Saira Riaz

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.

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.

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.

Optical Investigation of Sm3+ Doped Zinc-Lead-Phosphate Glass

Samarium doped lead-zinc-phosphate glasses having composition (60−x)P2O5-20PbO-20ZnO-xSm2O3 where x=0, 0.5, 1.0, 3.0mol% were prepared by using the melt quenching technique. The Archimedes method was used to measure their densities, which are used to calculate the molar volumes. The values of densities lie in the range 3.698–4.090 gm/cm3 whereas those of molar volume lie in the range of 37.24–40.00 cm−3. UV-vis-NIR absorption spectroscopy in the wavelength range 200–2000 nm was carried out. Absorption spectra consist of seven absorption peaks corresponding to the transitions from the 6H5/2 ground state to various excited energy levels. The energy band gap measured from the optical absorbance is found to be in the range of 3.88-4.43 eV and 3.68-4.33 eV for direct and indirect transitions, respectively. In addition, the photoluminescence spectrum shows four prominent emission bands centered at 560, 597, 642 and 700 nm corresponding to the 4G5/2−6HJ (J=5/2, 7/2, 9/2, 11/2) transitions respectively and the intensity of all the bands are enhanced as the concentration of Sm3+ ions increases.

Room Temperature Magnetic Behavior of Sol-Gel Synthesized Mn Doped ZnO

Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto-combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X-ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.

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.

Magnetic Properties of Polyvinyl Alcohol and Doxorubicine Loaded Iron Oxide Nanoparticles for Anticancer Drug Delivery Applications.

The current study emphasizes the synthesis of iron oxide nanoparticles (IONPs) and impact of hydrophilic polymer polyvinyl alcohol (PVA) coating concentration as well as anticancer drug doxorubicin (DOX) loading on saturation magnetization for target drug delivery applications. Iron oxide nanoparticles particles were synthesized by a reformed version of the co-precipitation method. The coating of polyvinyl alcohol along with doxorubicin loading was carried out by the physical immobilization method. X-ray diffraction confirmed the magnetite (Fe3O4) structure of particles that remained unchanged before and after polyvinyl alcohol coating and drug loading. Microstructure and morphological analysis was carried out by transmission electron microscopy revealing the formation of nanoparticles with an average size of 10 nm with slight variation after coating and drug loading. Transmission electron microscopy, energy dispersive, and Fourier transform infrared spectra further confirmed the conjugation of polymer and doxorubicin with iron oxide nanoparticles. The room temperature superparamagnetic behavior of polymer-coated and drug-loaded magnetite nanoparticles were studied by vibrating sample magnetometer. The variation in saturation magnetization after coating evaluated that a sufficient amount of polyvinyl alcohol would be 3 wt. % regarding the externally controlled movement of IONPs in blood under the influence of applied magnetic field for in-vivo target drug delivery.

Effect of Solvents on the Ferromagnetic Behavior of Undoped BiFeO 3 Prepared by Sol-Gel

We here report the preparation of undoped BiFeO3 (BFO) thin films with sol-gel method using two solvents, i.e., acetic acid (AA) and ethylene glycol (EG). Films are annealed in the temperature range 100-300 °C for 60 mins. Films deposited using AA show the presence of bismuth rich phase Bi46Fe2O72 along with BFO in the intermediary conditions. Pure phase BFO is obtained when films are deposited using EG as a solvent even under as-deposited conditions, and the pure phase persists after annealing in the temperature range 100 °C-300 °C. This is the lowest temperature reported for the preparation of phase pure BFO. Bandgap of AA-based films lies in the range 2.58-2.64 eV and that of EG-based films in the range 2.77-2.81 eV. Reduced value of dielectric constant, in AA-based films, is because of the presence of bismuth rich impurity phase as compared with the films prepared using EG. Bands in FTIR spectra at 487 and 552 cm-1 are characteristic bands of FeO6 and BiO6 groups, indicating the formation of BFO. Films deposited using AA show weak ferromagnetic behavior, while those deposited using EG show strong ferromagnetic behavior as opposed to antiferromagnetic nature of BFO, due to suppression of spiral spin structure.

BARIUM TITANATE FILMS FOR ELECTRONIC APPLICATIONS: STRUCTURAL AND DIELECTRIC PROPERTIES

Synthesis of the precursors, using research grade materials and locally available facilities, is optimized in order to obtain a suitable sol for BaTiO3. The optimally synthesized BaTiO3 sol is then spun onto Cu substrates to obtain films of thickness ~0.5 μm. The deposited BaTiO3 films are heated up to a temperature of 300°C. Surface and structural changes, with heating, are observed by optical microscope, scanning electron microscope, atomic force microscope, and X-ray diffraction. The surface cracked in some cases but is generally uniform, as seen with SEM and AFM, in case of optimized conditions. The SEM images reveal large crystallites, which are correlated to the XRD observation of tetragonal perovskite structure of these sol–gel films. The AFM scan, however, shows an rms roughness of 35.6 nm for an area of 3 μm × 3 μm. Tetragonal perovskite BaTiO3 is obtained at a temperature of as low as 300°C. The dielectric constant and loss angle, in the 30 Hz–3 MHz range, are calculated at room temperature and up to 200°C. At high frequencies the dielectric constant (~290) and loss angle (~2 × 10-6) values indicate the usefulness of such films in electronic applications. The leakage current is also measured at room temperature and a conductivity of 2.0 × 10-15 S/cm is obtained.