ag nanoplates ˜ Au nanoplates > Au nanospheres. The nanoplates do not respond to goat IgG below a concentration of 1000 ng/mL, showing excellent selectivity. This highly sensitive, selective, label-free, simple, and low cost method for sensing proteins may find use in biomedical applications. The long response times, about 24 hours for low protein concentration, needs improvement.

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