Titania Nanopillar Waveguide Illuminated Fluorescence Correlation Spectroscopy at High Concentrations
By: Stephan O'Brien, Ryan Bunyard, and Oskar Garcia
Department: Physics
Faculty Advisor: Dr. Huizhong Xu
Fluorescence Correlation Spectroscopy (FCS) measures the concentrations and dynamics of fluorescent particles by analyzing the correlation in the concentration fluctuation of particles diffusing in a solution. Due to its diffraction-limited sample volume, the method is only applicable for concentrations that are typically in the nM range. However, biological processes under physiological conditions often involve molecules in the μM concentration range and require sample volumes well below the established limit of about one femtoliter in traditional FCS. To guide visible light beyond the limits of traditional FCS, we have developed Nanowaveguide-Illuminated Fluorescence Correlation Spectroscopy (NIFS) which utilizes dielectric nanopillar waveguides to confine the excitation light well below the diffraction limit. While our previous studies using zinc oxide nanowire waveguides have shown that waveguides are efficient at creating an illumination volume of approximately 150 zeptoliters, it was challenging to fabricate these nanowaveguide devices due to difficulty in controlling the nanowire length. To overcome this obstacle, we have since introduced new nanofabrication techniques to develop titanium dioxide nanopillars with controlled lateral sizes and lengths. Furthermore, as a result of the high refractive index of titania in the visible regime, these nanopillar waveguides also exhibit superior transmission properties enabling better device performance with NIFS. Single molecule spectroscopy measurements using titania nanopillar waveguides of varying diameters will be presented and their application in studying the dynamics of protein molecules on the cell membrane will also be explored.