Tuning the electronic properties of conjugated polyelectrolytes via complexation with lipid vesicles or silica nanobeads

This thesis describes luminescent nanostructures involving the anionic poly(phenylene vinylene) MPS-PPV in complex with lipid vesicles or silica beads. The vesicular encapsulation of light-emitting polymer produced a "liposome beacon," whose fluorescence response to the electron-transfer quencher methyl viologen or an energy-accepting carbocyanine dye (DiD) reported on the extent of encapsulation via ensemble spectroscopy and single-particle imaging of immobilized vesicles. Divalent cation was furthermore used to modulate interactions between MPS-PPV and zwitterionic lipid vesicles. Binding to the lipid vesicles disrupted polymer aggregates, enhancing and shifting the polymer's fluorescence. Fluorescence resonance energy transfer (FRET) elucidated the effect of divalent cation in promoting lipid-polymer association. Finally, MPS-PPV was adsorbed onto silica nanoparticles via electrostatic interactions. The effects of silica bead adsorption on MPS-PPV photophysical properties were investigated via ensemble spectroscopy and single-particle total-internal-reflection fluorescence microscopy. The MPS-PPV-coated silica bead exhibited similar sensitivity to methyl viologen as the free polyelectrolyte, and was resistant to the fluorescence effects of nonspecific interactions. Our results provide insight towards tuning the sensitivity of fluorescent water-soluble conjugated polyelectrolytes and contributing to the development of new applications for conjugated poly(phenylene vinylene)s in fluorescent assays.