| Research and development of nanoscale materials have received increasing attention due to the small size scales and large surface-volume ratios involved, and the associated changes in properties compared to those of bulk systems. This dissertation introduces the design of two types of polymeric nanoparticles, intended for edible antimicrobials or for chemical oxygen sensors.;Recent outbreaks of foodborne pathogens have attracted public attention to food safety. Due to healthy life style trends, there is a demand for the development of an efficient, biocompatible sanitizing method for fresh and fresh-cut produce. We have developed chitosan-based nanoparticles modified with antimicrobial agents in order to achieve potent antimicrobial activity. Nisin, a widely used food preservative, has been attached to chitosan nanoparticles by electrostatic forces with a layer of anionic alginic acid in between. epsilon-poly-L-lysine, a natural and broad-spectrum antimicrobial, has been incorporated when forming chitosan nanoparticles. Particle properties have been studied, including the particle diameter, zeta potential, and morphology. Further investigation of antimicrobial activity is ongoing in Dr. Karl Matthews' group in the Department of Food Science, including determination of the minimum inhibitory concentration, bacterial viability monitoring assays, and application in food washing steps.;Oxygen is one of the most import analytes in the world due to its high relevance to living things. Determination of oxygen concentration has great importance in various fields. A series of new nanoparticle-based optical oxygen sensors were developed. The luminescent oxygen indicator dyes Pt(II)--5,15-di(pentafluorophenyl)-10,20-di(4-bromophenyl)porphyrin (PtTFPP), and Pt(II) meso-tetra(4-bromophenyl)tetra(tert-butyl) benzoporphyrin (PtTPTtBuBP) were covalently immobilized into two different conjugated polymers. The resulting polymers were rendered positively or negatively charged via chemical modification and were used to prepare oxygen-sensitive nanoparticles via a nanoprecipitation technique. This method improved the brightness of the oxygen sensor by a factor of 4-6. Efficient energy transfer was established from conjugated polymers to the oxygen indicator dye. Highly efficient two-photon excitation is expected. Different functional groups were also added to achieve adequate stability in aqueous dispersion and cell-penetration ability for different types of cells and tissues. Further investigation is ongoing in Dr. Dmitri Papkovsky's group at University College Cork (Ireland). |
