On existence of nanoparticles below the sooting threshold

Nanometer-sized particles were studied by photoionisation mass spectrometry and scanning mobility particle sizer in laminar premixed ethylene flames above and below the critical sooting threshold. For sooting flames, both techniques detected a large number of particles with masses between 1 and 50 ku or diameter around a few nanometers. Neither method detected an appreciable number of particles below the sooting threshold in flames similar to those studied earlier for UV absorption and scattering of transparent soot. The absence of particle signals in both experimental techniques raises the question about the origin of UV absorption under nonsooting conditions.     

磷钼酸作为光催化还原剂制备纳米金溶胶

选择二甲基甲酰(DMF)为电子牺牲剂,以磷钼杂多酸作为光催化还原剂制备了纳米金溶胶,由于DMF与磷钼杂多阴离子间的电荷转移作用,导致钼系杂多酸可成为制备纳米金溶胶的光催化还原剂.实验结果表明,紫外光照作用及光照时间、DMF用量等是影响纳米金的形成和形貌的主要因素,选择适宜的合成条件可以得到粒径均匀、分散性好的纳米金溶胶.     

Fluorescence quenching of 3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride by AgCl and Ag nanoparticles

Quenching of fluorescence of the dye 3,7-diamino-2,8-dimethyl-5-phenyl Phenazinium Chloride (Safranine T) has been investigated by AgCl nanoparticles in the W/O microemulsion medium at different [H₂O]/[AOT] ratios (ω) and with Ag nanoparticles and Ag⁺ in aqueous medium. A simple straightforward method has been introduced to prepare AgCl nanoparticles in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane. Experimental results reveal that the size of the AgCl nanoparticles increases with increase in hydration. The results of the quenching experiment were analysed in the light of Stern Volmer equation. Quenching of fluorescence of the dye has been found to decrease with decrease in the size of the nanoparticles of AgCl and the variation of Stern Volmer quenching constants (K_SV) with particle size is different for two different size regimes.     

Dielectric behavior of nano-structured and bulk Li Ni Zn ferrite samples

The ac conductivity and dielectric properties of spinel ferrite nanoparticles of Li_0.1(Ni_1−xZn_x)_0.8Fe_2.1O₄ (x=0.0–1.0) prepared by the chemical co-precipitation method were investigated as functions of frequency and temperature by using a complex impedance technique. Parts of the precipitated powders were pressed into a disk-shape and were sintered at 1473 K for 2 h to increase the particle size to the bulk scale (dimensions >100 nm). The ac conductivity of the samples increases with increasing temperature, ensuring the semiconducting behavior of both nano and bulk samples, in agreement with the Koops model to describe heterogeneous structures. The significant decrease in ac conductivity σ′_ac, dielectric constant, and dielectric loss of the as-prepared nanosamples compared to their bulk counterparts is correlated to the small size of the grain compared to the grain boundary size. This might be useful for many applications requiring the reduction of eddy current effects.     

Cu-DNAzyme facilitates highly sensitive immunoassay

A simple Cu-DNAzyme system is used for signal transduction of a CuO nanoparticle-labeled immunoassay, which makes the immunoassay fast, simple, cost-effective, and sensitive, thus promising for biomedical applications and point-of-care testing.     

Preparation and characterization of SnO2 nanoparticles using high power pulsed laser

Tin dioxide (SnO₂) nanoparticles having 3 nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO₂ crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV-vis absorption spectral studies showed a peak at 240 nm. FTIR spectrum showed a band in the range of 400-700 cm⁻¹ which was assigned to Sn-O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO₂ nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613 eV respectively.     

ZnO nanoparticles with controlled shapes and sizes prepared using a simple polyol synthesis

Nanocrystalline zinc oxide (ZnO) particles with controlled shapes and sizes were prepared at 180 ^°C by a simple polyol method. The amount of water and the method of addition played an important role in determining the characteristics of the synthesized particles. Rod-shaped ZnO particles with major axis lengths of ∼114 nm were obtained by heating the precursor solution, while equiaxial particles with average diameters of ∼24 nm were prepared by injecting water into hot precursor solution. Increasing the amount of water added to the precursor solution enlarged the aspect ratio of the rod-shaped particles and increased the particle size of the equiaxial particles due to enhanced hydrolysis and condensation of the Zn ion complex.     

Prion protein detection in serum using micromechanical resonator arrays

Prion proteins that have transformed from their normal cellular counterparts (PrP^c) into infectious form (PrP^res) are responsible for causing progressive neurodegenerative diseases in numerous species, such as bovine spongiform encephalopathy (BSE) in cattle (also known as mad cow disease), scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans. Due to a possible link between BSE and CJD it is highly desirable to develop non-invasive and ante mortem tests for the detection of prion proteins in bovine samples. Such ante mortem tests of all cows prior to slaughter will help to prevent the introduction of PrP^res into the human food supply. Furthermore, detection of PrP^res in donated blood will also help to prevent the transmission of CJD among humans through blood transfusion. In this study, we have continued development of a micromechanical resonator array that is capable of detecting PrP^c in bovine blood serum. The sensitivity of the resonators for the detection of PrP^c is further enhanced by the use of secondary mass labels. A pair of antibodies is used in a sandwich immunoassay format to immobilize PrP^c on the surface of resonators and attach nanoparticles as secondary mass labels to PrP^c. Secondary mass labeling is optimized in terms of incubation time to maximize the frequency shifts that correspond to the presence of PrP^c on the surface of resonators. Our results show that a minimum of 200 pg mL⁻¹ of PrP^c in blood serum can be detected using micromechanical resonator arrays.     

Semiconductor nanocrystals obtained by colloidal chemistry for biological applications

Semiconductor nanoparticles in the quantum confinement regime used as biolabels present many advantages over the other chemical species used as fluorophores. They are composed of 2000-6000 atoms rendering a far greater photostability and allowing for long time bioimaging experiments. In this work we present a synthetic route for the obtention of large quantities of highly fluorescent CdSe and CdTe/CdS core-shell nanocrystals based on aqueous colloidal chemistry. The methodologies were optimized and the systems were characterized by optical spectroscopy, transmission electronic microscopy and X-Ray diffractometry. The fluorescent biolabels were tested in live macrophages.     

Electrochemistry of platinum nanoparticles supported in polypyrrole (PPy)/C composite materials

Conducting polypyrrole (PPy)/C (Vulcan XC-72) composite materials were synthesized by chemical polymerization method. These materials were used as matrix to support platinum nanoparticles, which were produced by the carbonyl chemical route. For the same catalyst loading (50 μg cm⁻²), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum toward the oxygen reduction reaction in acid medium. The variation of the PPy/C ratio determines the so-called substrate effect for electrocatalysis. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.