Optimization and characterization of a biosensor assembly for detection of <Emphasis Type="Italic">Salmonella</Emphasis> Typhimurium

The performance of biosensors depends directly on the strategies adopted during their development. In this paper, a fast and sensitive biosensor for Salmonella Typhimurium detection was assembled by using optimization studies in separate stages. The pre-treatment assays, biomolecular immobilization (primary antibody and protein A concentrations), and analytical response (hydroquinone and hydrogen peroxide concentrations) were optimized via voltammetric methods. In the biosensor assembly, a gold surface was modified via the self-assembled monolayer technique (SAM) using cysteamine thiol and protein A for immobilization of anti-Salmonella antibody. The analytical response of the biosensor was obtained through the use of a secondary antibody labeled with a peroxidase enzyme, and the signal was evaluated by applying the chronoamperometry technique. The biosensor was characterized by infrared spectroscopy and cyclic voltammetry. Optimization of protein A and primary antibody concentrations enabled higher analytical signals of 7.5 and 75 mg mL^?1, respectively, to be achieved. The hydroquinone and H₂O₂ concentrations selected were 3 and 300 mM, respectively. The biosensor developed attained a very low detection limit of 10 CFU mL^?1 and a fast response with a final detection time of 125 min. These results indicate that this biosensor is very promising for the food safety and emergency response applications.     

Effect of N-doping on hard carbon nano-balls as anode for Li-ion battery: improved hydrothermal synthesis and volume expansion study

Using an improved single-step hydrothermal method, mesoporous hard carbon nano-balls, with nitrogen doping, have been successfully synthesized. These materials exhibit good reversible charge capacity during half-cell tests. Gravimetric capacity for undoped nano-sized and micron-sized mesoporous hard carbon balls is 506 and 475 mAh g^?1, respectively. After nitrogen doping, the specific gravimetric capacities of both nano- and micron-sized carbon balls increase by 6.9 and 8%, respectively. Nitrogen doping enhances retention in specific capacity of both anode materials, particularly in nano-sized carbon balls with capacity retention of 83.9% after 100 cycles. The enhancement is attributed to a significant decrease in volume expansion due to the nitrogen doping. Density functional theory-based computation confirms the reduction of volume expansion by 60%. Improved electrochemical performance of nitrogen-doped hard carbon is due to the drop in volume expansion rate during lithiation along with increased porosity and electronic conductivity. Furthermore, this one-step synthesis can be extended to other carbon sources to get nitrogen-doped hard carbon with sizes varying from micro to nano.     

Soft Phonon Modes Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe

Crystalline solids with intrinsically low lattice thermal conductivity (κ_L) are crucial to realizing high‐performance thermoelectric (TE) materials. Herein, we show an ultralow κ_L of 0.35 Wm^?1 K^?1 in AgCuTe, which has a remarkable TE figure‐of‐merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First‐principles DFT calculation reveals several soft phonon modes in its room‐temperature hexagonal phase, which are also evident from low‐temperature heat‐capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κ_L in the room‐temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high‐temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor.     

Oximato-bridged copper(II) compounds: syntheses,molecular structures,magnetic, thermal and spectroscopic properties

Reaction of the Schiff base, 1-(4-methylimidazol-5-yl) phenylhydrazonopropane-2-one oxime (LH), with copper(II) perchlorate hexahydrate and copper(II) nitrate trihydrate in a 1 : 1 M proportion in methanol affords [Cu₂L₂(H₂O)(ClO₄)](ClO₄) (1) and [Cu₂L₂(H₂O)₂](NO₃)₂] (2) in moderate yields. Both 1 and 2 have been characterized by elemental analysis, ESI-MS, FT-IR, UV–vis absorption spectroscopy, EPR, electric conductivity, and magnetic susceptibility measurements. The X-ray crystal structures of 1·CH₃COCH₃ and 2 have been determined. Both compounds are dinuclear copper(II) complexes, with each copper μ₂-bridged by two oxime ligands in a μ₂-η¹,η² fashion. Variable temperature magnetic studies on 1 and 2 show that both compounds are dominated by an antiferromagnetic coupling through the oxime bridges.     

Synthesis,characterizations, and electrochemical studies of ZnO/reduced graphene oxide nanohybrids for supercapacitor application

Herein the present article reports the fabrication of ZnO/reduced graphene oxide (ZnG) nanohybrid following a reduction-based process using a non-hazardous material, i.e., ascorbic acid. The morphology, structure, and bonding in the nanohybrid were analyzed using different techniques. Atomic force microscopy and scanning electron microscopy images show spherical particles of ZnO distributed over reduced graphene oxide (rGO). The X-ray diffraction analysis gives calculated values of crystallite size for ZnO as 15.62 nm. The successful incorporation of ZnO nanoparticles into rGO was confirmed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. The electrochemical studies were performed using an electrolyte (0.5 M H₂SO₄). The calculated value of specific capacitance for the nanohybrid was 345 Fg^-1, which was found to be almost double as compared to that of rGO, which is having a value of only 190.5 Fg^-1 at the same scan rate. The nanohybrid also showed excellent capacitance retention after 1,000 cycles.     

SAXS investigations on chiral liquid crystalline polymers: antiferroelectric and ferrielectric structures?

The structure and phase behavior of liquid crystalline polymers (LCPs) having a common chiral side chain mesogen but different main chain structures have been investigated using small-angle X-ray scattering (SAXS). While the low molecular weight chiral side chain mesogen by itself exhibits ferroelectricity, the SAXS data of the side chain LCP with a flexible polyacrylate backbone contains a bilayered superstructure peak that is indicative of antiferroelectric order. The combined LCP with a nonpolar main chain mesogen also has a bilayered superstructure, but has a different structural organization in the proposed antiferroelectric phase compared to the side chain LCP. Further changes in the phase behavior and structural organization occur when a polar group is introduced into the main chain mesogen. A ferrielectric phase has been proposed to explain the observation of a trilayered superstructure in the corresponding SAXS data. The influence of the chemical structure and connectivity on the phase behavior and superstructure formation in the chiral LCPs is discussed.     

Vanadium Oxide: From Gels to Nanotubes

Vanadium oxide nanotubes (VO _x -NT) have been prepared by mixing hexadecylamine with V₂O₅·nH₂O gels. This procedure was followed by an hydrothermal treatment (150–180°C, 2–7 days) which leads to a large quantity of VO _x -NT. SEM and XRD analysis have been used to optimize the temperature and reaction time required for production of VO _x -Nt and morphology of the nanotubes investigated by TEM.