Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging

Ultrahigh-molecular-weight poly[( R )-3-hydroxybutyrate] [UHMW-P(3HB)] synthesized by genetically engineered Escherichia coli is an environmentally friendly bioplastic material which can be processed into strong films or fibers. An operon of three genes (organized as phaCAB ) encodes the essential proteins for the production of P(3HB) in the native producer, Ralstonia eutropha . The three genes of the phaCAB operon are phaC , which encodes the polyhydroxyalkanoate (PHA) synthase, phaA , which encodes a 3-ketothiolase, and phaB , which encodes an acetoacetyl coenzyme A (acetoacetyl-CoA) reductase. In this study, the effect of gene order of the phaCAB operon ( phaABC , phaACB , phaBAC , phaBCA , phaCAB , and phaCBA ) on an expression plasmid in genetically engineered E. coli was examined in order to determine the best organization to produce UHMW-P(3HB). The results showed that P(3HB) molecular weights and accumulation levels were both dependent on the order of the pha genes relative to the promoter. The most balanced production result was achieved in the strain harboring the phaBCA expression plasmid. In addition, analysis of expression levels and activity for P(3HB) biosynthesis enzymes and of P(3HB) molecular weight revealed that the concentration of active PHA synthase had a negative correlation with P(3HB) molecular weight and a positive correlation with cellular P(3HB) content. This result suggests that the level of P(3HB) synthase activity is a limiting factor for producing UHMW-P(3HB) and has a significant impact on P(3HB) production.