Enhanced bioactivity of ZnO nanoparticles—an antimicrobial study

Abstract

In this study, we investigate the antibacterial activity of ZnO nanoparticles with various particle sizes. ZnO was prepared by the base hydrolysis of zinc acetate in a 2-propanol medium and also by a precipitation method using Zn(NO₃)₂ and NaOH. The products were characterized by x-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. Bacteriological tests such as minimum inhibitory concentration (MIC) and disk diffusion were performed in Luria-Bertani and nutrient agar media on solid agar plates and in liquid broth systems using different concentrations of ZnO by a standard microbial method for the first time. Our bacteriological study showed the enhanced biocidal activity of ZnO nanoparticles compared with bulk ZnO in repeated experiments. This demonstrated that the bactericidal efficacy of ZnO nanoparticles increases with decreasing particle size. It is proposed that both the abrasiveness and the surface oxygen species of ZnO nanoparticles promote the biocidal properties of ZnO nanoparticles.     

Enhanced photocatalytic activity of Fe-doped ZnO nanoparticles synthesized via a two-step sol–gel method

A series of Zn_1–x Fe _x O (x = 0, 1, 2, 3, 4 %) powders via a two-step sol–gel method in open system were successfully fabricated. Influence of Fe doping concentration on the structure, morphology, optical properties and photo catalysis properties were investigated by means of X-ray diffraction, scanning electron microscopy, UV–Vis spectrophotometer and photochemical reaction instrument. The results showed that the ZnO powders were hexagonal wurtzite structures and their crystalline sizes and particle diameters decreased with the increase of Fe doping concentration. An increase of visible light absorption value and a decrease in band gap from 3.219 to 3.167 eV were found with the increase of Fe doping concentration, which enable the sample harvest more photons to excite the electron from the valence. Enhanced visible light induced photocatalytic activity has been found in Fe doped ZnO and the ultraviolet light induced photocatalytic properties of the Fe-doped ZnO have been improved greatly compared with undoped ZnO and commercially available TiO₂ (P25). The photocatalytic activities were not significantly affected by the particle size, and the best Fe doping concentration is 1 %.     

Mössbauer study of maghemite nanoparticles

Mössbauer spectroscopy has been used to study maghemite (γ-Fe₂O₃) particles with average dimensions on the microscopic (～1 μm, “bulk” state) and nanoscopic (15 and 20 nm) levels. Data provided by this method on the thickness of a surface region of magnetic nanoparticles and features of their magnetic state have been analyzed. It is suggested that the proposed approach is promising for a large number of nanomagnetic materials.     

Hydrothermal ageing of jute-glass fibre hybrid composites — an acousto-ultrasonic study

Studies of damage under hydrothermal ageing incurred by random fibre glass-reinforced laminates and jute-glass fibre hybrid composites have been carried out using an acoustoultrasonic technique. It is shown that the stress wave factor is a sensitive indicator of flexural strength reduction due to hydrothermal effects in both these composites. The incorporation of jute into glass fibre composites brings about a reduction in the rate of degradation of these composites. The treatment of jute with a silane coupling agent marginally improves the strength properties of the hybrids.     

Effect of an external electrostatic field on ultrasonic machining of a dielectric material—an experimental study

The paper deals with the experimental study of the effect of an applied electrostatic field on ultrasonic machining of glass. Cylindrical cavities are machined in glass specimens (? 1-3 mm thick), both without and in the presence of a field. It is found that the time required for a 0-38 mm deep cut is reduced by about 10-20% due to the presence of a field. Further, the tool penetration rate is found to increase with the penetration of the tool into the workpiece. Using the analysis of variance technique, the observed data are analysed to show that the change in the rate of machining in the two cases is not due to chance but due to the presence of the field.     

Functionalized Fe₃O₄@Au superparamagnetic nanoparticles: in vitro bioactivity

The interaction of nanoparticles with cells has been a focus of interest during the past decade. We report the fabrication and characterization of hydrosoluble Fe?O?@Au nanoparticles functionalized with biocompatible and fluorescent molecules and their interaction with cell cultures by visualizing them with confocal microscopy. Gold covered iron oxide nanoparticles were synthesized by reducing metal salts in the presence of oleylamine and oleic acid. The functionalization of these particles with an amphiphilic polymer provides a water soluble corona as well as the possibility to incorporate different molecules relevant for bio-applications such as poly(ethylene glycol), glucose or a cadaverine derived dye. The particle size, and the presence of polymer layers and conjugated molecules were characterized and confirmed by transmission electron microscopy, thermogravimetric measurements and infrared spectroscopy. A complete magnetic study was performed, showing that gold provides an optimum coating, which enhances the superparamagnetic behaviour observed above 10-15 K in this kind of nanoparticle. The interaction with cells and the cytotoxicity of the Fe?O?@Au preparations were determined upon incubation with the HeLa cell line. These nanoparticles showed no cytotoxicity when evaluated by the MTT assay and it was demonstrated that nanoparticles clearly interacted with the cells, showing a higher level of accumulation in the cells for glucose conjugated nanoparticles.     

Local structure of β′-sialons: an EXAFS study study

The local environments of aluminium and silicon in -sialons, Si_6–zAl_zN_8–zO_z, have been studied by extended X-ray absorption fine structure spectroscopy. The silicon and aluminium atoms are always in tetrahedral coordination and the refined average bond length between two atomic positions becomes a measure of the distribution of nitrogen and oxygen over the nearest neighbour positions to the absorbing atom. Two -sialons samples with different composition, z=1 and z=2.7, were used in the study with -Si₃N₄, SiO₂ (cristobalite, albite and a xerogel), zeolite NaA, anorthite and AIN as reference substances. The calculated distances to the first coordination sphere for silicon were 0.169 nm for z=1 and 0.168 nm for z=2.7, compared to 0.171 nm for Si₃N₄ under the same conditions. In the aluminium environment, the calculated distances were 0.177 nm for z=1 and 0.176 nm for z=2.7. The results indicate that the -sialons are built up by aluminium- and silicon-containing tetrahedra with mixed oxygen and nitrogen environments, although there seems to be a stronger tendency for the formation of Si-N and Al-O bonds, compared to Si-O and Al-N bonds. The results are not precise enough to allow calculation of the contribution from different bond types to the observed average bond lengths; in particular this is due to the short (< 200 eV) AlK edge available for structural studies of the -sialons.     

Aspects of the in vitro bioactivity and antimicrobial properties of Ag+- and Zn2+-exchanged 11 Å tobermorites

11 Å tobermorite, Ca₅Si₆O₁₆(OH)₂ · 4H₂O, is a layer lattice ion exchange mineral whose potential as a carrier for Ag⁺ and Zn²⁺ ions in antimicrobial, bioactive formulations has not yet been explored. In view of this, the in vitro bioactivity of Ag⁺- and Zn²⁺-exchanged 11 Å tobermorites and their bactericidal action against S. aureus and P. aeruginosa are reported. The in vitro bioactivity of the synthetic unsubstituted tobermorite phase was confirmed by the formation of bone-like hydroxycarbonate apatite (HCA) on its surface within 48 h of contact with simulated body fluid. The substitution of labile Ag⁺ ions into the tobermorite lattice delayed the onset of HCA-formation to 72 h; whereas, the Zn²⁺-substituted phase failed to elicit an HCA-layer within 14 days. Both Ag⁺- and Zn²⁺-exchanged tobermorite phases were found to exhibit marked antimicrobial action against S. aureus and P. aeruginosa, two common pathogens in biomaterial-centred infections.     

The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet–Visible region

Zn_1?xMo_xO (x = 0.0, 0.01, 0.03, and 0.05) nanoparticles (NPs) are synthesized by using gelatin, via the sol-gel method. A calcination temperature of 600 °C is maintained for 2 h. The influence of molybdenum concentration on the structural and optical properties of these NPs is demonstrated. Synthesized NPs are characterized using X-ray diffraction (XRD), UV–vis spectroscopy, and transmission electron microscopy (TEM). XRD patterns reveal the crystallite nature of samples that exist in the hexagonal wurtzite phase. TEM images manifest the existence of nearly spherically-shaped NPs. The UV–vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is red-shifted by adding molybdenum. Finally, the optical parameters of the refractive index and permittivity of the synthesized samples were calculated using Kramers-Kronig relations using the UV–vis spectra.     

Enhanced photocatalytic,electrochemical and antimicrobial activities of α-Mn2V2O7 nanopebbles

Journal of Materials Science: Materials in Electronics - Manganese(II) divanadate nanopebbles (α-Mn2V2O7) were prepared by a simple solution combustion method and calcinated at...     

Synthesis of hybrid Au–ZnO nanoparticles using a one pot polyol process

In this work, we report on the synthesis of hybrid Au–ZnO nanoparticles using a one-pot chemical method that makes use of 1,3-propanediol as a solvent, a reducing agent and a stabilizing layer. The produced nanoparticles consisted of Au cores decorated with ZnO nanoparticles. The structure and morphology of the nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDX) and Raman spectroscopy. Optical extinction measurements, combined with numerical simulations, showed that the Au–ZnO nanoparticles exhibit a localized surface plasmon resonance (SPR) clearly red-shifted with respect to that of bare Au nanoparticles (AuNPs). This work contributes to the emergence of multi-functional nanomaterials with possible applications in surface plasmon resonance based biosensors, energy-conversion devices, and in water-splitting hydrogen production.     

Cytocompatibility testing of cyclodextrin-functionalized antimicrobial textiles—a comprehensive approach

Functionalized textiles can be used in wound management to reduce the microbial burden in the wound area, to prevent wound infections, and to avoid cross-contamination between patients. In the present study, a comprehensive in vitro approach to enable the assessment of antibacterial activity of functionalized textiles and cytotoxicity of cyclodextrin (CD)-complexes with chlorhexidine diacetate (CHX), iodine (IOD), and polihexanide (PHMB) is suggested to evaluate their properties for supporting optimal conditions for wound healing. For all β-CD-antiseptic functionalized cotton samples a strong antibacterial effect on the Gram-positive bacteria Staphylococcus aureus and Staphylococcus epidermidis as well as on the Gram-negative bacteria Klebsiella pneumoniae and Escherichia coli was proven. In addition, β-CD-CHX and β-CD-PHMB were effective against the yeast Candida albicans. The growth of Pseudomonas aeruginosa could be reduced significantly by β-CD-IOD and β-CD-PHMB. The established comprehensive testing system for determination of biocompatibility on human HaCaT keratinocytes is suitable for obtaining robust data on cell viability, cytotoxicity and mode of cell death of the β-CD-antiseptic-complexes. The promising results of the high antimicrobial activity of these functionalized textiles show the high potential of such materials in medical applications.     

Phase relation in titanium-aluminide alloy — an X-ray study

Results of X-ray diffraction studies on titanium aluminides stabilized by niobium, vanadium and molybdenum are reported to establish a phase relation in the Ti-25Al-10Nb-3V-1Mo at% (Ti-25-10-3-1) alloy. It is shown that the composition of the phases probably deviated slightly from ideal stoichiometry Ti₃Al for ₂ and Ti₂AlNb for -type; its partial ordering in of the -phase type and the phase relation is 64% -type and 36% ₂ phase.     

In vivo comparative property study of the bioactivity of coated Mg–3Zn–0.8Zr alloy

In this in vivo study, degradable Mg–3Zn–0.8Zr cylinders were coated with a calcium phosphorus compound (Ca–P) layer or a magnesium fluoride (MgF₂) layer; uncoated Mg–3Zn–0.8Zr alloy was used as a control. These were then implanted intramedullary into the femora of nine Japanese big-ear white rabbits for implantation periods of 1, 2 and 3 months. During the postoperative observation period with radiographic examination, the results showed that the MgF₂-coated implants were tolerated well compared to the Ca–P-coated implants and uncoated implants. Moreover, large amounts of cells, rich fibrillar collagen and calcium and phosphorus products were found on the surface of the MgF₂-coated implants using scanning electron microscopy. Micro-computed tomography further showed a slight decrease in volume (23.85%) and a greater increase in new bone mass (new bone volume fraction = 11.56%, tissue mineral density = 248.81 mg/cm³) for the MgF₂-coated implants in comparison to uncoated and Ca–P compound-coated implants after 3 months of implantation.     

Synthesis of minimal-size ZnO nanoparticles through sol–gel method: Taguchi design optimisation

Zinc oxide (ZnO) has excellent potential to be used in water and wastewater treatment, either as a photocatalyst or in membrane incorporation. In this work, the synthesis of smaller ZnO NPs through a sol–gel approach was enhanced by applying Taguchi design. Recent work on the synthesis of ZnO NPs was optimised to ensure relatively smaller sized particles were obtained. Several parameters of the synthesis process, such as molar ratio of starting materials, molar concentration and calcination temperature, were selected as they have the dominant effects on the particle size of ZnO NPs. Each of these factors was studied at three levels. Various analyses such as ANOVA, model adequacy check and numerical optimisation were performed to validate the predicted optimal model. As a result, the optimum conditions were estimated at a molar ratio of 50:50, an oxalic acid molar concentration of 0.1 M and a calcination temperature of 400 °C. Experiments were performed to validate the model at the selected conditions and the particle size was around 20 ± 2 nm according to XRD analysis, which was in good agreement with the predicted size of 19.8 nm. In addition, the actual size of the synthesised NPs was confirmed by TEM analysis, with the average size of 13 ± 5 nm. Hence, the Taguchi design was an essential tool in the optimisation of ZnO NP synthesis process with fewer experimental runs and relatively low cost approach.     

Theoretical study of the optical absorption behavior of Au/Ag core–shell nanoparticles

The dependence of linear optical response properties of bimetallic core–shell spherical nanoparticles is investigated as a function of size and relative composition. Two kinds of schematic models have been tested for describing the dielectric behavior of bimetallic particles and the related linear electromagnetic response: (i) Drude model, in conjunction with bulk dielectric data relative to the pure metals, in the assumption of a simple combination law; (ii) DFT-based approach to the dynamic polarizability of a binary particle, with the nature of the metals involved taken into account through their Wigner–Seitz radius.