Shahzad Naseem

Size- and Shape-Dependent Antibacterial Studies of Silver Nanoparticles Synthesized by Wet Chemical Routes

Silver nanoparticles (AgNPs) of different shapes and sizes were prepared by solution-based chemical reduction routes. Silver nitrate was used as a precursor, tri-sodium citrate (TSC) and sodium borohydride as reducing agents, while polyvinylpyrrolidone (PVP) was used as a stabilizing agent. The morphology, size, and structural properties of obtained nanoparticles were characterized by scanning electron microscopy (SEM), UV-visible spectroscopy (UV-VIS), and X-ray diffraction (XRD) techniques. Spherical AgNPs, as depicted by SEM, were found to have diameters in the range of 15 to 90 nm while lengths of the edges of the triangular particles were about 150 nm. The characteristic surface plasmon resonance (SPR) peaks of different spherical silver colloids occurring in the wavelength range of 397 to 504 nm, whereas triangular particles showed two peaks, first at 392 nm and second at 789 nm as measured by UV-VIS. The XRD spectra of the prepared samples indicated the face-centered cubic crystalline structure of metallic AgNPs. The in vitro antibacterial properties of all synthesized AgNPs against two types of Gram-negative bacteria, Pseudomonas aeruginosa and Escherichia coli were examined by Kirby–Bauer disk diffusion susceptibility method. It was noticed that the smallest-sized spherical AgNPs demonstrated a better antibacterial activity against both bacterial strains as compared to the triangular and larger spherical shaped AgNPs.

Effects of oxygen partial pressure on the properties of reactively evaporated thin films of indium oxide

Abstract Thin films of indium oxide were prepared by evaporating indium in the presence of oxygen. The effects of varying the oxygen partial pressure on the optical, electrical and structural properties were investigated. Films evaporated under the optimum oxygen partial pressure of 0.133 Pa exhibited a resistivity of 4.8 × 10 -4 Ω cm and a transmittance of more than 80% at wavelengths of 600 nm and above, for a film thickness of 225 nm. All the films, in the range of partial pressure of oxygen used, were found to be n type. The films showed a b.c.c. structure with a0 = 1.0118 nm and a preferred orientation along the 〈400〉 axis.

Preparation and characterization of hybrid pH-sensitive hydrogels of chitosan-co-acrylic acid for controlled release of verapamil

In the present work crosslinked hydrogels based on chitosan (CS) and acrylic acid (AA) were prepared by free radical polymerization with various feed compositions using N,N methylenebisacrylamide (MBA) as crosslinking agent. Benzoyl peroxide was used as catalyst. Fourier transform infrared spectra (FTIR) confirmed the formation of the crosslinked hydrogels. This hydrogel is formed due to electrostatic interaction between cationic groups in CS and anionic groups in AA. Prepared hydrogels were used for dynamic and equilibrium swelling studies. For swelling behavior, effect of pH, polymeric and monomeric compositions and degree of crosslinking were investigated. Swelling studies were performed in USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing AA contents in structure of hydrogels in solutions of higher pH values. This is due to the presence of more carboxylic groups available for ionization. On the other hand by increasing the chitosan content swelling increased in a solution of acidic pH, but this swelling was not significant and it is due to ionization of amine groups present in the structure of hydrogel. Swelling decreased with increase in crosslinking ratio owing to tighter hydrogel structure. Porosity and sol-gel fraction were also measured. With increase in CS and AA contents porosity and gel fraction increased, whereas by increasing MBA content porosity decreased and gel fraction increased. Furthermore, diffusion coefficient (D) and the network parameters i.e., the average molecular weight between crosslinks (Mc), polymer volume fraction in swollen state (V2s), number of repeating units between crosslinks (Mr) and crosslinking density (q) were calculated using Flory-Rehner theory. Selected samples were loaded with a model drug verapamil. Release of verapamil depends on the ratios of CS/AA, degree of crosslinking and pH of the medium. The release mechanisms were studied by fitting experimental data to model equations and calculating the corresponding parameters. The result showed that the kinetics of drug release from the hydrogels in both pH 1.2 and 7.5 buffer solutions was mainly non-Fickian diffusion.

Gold Nanoparticles: An Efficient Antimicrobial Agent against Enteric Bacterial Human Pathogen

Enteric bacterial human pathogens, i.e., Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Klebsiella pneumoniae, are the major cause of diarrheal infections in children and adults. Their structure badly affects the human immune system. It is important to explore new antibacterial agents instead of antibiotics for treatment. This project is an attempt to explain how gold nanoparticles affect these bacteria. We investigated the important role of the mean particle size, and the inhibition of a bacterium is dose-dependent. Ultra Violet (UV)-visible spectroscopy revealed the size of chemically synthesized gold nanoparticle as 6–40 nm. Atomic force microscopy (AFM) analysis confirmed the size and X-ray diffractometry (XRD) analysis determined the polycrystalline nature of gold nanoparticles. The present findings explained how gold nanoparticles lyse Gram-negative and Gram-positive bacteria.

Optoelectrical and structural properties of evaporated indium oxide thin films

Abstract Indium oxide thin films have been prepared by evaporating indium metal in the presence of oxygen atmosphere. The oxygen partial pressure was kept at a fixed value, of 1 mTorr, previously found to be optimum for the present investigations. The substrate temperature was varied from room temperature to 300°C. Once an optimum substrate temperature of 250° wass established, more films were prepared at this temperature and these films were then given a post-deposition heat treatment in nitrogen and oxygen atmospheres. The resultant films were characterized for their optical, electrical and structural properties. The results show that films with a resistivity as low as 3.38×10-4 ω cm, and with a transmittance as high as 91/s% can be achieved by controlling the preparation conditions.

Enhanced magnetization of sol-gel synthesized Pb-doped strontium hexaferrites nanocrystallites at low temperature

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12-xO19 (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized by sol-gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M-type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution. The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required.The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature.

Fabrication and properties of zinc oxide thin film prepared by sol-gel dip coating method

Abstract ZnO thin films were deposited on a glass substrate by dip coating technique using a solution of zinc acetate, ethanol and distilled water. Optical constants, such as refractive index n and extinction coefficient k. were determined from transmittance spectrum in the ultraviolet-visible-near infrared (UV-Vis-NIR) regions using envelope methods. The films were found to exhibit high transmittance, low absorbance and low reflectance in the visible regions. Absorption coefficient α and the thickness of the film t were calculated from interference of transmittance spectra. The direct optical band gap of the films was in the range of 3.98 to 3.54 eV and the thickness of the films was evaluated in the range of 173 to 323 nm, while the refractive index slightly varied in the range of 1.515 to 1.622 with an increase in withdrawal speed from 100 to 250 mm/s. The crystallographic structure of the films was analyzed with X-ray diffractometer. The films were amorphous in nature.

Iron Oxide Nanoparticles Prepared by Modified Co-Precipitation Method

The safe, targeted and effective release of drugs for therapeutics from nanostructured functional materials, particularly nanoparticles (NPs), has attracted much attention due to the ability to diagnose and cure of cancer and other ailments. The potential of magnetic NPs, that stems from intrinsic properties of their magnetic cores combined with their drug, can be exploited for clinical applications. Two main magnetic requirements for bionanotechnology-a high saturation magnetic moment and a near-zero remanence-occur in superparamagnetic materials. Here, we report synthesis of magnetite NPs by modified coprecipitation method. The effect of pH on the shape and size of NPs has also been reported in this paper. For superparamagnetic nature, the size of the NPs has great significance and should be compatible with the living cell. Ferric and ferrous chlorides are used as precursors and the amount of NaOH was varied to control the size and shape of the nanoparticles. X-ray diffraction patterns show the formation of magnetites. Scanning electron microscopy reveals that the prepared nanoparticles have size compatible with the diseased cell. M-H curves show the superparamagnetic nature of the nanoparticles, hence these NPs are well suited for the magnetic resonance imaging as the contrast agents, for cell tagging, magnetic separation, and hyperthermia treatments.

Microwave Assisted Iron Oxide Nanoparticles—Structural and Magnetic Properties

Microwave energy is used as an alternative source of high temperature treatment for synthesis and sintering. Till 1990s, the main focus was on the thermal effects caused by microwave heating. After 1990s reports began to emerge on the effects called microwave effects, including changes in materials structure and so on. We here report the effects of microwave assisted sol-gel method on structural and magnetic properties of iron oxide nanoparticles (NPs). Microwave power (MP) is varied as 136, 264, 440, 616, and 800 W. The MPs used in this paper are among the lowest for the synthesis of NPs. X-ray diffractometer result of NPs with 136-W MP shows amorphous behavior with paramagnetic properties. Magnetite NPs are observed with MPs of 264-440 W. Magnetite phase tends to transform to maghemite phase with the appearance of characteristic (310) peak at MPs of 616-800 W. Scanning electron microscope results show NPs with diameter ~20 nm for MPs of 264 and 440 W. Relatively larger diameters ~50 nm are observed with MPs of 616 and 800 W. Variations in phase and size of iron oxide NPs strongly affect magnetic properties from superparamagnetic to ferromagnetic. It is observed that microwave assisted synthesis can be fast, low cost, and low energy consumption method to synthesize NPs with uniform shape and size distribution along with strengthened magnetic properties as compared with the conventional high-temperature annealing process.

Reactively evaporated multilayer antireflection coatings for Ge optical window

Two multilayer antireflection (AR) coating configurations are designed, prepared and characterized. These AR coatings are designed for a 1 mm thick Ge optical window in the 3.25–5.25 µm band. Ta2O5 and TiO2 are used as high index materials along with SiO2 as low index material. Configuration 1 comprises nine alternating layers of SiO2 and Ta2O5, whereas configuration 2 comprises seven alternating layers of SiO2 and TiO2. Post-deposition annealing is also carried out in the temperature range 150–450 °C for 10 h. The prepared multilayered structures are characterized optically and structurally using a spectrophotometer, an atomic force microscope, x-ray diffraction and a scanning electron microscope. Optical characterization shows that multilayered structures have high absorption for as-deposited samples. A considerable improvement in the transmission profiles for the two multilayered configurations is observed at 350 °C with peak and average transmission for both the configurations exceeding 90%. The as-prepared samples show predominantly amorphous-like structure with pronounced peaks for configuration 2 only. Delamination (for configuration 1) and cracking (for configuration 2) of the multilayered structures are witnessed at an annealing temperature of 450 °C.