Silica nanoparticle platform to generate new molecular probes for fluorescence lifetime imaging

Fluorescence microscopy is the most widely used detection method to image molecular probes, but is currently hindered due to the limited number of fluorescent probes available. The fluorescence lifetime of fluorescent probes that is the time an excited fluorophore takes to return to the ground state; this thesis studied a novel system to manipulate the fluorescent molecules’ lifetime using the nanoprobe format. This system can exponentially increase the number of fluorescent probes. The first part of this thesis reports ~130nm silica nanoparticles labeled with silanized fluorescent dyes – Oregon Green 488, BODIPY, and rhodamine – using various total dye loadings. As the total dye loading increased, the relative fluorescence efficiency decreased due to self-quenching. This self-quenching effect was characterized by the phasor approach to fluorescence lifetime that gave unique and distinguishable spatial values of the nanoparticles. Utilizing the synthetic versatile properties of silica in accommodating other materials, the second part of this thesis discussed core-shell structured silica nanoparticles with an independent control to the fluorescence lifetimes of the cores and the shells. 35nm Silica cores were synthesized using a reverse microemulsion method. Various concentrations of fluorescent nanomaterials encapsulated inside the cores govern the cores’ phasor values. Subsequently, silica shells with various thicknesses were synthesized using the Stober sol-gel reaction. Various total dye loadings govern the shells’ phasor values while the shell thicknesses control their fluorescence intensity. The distinct fluorescence lifetime phasor values enable nanoprobes to have visually effective representations that can be easily expanded by simply manipulating the molecular proximities between fluorophores