Ultrasensitive Hydrogen Peroxide Biosensor Based on Enzyme Bound to Layered Nonoriented Multiwall Carbon Nanotubes/Polyelectrolyte Electrodes

A sensitive hydrogen peroxide sensor based on horseradish peroxidase covalently attached to layered nonoriented MWNTs modified electrode is presented. Cyclic voltammetry results gave quasi‐reversible Fe^III/Fe^II voltammetry. The electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M) in pH 7 is 48.8±0.9 s^?1 and 0.13±0.05 mM respectively. A linear calibration curve for hydrogen peroxide was obtained up to 120 nM under the optimized conditions with a remarkable detection limit of (S/N=3) 1.5 nM. Results suggest that the nonoriented nanotubes act as electrical conductors and may also provide large surface area facilitating facile electron transfer and excellent electrochemical catalysis.     

Magnetic insulator glasses

An outline is given of the use of Mössbauer spectroscopy as a probe of the amorphous structure and magnetic coordination in magnetic insulator glasses. Using the⁵⁷Fe Mössbauer resonance as an example in the context of amorphous ferric oxides and fluorides, the manner in which both paramagnetic and hyperfine-field-split spectra can be analyzed is presented. Emphasis is given to the information contained in Mössbauer lineshapes and linewidths in addition to the more obvious line-position data. A number of general findings are set out for ferric speromagnetics with particular references to Mössbauer studies of amorphous Fe₂O₃, Y₃Fe₅O₁₂ (YIG), FeF₃ and NaFeF₄.     

Hyperfine fields in iron-metalloid ferromagnetic metals

A new coordination parameter Z_eff is defined at each inequivalent iron site in the interstitial iron-metalloid ferromagnetic metals which uniquely determines the hyperfine field at that site with considerable accuracy. The dependence of Z_eff upon bonding lenghts is defined and can be directly used to generate hyperfine field distributions for amorphous aggregates. It thereby promises to provide a fairly quantitative bridge between computer models and hyperfine field probes in iron metglasses.     

Effect of electric field gradient sign on iron mossbauer spectra in amorphous materials

This paper establishes the fact that a significant asymmetry develops in ⁵⁷Fe Mössbauer spectra at high magnetic fields in amorphous materials containing iron if the electric field gradient (EFG) distribution at the iron sites is dominantly of one sign. The manner in which the symmetric quadrupole doublet develops asymmetrically into the familiar six line Zeeman pattern with increasing (spontaneous or applied) field is computed numerically for general fields, and analytically for high fields, using a broad (amorphouslike) model EFG distribution. It follows that information concerning the dominant sign (or alternatively the absence of a dominant sign) of the EFG can be obtained from iron Mössbauer spectra. Such information concerning EFG sign is potentially important evidence in a probe of the nature of the local packing (i.e. random packing vis-a-vis local crystalline unit-cell distortion) in many amorphous magnetic materials.