Cristina Ghitulica

Gold Nanowire Networks: Synthesis, Characterization, and Catalytic Activity

Gold nanowire networks (AuNWNs) with average widths of 17.74 nm (AuNWN(1)) or 23.54 nm (AuNWN(2)) were synthesized by direct reduction of HAuCl(4) with sodium borohydride powder in deep eutectic solvents, such as ethaline or reline, at 40 °C. Their width and length were dependent on the type of solvent and the NaBH(4)/HAuCl(4) molar ratio (32 in ethaline and 5.2 in reline). High resolution transmission electron microscopy (HR-TEM) analysis of the gold nanowire networks showed clear lattice fringes of polycrystalline nanopowder of d = 2.36, 2.04, 1.44, and 1.23 Å corresponding to the (111), (200), (220), or (311) crystallographic planes of face centered cubic gold. The purified AuNWNs were used as catalysts for the chemical reduction of p-nitroaniline to diaminophenylene with sodium borohydride in aqueous solution. The reaction was monitored in real time by UV-vis spectroscopy. The results show that the reduction process is six times faster in the presence of gold nanowire networks stabilized by urea from the reline (AuNWN(2)) than in the presence of gold nanowire networks stabilized by ethylene glycol from ethaline (AuNWN(1)). This is due to a higher number of corners and edges on the gold nanowires synthesized in reline than on those synthesized in ethaline as proven by X-ray diffraction (XRD) patterns recorded for both types of gold nanowire networks. Nevertheless, both types of nanomaterials determined short times of reaction and high conversion of p-nitroaniline to diaminophenylene. These gold nanomaterials represent a new addition to a new generation of catalysts: gold based catalysts.

Montmorillonite-alginate nanocomposite as a drug delivery system--incorporation and in vitro release of irinotecan.

The scope of the present study was the preparation and characterization of irinotecan nanocomposite beads based on montmorillonite (Mt) and sodium alginate (AL) as drug carriers. After irinotecan (I) incorporation into Mt, the resulting hybrid was compounded with alginate, and I-Mt-AL nanocomposite beads were obtained by ionotropic gelation technique. The structure and surface morphology of the hybrid and composite materials were established by means of X-ray diffraction (XRD), IR spectroscopy (FT-IR), thermal analysis (TG-DTA) and scanning electron microscopy (SEM). Irinotecan incorporation efficiency in Mt and in alginate beads was determined both by UV-vis spectroscopy and thermal analysis and was found to be high. The hybrid and composite materials were tested in vitro in simulated intestinal fluid (pH 7.4, at 37 °C) in order to establish if upon administering the beads at the site of a resected colorectal tumor, the delivery of the drug is sustained and can represent an alternative to the existing systemic chemotherapy. The in vitro drug release test results clearly suggested that Mt, and Mt along with AL were able to control the release of irinotecan by making it sustained, without any burst effect, and by reducing the released amount and the release rate. The nanocomposite beads may be a promising drug delivery system in chemotherapy.

In vitro activity of the new water-dispersible Fe3O4@usnic acid nanostructure against planktonic and sessile bacterial cells

A new water-dispersible nanostructure based on magnetite (Fe3O4) and usnic acid (UA) was prepared in a well-shaped spherical form by a precipitation method. Nanoparticles were well individualized and homogeneous in size. The presence of Fe3O4@UA was confirmed by transmission electron microscopy, Fourier transform-infrared spectroscopy, and X-ray diffraction. The UA was entrapped in the magnetic nanoparticles during preparation and the amount of entrapped UA was estimated by thermogravimetric analysis. Fabricated nanostructures were tested on planktonic cells growth (minimal inhibitory concentration assay) and biofilm development on Gram-positive Staphylococcusaureus (S.aureus),Enterococcus faecalis (E.faecalis) and Gram-negative Escherichia coli (E.coli),Pseudomonasaeruginosa (P.aeruginosa) reference strains. Concerning the influence of Fe3O4@UA on the planktonic bacterial cells, the functionalized magnetic nanoparticles exhibited a significantly improved antimicrobial activity against E.faecalis and E.coli, as compared with the Fe3O4 control. The UA incorporated into the magnetic nanoparticles exhibited a very significant inhibitory effect on the biofilm formed by the S.aureus and E.faecalis, on a wide range of concentrations, while in case of the Gram-negative microbial strains, the UA-loaded nanoparticles inhibited the E.coli biofilm development, only at high concentrations, while for P.aeruginosa biofilms, no inhibitory effect was observed. The obtained results demonstrate that the new water-dispersible Fe3O4@UA nanosystem, combining the advantages of the intrinsic antimicrobial features of the UA with the higher surface to volume ratio provided by the magnetic nanocarrier dispersible in water, exhibits efficient antimicrobial activity against planktonic and adherent cells, especially on Gram-positive strains.

New silica nanostructure for the improved delivery of topical antibiotics used in the treatment of staphylococcal cutaneous infections

In this paper, we report the synthesis, characterization (FT-IR, XRD, BET, HR-TEM) and bioevaluation of a novel γ-aminobutiric acid/silica (noted GABA-SiO₂ or γ-SiO₂) hybrid nanostructure, for the improved release of topical antibiotics, used in the treatment of Staphylococcus aureus infections. GABA-SiO₂ showed IR bands which were assigned to Si-O-Si (stretch mode). The XRD pattern showed a broad peak in the range of 18-30° (2θ), indicating an amorphous structure. Based on the BET analysis, estimations about surface area (438.14 m²/g) and pore diameters (4.76 nm) were done. TEM observation reveals that the prepared structure presented homogeneity and an average size of particles not exceeding 10nm. The prepared nanostructure has significantly improved the anti-staphylococcal activity of bacitracin and kanamycin sulfate, as demonstrated by the drastic decrease of the minimal inhibitory concentration of the respective antibiotics loaded in the GABA-SiO₂ nanostructure. These results, correlated with the high biocompatibility of this porous structure, are highlighting the possibility of using this carrier for the local delivery of the antimicrobial substances in lower active doses, thus reducing their cytotoxicity and side-effects.

Caprolactam-silica network, a strong potentiator of the antimicrobial activity of kanamycin against gram-positive and gram-negative bacterial strains.

Here, we report the fabrication of a novel ε-caprolactam-silica (ε-SiO2) network and assessed its biocompatibility and ability to improve the antimicrobial activity of kanamycin. The results of the quantitative antimicrobial assay demonstrate that the obtained ε-SiO2 network has efficiently improved the kanamycin activity on Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 strains, with a significant decrease of the minimum inhibitory concentration. The ε-SiO2 network could be feasibly obtained and represents an alternative for the design of new antibiotic drug carriers or delivery systems to control bacterial infections.

Preparation and characterization of undoped and cobalt doped ZnO for antimicrobial use.

The objective of this study was to carry out the synthesis by sol-gel method of undoped and cobalt doped ZnO, with different cobalt concentrations (0.5-5mol%), using as stabilizer monoethanolamine (MEA) in a molar ratio ZnO:MEA=1:2. The dry gel was thermally treated at 500°C/5h, respectively at 1100°C/30min. All the thermal treated samples were of wurtzite type with an hexagonal structure. The doping with Co(2+) induced change of lattice parameters and of crystallite size, proving the successful interleaving of Co(2+) into the ZnO lattice. From the morphological point of view, the thermal treatment at 1100°C/30min led to a higher degree of compactness of the ZnO granules. At 500°C/5h there were formed polyhedral or spherical nanometric particles (25-50nm) which have been agglomerated into aggregates with sizes over 1μm. From the biological point of view, the quantitative analyses of antimicrobial activity have shown that the ZnO doped with cobalt has inhibited the ability of the Bacillus subtilis and Escherichia coli bacterial strains to colonize the inert substrate and therefore, can be used in the design of new antimicrobial strategies.

Analysis of the Structure and Morphology of Hydroxyapatite Nanopowder Obtained by Sol-Gel and Pirosol Methods

Nano-size hydroxyapatite is the main inorganic component of bone. There is a critical particle size that each property starts to change. Each property can be modified under controlled conditions. Multifunctional materials for applications, one must consider several properties change. Bone properties, are those which dictate the properties of hydroxyapatite, properties to be followed the synthetic materials to be used successfully as implants. Of these mention those related to surface materials, solubility and biocompatibility and their mechanical strength. Depending on the location and functionality of the implant have met some of these properties. The purpose of this study is to develop a synthetic hydroxyapatite at nano scale, using sol-gel and pyrosol method, for its use in medicine

Bioglasses in the SiO2-CaO-P2O5 System

The aim of the study was the synthesis and characterization of bioactive osteoinductive glasses, in the SiO2 – CaO – P2O5 system. In order to maintain the bioactive character of bioglasses, for SiO2 contents higher than 60%, the sol – gel method was used for preparation. On the obtained powders, thermal, grain size and X - ray diffraction analysis were performed. The X - ray diffraction emphasized the formation of phosphate phases, whose proportion decreases as the silica content is increased. Later, the powders were thermally treated at temperatures between 1000 and 14000C, the phase composition evolution being monitored through XRD analysis. On the powder suspensions in physiological serum, the evolution of pH was investigated, in order to establish the chemical stability. The behavior of the obtained powders in physiological medium was studied, by immersing samples in simulated body fluid and excerpted after different periods of time.

Composite Ceramics Reinforced with Zirconia Nanopowders

Dental porcelain fused to metals (PFM) is one of the most widely applied restoration material, because of its excellent esthetics, biocompatibility and wear resistance [1, 2]. In the literature of specialty (dentistry) there is not made a clear distinction between porcelain and ceramic, while referring to ceramics as being all these materials derived from mixtures of metallic oxides, being in opposition with metal alloys [3-5]. The aim of this study was to obtain and characterize dental porcelains, dentine type, in the following oxide system: SiO2-K2O-Al2O3-Na2O-B2O3-MgOCaO, reinforced with nanometric particles of monoclinic zirconia. The method selected for the preparation of the porcelain powders is through solid-state reactions.

Porous Ceramics for High Temperature Filters

Cordierite based ceramic porous materials are very promising for filtering applications, due to their low thermal expansion coefficient, but also due to high chemical stability and good mechanical resistance. The cordierite powders were obtained through the co-precipitation method, while the porous ceramics were prepared by mixing the ceramic powder with an organic compound, which will burn during consequent thermal treatments, leading to an open pore ceramic web. Samples with different proportions of glucose were thermally treated at temperatures between 1050 and 1400oC. The samples were analyzed in what it concerns the mineralogical composition, open porosity and pores distribution, compressive strength and microstructure.