Perfusion in microfluidic cross-flow: separation of white blood cells from whole blood and exchange of medium in a continuous flow

We describe a microfluidic technique for separation of particles and cells and a device that employs this technique to separate white blood cells (WBC) from whole human blood. The separation is performed in cross-flow in an array of microchannels with a deep main channel and large number of orthogonal, shallow side channels. As a suspension of particles advances through the main channel, a perfusion flow through the side channels gradually exchanges the medium of the suspension and washes away particles that are sufficiently small to enter the shallow side channels. The microfluidic device is tested with a suspension of polystyrene beads and is shown to efficaciously exchange the carrier medium while retaining all beads. In tests with whole human blood, the device is shown to reduce the content of red blood cells (RBC) by a factor of approximately 4000 with retention of 98% of WBCs. The ratio between WBCs and RBCs reached at an outlet of the device is 2.4 on average. The device is made of a single cast of poly(dimethylsiloxane) sealed with a cover glass and is simple to fabricate. The proposed technique of separation by perfusion in continuous cross-flow could be used to enrich rare populations of cells based on differences in size, shape, and deformability.     

Selective and quantitative detection of influenza virus proteins in commercial vaccines using two-dimensional high-performance liquid chromatography and fluorescence detection

In this work, we report on the applicability of two-dimensional high-performance liquid chromatography (2D-HPLC) for the comprehensive characterization of inactivated influenza vaccine proteins. This novel procedure features minimal sample treatment and combines the on-line coupling of size exclusion HPLC to reversed-phase HPLC. A comparative analysis of commercial vaccines from three different manufacturers showed the method to be highly selective by providing characteristic reproducible chromatographic profiles for each vaccine. In addition, the method provided enhanced sensitivity for most constituents as a result of the use of native fluorescence detection in the reversed-phase HPLC step. The limits of detection (at a signal-to-noise ratio of >3) for hemagglutinin (HA) antigens were 105 and 172 ng/mL for influenza A/New Caledonia/20/99 and B/Jiangsu/10/2003 strains, respectively. The potential of this 2D-HPLC procedure in terms of quantitative antigen analysis was assessed by determination of the HA content of commercial vaccines. Results provided very good correlation with nominal HA values. The reproducibility (RSD) of the whole procedure was also evaluated and was found to be better than 2 and 3% for calculated antigen concentrations expressed as micrograms of HA per milliliter in commercial vaccines for samples of the same lot (n = 5) or different lots (n = 3), respectively. In addition, it allowed the selective detection of several influenza constituents including nucleoproteins from type A and B viruses and the highly hydrophobic matrix protein 1 from both virus strains.     

Rheological behavior of anionic collagen injectable gels in the presence of rhamsan for plastic surgery applications

The present paper describes the rheological properties of anionic collagen gels and anionic collagen:rhamsan composites gels in the concentration of 0.7, 4 and 6%, estimated to be used as injectable biomaterials for plastic reconstruction. Rheological studies of these gels showed that independently of pH, composition and concentration the viscoelastic behavior was dependent on the frequency, with the storage modulus always greater than the loss modulus (G′ > G″ and δ < 45°). Creep experiments showed that anionic collagen:rhamsan composites equilibrated at pH 7.4 were less elastic and more susceptible to deformation in comparison to gels equilibrated at pH 3.5. Flow experiments indicated that the force needed for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smoother flow, suggesting the association with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations. Finally, on the basis of dynamic viscosity profiles found for different preparations, some of these composites are potential candidates to be utilized in laryngology.     

Antimicrobial susceptibility of Listeria monocytogenes isolated from food and clinical cases in Navarra, Spain

The susceptibility of 440 Listeria monocytogenes strains isolated from food (n=401) and clinical cases (n=39) between 1995 and 2005 was determined by standard agar dilution and E-test methods. Antimicrobial drugs currently used in veterinary and human therapy were tested, and they included penicillin G, ampicillin, cephalothin, gentamicin, chloramphenicol, tetracycline, doxycycline, trimethoprim, erythromycin, and clindamycin. The sensitivity of strains was established using Clinical and Laboratory Standards Institute (formerly NCCLS) breakpoints and MIC50 (the MIC for 50% of the strains) to MIC90 values. In general, isolates were susceptible to the majority of the antimicrobials tested, including beta-lactamics and aminoglycosides, which are normally used in the treatment of listeriosis. Resistance to tetracycline and doxycycline was found in five strains isolated from fresh trout belonging to the same fish farm. Molecular analysis by restriction endonuclease analysis showed a similar profile, suggesting the persistence of a strain well adapted to the presence of tetracycline in the environment of a fish farm, which is frequently used in aquaculture in order to prevent infections of fish.     

Ochratoxin A in red paprika: relationship with the origin of the raw material

The occurrence of ochratoxin A (OA) in paprika elaborated from peppers grown in several countries (Peru, Brazil, Zimbabwe and Spain) was studied, using an immunoaffinity clean-up column coupled to liquid chromatography and fluorescence detection. The preparation of the methyl ester (OA-Me) and liquid chromatography-electrospray-ion trap-mass spectrometry was used both to confirm the identity of the chromatographic peak that correspond to OA and to quantify it at low levels or in dirty fractions. A total of 115 strains of moulds were isolated; 85 of the fungal strains were obtained from OA contaminated paprika samples and identified as belonging to the Aspergillus Section Circumdati group (A. ochraceus) and Section Nigri group (A. niger, A. carbonarius). Among the latter ones, 31% of the A. ochraceus isolates and one A. niger were OA producers in vitro. None of the mould strains isolated from paprika samples with undetectable levels of OA or concentrations below 1 microg kg(-1) were toxin producers. Great differences in OA content in paprika samples were found, and a relationship with the climatic conditions of the geographic origin of the samples, and with cultural and technical practices in pepper manipulation is suggested.     

Electronic and structural characteristics of zinc-blende wurtzite biphasic homostructure GaN nanowires

We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.     

Aflatoxin production in three selected samples of triticale,wheat and rye grown in Argentina

Little is known about mycotoxin contamination of triticale, a hybrid resulting from crossing wheat and rye. The purpose of the present work was to evaluate triticale as a substrate for aflatoxin accumulation in comparison with its parents. Aflatoxin (B₁, B₂, G₁ and G₂) accumulation curves were obtained for the three substrates inoculated with Aspergillus parasiticus NRRL 2999 and incubated at 25 °C and water activity 0.925 for 10 weeks. Wheat and triticale were poor substrates for aflatoxin production. Rye was more prone than the other substrates to fast colonisation by A parasiticus and accumulated larger aflatoxin quantities over the whole incubation period. The maximum aflatoxin concentration in rye (11 840 µg kg⁻¹) was significantly larger (p < 0.05) than those obtained in wheat (2150 µg kg⁻¹) and triticale (2850 µg kg⁻¹). © 2000 Society of Chemical Industry     

Crosslinking of trimellitimide glycidyl ester derivatives

The cure reaction of diglycidyl trimellitimide esters with 4‐dimethylaminopyridine, diaminodiphenylmethane, and dicyandiamide as hardener was studied by differential scanning calorimetry (DSC). Isoconversional kinetic analysis was applied to nonisothermal DSC data and the dependences of activation energies on conversion degrees were obtained. Differences in the shape of these plots were found in accordance to the different kinetic schemes of the curing agents. The thermal properties of the final products evaluated by thermogravimetry do not show noteworthy differences. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 537–542, 1999     

Distribution of serotypes and pulsotypes of Listeria monocytogenes from human,food and environmental isolates (Italy 2002–2005)

This work was undertaken to study the serotypes and pulsotypes of 674 Listeria monocytogenes isolates from human (57), food (558) and environmental (59) sources, collected from different Italian geographical areas during 2002–2005, to determine whether certain subtypes were associated with certain foods and more often involved in cases of listeriosis, and to determine possible geographical or temporal associations. Eleven different L. monocytogenes serotypes were found in the food, environmental and human isolates. Most isolates belonged to only four serotypes (1/2a, 1/2b, 1/2c, 4b). The isolates were divided into 133 distinct AscI pulsotypes grouped into 26 pulsogroups. Pulsogroups ranged from a minimum of 2 up to 212 isolates, and contained 1–19 different pulsotypes. When associations between subtypes and isolates from specific foods selected as being most frequently involved in cases of listeriosis were tested some of these associations were highly significant but not exclusive, indicating that there was no close correlation between specific subtypes and specific food products. Despite the limitations of this study (few human isolates versus many food isolates prevalently collected from one food category), we believe that a large-scale database of L. monocytogenes subtypes and a timely epidemiological investigation can facilitate risk assessment and outbreak detection and control.     

不断进步的小型显示器

当今的液晶显示器(LCD),其性能和图像品质在仅仅几年以前还是可梦而不可求的.它们在若干相互关联的前沿方向上还在继续发展.没有什么器件比小型LCD更能体现这一发展潮流.在该领域,手机的严酷的竞争和用户日渐攀升的期望,正推动显示器技术满足各种将通信与移动计算和/或移动信息娱乐融为一体的融合应用的需求.