The trajectories of particles suspended in electrolytes under the influence of crossed electric and magnetic fields

We observed that particles, suspended in an electrolyte and brought into crossed magnetic and electric fields of low intensities, will deviate in the central part of the electrophoresis chamber of a standard Zeiss Cytopherometer with a component vertical to both fields. The direction and magnitude, however, were sharply at variance with what would be expected by the action of the Lorentz force (EMF) on the surface of the particles. The magnitude of the deviation depends upon the magnetic and electric field strength, the ion concentration of the suspension medium and the geometry of the chamber. The movement of the particles is due to streaming of the electrolyte which is mainly caused by inhomogeneities of the electric field in the electrophoresis chamber. The magnitude of the effect is high enough to occur under physiological conditions. Magneto-electrophoretic streaming might eventually act as a transducer mechanism which could explain the ability of some animals to orientate themselves in the geomagnetic field.     

Particle size distribution and chemical parameters of the sediments of a shallow turbid impoundment

As part of an ecosystem study of a small mesotrophic turbid impoundment in the semi-arid part of South Africa, an investigation was made of the particle size distribution, organic content and inorganic chemical composition of the sediment. Nine transects 50 m apart were made during February 1980. Sediments were sampled with an Eckman grab. The following analyses were made: size fractionation by wet sieving, cation exchange capacity, exchangeable Na, K, Ca, Mg and PO₄, total P, and loss on ignition. From the results it was clear that the finer particles, in or near the original river bed, had higher cation exchange capacity, total P, exchangeable phosphorus and organic content. Littoral areas with avian habitat and extensive macrophyte vegetation, contained coarser sediments. Organic detritus apparently migrated to the deeper part of the impoundment. Sediments of lacustrine and fluvial origin were identified by means of the Passega classification.     

Structure and Stoichiometry of Template-Directed Recombinant HIV-1 Gag Particles

Size polydispersity of immature human immunodeficiency virus type 1 (HIV-1) particles represents a challenge for traditional methods of biological ultrastructural analysis. An in vitro model for immature HIV-1 particles constructed from recombinant Gag proteins lacking residues 16-99 and the p6 domain assembled around spherical nanoparticles functionalized with DNA. This template-directed assembly approach led to a significant reduction in size polydispersity and revealed previously unknown structural features of immature-like HIV-1 particles. Electron microscopy and image reconstruction of these particles suggest that the Gag shell formed from different protein regions that are connected by a “scar”—an extended defect connecting the edges of two continuous, regularly packed protein layers. Thus, instead of a holey protein array, the experimental model presented here appears to consist of a continuous array of ∼ 5000 proteins enveloping the core, in which regular regions are separated by extended areas of disorder.     

Long and short distance movements of β2-adrenoceptor in cell membrane assessed by photoconvertible fluorescent protein dendra2-β2-adrenoceptor fusion

Local movements of receptors in the plasma membrane have been extensively studied, as it is generally believed that the dynamics of membrane distribution of receptors regulate their functions. However, the properties of large-scale (> 5 μm) receptor movements in the membrane are relatively obscure. In the present study, we addressed the question as to whether the large-scale movement of receptor in the plasma membrane at the whole cell level can be explained quantitatively by its local diffusive properties. We used HEK 293 cells transfected with human β2-adrenoceptor fused to photoconvertible fluorescent protein dendra2 as a model system; and found that 1) functional integrity of the dendra2-tagged receptor remains apparently intact; 2) in a mesoscopic scale (~ 4 μm), ~ 90% of the receptors are mobile on average, and receptor influx to, and out-flux from a membrane area can be symmetrically explained by a diffusion-like process with an effective diffusion coefficient of ~ 0.1 μm²/s; 3) these mobility parameters are not affected by the activity state of the receptor (assessed by using constitutively active receptor mutants); 4) in the macroscopic scale (4-40 μm), although a slowly diffusing fraction of receptors (with D < 0.01 μm²/s) is identifiable in some cases, the movement of the predominant fraction is perfectly explained by the same effective diffusion process observed in the mesoscopic scale, suggesting that the large scale structure of the cell membrane as felt by the receptor is apparently homogeneous in terms of its mesoscopic properties. We also showed that intracellular compartments and plasma membrane are kinetically connected even at steady-state.     

Catalytic effect of ReAu nanoalloy on the Te particle reaction and its application to resonance scattering spectral assay of CA125

ReAu nanoparticles with a molar ratio of 2:8 Re and Te nanoparticles were prepared by NaBH₄ reduction. In HCl medium at 65°C, ultratrace Re, Te and ReAu bimetallic nanoparticles strongly catalyzed the slow reaction between Sn(II) and Te(VI) to form Te particles, which exhibited the strongest resonance scattering (RS) peak at 782 nm. As the amount of nanocatalyst increased, the RS intensity at 782 nm (I_{782 nm}) increased linearly, and the increase in intensity ΔI_{782 nm} was linear to the ReAu, Re and Te concentrations in the ranges 0.07–9.0, 0.01–4.5 and 30–1200 nm , respectively. As a model, a ReAu immunonanoprobe catalytic Te–particle resonance scattering spectral (RSS) method was established for detection of CA125, using ReAu nanoparticle labeling CA125 antibody (CA125Ab) to obtain an immunonanoprobe (ReAuCA125Ab) for CA125. In pH 7.6 citric acid–Na₂HPO₄ buffer solution, ReAuCA125Ab aggregated nonspecifically. Upon addition of CA125, the immunonanoprobe reacted with it to form ReAuCA125Ab–CA125 dispersive immunocomplex in the solution. After the centrifugation, the supernatant containing the immunocomplex was used to catalyze the reaction of Te(VI)–Sn(II) to produce the Te particles that resulted in the I_{782 nm} increasing. The ΔI_{782 nm} was linear to CA125 concentration (C_CA125) in the range 0.1–240 mU/mL. The regression equation, correlation coefficient and detection limit were ΔI_{782 nm} = 1.61 C_CA125 + 1.5, 0.9978 and 0.02 mU/mL, respectively. The proposed method was applied to detect CA125 in serum samples, with satisfactory results. Copyright © 2010 John Wiley & Sons, Ltd.     

Transport and binding characterization of a novel hybrid particle impregnated membrane material for bioseparations

The transport and binding properties of a novel hybrid particle-nonwoven membrane medium are described. In this construct, a polymeric chromatographic resin is entrapped between two layers of a nonwoven polypropylene membrane. The membrane-supported resin medium offers the advantage of increased interstitial pore diameter to allow passage of cells and other debris in the feed, while providing sufficiently high surface area for product capture within the resin particles. Columns packed with PIM displayed excellent flow distribution and had interstitial porosities of 0.48 ± 0.01, 25-60% larger than those typical of a packed bed. These columns were able to pass over 95% of E. coli cells and human red blood cell concentrate in 30 column volumes while maintaining a pressure drop significantly lower than that of a packed bed with a similar amount of resin. The dynamic binding capacity of bovine serum albumin (BSA) to the chromatographic resin entrapped in the PIM packed column was essentially the same as that observed with the same volume of resin in a packed bed. The General Rate (GR) model of chromatography was used to analyze experiments indicating the breakthrough behavior of the PIM columns is predictable, and very similar to those of a normal packed bed. These results suggest that PIM constructs can be designed to process viscous mobile phases containing particulates while retaining the desirable binding characteristics of the embedded chromatographic resin and could find uses in adsorption separation processes from complex feed streams such as whole blood, cell culture, and food processing.     

Improved particle counting and size distribution determination of aggregated virus populations by asymmetric flow field-flow fractionation and multiangle light scattering techniques

A method using a combination of asymmetric flow field-flow fractionation (AFFFF) and multiangle light scattering (MALS) techniques has been shown to improve the estimation of virus particle counts and the amount of aggregated virus in laboratory samples. The method is based on the spherical particle counting approach given by Wyatt and Weida in 2004, with additional modifications. The new method was tested by analyzing polystyrene beads and adenovirus samples, both having a well-characterized particle size and concentration. Influenza virus samples were analyzed by the new AFFFF-MALS technique, and particle size and aggregate state were compared with results from atomic force microscopy analysis. The limitations and source of possible errors for the new AFFFF-MALS analysis are discussed.     

Mesoporous TiO2 nanoparticles: A new material for biolistic bombardment

To date, only solid heavy metals such as gold or tungsten have been used as DNA carriers in biolistic bombardment of algae. In this study, we show that even a metal oxide of lower density can act as a DNA carrier. We investigated the potency of size‐controlled mesoporous titanium dioxide (TiO₂) particles. Among the six tested gas pressures, TiO₂ particles best facilitated transformation of the green alga Chlamydomonas reinhardtii at 1100 psi (approximately 7.6 MPa) and 2000 psi (approximately 14 MPa). Surprisingly, a mesoporous metal oxide with a density of approximately only one‐tenth that of gold or tungsten could be effective as a DNA carrier in biolistic bombardment of a rigid cell wall‐containing alga. In addition, we found two peaks of gas pressures in the transformation ratio irrespective of whether the particles were made of gold, tungsten, or TiO₂.     

Intercoupling surface plasmon resonance and diffusion reflection measurements for real‐time cancer detection

Spatial diffusion reflection (DR) measurements of gold nanorods (GNR) were recently suggested as a simple and highly sensitive non‐invasive and non‐ionizing method for real‐time cancer detection. In this paper we demonstrate that wavelength dependent DR measurements enable the spectral red‐shift observation of highly concentrated GNR. By conjugating targeting moieties to the GNR, large density of GNR can specifically home onto cancer cells. The inter‐particle plasmon resonance pattern of the highly concentrated GNR leads to an extension and a red‐shift (Δλ) in the absorption spectrum of the concentrated GNR. Dark‐field microscopy was used in order to measure the expected Δλ in different GNR concentrations in vitro. Double‐wavelength DR measurements of tissue‐like phantoms and tumor bearing mice containing different GNR concentrations are presented. We show that the DR profile of the highly concentrated GNR directly correlate with the spectral extension and red‐shift. This presented work suggests that wavelength dependent DR method can serve as a promising tool for real‐time superficial tumor detection. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthetic antibodies and peptides recognizing progressive multifocal leukoencephalopathy-specific point mutations in polyomavirus JC capsid viral protein 1

Polyomavirus JC (JCV) is the causative agent of progressive multifocal leukoencephalopathy (PML), a rare and frequently fatal brain disease that afflicts a small fraction of the immune-compromised population, including those affected by AIDS and transplantation recipients on immunosuppressive drug therapy. Currently there is no specific therapy for PML. The major capsid viral protein 1 (VP1) involved in binding to sialic acid cell receptors is believed to be a key player in pathogenesis. PML-specific mutations in JCV VP1 sequences present at the binding pocket of sialic acid cell receptors, such as L55F and S269F, abolish sialic acid recognition and might favor PML onset. Early diagnosis of these PML-specific mutations may help identify patients at high risk of PML, thus reducing the risks associated with immunosuppressive therapy. As a first step in the development of such early diagnostic tools, we report identification and characterization of affinity reagents that specifically recognize PML-specific mutations in VP1 variants using phage display technology. We first identified 2 peptides targeting wild type VP1 with moderate specificity. Fine-tuning via selection of biased libraries designed based on 2 parental peptides yielded peptides with different, yet still moderate, bindinspecificities. In contrast, we had great success in identifying synthetic antibodies that recognize one of the PML-specific mutations (L55F) with high specificity from the phage-displayed libraries. These peptides and synthetic antibodies represent potential candidates for developing tailored immune-based assays for PML risk stratification in addition to complementing affinity reagents currently available for the study of PML and JCV.