Nanowaveguide-Illuminated Fluorescence Correlation Spectroscopy at Micromolar Concentrations
Cristian A. Rodriguez, Colin V. Williams
Department of Physics & Astronomy
Faculty Supervisor: Huizhong Xu
Probing molecular dynamics in real time at the single-molecule level has provided unprecedented insight into molecular interactions. Fluorescence correlation spectroscopy (FCS) has been instrumental in probing biological processes within live cells. However, conventional FCS is restricted to diffraction-limited detection volumes of approximately one femtoliter, which is sufficient for single-molecule studies at nanomolar concentrations but inadequate under physiological conditions, where concentrations typically reach the micromolar range and require detection volumes on the order of 100 zeptoliters. In this study, we present the fabrication of nanowaveguide devices consisting of a titania core with plasmonic metal cladding in cylindrical and slit geometries. This design surpasses the diffraction limit, achieving sampling volumes on the order of 200 zeptoliters. Furthermore, the near-field confinement of the transmitted light enables an illumination spot with dimensions of sub-50-nm laterally and 20 nm longitudinally, rendering this system particularly suitable for investigating single-molecule dynamics in cell membranes under physiological conditions. We further examine how dry-etching parameters in an Oxford PlasmaLab 100 Viper system affect the etch rate and anisotropic sidewall profile of the titania dielectric core, and we characterize the optical performance of the fabricated nanowaveguides through far-field transmission and FCS measurements.