Blending Approach Preparation of PVA-g-PMA Films with Embedded "Green" Synthesized Silver Nanoparticles for Acetone Optical Detection

The blending approach (also known as the ex-situ approach) was used for the deposition of thin composite films comprising poly(vinyl alcohol-graft-methyl acrylate) (PVA-g-PMA) and silver nanoparticles (AgNPs). Firstly, the copolymer aqueous dispersion was synthesized through the redox polymerization of methyl acrylate (MA) on poly(vinyl alcohol) (PVA) using ammonium cerium (IV) nitrate as the initiator. Then, AgNPs were synthesized through a "green" method using the water extract of lavender based on by-products of the essential oil industry, and then they were blended with the polymer. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to determine nanoparticle size, along with their stability over time in suspension, during the 30-day period. Thin films of the PVA-g-PMA copolymer, with different AgNP volume fractions varying between 0.008 and 0.260%, were deposited via the spin-coating method on Si substrates, and their optical properties were explored. UV-VIS-NIR spectroscopy and non-linear curve fitting were used for the determination of the refractive index, extinction coefficient, and thickness of the films, while photoluminescence measurements at room temperature were conducted for studying the emission of the films. The concentration dependence of film thickness was observed and showed that thickness increased linearly from 31 nm to 75 nm when the nanoparticles' weight content increased from 0.3 wt% to 2.3 wt%. The sensing properties toward acetone vapors were tested in a controlled atmosphere by measuring reflectance spectra before and during exposure to the analyte molecules in the same film spot; the swelling degree of films was calculated and compared to the corresponding undoped samples. It was shown that the concentration of AgNPs of 1.2 wt% in the films is optimal for the enhancement of the sensing response toward acetone. The influence of AgNPs on the films' properties was revealed and discussed.

Novel Approach for Synthesis of Graphene-like Phases by Pulsed Laser Ablation in a Flow-Mode Suspension

The present study investigates the possibility of obtaining graphene-like phases (defected graphene, graphene oxide, and reduced graphene oxide) as fine suspensions by applying a novel pulsed laser ablation (PLA) approach in flow mode. Two types of suspensions of microcrystalline graphite in aqueous suspensions and two types of microcrystalline graphite in suspensions of 6% hydrogen peroxide solution were irradiated in a quartz tube through which they flow. The third (λ = 355 nm) and fourth harmonics (λ = 266 nm) of an Nd:YAG laser system (15 ns pulse duration and 10 Hz pulse repetition rate) were used. The morphology of the obtained particles was studied by transmission electron microscopy (TEM). Their phase composition and structure were explored by X-ray photoelectron spectroscopy, X-ray diffractometry, and Raman spectroscopy.

Optical Sensing of Humidity Using Polymer Top-Covered Bragg Stacks and Polymer/Metal Thin Film Structures

Thin films with nanometer thicknesses in the range 100-400 nm are prepared from double hydrophilic copolymers of complex branched structures containing poly(N,N-dimethyl acrylamide) and poly(ethylene oxide) blocks and are used as humidity sensitive media. Instead of using glass or opaque wafer for substrates, polymer thin films are deposited on Bragg stacks and thin (30 nm) sputtered Au-Pd films thus bringing color for the colorless polymer/glass system and enabling transmittance measurements for humidity sensing. All samples are characterized by transmittance measurements at different humidity levels in the range from 5% to 90% relative humidity. Additionally, the humidity induced color change is studied by calculating the color coordinates at different relative humidity using measured spectra of transmittance or reflectance. A special attention is paid to the selection of wavelength(s) of measurements and discriminating between different humidity levels when sensing is performed by measuring transmittance at fixed wavelengths. The influence of initial film thickness, sensor architecture, and measuring configuration on sensitivity is studied. The potential and advantages of using top covered Bragg stacks and polymer/metal thin film structures as humidity sensors with simple optical read-outs are demonstrated and discussed.

Nanosized thin SnO₂ layers doped with Te and TeO₂ as room temperature humidity sensors

In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques—SEM, EDS in SEM, TEM, SAED, AES and electrical measurements—are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio R_Sn/Te and the evaporation conditions. It is shown that as-deposited layers with R_Sn/Te ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature—very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers' surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.

C283Y gamma-sarcoglycan gene mutation in the Bulgarian Roma (Gypsy) population: prevalence study and carrier screening in a high-risk community

Limb-girdle muscular dystrophy type 2C (LGMD2C) is caused by mutations in the gamma-sarcoglycan gene where a founder Gypsy mutation C283Y was detected. The Bulgarian Gypsy LGMD2C patients, as the Gypsy patients from other countries, were found to be homozygous for this mutation. Considering the large number of Gypsies in Bulgaria and the high percent of consanguinity and endogamy a raised carrier frequency of the C283Y mutation was expected especially in North-Eastern Bulgaria where most of the patients originate from. Here, we present the precise geographic distribution of the C283Y mutation in the general Roma population from the whole Bulgarian territory by determining the carrier frequency of the mutation in dry blood newborn samples. Our results show that the geographic distribution of this founder mutation and the disease are not geographically restricted only among Gypsies from North-Eastern Bulgaria. We stress upon the regions with detected high carrier and/or disease frequency and upon the results from the performed carrier screening on volunteers in one of these regions. The ongoing carrier-screening programs in isolated Gypsy groups would be of a great benefit for the genetic prophylaxis of the disease. Such regions should be with priority in the Bulgarian healthcare system for performing a carrier-screening program.

About the biological effects of high and extremely high frequency electromagnetic fields

This paper deals with the effects of high (microwave) and extremely high (millimetre waves, MMW) frequency electromagnetic fields on the membrane processes and ion channels, molecular complexes, excitable and other structures. Microwaves as well as millimetre waves are widely used in medical practice and in everyday life. The existence of interaction between the exogenous and endogenous electromagnetic fields with biological systems is now a subject of intense discussion. The most contentious question is the existence of a possible specific (non-thermal) effect of microwaves, unrelated to that caused by increased temperature. Although numerous data have been published on the possible non-thermal effects of the studied electromagnetic fields on different kinds of living systems, only little understanding is gained about the modes of microwave action. Here we review data, which provide evidence that non-thermal microwave effects do exist and may play a significant role. This evidence is based on research at all biological levels, from cell-free systems through cells, tissues and organs, to animal and human organisms.

Effect of microwave electromagnetic field on skeletal muscle fibre activity

The aim of the present study was to investigate the influence of microwave irradiation on fatiguing activity of isolated frog skeletal muscle fibres. The changes in the electrical and mechanical activity were used as criteria for the exposure effects. Repetitive suprathreshold stimulation with interstimulus interval of 200 ms for 3 min was applied. Intracellular (ICAP) and extracellular (ECAP) action potentials and twitch contractions (Tw) of muscle fibres after 1 hour microwave exposure (2.45 GHz, 20 mW/cm( 2) power density) were compared with those recorded after one hour sham exposure (control). The duration of uninterrupted activity in the trial (endurance time; ET) was not significantly affected by microwave field exposure. After microwave irradiation, the ICAP amplitude was higher, the rising time was shorter, and the resting membrane potential was more negative compared to controls. There was a slower rate of parameters changes during ET in potentials obtained from irradiated fibres. Microwave exposure increased the propagation velocity of excitation, the ECAP and Tw amplitudes, as well as shortened their time parameters. We concluded that a 2.45 GHz microwave field possesses a stimulating effect on muscle fibre activity, which is in part due to its specific, non-thermal properties. The microwave induced-changes in muscle fibre activity may reduce development of skeletal muscle fatigue.

Long-lasting (fatiguing) activity of isolated muscle fibres influenced by microwave electromagnetic field

The study aims to clarify the effect of exposure to microwave electromagnetic field (MMW) on muscle fibre fatigue. Repetitive stimulation with interstimulus interval of 200 ms was applied on isolated frog muscle fibre to evoke intracellular action potentials and twitch contractions. After their recording muscle fibre preparation was moved in a Petri dish with radius of 28 mm on open air for one hour exposure to continuous MMW with frequency of 2.45 GHz and power density of 20 mW/cm2. Then it was again moved in the chamber with non irradiated Ringer's solution at controlled temperature for the repeated records. After MMW exposure the changes in amplitude and time parameters characterizing fatigue were attenuated and delayed vs. controls. The twitch amplitude curve described an drastic fall in the first 5 sec followed by an increase and next decrease. MMW (2.45 GHz) have a specific, non-thermal influence on muscle fibre activity resulting in some resistance to fatigue.

Mutational and structural analyses of the ribonucleotide reductase inhibitor Sml1 define its Rnr1 interaction domain whose inactivation allows suppression of mec1 and rad53 lethality

In budding yeast, MEC1 and RAD53 are essential for cell growth. Previously we reported that mec1 or rad53 lethality is suppressed by removal of Sml1, a protein that binds to the large subunit of ribonucleotide reductase (Rnr1) and inhibits RNR activity. To understand further the relationship between this suppression and the Sml1-Rnr1 interaction, we randomly mutagenized the SML1 open reading frame. Seven mutations were identified that did not affect protein expression levels but relieved mec1 and rad53 inviability. Interestingly, all seven mutations abolish the Sml1 interaction with Rnr1, suggesting that this interaction causes the lethality observed in mec1 and rad53 strains. The mutant residues all cluster within the 33 C-terminal amino acids of the 104-amino-acid-long Sml1 protein. Four of these residues reside within an alpha-helical structure that was revealed by nuclear magnetic resonance studies. Moreover, deletions encompassing the N-terminal half of Sml1 do not interfere with its RNR inhibitory activity. Finally, the seven sml1 mutations also disrupt the interaction with yeast Rnr3 and human R1, suggesting a conserved binding mechanism between Sml1 and the large subunit of RNR from different species.

Influence of a protein hydrolysate from green algae on the activity of some ATPase systems in frog skeletal muscle

The present study investigated the effect of a protein hydrolysate from green algae cultured in the Bulgarian region of Rupy, on the enzyme activity of frog skeletal muscle. The activity of pure Mg(2+)-ATPase, Mg2+,Ca(2+)-ATPase, NaHCO3-stimulated Mg(2+)-ATPase and the latter in the presence of the inhibitors NaSCN and NaN3 in mitochondrial (B-3) and membrane (B-12) fractions were determined before and after treatment with the protein hydrolysate from green algae (30 and 300 micrograms/ml). The differences between ATPase activity of mitochondrial and membrane fractions were described and it was established that in the B-3 fraction, the activity of the NaHCO3-stimulated Mg(2+)-ATPase and Ca(2+)-dependent Mg(2+)-ATPase were accelerated by increasing concentrations of the algae protein hydrolysate. Irrespective of the different (equal or inverse) dose-dependent effects, the protein hydrolysate stimulated Mg(2+)-ATPase and that inhibited by NaSCN an NaN3 bicarbonate-stimulated Mg(2+)-ATPase activity. In most of the probes, the protein hydrolysate produced some increase in enzyme activity of NaHCO3-stimulated Mg(2+)-ATPase and Ca(2+)-dependent Mg(2+)-ATPase in B-12 fractions. The observed properties of the algae protein hydrolysate suggest that it is capable of stimulating enzyme processes in addition to having some antitoxic effect in skeletal muscle.

Further studies on Nivalin P-induced changes in muscle fiber membrane processes

Nivalin P, composed of Nivalin (galanthamine hydrobromide) and Pymadin (4-aminopyridine hydrochloride), was applied extracellularly to isolated skeletal muscle fibers during prolonged activity (fatiguing) to better understand the effects of the drug on membrane ionic processes. Changes in intracellular action potential (ICAP) and twitch (Tw) parameters were monitored from treated and untreated fibers during uninterrupted activity (endurance time, ET) produced by repetitive stimulation every 200 msec for 3 min. Nivalin P-induced a shortening of the ET, drastic changes in repolarization of the ICAP corresponding to changes in negative afterpotential and falling area and an initial increase of the Tw amplitude and duration. These results suggest that Nivalin P: (i) inhibits the Na+, K(+)-pump due to nonspecific reduction of Na+ influx, stimulates the Na(+)-Ca2+ exchanger and inhibits K+ conductance; (ii) increases Ca2+ release and delays Ca2+ uptake under sufficient depolarization. It was concluded that fatigue develops faster in the presence of Nivalin P.