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American Society for Testing and Materials

Elements Of X Ray Diffraction

Multidrug resistance of the pathogenic microorganisms to the antimicrobial drugs has become a major impediment toward successful diagnosis and management of infectious diseases. Recent advancements in nanotechnology-based medicines have opened new horizons for combating multidrug resistance in microorganisms. In particular, the use of silver nanoparticles (AgNPs) as a potent antibacterial agent has received much attention. The most critical physico-chemical parameters that affect the antimicrobial potential of AgNPs include size, shape, surface charge, concentration and colloidal state. AgNPs exhibits their antimicrobial potential through multifaceted mechanisms. AgNPs adhesion to microbial cells, penetration inside the cells, ROS and free radical generation, and modulation of microbial signal transduction pathways have been recognized as the most prominent modes of antimicrobial action. On the other side, AgNPs exposure to human cells induces cytotoxicity, genotoxicity and inflammatory response in human cells in a cell-type dependent manner. This has raised concerns regarding use of AgNPs in therapeutics and drug delivery. We have summarized the emerging endeavors that address current challenges in relation to safe use of AgNPs in therapeutics and drug delivery platforms. Based on research done so far, we believe that AgNPs can be engineered so as to increase their efficacy, stability, specificity, biosafety and biocompatibility. In this regard, three perspectives research directions have been suggested that include 1) synthesizing AgNPs with controlled physico-chemical properties, 2) examining microbial development of resistance towards AgNPs, and 3) ascertaining the susceptibility of cytoxicity, genotoxicity, and inflammatory response to human cells upon AgNPs exposure.

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Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles.

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

We report the synthesis of Co doped ZnO nanoparticles by combustion method using citric acid as a fuel for 0%, 1%, 3%, 5% and 10% of Co doping. The structural, optical and dielectric properties of the samples were studied. Crystallite sizes were obtained from the X-ray diffraction (XRD) patterns whose values are decreasing with increase in Co content up to 5%. The XRD analysis also ensures that ZnO has a hexagonal (wurtzite) crystal structure and Co2+ ions were successfully incorporated into the lattice positions of Zn2+ ions. The TEM image shows the average particle size in the range of 10–20 nm for 3% Co doped ZnO nanoparticles. The energy band gap as obtained from the UV–visible spectrophotometer was found gradually increasing up to 5% of Co doping. The dielectric constants (ɛ′, ɛ″), dielectric loss (tan δ) and ac conductivity (σac) were studied as the function of frequency and composition, which have been explained by ‘Maxwell Wagner Model’.

Investigation on structural, optical and dielectric properties of Co doped ZnO nanoparticles synthesized by gel-combustion route

During the last several years, various chemical methods have been used for synthesis of a variety of metal nanoparticles. Most of these methods pose severe environmental problems and biological risks; therefore the present study reports a biological route for synthesis of zinc oxide nanoparticles using Pseudomonas aeruginosa rhamnolipids (RLs) (denoted as RL@ZnO) and their antioxidant property. Formation of stable RL@ZnO nanoparticles gave mostly spherical particles with a particle size ranging from 35 to 80 nm. The RL@ZnO nanoparticles were characterized by UV-visible (UV-vis) spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and thermal gravimetric analysis. The UV-vis spectra presented a characteristic absorbance peak at ∼ 360 nm for synthesized RL@ZnO nanoparticles. The XRD spectrum showed that RL@ZnO nanoparticles are crystalline in nature and have typical wurtzite type polycrystals. Antioxidant potential of RL@ZnO nanoparticles was assessed through 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, and superoxide anion free radicals with varying concentration and time of the storage up to 15 months, while it was found to decline in bare ZnO nanoparticles. Similarly, the inhibitory effects on β-carotene oxidation and lipid peroxidation were also observed. These results elucidate the significance of P. aeruginosa RL as effective stabilizing agents to develop surface protective ZnO nanoparticles, which can be used as promising antioxidants in biological system.

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Biosynthesis of Stable Antioxidant ZnO Nanoparticles by Pseudomonas aeruginosa Rhamnolipids

Quorum sensing (QS) is a chemical communication process that Pseudomonas aeruginosa uses to regulate virulence and biofilm formation. Disabling of QS is an emerging approach for combating its pathogenicity. Silver nanoparticles (AgNPs) have been widely applied as antimicrobial agents against human pathogenic bacteria and fungi, but not for the attenuation of bacterial QS. Here we mycofabricated AgNPs (mfAgNPs) using metabolites of soil fungus Rhizopus arrhizus BRS-07 and tested their effect on QS-regulated virulence and biofilm formation of P. aeruginosa. Transcriptional studies demonstrated that mfAgNPs reduced the levels of LasIR-RhlIR. Treatment of mfAgNPs inhibited biofilm formation, production of several virulence factors (e.g. LasA protease, LasB elastrase, pyocyanin, pyoverdin, pyochelin, rhamnolipid, and alginate) and reduced AHLs production. Further genes quantification analyses revealed that mfAgNPs significantly down-regulated QS-regulated genes, specifically those encoded to the secretion of virulence factors. The results clearly indicated the anti-virulence property of mfAgNPs by inhibiting P. aeruginosa QS signaling.

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Mycofabricated biosilver nanoparticles interrupt Pseudomonas aeruginosa quorum sensing systems.

The microstructural, optical and photocatalytic properties of undoped and 5% Zn doped CeO2 nanocrystals (NCs) have been explored through various analytical techniques, viz. powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-visible, Raman and photoluminescence (PL) spectroscopy. XRD data analysis revealed face centred cubic (FCC) crystal symmetry of the samples with average crystallite size in the range of 19–24 nm. XPS results confirmed that the Zn ions exist in +2 states and successfully incorporated into the CeO2 matrix. Internal structure and morphology observed by TEM exhibited almost uniform cubical shape of the particles of average size ~20–26 nm. The enegy bandgap of undoped and Zn doped CeO2 NCs had a direct transition of 3.46 eV and 3.57 eV respectively as estimated by the optical absorption data. The increase in the bandgap revealed blue shift of absorption edge due to the quantum confinement effects. The NCs exhibited an inherent luminescence emission peak at ~408 nm in PL spectra. Improvement in the photocatalytic activity was observed for Zn incorporated sample attributed to the enhanced light absorption or/and fall in charge recombination rate between CeO2 and Zn.

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Microstructural properties and enhanced photocatalytic performance of Zn doped CeO 2 nanocrystals.

The structural and electrical transport properties of LaMn1−xFexO3 (0.1 ≤ x ≤ 0.6) bulk samples have been investigated. The powder x-ray diffraction patterns at room temperature show that all samples are formed in single phase. The temperature dependent resistivity data have been fitted with the Mott's variable-range hopping (VRH) model for an entire studied range of the temperature (77–300 K) to calculate the hopping distance (Rh) and the density of states at Fermi level (N(EF)). It is found that all parameters vary systematically with the increase in Fe concentration. Moreover, the resistivity data were also fitted in the small polaron hopping (SPH) model. The non-adiabatic SPH conduction mechanism is followed by all samples. This type conduction mechanism is far accompanied by subtle electronically induced structural changes involving in Fe–O–Fe and Fe–O–Mn bond angles and bond lengths. Thus we suggest that the transport properties can be explained according to the additional localization of charge car...

Wasi Khan

Papers

Investigation on structural, optical and dielectric properties of Co doped ZnO nanoparticles synthesized by gel-combustion route

Biosynthesis of Stable Antioxidant ZnO Nanoparticles by Pseudomonas aeruginosa Rhamnolipids

Mycofabricated biosilver nanoparticles interrupt Pseudomonas aeruginosa quorum sensing systems.

Microstructural properties and enhanced photocatalytic performance of Zn doped CeO 2 nanocrystals.

Small polaron hopping conduction mechanism in Fe doped LaMnO3