Publications

In this work, the preparation and characterization of silver doped hydroxyapatite thin films were reported and their antimicrobial activity was characterized. Silver doped hydroxyapatite (Ag:HAp) thin films coatings substrate was prepared on commercially pure Si disks by sol-gel method. The silver doped hydroxyapatite thin films were characterized by various techniques such as Scanning electron microscopy (SEM) with energy Dispersive X-ray attachment (X-EDS), Fourier transform infrared spectroscopy (FTIR), and glow discharge optical emission spectroscopy (GDOES). These techniques have permitted the structural and chemical characterisation of the silver doped hydroxyapatite thin films. The antimicrobial effect of the Ag:HAp thin films on Escherichia coli and Staphylococcus aureus bacteria was then investigated. This is the first study on the antimicrobial effect of Ag:HAp thin films obtained by sol-gel method. The results of this study have shown that the Ag:HAp thin films with x(Ag) = 0.5 are effective against E. coli and S. aureus after 24 h.

Thin films of Bi2Sr2CuO6 (Bi-2201) with (001) or (115) orientation were grown on SrTiO3 substrates. These films are expected to be useful as component films of heterostructures and devices (e.g. as insulators). We used two chemical routes, namely spin coating followed by thermal annealing and MOCVD. For both routes we demonstrated growth of c-axis and non-c axis thin films depending on the selected orientation of the SrTiO3 substrate. To our knowledge, films of (115) Bi2201 obtained by spin coating or MOCVD are reported for the first time.

Low dimensional nanostructures represent a hot scientific field nowadays due mainly to the tremendous potential for applications. Low dimensions open the possibilities for both ultra-miniaturization and increase in functionality. Numerous procedures were developed for fabricating such nanostructures. Template replication represents a highly effective method in fabricating metallic nanowires and nanotubes. The approach is characterized by the excellent control in obtaining nano objects with the desired shape and dimensions. A large variety of templates are available ranging from viruses and proteins to nanoporous membranes fabricated by using swift heavy ion accelerators. In the following chapter the main steps involved in employing the method for fabricating metalic nanowires and nanotubes by replicating ion track nanoporous membranes were described. The steps include here membrane fabrication and replication and involve track etching and electrochemical metal deposition. The influence of the process parameters on the properties of the nanoobjects prepared by this approach was reviewed. It was found that simple experimental parameters can be chosen in such a way that the functionality of the nanowires or nanotubes can be finely tuned.

One of the focal subjects in insulin delivery is the development of insulin formulations that protect the native insulin from degradation under acidic pH in the stomach. In this work we show, for the first time, that a graphene oxide (GO) based matrix can ensure the stability of insulin at low pH. GO and GO modified with 2-nitrodopamine coated magnetic particle (GO-MPdop) matrices loaded with insulin were prepared and the pH triggered release of the insulin was studied. The loading of insulin on the GO nanomaterials proved to be extremely high at pH < 5.4 with a loading capacity of 100 +/- 3% on GO and 88 +/- 3% on GO-MPdop. The insulin-containing GO matrices were stable at acidic pH, while insulin was released when exposed to basic solutions (pH = 9.2). Using Xenopus laevis oocytes as a model we showed that the meiotic resumption rate of GO and GO-MPdop remained unaltered when pre-treated in acidic conditions, while pre-incubated insulin (without GO nanomaterials) has lost almost entirely its maturation effect. These results suggest that GO based nanomatrices are promising systems for the protection of insulin.

Monte-Carlo estimations of the integrals of Bose-Einstein distribution function for magnons are performed, by avoiding number of approximations involved in the usual derivation of the Bloch T-3/2 law, describing the dependence of magnetization with temperature in the low temperature regime, where the main mechanism of magnetization decrease is due to spin waves. More precisely: (i) the magnon dispersion law is considered the exact one (depending on the crystal structure) and not the quadratic approximation epsilon(k) alpha k(2); (ii) the integrals are performed over the first Brillouin zone and the limit of the integral is not extended to infinity; (iii) the dimensionality of the system is taken into account: 1D, 2D and 3D systems are considered; (iv) finite size magnetic systems are treated by rigorous summation of the Bose-Einstein distribution function, without using the continuous limit. The results can be summarized as follows: (a) Infinite three-dimensional (3D) systems exhibit deviations from the Bloch T-3/2 law, namely the deviation from zero Kelvin magnetization vertical bar Delta M vertical bar/M(0) behaves as T-gamma, where gamma is sensibly (by some 10 %) larger than 3/2 and, also, depends on the crystal structure considered. (b) Finite 3D systems exhibit more drastic deviation from the Bloch law, in that the gamma exponent deviates seriously from 3/2, going up to 2.5 for small systems of about 1,000 atoms. (d) Finite 2D systems also show serious deviations from the Bloch-like T law. As described a few years ago [C.M. Teodorescu, Surf. Sci. 601, 4292 (2007)], finite temperature magnetization may be considered only in finite size 2D systems. Several recent examples from literature are analyzed in the framework of the actual theoretical results. It is shown that M(T) analysis in the low temperature regime allows one to extract the average nanoparticle size of the magnetic moieties, and as well the exchange interaction and average spin quantum number.

X-ray photoelectron spectroscopy (XPS) analyses of lead zirco-titanate Pb(Zr,Ti)O-3(001) single crystal thin layers as a function of the time spent between sample preparation by pulsed laser deposition and introduction in to a ultrahigh vacuum revealed the fact that freshly prepared samples showed a shift of the C 1s towards a higher binding energy, together with shifts of core levels originating from the substrate (particularly Ti 2p and O 1s) towards a lower binding energy. This behaviour is explained by considering that the molecules of contaminants (fatty acids, alcohols, esters) are adsorbed preferentially on areas exhibiting outwards polarization P(+). Thus, photoelectrons originating from contaminants will have larger binding energies because of the charge state of the P(+) areas, whereas the substrate XPS signals from these P(+) areas are attenuated by the contaminants, with the consequence of a prevalence of XPS substrate signals originating from the P(-) areas, shifted towards lower binding energies. Piezoresponse force microscopy confirmed the assumptions derived from XPS results and suggests the existence of an interplay between the adsorption of contaminants and the surface polarization state.

The inhibition ability of dissolved 5,10,15,20-tetrakis(4-pyridyl)-21H, 23H-porphine (TPyP) on the corrosion of carbon steelin H2SO4 5% was investigated by evaluating the mass loss from the volume of the evolved hydrogen and by direct weight measurements at different temperatures. Results indicated that the presence of TPyP was able to reduce the corrosion rate of steel with over 50% efficiency, depending on TPyP concentration and temperature. The surface state of steel was characterized by AFM before and after the steel sample was corroded in H2SO4 solution (5%), the smoothing and uniforming effect of porphyrin being obvious, especially at higher temperature.

The iron oxide nanoparticles were synthetized by an adapted coprecpitation method. Stuctural and morphological characterization of the obtained iron oxide nanoparticles were investigated by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Furthermore, in vitro and in vivo studies were investigated by cell viability assay and HeLa cells. For the analysis of iron oxide toxicity in vivo, several mice were treated with normal saline and iron oxide via intraperitoneal injection (IP). The XRD spectra showed the peaks associated to the spinel cubic lattice type with the lattice of 0.835 nm. By magnified TEM image, it could be observed that the samples have a uniform morphology with relatively spherical shape and nanometric size. Moreover, inverted fluorescence microscopy images of HeLa cells with normal phenotype and HeLa cells treated for 72 hourswith a suspension of gamma-Fe2O3 nanoparticles revealed the non-toxic character. The histophtological studies have demonstrated that at 72 hours after IP administration, the iron oxide nanoparticles are not accumulating in kidney and spleen, thus establishing their utility as drug delivery systems targeted to these organs.

The aim of this study was to synthetize new nanoparticles based on methyltrimethoxysilane coated hydroxyapatite (MTHAp) for lead removal in aqueous solutions. The morphological and compositional analysis of MTHAp was investigated by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Removal experiments of Pb2+ ions were carried out in aqueous solutions with controlled concentration of Pb2+ and at fixed pH of 5. After the removal experiment of Pb2+ ions from solutions, porous hydroxyapatite nanoparticles were transformed into PbMTHAp_5 via the adsorption of Pb2+ ions followed by a cation exchange reaction. Our results demonstrate that the porous hydroxyapatite nanoparticles can be used as an adsorbent for removing Pb2+ ions from aqueous solution.

ZnO nanofibers were obtained by calcination of electrospun Zn(Ac)(2)center dot 2H(2)O/PMMA composite fibers and characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. The thermal treatment led to polymer burning and polycrystalline hexagonal ZnO phase formation. The average fiber diameters range between 450 and 600 nm before calcination and 200 - 300 nm after calcination. PL investigation revealed a strong dependence of ZnO fibers emission band on the calcination temperature. Furthermore, electrical contacts were fabricated by photolithography and electric characteristics were measured.