Carbon composite-based DNA sensor for detection of bacterial meningitis caused by Neisseria meningitidis

Carbon/1-octadecanethiol-carboxylated multiwalled carbon nanotubes (cMWCNT) composite was used to construct a DNA sensor for detection of human bacterial meningitis caused by Neisseria meningitidis. The carbon composite electrode was used to covalently immobilize 5′-amine-labeled 19-mer single-stranded DNA (ssDNA) probe, which was hybridized with 1.35?×?10²–3.44?×?10⁴ pM (0.5–128 ng/5 μl) of single-stranded genomic DNA (ssG-DNA) of N. meningitidis for 10 min at room temperature (RT). The surface topography of the DNA sensor was characterized by using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) while electrochemically characterized by electrochemical impedance. The immobilization of ssDNA probe and hybridization with ssG-DNA were detected electrochemically by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at RT in 30 min with a response time of 1 min. The DNA sensor showed high pathogenic specificity and can distinguish among complement, noncomplement, one base mismatch, and triple base mismatch oligomer targets. The limit of detection (LOD) and sensitivity of the sensor were approximately 68 pM and 38.095 (μA/cm²)/nM of ssG-DNA, respectively, using DPV. The improved sensitivity and LOD of the sensor can be attributed to the higher efficiency of probe immobilization due to high surface area-to-volume ratio and good electrical activity of cMWCNT. Figure

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Chemical enrichment at high redshifts

We have tried to understand the recent observations related to metallicity in Ly-α forest clouds in the framework of the two component model. The model consists of mini-halos having circular velocities smaller than ∼ 55 km s⁻¹, with no star formation and galactic halos with higher circular velocities ≤ 250 km s⁻¹, having clouds, star formation and consequent metal enrichment. We find that even if the mini-halos were chemically enriched by an earlier generation of stars, to have [C/H] ≃ −2.5, the number of C IV lines with column density >10¹² cm⁻², contributed by the mini-halos, at the redshift of 3, would be only about 10% of the total number of lines, for a chemical enrichment rate of (1 + z)⁻³ in the galaxies. Recently reported absence of heavy element lines associated with most of the Ly-α lines with HI column density between 10^13.5 cm⁻² and 10¹⁴ cm⁻² by Lu et al [13], if correct, gives an upper limit on [C/H]= −3.7, not only in the mini-halos, but also in the outer parts of galactic halos. However, the mean value of 7×10⁻³ for the column density ratio of C IV and HI, determined by Cowie and Songaila (1998) for low Ly-α optical depths, implies an abundance of [C/H]= −2.5 in mini-halos as well as most of the region in galactic halos. The redshift and column density distribution of C IV has been shown to be in reasonable agreement with the observations.     

K-shell ionisation of atoms by positron and electron impacts

Recent developments in the calculation of the K-shell ionisation cross sections of atoms by positron and electron impacts are reviewed. The application of the first Born and other approximations derived by the modification of the first Born are discussed. It is pointed out that the first Born approximation modified to include exchange and the effect of the atomic field on the projectile yields satisfactory results for the light atoms.     

Influence of multiwall carbon nanotubes on morphology and electrical conductivity of PP/ABS blends

Polypropylene (PP) and acrylonitrile‐butadiene‐styrene (ABS) blends with multiwall carbon nanotubes (MWNT) were prepared by melt mixing. PP/ABS blends without MWNT revealed coarse co continuous structures on varying the ABS content from 40 to 70 wt %. Bulk electrical conductivity of the blends showed lower percolation threshold (0.4–0.5 wt %) in the 45/55 co continuous blends whereas the percolation threshold was between 2 and 3 wt % in matrix‐particle dispersed morphology of 80/20 blends. Interestingly, droplet size was observed to decrease with addition of MWNT above percolation threshold in 80/20 blends. Further, the bulk electrical conductivity was found to be dependent on the melt flow index of PP. The non‐polar or weakly polar nature of blends constituents resulted in the temperature independent dielectric constant, dielectric loss, and DC electrical conductivity. Rheological analysis revealed the formation of 3D network‐like structure in 80/20 PP/ABS blends at 3 wt % MWNT. An attempt was made to understand the relationship between rheology, morphology, and electrical conductivity of these blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2286–2295, 2008     

Performance of 2-hole YBCO rf SQUID in flux-locked-loop mode at 77 K

A 2-hole rf SQUID has been fabricated using naturally present grain boundary Josephson weaklinks in a microbridge of bulk Y-Ba-Cu-O superconductor. Periodic oscillations in voltage-flux characteristics have been observed up to 80.5 K. The spectral density of flux noise of the SQUID is 8 × 10⁻⁴ Φ₀/√Hz at 100 Hz and 77 K for open-loop mode. The SQUID has been successfully operated in flux-locked-loop mode at 77 K, demonstrating the feasiblity of the device for practical applications. In the flux-locked-loop mode the stability as well as flux noise of the SQUID has been found to improve considerably as compared to that in the open-loop mode. Various SQUID parameters have also been estimated and reported here.     

Origin of bulklike structure and bond length disorder of Pt37 and Pt6Ru31 clusters on carbon: comparison of theory and experiment

We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier experimental studies. With clusters deposited via metallo-organic Pt or PtRu(5) complexes, previous experiments [Nashner et al. J. Am. Chem. Soc. 1997, 119, 7760; Nashner et al. J. Am. Chem. Soc. 1998, 120, 8093; Frenkel et al. J. Phys. Chem. B 2001, 105, 12689] showed that the Pt and Pt-Ru based clusters are formed with fcc(111)-stacked cuboctahedral geometry and essentially bulklike metal-metal bond lengths, even for the smallest (few atom) nanoparticles for which the average coordination number is much smaller than that in the bulk, and that Pt in bimetallic [PtRu(5)] clusters segregates to the ambient surface of the supported nanoparticles. We explain these observations and characterize the cluster structures and bond length distributions using density functional theory calculations with graphite as a model for the support. The present study reveals the origin of the observed metal-metal bond length disorder, distinctively different for each system, and demonstrates the profound consequences that result from the cluster/carbon-support interactions and their key role in the structure and electronic properties of supported metallic nanoparticles.     

Structural and redox properties of mitochondrial cytochrome c co-sorbed with phosphate on hematite (alpha-Fe2O3) surfaces

The interaction of metalloproteins with oxides has implications not only for bioanalytical systems and biosensors but also in the areas of biomimetic photovoltaic devices, bioremediation, and bacterial metal reduction. Here, we investigate mitochondrial ferricytochrome c (Cyt c) co-sorption with 0.01 and 0.1 M phosphate on hematite (alpha-Fe2O3) surfaces as a function of pH (2-11). Although Cyt c sorption to hematite in the presence of phosphate is consistent with electrostatic attraction, other forces act upon Cyt c as well. The occurrence of multilayer adsorption, and our AFM observations, suggest that Cyt c aggregates as the pH approaches the Cyt c isoelectric point. In solution, methionine coordination of heme Fe occurs only between pH 3 and 7, but in the presence of phosphate this coordination is retained up to pH 10. Electrochemical evidence for the presence of native Cyt c occurs down to pH 3 and up to pH 10 in the absence of phosphate, and this range is extended to pH 2 and 11 in the presence of phosphate. Cyt c that initially adsorbs to a hematite surface may undergo conformation change and coat the surface with unfolded protein such that subsequently adsorbing protein is more likely to retain the native conformational state. AFM provides evidence for rapid sorption kinetics for Cyt c co-sorbed with 0.01 or 0.1 M phosphate. Cyt c co-sorbed with 0.01 M phosphate appears to unfold on the surface of hematite while Cyt c co-sorbed with 0.1 M phosphate possibly retains native conformation due to aggregation.