Laser synthesis and magnetic properties of monodispersed core–shell nanoparticles

This paper presents a method for fabricating size-selected nickel nanoparticles coated with oxide shells (shell thickness of about 2 nm). The size of the generated particles was controlled by a low-pressure differential mobility analyzer. The total mass of the deposited particles was estimated on the basis of their measured electric current. A high-resolution transmission electron microscope was used to observe the morphologies of the particles. We successfully synthesized a series of monodispersed (geometric standard deviation <1.2) core–shell particles with oxidized surface layers of 2 nm and analyzed their magnetic properties. PACS 75.50.Te; 75.30.Gw; 75.70.Cn     

Effect of insitu annealing on physical properties of Si nanoparticles synthesized by pulsed laser ablation

Silicon nanocrystalline particles with a uniform size were successfully synthesized by a sequential system of pulsed-laser ablation, insitu annealing and a size classification using a differential mobility analyzer (DMA). Transmission electron microscopy (TEM) observations revealed that the insitu annealing was quite effective in improving morphological uniformity of the particles; most of the nanoparticles annealed above a temperature of 900 °C showed a spherical shape. The silicon nanoparticles classified after the annealing showed a very narrow size-distribution with a geometrical standard deviation of approximately 1.1. Raman scattering measurement and high-resolution TEM observation showed that the annealing was also effective in improving a crystallinity of the particles. The silicon nanoparticles showed photoluminescence (PL) in near-IR and visible region at room temperature, which depended on the insitu annealing condition; the full-width at half-maximum (FWHM) of the PL spectrum decreased with the increase in annealing temperature and reached as narrow as 190 meV corresponding to the sharp size distribution of the emitting particles. PACS 81.40.Pq; 81.07.Bc     

Temperature dependence of photoluminescence from mono-dispersed Si nanoparticles

The temperature dependence of photoluminescence (PL) from mono-dispersed Si nanoparticles was studied from 4 to 300 K. Si nanoparticles produced by pulsed laser ablation in He background gas were sorted into the 6 nm size range by a differential mobility analyzer (DMA). The spread of the size distribution was narrowed to a geometrical standard deviation _g = 1.05. On decreasing the temperature from 300 to 4 K, the intensity of the PL spectra increased gradually, peaked at about 60 K, and then decreased rapidly. The temperature dependences of the intensity and the full width at half maximum (FWHM) on the PL spectra are discussed in terms of radiative and nonradiative decay rates.     

Growth of single-walled carbon nanotubes from size-selected catalytic metal particles

Single-walled carbon nanotubes (SWNTs) were synthesized using size-controlled catalyst nanoparticles created by the pulsed laser ablation method. Specifically, the alloy particles (Co/Mo or Co/Pt) were prepared by ablation of the target alloy materials in an inert gas atmosphere. Size selection was performed using a differential mobility analyzer (DMA). The obtained nanoparticles were deposited on a quartz substrate from which SWNTs were grown by the alcohol catalytic CVD (ACCVD) technique that was developed by the authors group. AFM and Raman scattering analysis revealed that SWNTs were successfully synthesized. It seems the Co/Mo alloy catalyst was more effective for the synthesis of SWNTs than the Co/Pt catalyst, though this is a preliminary result to be further investigated. PACS 36.40.-c; 61.46.+w; 65.80.+n; 78.30.Na; 81.07.de     

Direct measurement of iron in serum by electrothermal atomic absorption spectrometry

A simple and rapid method is described for the determination of iron in serum by atomic absorption spectrometry with a graphite furnace atomiser. The serum is diluted 40 times with water, and injected into the graphite tube. Optimal conditions are established, and interferences from proteins and salts eliminated. Since the procedure requires no sample pretreatment such as protein precipitation or wet digestion, contamination and losses by co-precipitation are excluded. The method can determine any species of iron in serum.     

Binding of 67 Ga and 59 Fe to ferritin or transferrin

The bindings of 67Ga and 59Fe to ferritin or transferrin in vitro has been investigated. Affinity constants have been measured using the equilibrium dialysis, and the results have been obtained as follows: 1 Apo-ferritin could not bind to 67Ga until it was transformed into ferritin in presence of Fe-citrate. On the contrary, the affinity of 67Ga to ferritin was reduced when Fe was released from ferritin; thus indicating that Fe-core has been required for the binding of 67Ga to ferritin. 2 Binding of 67Ga to ferritin was inhibited with apo-transferrin, and this was also shown in the case of 59Fe. In the presence of NaHCO3 or citrate, more remarkable inhibitions were observed. NaHCO3 or citrate was found to give a synergistic effect on the binding of 67Ga to transferrin, as well as Fe-transferrin. Therefore, both 67Ga and 59Fe could not bind to ferritin in the state of 67Ga- or 59Fe-transferrin. 3 The release of 59Fe from 59Fe-transferrin was enhanced with adenosine triphosphate (ATP), citrate, or ascorbic acid, while any of these reagents did not affect the release of 67Ga from 67Ga-transferrin. The comparison of 59Fe and 67Ga through their bindings to ferritin or transferrin has suggested one of points to distinguish 67Ga from 59Fe in the cell.     

KINETIC CHARACTERIZATION OF THE REDOX COMPONENTS IN SOLUBILIZED MEMBRANES FROM PORCINE NEUTROPHILS: REDUCTION WITH DITHIONITE AND PHOTOEXCITED NAD(P)H

Abstract— Cytochrome b₅₅₈ in solubilized membranes prepared from porcine neutrophils was reduced by dithionite with a second-order rate constant of 2.5 times 10⁶ M^-1 s^-1 at pH 7.4 and 20°C accompanied by spectral changes with peaks at 428 nm and 560 nm and isosbestic points at 420 and 441 nm. When an anaerobic mixture of solubilized membranes and NAD(P)H was exposed to a white light, cytochrome b₅₅₈ was reduced biphasically but with almost the same spectral profiles as in the dithionite reduction. Thus, participation of redox component(s) of unknown nature in the photochemical reduction was suggested. The NAD(P)- radical generated by photoexcitation of NAD(P)H with a 355 nm laser pulse under anaerobic conditions also reduced cytochrome b₅₅₈ with a high rate constant of 4.3 times 10⁸M^-1 s^-1 at pH 7.4 and 20°C. The reduction of cytochrome b₅₅₈ accompanied a simultaneous reduction of a component having an absorption band around 420 nm, suggesting participation of an iron-sulfur (Fe-S) cluster. The cytochrome b₅₅₈ reduction was followed by its reoxidation by another component with an apparent second-order rate constant of 6.5 times 10⁵M^-1 s^-1. During the reoxidation, the Fe-S-like component remained in the reduced state, and thus its role other than as electron mediator in neutrophils NADPH oxidase is suggested. Not only the rate constant but also the extent of cytochrome b₅₅₈ reoxidation decreased as the same reaction mixture was exposed to the laser pulse repeatedly. This result clearly indicates that an electron accumulates in this electron-accepting component designated tentatively as the ω component.     

Cover Picture: Electrochemical Lossy Mode Resonance-based Fiber Optic Sensing for Electroactive Species (Electroanalysis 3/2023)

We present an electrochemical-lossy mode resonance (LMR) sensing method that detects refractive indices and electroactive species. The LMR peaks of indium-tin-oxide in the transmittance-wavelength spectra were significantly shifted as the applied potential between 1.0 and −0.5 V at 209 nm/V. The modulation was exploited for sensing the refractive index and electroactive species (ferrocyanide and methylene blue) in two ways: peak-wavelength tracking and potential scanning. The potential-scanning technique produced clear potential LMR peaks in the transmittance-potential spectra for the first time, which were corresponded to the external refractive index. Meanwhile, the limits of detection of ferrocyanide and methylene blue were 7.5 and 25.3 μM, respectively, in peak-wavelength tracking and 18.2 and 20.8 μM, respectively, in the potential scanning technique.