Mass transfer in amperometric gas sensors

The mass transfer in amperometric gas sensors intended for atmosphere monitoring is studied theoretically and experimentally. External and internal constituents of the diffusion resistance (DR) of the sensors are determined. The external constituent is defined by conditions of convective diffusion of air under analysis relative to the sensor. The internal constituents are defined by parameters of construction of sensor elements, and electrolyte film, as well as the structure of the indicator electrode, and solubility of the gas under analysis in the electrolyte. Testing a chlorine sensor shows that the DR of the internal constituents is independent of the conditions of convective diffusion of the environment under analysis near the sensor. The similarity criterion of sensors of different types is shown to be the relative share of DRs of individual constituents in the overall DR of the sensor. The results obtained can be used for the development and design of sensors with required range and resolution.     

Highly luminescent water-dispersed silicon quantum dots for fluorometric determination of oxytetracycline in milk samples

A fluorescent probe based on silicon quantum dots (SiQDs) was developed for the selective and sensitive detection of oxytetracycline (OTC) via the inner filter effect (IFE). The water-soluble fluorescent SiQD was synthesized based on the reaction of 3-Aminopropyltriethoxysilane (APTES) and sodium citrate as precursors by the one-pot hydrothermal process. The strong fluorescence emission of quantum dots (QDs) was obtained at 440 nm when excited at 350 nm and OTC had a broad absorption band between 200 and 400 nm. The excitation spectrum of SiQDs was completely overlapped with the absorption spectrum of OTC. The light at an excitation wavelength of QDs absorbed by OTC caused a decrease in fluorescence intensity with an increase in the concentration of OTC. Under optimal conditions, the linear concentration range was 0.92–9.2 µg mL1 with a detection limit (LOD; S/N = 3) of 0.19 µg mL ^-1 . The proposed method was applied to the determination of OTC in milk samples and satisfactory recoveries (98.8–100.5%) with low RSD % values (0.93–2.31%) were achieved. This simple, selective, sensitive, rapid, and cheap method can be used as a promising tool for OTC analysis in food safety.     

Effects of ELF Magnetic Field in Combination with Iron(III) Chloride (FeCl3) on Cellular Growth and Surface Morphology of Escherichia coli (E. coli)

This study investigated the effects of extremely low frequency (ELF) magnetic field with/without iron(III) chloride (FeCl₃) on bacterial growth and morphology. The ELF exposures were carried out using a pair of Helmholtz coil-based ELF exposure system which was designed to generate 50 Hz sinusoidal magnetic field. The field was approximately uniform throughout the axis of the coil pair. The samples which were treated or non-treated with different concentrations FeCl₃ were exposed to 50 Hz, 2 millitesla (mT) magnetic field for 24 h. ELF effect on viability was assessed in terms of viable colony counts (in colony-forming unit per milliliter) with the standard plate count technique. Scanning electron microscopy was used to investigate the magnetic field effect on surface morphology of Escherichia coli. No significant results were seen in terms of cell viability between ELF and sham-exposed bacterial strains. Similarly, FeCl₃ treatment did not change cell viability of E. coli samples. However, we observed some morphological changes on E. coli cell surfaces. Pore formations and membrane destruction were seen on the surface of 24 h ELF field-exposed cells. We concluded that ELF magnetic field exposure at 2 mT does not affect cell viability; however, it may affect bacterial surface morphology.     

Thermal conductivities of solid and liquid phases for pure Al,pure Sn and their binary alloys

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Al and Sn–0.5 wt.% Al, Sn–2.2 wt.% Al, Sn–25 wt.% Al, Sn–50 wt.% Al, Sn–75 wt.% Al binary alloys were measured with a radial heat flow apparatus. From thermal conductivity variations versus temperature, the thermal conductivities of the solid phases at their melting temperature and temperature coefficients for same materials were also found to be 60.60 ± 0.06, 208.80 ± 0.22, 69.70 ± 0.07, 80.30 ± 0.08, 112.30 ± 0.12, 142.00 ± 0.15, 188.50 ± 0.20 W/K m and 0.00098, 0.00062, 0.00127, 0.00114, 0.00112, 0.00150, 0.00116 K⁻¹, respectively. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Al and eutectic Sn–0.5 wt.% Al alloy at their melting temperature are found to be 1.11, 1.13, 1.06 with a Bridgman type directional solidification apparatus, respectively. Thus the thermal conductivities of liquid phases for pure Sn, pure Al and eutectic Sn–0.5 wt.% Al binary alloy at their melting temperature were evaluated to be 67.26, 235.94 and 73.88 W/K m, respectively by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.     

Synthèse rationelle de clusters mixtes à trois au quatre métaux differents et contenant le ligand Ph2PCH2PPh2 (dppm)

Reaction of PdPtCl₂(dppm)₂ with Co(CO)₄^? or Mn(CO)₅^? affords the tetrametallic clusters PdPtCo₂(CO)₇(dppm)₂ and PdPtMn₂(CO)₉(dppm)₂. The cobalt cluster reacts with iodide to give PdPtCoI(CO)₃(dppm)₂ which upon reaction with Fe(CO)₃NO^? or Mn(CO)₅^? yields PdPtFeCo(CO)₆NO(dppm)₂ and PdPtMnCo(CO)₈(dppm)₂, respectively.     

Experimental determination of solid-liquid interfacial energy for solid Sn in the Sn-Mg system

The equilibrated grain boundary groove shapes for solid Sn in equilibrium with the Sn-9 at.% Mg eutectic liquid were directly observed annealing a sample at the eutectic temperature for about 5 days with a radial heat flow apparatus. The thermal conductivities of the solid phase, κ_S, and the liquid phase, κ_L, for the groove shapes were measured. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient, the solid-liquid interfacial energy and grain boundary energy for solid Sn in equilibrium with the Sn-9 at.% Mg eutectic liquid have been determined to be (7.35 ± 0.36) × 10⁻⁸ Km, (136.41 ± 13.64) × 10⁻³ J m⁻² and (230.95 ± 25.40) × 10⁻³ J m⁻², respectively.     

Environmental noise classifier using a new set of feature parameters based on pitch range

Automatic Noise Recognition was performed in two stages: (1) feature extraction based on the pitch range, found by analyzing the autocorrelation function and (2) classification using a classifier trained on the extracted features. Since most environmental noise types change their acoustical characteristics over time, we focused on the “pitch range” of the sounds in order to extract features. Two different classifiers, Support Vector Machines (SVM) and k-means clustering, were performed and compared using the proposed features. The SVM and k-means clustering classifiers achieve recognition rates up to 95.4% and 92.8%, respectively. Although both classifiers provided high accuracy, the SVM-based classifier outperformed the k-means clustering classifier by approximately 7.4%.     

Evaluation of Antibacterial and Antifungal Effects of Calcium Hydroxide Mixed with Two Different Essential Oils

Background: Calcium hydroxide is a routinely used material for root canal disinfection during root canal treatment. Natural products have great potential in terms of their antibacterial effects. This study aimed to establish an effective alternative intracanal medicament using Origanum dubium (O. dubium) and Mentha spicata (M. spicata) essential oils. Materials and Methods: O. dubium and M. spicata, collected from Lefke, Cyprus, were separately subjected to hydrodistillation. The obtained essential oil compositions were analysed simultaneously by gas chromatography (GC) and gas chromatography/mass spectrometry (GC-MS). The compositions were then divided into groups and mixed with calcium hydroxide at a 1:1 concentration; after that, the pastes were tested on Enterococcus faecalis (E. faecalis) and Candida albicans (C. albicans), which are the most common resistant pathogenic microorganisms in the root canal. The antibacterial activity of the pastes was measured using a disk diffusion assay. Results: The GC and GC-MS analyses revealed that O. dubium and M. spicata had major compositions of carvacrol (75.8%) and carvone (71.3%), respectively. Antimicrobial activity was found to be significantly higher when study groups with O. dubium essential oil were applied to both E. faecalis and C. albicans. The results also show that M. spicata, together with calcium hydroxide, demonstrated a significant antifungal effect on C. albicans when incubated for 72 h. Conclusions: M. spicata was found to be an effective antimicrobial agent on C. albicans, whereas O. dubium was found to be very effective on both E. faecalis and C. albicans. These data demonstrate that these natural essential oils may be promising candidates for alternative intracanal medicament in future routine clinical applications.     

Electrochemical DNA biosensor for the detection of TT and Hepatitis B virus from PCR amplified real samples by using methylene blue

DNA biosensors based on nucleic acid hybridization processes are rapidly being developed towards the goal of rapid and inexpensive diagnosis of genetic and infectious diseases. Electrochemical transducers are often being used for detecting the DNA hybridization event, due to their high sensitivity, small dimensions, low cost, and compatibility with microfabrication technology. In this study, an electrochemical biosensor for the voltammetric detection of DNA sequences related to the Hepatitis B virus (HBV) and TT virus (TTV) from polymerase chain reaction (PCR) amplified real samples is described for the first time. The biosensor relies on the immobilization of the 21- or 24-mer single stranded oligonucleotides (probe) related to the HBV and TTV sequences and hybridization of these oligonucleotides with their complementary sequences (target) at carbon paste electrode (CPE). The extent of hybridization between the probe and target sequences was determined by using square wave voltammetry (SWV) with moving average baseline correction and methylene blue (MB) as the hybridization indicator. As a result of the interaction between MB and the bound guanine bases of hybrid at CPE surface, the MB signal decreased, when it was compared with the MB signal, which was observed with probe modified CPE. The difference between the MB signals, obtained from the hybrid modified and the probe modified CPE is used to detect the DNA sequences of the infectious diseases from PCR amplified real samples. Numerous factors affecting the target hybridization and indicator binding reactions are optimized to maximize the sensitivity.     

DNA sensing on glassy carbon electrodes by using hemin as the electrochemical hybridization label

The electrochemical behavior of hemin, an iron complex of porphyrin, on binding to DNA at a glassy carbon electrode (GCE) and in solution, is described. Hemin, which interacts with covalently immobilized calf thymus DNA, was detected by use of a bare GCE, a double-stranded DNA-modified GCE (dsDNA-modified GCE), and a single-stranded DNA-modified GCE (ssDNA-modified GCE), in combination with differential pulse voltammetry (DPV). The structural conformation of DNA was determined from changes in the voltammetric signals acquired on reduction of hemin. As a result of its large steric structure and anionic substitution on its porphyrin plane, hemin intercalates between the base pairs of dsDNA. A scan-rate study for hemin and the dsDNA-hemin complex were also performed to determine the electrochemical behavior of the complex. The partition coefficient was obtained from the peak currents measured when different concentrations of hemin were in the presence of dsDNA. By observing the oxidation signals of guanine, damage to DNA after reaction with hemin at the GCE surface was also detected. The electrochemical detection of hybridization between the covalently immobilized probe and its target sequence was detected by use of hemin. These results demonstrate the use of DNA biosensors in conjunction with hemin for electrochemical detection of hybridization and damage to DNA.