As antibiotic resistance increases and antibiotic development dwindles, new antimicrobial agents are needed. Recent advances in nanoscale engineering have increased interest in metal oxide ...nanoparticles, particularly zinc oxide nanoparticles, as antimicrobial agents. Zinc oxide nanoparticles are promising due to their broad-spectrum antibacterial activity and low production cost. Despite many studies demonstrating the effectiveness of zinc oxide nanoparticles, the antibacterial mechanism is still unknown. Previous work has implicated the role of reactive oxygen species such as hydrogen peroxide, physical damage of the cell envelope, and/or release of toxic Zn
2+
ions as possible mechanisms of action. To evaluate the role of these proposed methods, we assessed the susceptibility of
S. aureus
mutant strains, Δ
katA
and Δ
mprF
, to zinc oxide nanoparticles of approximately 50 nm in size. These assays demonstrated that hydrogen peroxide and electrostatic interactions are not crucial for mediating zinc oxide nanoparticle toxicity. Instead, we found that Zn
2+
accumulates in Mueller-Hinton Broth over time and that removal of Zn
2+
through chelation reverses this toxicity. Furthermore, we found that the physical separation of zinc oxide nanoparticles and bacterial cells using a semi-permeable membrane still allows for growth inhibition. We concluded that soluble Zn
2+
is the primary mechanism by which zinc oxide nanoparticles mediate toxicity in Mueller-Hinton Broth. Future work investigating how factors such as particle morphology (e.g., size, polarity, surface defects) and media contribute to Zn
2+
dissolution could allow for the synthesis of zinc oxide nanoparticles that possess chemical and morphological properties best suited for antibacterial efficacy.
As-received BaTiO₃ nanopowders of average grain sizes 50 nm and 100 nm were functionalized by (3-aminopropyl)triethoxysilane (APTES) and mixed with poly(methyl methacrylate)/toluene solution. The ...nanocomposite solution was spin coated on Si substrates to form thin films. The photoluminescence spectrum of the pure powder was composed of a bandgap emission at 3.0 eV and multiple bands centered about 2.5 eV. Surface functionalization of the BaTiO₃ powder via APTES increases overall luminescence at room temperature while only enhancing bandgap emission at low-temperature. Polymer coating of the functionalized nanoparticles significantly enhances bandgap emissions while decreasing emissions associated with near-surface lattice distortions at 2.5 eV.
The cubic zirconia (ZrO
) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition ...of the oxides of trivalent metals, such as Sc
O
. Another method is the stabilization of the cubic phase in nanostructures-nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO
)
(Sc
O
)
, with
from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc
O
content from 6.5 to 17.5 mol%, which is much broader than the range of 8-12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4-11 mol% of Sc
O
content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films.
Nano- and microscale zinc oxide (ZnO) exhibits significant potential as a novel antibacterial agent in biomedical applications. However, the uncertainty regarding the underlying mechanisms of the ...observed antimicrobial action inhibits the realization of this potential. Particularly, the nature of interactions at the free crystalline surface and the influence of the local bacterial environment remains unclear. In this investigation, we utilize ZnO particles synthesized via tunable hydrothermal growth method as a platform to elucidate the effects of interactions with phosphate-rich environments and differentiate them from those with bacteria. This is achieved using the time- and energy-dependent surface photovoltage (SPV) to monitor modifications of the surface electronic structure and surface charge dynamics of the ZnO particles due to these interactions. It is found that there exists a dramatic change in the SPV transients after exposure to phosphate-rich environments. It also presents differences in the sub-bandgap surface electronic structure after these exposures. It can be suggested that these phenomena are a consequence of phosphate adsorption at surface traps corresponding to zinc deficiency defects. This effect is shown to be suppressed in the presence of
bacteria. Our results support the previously proposed model of the competitive nature of interactions between
and aqueous phosphates with the free surface of ZnO and bring greater clarity to the effects of phosphate-rich environments on bacterial growth inhibition of ZnO.
We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) films. With UV (285 nm) excitation, the phosphorescence spectrum of tryptophan appears at about 460 ...nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S
→S
absorption. This excitation reaches the triplet state of tryptophan directly without the involvement of the singlet excited state. The phosphorescence lifetime of tryptophan is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.
Nano- and microcrystalline ZnO is an inexpensive, easily synthesized material with a multitude of applications. Its usefulness in the present and future stems from its exceptional optoelectronic, ...structural, and chemical characteristics as well as a broad range of production techniques. One application comes from its ability to inhibit bacterial growth. Despite the well-documented, vigorously studied antimicrobial action of ZnO particles, the most fundamental physical and chemical mechanisms driving growth inhibition are still not well identified. Particularly, the nature of interactions between ZnO surfaces and extracellular material is not totally clear. This is important given the anisotropic lattice of ZnO leading to two characteristically different lattice terminations: polar and nonpolar, polar being electrically charged with many defect sites and nonpolar being electrically neutral while remaining relatively defect-free. In this work, we employ a hydrothermal growth protocol that allows us to produce ZnO microcrystals with dependable control of morphology and, particularly, the relative abundances of polar and nonpolar free surfaces. This functions as a platform for our investigations into surface-surface interactions behind the antibacterial action of ZnO microcrystals. In our studies, we produced ZnO crystals comparable in size or larger than Staphylococcus aureus bacteria. This was done intentionally to ensure that the ZnO particles would not internalize into the bacterial cells. Our experiments were performed in conjunction with surface photovoltage studies of ZnO crystals to characterize electronic structure and charge dynamics that might be contributing to the antibacterial properties of our samples. We report on the interactions between ZnO microcrystalline surfaces and extracellular material of Staphylococcus aureus bacteria.
Nano- and microscale ZnO demonstrate robust antibacterial action, although the driving mechanisms remain undetermined. In this study for commercial ZnO nano-powders and home-grown ZnO microparticles ...of varying morphologies we probe the response to bacterial growth media in isolation and with Staphylococcus aureus bacteria. ZnO microparticles are synthesized via a controllable hydrothermal method and subjected to biological assays with varying microbial environments. Changes in the optoelectronic, structural and chemical properties of these crystals before and after such exposure are characterized utilizing temperature-dependent photoluminescence spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. This is done to evaluate the impact of surface-surface interactions in antibacterial assays and the role ZnO surface and morphological properties play in these processes. In our experiments various bacterial environments are employed to elucidate the effects of media interactions on the cytotoxic efficacy of ZnO. In particular, minimum inhibitory concentration assays with Staphylococcus aureus reveal that microscale particles exhibit antibacterial efficacy comparable to that of the nano-powders, indicating that intra-bacterial internalization is not necessary for antimicrobial action. In our studies we determine that the nature of structural and optoelectronic changes in ZnO depends on both the media type and the presence (or absence) of bacteria in these media. Further evidence is provided to support significant cytotoxicity in the absence of particle internalization in bacteria, further highlighting the role of surface and media interactions in this process.
ZnO nanorods were prepared at relatively low temperatures by homogeneous precipitation from zinc nitrate and urea in a water/ethylene glycol mixture. Crystal size and morphology are controlled by ...growth time and solvent composition. We observed a strong correlation between nanocrystals’ size/morphology and their optoelectronic defect-related properties. Smaller crystallites exhibited intense deep-defect luminescence and enhanced emission related to near-surface excitonic recombination. Longer growth times lead to formation of well-defined nanorods with hexagonal symmetry exhibiting reduced defect emission.
Hydrozincite (Zn5(OH)6(CO3)2) is, among others, a popular precursor used to synthesize nanoscale ZnO with complex morphologies. For many existing and potential applications utilizing nanostructures, ...performance is determined by the surface and subsurface properties. Current understanding of the relationship between the morphology and the defect properties of nanocrystalline ZnO and hydrozincite systems is still incomplete. Specifically, for the latter nanomaterial the structure-property correlations are largely unreported in the literature despite the extensive use of hydrozincite in the synthesis applications. In our work, we addressed this issue by studying precipitated nanostructures of Zn5(OH)6(CO3)2 with varying quasi-fractal dimensionalities containing relatively small amounts of a ZnO phase. Crystal morphology of the samples was accurately controlled by the growth time. We observed a strong correlation between the morphology of the samples and their optoelectronic properties. Our results indicate that a substantial increase of the free surface in the nanocrystal samples generates higher relative concentration of defects, consistent with the model of defect-rich surface and subsurface layers.
Zinc hydroxide particles were prepared by a two-step process employing zinc nitrate hexahydrate, urea, ethylene glycol, water and p-toluene-sulfonic acid monohydrate (p-TSA). We used different ...concentrations of the reactants as well as different volume ratios of the solvents. ZnO particles were obtained by thermal treatment of the reaction products at two different temperatures: 350°C and 500°C. The samples were characterized by scanning field emission electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, BET analysis, thermogravimetry (TG) analysis and photoluminescence (PL) spectroscopy. It was found that after the thermal treatment particles become smaller, with the p-TSA concentration strongly affecting the morphology of the particles. Luminescence properties of the samples probed by PL at 8K and room temperature exhibited a remarkable correlation with specimens′ nanomorphology. Luminescent features at ∼2.0–2.2eV, ∼2.4–2.5eV, ∼2.65eV, ∼2.9eV, ∼3.0–3.1eV and ∼3.3eV were observed in most specimens, although their relative intensity and temperature dependence were specific to an individual group of samples vis-à-vis their growth history and morphology.
► ZnO-containing nanostructures grown by precipitation were investigated. ► Samples' morphology can be carefully tailored via growth control parameters. ► Strong dependence of optoelectronic properties on specimens' morphology was observed. ► Efficient control of composition, morphology and luminescence via synthesis parameters.
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