Reduced graphene oxide/ZnO nanocomposite modified electrode for the detection of tetracycline

Journal of Materials Science - In this work, rGO-ZnO (reduced graphene oxide–zinc oxide) nanocomposite was prepared and used for modification of GC (glassy carbon) surface in order to obtain...     

Green synthesis of silver nanoparticles and biopolymer nanocomposites: a comparative study on physico-chemical,antimicrobial and anticancer activity

The current report was intended towards comparative study of green-synthesized biogenic Rhubarb silver nanoparticles (RS-AgNPs) and chitosan crosslinked silver nanocomposites (CSHD-AgNCs). The physico-chemical characterization was done by UV–visible, FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX, TGA, XRD and zeta potential (\(\zeta \)). The analysis and spectroscopic characterization was done by SEM and TEM and their results reveal that the nanoparticles are spherical in shape, with average size ranges from 5 to 50 nm, and was gathered by face centered cubic (FCC) structure throughout the polymer matrix and stable without any protecting or capping reagents over 450 days. The antimicrobial property of RS-AgNPs and CSHD-AgNCs (\(\zeta = +29.6\) and \(+\)32.8 mV) was evaluated against E. coli and S. aureus and showed an effective inhibitory property. The RS-AgNPs and CSHD-AgNCs were assessed for their anticancer activity against HeLa cell line by MTT method, and it reveals a dose–response activity, time and cell line-dependent cytotoxicity. Based on the results obtained, the RS-AgNPs exhibited higher toxicity over CSHD-AgNCs after 24 h incubation of HeLa cells with different concentrations and is negligible for the aqueous Rhubarb extract. It was concluded that the changes in anticancer activity towards HeLa cells due to biological activity of silver nanoparticles depend on their method of biosynthesis and their physico-chemical nature.     

Cellular internalization of enhanced green fluorescent protein ligated to a human calcitonin-based carrier peptide

Carrier peptides offer new opportunities to overcome problems in cellular drug delivery. Their objectives are improved cellular uptake or permeation of biological membranes, which are important pharmacokinetic features for the cellular distribution of therapeutics. Previously, human calcitonin (hCT) and selected C-terminal hCT fragments have been shown to be internalized and to permeate the epithelium of the nasal mucosa. To assess the potential of hCT-derived carrier peptides for cellular internalization of a model protein we fused enhanced green fluorescent protein (EGFP) and the [C(8)]hCT8-32 fragment by using expressed protein ligation (EPL). EGFP thioester was obtained by intein-mediated purification with an affinity chitin-binding tag (the IMPACT system, based on protein splicing). Internalization of EGFP-[C(8)]hCT8-32 by excised bovine nasal mucosa was monitored by confocal laser scanning microscopy. This novel conjugate displayed internalization into some sectors of the mucosa, whereas EGFP itself was not capable of translocation. Thus, we demonstrate successful internalization of a model protein through ligation to an hCT-derived carrier peptide, which has potential for the delivery of therapeutics. At this point the respective mechanism of translocation is unknown.     

Nearest neighbor analysis of dopamine D1 receptors and Na(+)-K(+)-ATPases in dendritic spines dissected by STED microscopy

Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na(+),K(+)-ATPase. The analysis gave new information on how dense the D1 receptor and Na(+),K(+)-ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na(+),K(+)-ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes.     

Dissipative particle dynamics simulations of polyelectrolyte self-assemblies. Methods with explicit electrostatics

This feature article is addressed to a broad community of polymer scientists, both theoreticians and experimentalists. We present several examples of our dissipative particle dynamics (DPD) simulations of selfand co-assembling polyelectrolyte systems to illustrate the power of DPD. In the first part, we briefly outline basic principles of DPD. Special emphasis is placed on the incorporation of explicit electrostatic forces into DPD, on their calibration with respect to the soft repulsion forces and on the use of DPD for studying the self-assembly of electrically charged polymer systems. At present, the method with explicit electrostatics is being used in a number of studies of the behavior of single polyelectrolyte chains, their interaction with other components of the system, etc. However, in DPD studies of self-assembly, which require high numbers of chains, only a few research groups use explicit electrostatics. Most studies of polyelectrolyte self-assembly are based on the “implicit solvent ionic strength” approach, which completely ignores the long-range character of electrostatic interactions, because their evaluation complicates and considerably slows down the DPD simulation runs. We aim at the analysis of the impact of explicit electrostatics on simulation results.     

Conducting composites prepared by the reduction of silver ions with poly(p‐phenylenediamine)

Poly(p‐phenylenediamine) (PPDA) and also its ladder‐like analogue were prepared by oxidation of p‐phenylenediamine with ammonium peroxydisulfate in an aqueous solution of 0.4 mol L^?1 hydrochloric acid and converted to PPDA bases. These were used as reductants of silver nitrate to silver nanoparticles in 1 mol L^?1 methanesulfonic acid or in water at various mole ratios of silver nitrate to p‐phenylenediamine units from 0 to 1.8. The original conductivity of the PPDA, 10^?12 S cm^?1, increased to the order of 100 S cm^?1 for the PPDA–silver composites containing 27–40 wt% (i.e. 4.5–6.6 vol%) silver. Fourier transform infrared spectra indicated a practically unchanged molecular structure of PPDA in the composites. In contrast, Raman spectroscopy showed the existence of regions with unchanged molecular structure of PPDA as well as the presence of regions containing silver particles and oxidized PPDA moieties. © 2014 Society of Chemical Industry     

Thermal conductivity of porous alumina ceramics prepared using starch as a pore-forming agent

The thermal conductivity of porous alumina ceramics prepared using different types of starch (potato, wheat, corn, and rice starch) as pore-forming agents is investigated from room temperature up to 500 °C. The temperature dependence measured for alumina ceramics of different porosity (in the range 6–47%) is fitted with second-order polynomials and 1/T-type relations, and compared to available literature data for dense alumina. It is found that the porosity dependence of the relative thermal conductivity k_r = k/k₀ is well described by a modified exponential relation of the form k_r = exp(?1.5?/(1 ? ?)), where ? is the porosity. This finding is in agreement with other literature data and seems to indicate a common feature of all porous materials with microstructures resulting from fugitive pore-forming agents.     

Porous alumina ceramics prepared with wheat flour

It is shown that wheat flour can be used as a pore-forming and body-forming agent in ceramic technology. In contrast to pure native starch, however, the pores do not result from the swelling starch granules alone but are mainly due to protein-assisted foaming. Therefore the porosity is significantly higher and the pore size larger than that resulting from the starch granules alone, and the wet milling time applied for homogenizing the ceramic suspensions becomes the most critical process parameter. Alumina suspensions with 70 wt.% alumina and 20–30 vol.% wheat flour with different initial particle size (fine grade and semolina, respectively) have been prepared using milling times of up to 8 h. Porosities of up to approx. 60% can be achieved with only 20 vol.% of flour or semolina after 8 h of milling time, with the cell sizes (diameters of pore cavities resulting from foam bubbles) being essentially independent of the milling time (median diameters of 120–240 μm). Effective pore throat sizes (i.e. diameters of cell windows or channels between cells), measured via mercury porosimetry, are 1–2 μm for short milling times (2–3 h), but for long milling times (8 h) they change by more than one order of magnitude to median sizes of 20–30 μm, closely corresponding to the median size of wheat starch granules (approx. 20 μm).     

Structural characteristics of modified natural zeolite

Natural zeolite of Slovak provenience has been modified with magnetic nanoparticles at selected temperatures of 20, 50 and 85 °C with the aim to enhance its sorption properties. The pore, surface and structural properties of zeolite/iron oxide composite were characterized using nitrogen adsorption measurements, electron probe microanalysis and powder X-ray diffraction. The crystallinity of the host zeolite was strongly influenced by the temperature of iron oxide particles precipitation, but it was still retained. It followed from the nitrogen adsorption measurements that the surface area and the pore volume of zeolite composites have increased in relation to the precipitation temperature, the best sorption properties were revealed at the composite prepared at 85 °C. As followed also from the SEM images, the iron oxide nanoparticles being of size 30 nm are forming mesoporous aggregates adsorbed on the zeolite surface. Fractal analysis used to describe the modified geometry of zeolite composites has given the values of surface fractal dimension between 2.36 and 2.51.