Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. These were evaluated for antimicrobial activity against Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7. The ZnO QDs were utilized as a powder, bound in a polystyrene film (ZnO-PS), or suspended in a polyvinylprolidone gel (ZnO-PVP). Bacteria cultures were inoculated into culture media or liquid egg white (LEW) and incubated at 22• C. The inhibitory efficacies of ZnO QDs against 3 pathogens were concentration dependent and also related to type of application. The ZnO-PVP (3.2 mg ZnO/mL) treatment resulted in 5.3 log reduction of L. monocytogenes and 6.0 log reduction of E. coli O157:H7 in growth media after 48 h incubation, as compared to the controls. Listeria cells in the LEW control increased from 3.8 to 7.2 log CFU/mL during 8 d incubation, while the cells in the samples treated with 1.12 and 0.28 mg ZnO/mL were reduced to 1.4 and 3.0 log CFU/mL, respectively. After 8 d incubation, the cell populations of Salmonella in LEW in the presence of 1.12 and 0.28 mg ZnO/mL were reduced by 6.1 and 4.1 log CFU/mL over that of controls, respectively. ZnO powder and ZnO-PVP showed significant antimicrobial activities against all 3 pathogens in growth media and LEW. ZnO-PVP coating had less inhibitory effect than the direct addition of ZnO-PVP. No antimicrobial activities of ZnO-PS film were observed. This study suggested that the application of ZnO nanoparticles in food systems may be effective at inhibiting certain pathogens.
High-crystallinity α-zirconium phosphate (α-ZrP) crystals which contain stacks of high aspect ratio
nanoplatelets were synthesized and exfoliated with tetra-n-butylammonium hydroxide in aqueous
dispersion. The exfoliated α-ZrP nanoplatelets were then transferred into water-miscible organic solvents,
such as acetone, by centrifugation and re-dispersion. The resulting exfoliated α-ZrP nanoplatelets in
organic solvents can be easily utilized to prepare polymer nanocomposites. Through such an approach,
epoxy/α-ZrP nanocomposites containing high aspect ratio α-ZrP nanoplatelets have been prepared. The
presence of the well-exfoliated nanocomposite structure is confirmed by powder X-ray diffraction and
transmission electron microscopy.
We report the nematic and smectic ordering in a new aqueous suspension of monolayer α-Zirconium phosphate platelets possessing a high polydispersity in diameter but uniform thickness. We observe an isotropic-nematic transition as the platelet volume fraction increases, followed by the formation of a smectic, an elusive phase that has been rarely seen in discotic liquid crystals. The smectic phase is characterized by X-ray diffraction, high-resolution transmission electron microscopy, and optical microscopy. The phase equilibria in this highly polydisperse suspension is rationalized in terms of a theoretical approach based on density-functional theory.
Controllable assembly of three-dimensional (3D) superlattices composed of different types of nanoscale objects opens new opportunities for material fabrication. Herein we show the successful assembly of heterogeneous 3D structures from gold nanoparticles (AuNPs) and quantum dots (QDs) using DNA encoding. By applying synchrotron-based small-angle X-ray scattering, we found that AuNPs and QDs are positioned in a body-centered cubic lattice, while each particle type, AuNP and QD, is arranged in a simple-cubic manner. Our studies demonstrate a route for assembly of integrated heterogeneous 3D structures from different nano-objects by DNA-encoded interactions.
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