Nitric oxide (NO) is an important mammalian bioregulator involved in various physiological processes, such as blood pressure regulation, immune response, and apoptosis. Therefore, the use of NO releasing molecules has potential therapeutic application. Our group has focused on photochemical NO releasing molecules because they can offer spacial, temporal, and dosage control through modulation of the light source. To this end, the following thesis addresses efforts to improve the photosensitization of these compounds by exploiting the novel physical and optical properties of nanoparticles. Specifically, we synthesized and studied supramolecular constructs where, semiconductor quantum dots (QDs) and upconvering nanoparticles (UCNPs) acted as light harvesting antennae capable of photosensitizing nitric oxide release from NO donor molecules.

Investigations began with the development of a model system for probing the mechanism by which aqueous solutions of CdSe QDs photosenstized NO release from trans-Cr(cyclam)(ONO)2+ (a photochemical NO donor). Steady state and time resolved QD photoluminescence quenching studies performed on the model system helped elucidate that Forester Resonance Energy Transfer (FRET) was the primary mechanism of sensitization, and a model was developed to provide general guidelines for other QD-sensitized applications.

Next, UCNPs (composed of NaYF4 doped with rare earth ions) were investigated as photosensitizers due to their unique ability to efficiently generate visible emission through sequential absorption of multiple near infrared photons (which have deep tissue penetration). UCNPs and Roussin's Black Salt [Fe4S 3(NO)7+], (a photochemical NO donor) were encapsulation within a polymer, and investigated as a potential photochemical NO delivery implant. The polymer-UCNP constructs reproducibly generated high concentrations of NO from Roussin's Black Salt upon near infrared excitation, thereby providing a proof of concept for solid state NO delivery methods.

Other findings discussed herein include, the synthesis and investigation of zinc-based QDs as biocompatible photosensitizers, as well as QD catalyzed surface ligand decomposition. In the case of the latter, CdSe QDs were found to photo-catalytically sensitize the oxidation of 1,1-dithiooxalate (DTO) resulting in the release of carbon disulfide (a potential mammalian bioregulatory molecule). Preliminary data suggests that DTO-type surface ligands may have potential as generic photo-cleavable anchors for the selective delivery of QD-appended target molecules.