Net Negative Surface Charge Density Research Articles

Single positively charged particle trapping in nanofluidic systems

High-throughput and contact-free trapping of single nano-objects in an aqueous solution is of substantial interest for fundamental and applied research. One of the several trapping methods is geometry-induced electrostatic (GIE) trapping that allows for passive spatial confinement of single nanoparticles in nanofluidic devices. In aqueous environments (pH>2) glass and silicon dioxide surfaces acquire a net negative surface charge density due to the self-dissociation of terminal silanol groups. Thus, with native glass/silicon-based GIE-trapping devices only negatively charged nano-objects can be trapped, limiting the applications of this method. In this work, we have performed surface modifications of glass-based GIE-trapping nanofluidic devices to enable the trapping of positively charged nanoparticles. For surface functionalization of the devices, a layer transfer of poly-(ethyleneimine) electrolytes were used which provides a net positive surface charge density. We demonstrate the successful confinement of positively charged 60nm gold nanoparticles inside the functionalized devices, and present a comparison study between trapping of negatively- and positively charged particles in native and functionalized devices, respectively.

Investigation of Surface Band Bending of Ga-Face GaN by Angle-Resolved X-ray Photoelectron Spectroscopy

The surface band bending of Ga-face n-type GaN is clarified via angle-resolved X-ray photoelectron spectroscopy (ARXPS) of test samples with and without hydrofluoric acid (HF) cleaning. For samples without HF cleaning, a slight downward band bending is obtained, indicating an accumulated GaN surface. On the other hand, a 0.3-eV upward band bending is observed on samples with HF cleaning, pointing to a depleted surface region. The change may be ascribed to the removal of the native gallium oxide (and the associated positive surface charges) by the HF etchant, thus resulting in the n-type GaN being depleted by the polarization-induced negative surface charges (previously compensated). Based on the ARXPS results and an electrostatics analysis, a net positive surface charge density of 2.09 × 1012 cm−2 is obtained for samples without HF cleaning, whereas a net negative surface charge density of 1.0 × 1012 cm−2 is obtained for samples with HF cleaning.

Вплив аміксину на електрофоретичну рухомість Т-лімфоцитів миші

The amixine-induced early changes in the electrophoretic mobility (EPM) of murine splenic T lymphocytes were studied in vitro by the microelectrophoresis technique. It has been found that T lymphocytes treated with amixine have a greater EPM within the first hours of amixine addition than control cells. This change in EPM depends on the concentration of amixine in the medium and the duration ofamixine exposure. It was concluded that the amixine-treated cells have a greater net negative surface charge density than control cells. This effect may play an important role in the cell-cell interaction during the immune response.

Improving phosphorus availability in two upland soils of Vietnam using Tithonia diversifolia H.

Phosphorus was added to two acidic upland soils (a Cambisol and a Ferralsol) at two rates (9 mg P kg−1 and 145 mg P kg−1) either in an inorganic P form (KH2PO4) or as a green manure (Tithonia diversifolia H. at 2.5 g kg−1 and 40 g kg−1). The effect of P source on the chemical availability of P was assessed in an incubation experiment by measuring resin extractable P, soluble molybdate reactive (DMR-P) and unreactive P (DMU-P). Soil pH and extractable Al were monitored during the incubation period of 49 days. Green manure addition caused an immediate and sustained increase in soil pH and an immediate and sustained decrease in extractable Al. Labile P (resin P + DMR-P + DMU-P) was increased more by P added as a green manure than when added in inorganic form in one soil (Ferralsol), while it decreased or did not differ in the other one (Cambisol). In both soils, the concentrations of soluble DMU-P were frequently higher where Tithonia had been added. The effects of green manure amendment on physical factors governing the phosphorus supply through diffusive transport were also investigated. Aggregate size distribution was substantially changed by green manure amendment due to a shift in the percentage of microaggregates (<250 μm in diameter) to larger sizes. Changes in soil aggregation as a consequence of green manure amendment led to a reduction in specific surface area (SSA) of the whole soil. Coupled with the large increase in effective cation exchange capacity caused by green manure amendment in both soils, and the decrease in SSA, there was an increase in the net negative surface charge density in both soils. In summary, at a large addition rate – and in addition to the well-known effect derived from the extra supply in P, green manure amendment may improve the chemical availability and diffusive supply of P through the following mechanisms: (i) an increase in soil pH increasing the solubility of phosphate sources; (ii) a decrease in extractable Al reducing the fixation of added P; (iii) increased macro-aggregation and reduced specific surface area and porosity leading to fewer sorption sites for P and hence enhanced diffusion rates; and (iv) increased negative charges and reduced positive charges at the soil surface resulting in a net increase in repulsive force for P. The induced changes in most measured soil properties were smaller in the Ferralsol than in the Cambisol.

Effects of gamma-irradiation on the electrokinetic properties of purple membranes.

The effect of gamma-irradiation (5, 10 and 15 Gy) on the kinetic surface charge of purple membranes (PM) was followed by means of particle microelectrophoresis. The changes in electrophoretic mobility (EPM) were examined at 2, 5 and 26 h, respectively, following irradiation of native PM, and at 2, 26, 50 h and 5 days following irradiation of delipidated PM. It was concluded that the high inhomogeneity of the suspension, even after sonication, largely affects the measured zeta-potential. The 15-Gy treatment significantly increased the net negative surface charge density at 5 and 26 h after irradiation of native PM. However, the opposite effect of approximately twofold reduction of EPM values was derived from simultaneous studies concerning their delipidated form. Low irradiation doses clearly induced an enhancement of negative surface charge density at 2 h post-exposure as well as the formation of unstable structures of delipidated PM. The changes in electrokinetic properties might reflect the specific aggregate formation in both native and delipidated PM. It was suggested that the effect observed of both types of PM was mainly a structural phenomenon possibly related to the modification of functionally active residues.

A comparative analysis of the effects of in-vivo and in-vitro abscisic-acid treatment on the surface electrical properties of barley chloroplast membranes

The effects of in-vivo and in-vitro abscisic acid (ABA) treatments on the surface charge density (σ) of barley (Hordeum vulgare L.) thylakoids were compared using 9-aminoacridine fluorescence. The estimated surface charge density of isolated thylakoid membranes from control (non-treated) barley leaves was-0.065 C · m(-2). The net negative surface charge density decreased after application of various concentrations of ABA (10(-6), 10(-5) M) for 7 d in-vivo, the more pronounced effect being observed at 10(-5) M ABA. When ABA was added to the suspension of isolated thylakoids the opposite effect was observed. The average charge density increased in in-vitro-treated thylakoids at 10(-5) M ABA to -0.081 C · m(-2). The results are discussed in terms of a specific ABA-induced influence of the composition and-or stoicheometry of charged protein complexes within the thylakoid membranes.

Surface Charge Density Changes in Isolated Photosystem II Membranes Induced by Depletion of the Extrinsic Polypeptides of the Oxygen Evolving System

Abstract Treatment of PS II particles with either 1 M NaCl or alkaline Tris (1 M , pH 8.4) caused a considerable decrease in the average net negative surface charge density, concomitant with depletion of the extrinsic 17, 24 and 33 kDa proteins of the oxygen evolving complex from the membranes. The partial recovery of the values for surface charge in both NaCl- and Tris-treated membranes was registered after reconstitution experiments with the three proteins. These results are compared with the data for the charge densities of the thylakoid membranes, to examine the role of the three extrinsic proteins in the formation of heterogeneous arrangement of surface charge across the appressed (granal) thylakoids.

Effects of Colchicine on the Surface Electrical Properties and Sodium Channel Current in Neuroblastoma Cells

We studied the effect of colchicine, an agent that suppresses microtubule assembly, on the passive membrane electrical properties (surface charge density, surface potential) and functioning of the sodium channel in neuroblastoma cells, N1E 115 clone. Colchicine (0.1 mM) caused an increase in net negative surface charge density, but the surface potential was not strongly affected. Colchicine strongly affected the sodium-channel currents: (a) colchicine blocked sodium currents through open sodium channels and the mean amplitude decreased about 50%; (b) the maximum sodium conductance was reduced to 6.0 pS; and (c) the voltage-dependent activation shifted by 10 mV in the direction of depolarization. Effects on the reversible potential and channel inactivation were not seen. Microtubules may play an important role in sodium channel current, and they could be involved in the regulation of the molecular structure of sodium channels.

Surface Properties of Right Side-Out Plasma Membrane Vesicles Isolated from Barley Roots and Leaves

Highly purified plasma membrane vesicles were obtained from roots and leaves of 7-day-old light-grown barley (Hordeum vulgare L. cv Kristina) seedlings by partitioning of crude microsomal fractions in a dextran-polyethylene glycol two-phase system. Sodium dodecylsulfate polyacrylamide gel electrophoresis showed the polypeptide composition of plasma membranes from the two organs to be qualitatively similar, but with different relative amounts of some of the polypeptides. Between 80 and 100% of the K(+),Mg(2+)-ATPase activity was latent indicating that the vesicles were sealed and right side-out. The isoelectric points of the outer surface of root and leaf plasma membranes as determined by cross-partitioning were similar and quite acidic-about pH 3.6. In contrast, the net negative surface charge density at pH 7.0 as measured by 9-aminoacridine fluorescence differed significantly, being -29 mC.m(-2) for the leaf plasma membrane and only -19 mC.m(-2) for the root plasma membrane. As isolated, both types of plasma membrane vesicles had Ca(2+) and Mg(2+) bound to the outer surface as shown by the combined use of chelators and 9-aminoacridine fluorescence; however, the leaf plasma membrane had a relatively higher proportion of Ca(2+) bound (0.57) than did the root plasma membrane (0.45). This difference probably reflects differences in the in vivo conditions as no chelator was present during the isolation procedure. Also Ni(2+) could bind to the root vesicles as indicated by the effect of Ni(2+) on 9-aminoacridine fluorescence, and by the binding of (63)Ni(2+) (44 nanomoles bound per milligram protein) at 100 micromolar NiCl(2).

The negative surface charge density of plasmalemma vesicles from wheat and oat roots

Plasmalemma vesicles were isolated in a sucrose-containing medium from wheat and oat roots and the net negative surface charge density was determined with 9-aminoacridine fluorescence [Chow, W.S. and Barber, J. (1980) J. Biochem. Biophys. Methods 3, 173-185]. The outer surface of the vesicles (measured in the presence of sucrose) had densities of − 16 to − 20 mC·m −2 and −29 mC·m −2 for wheat and oat roots, respectively. The inner surface - presumed to be the cytoplasmic side and calculated from the values measured in the presence and absence of sucrose - was more negative, and its size depended on the salt status of the roots.

Electrophoretic quantification of the changes in the average net negative surface charge density of mouse blastocysts implanting in vivo and in vitro.

An apparatus for free-zone electrophoresis was used to measure changes in the zeta potential or net negative surface charge density of mouse blastocysts. Delayed (inactive) and implanting blastocysts, recovered from the uterine cavity, were analyzed before and after incubation with neuraminidase. Growth-arrested and growth-activated blastocysts, obtained by blastocyst culture, were also examined. The results showed that the net negative surface charge density of the blastocysts decreased by 30% at implantation and at growth in culture, suggesting that the changes of the blastocyst surface at implantation are intrinsic cell membrane changes, and not caused by environmental alterations. The neuraminidase treatment decreased the net negative charge density of both delayed and implanting blastocysts by 30-60%. Thus the influence of this treatment varied too greatly among the blastocysts to permit any conclusions to be drawn about differences in the total amount of sialic acid between delayed and implanting blastocysts. Further, both delayed and implanting blastocysts carried negatively charged groups other than sialic acid containing ones. Scanning electron microscopy revealed surface changes on the blastocysts both after electrophoresis and after neuraminidase incubation; the former changes were probably normally occurring contractions, while the latter represented true alterations of the cell surface.

The effect of neuraminidase- and ribonuclease-susceptible surface anionic groups on the aggregation of embryonic chick neural retina cells.

The role of cell surface charge in cellular interactions has been the subject of conflicting reports. The major contribution to the net cell surface negativity of all mammalian cells studied is made by the sialic acid moieties of the surface glycoproteins, while ribonuclease-susceptible sites have been shown to contribute to the lesser extent on some cell types. Experiments were done to determine whether these anionic groups at the cell periphery affect the aggregation and sorting behaviour of embryonic chick neural retina cells when cultured alone or in combination with embryonic heart cells. The net negative surface charge density, as determined by cell electrophoretic mobility, of neuraminidase- or ribonuclease-treated cells was significantly decreased immediately after incubation with the enzymes, and the treatment with neuraminidase resulted in a reduction in the binding of colloidal iron hydroxide particles at the cell surface. Both enzymes caused reduced aggregate size in gyratory shaker cultures of neural retina and mixed cell suspensions, and fewer neural retina cells adherent to microtest plate surfaces, but no differences were seen in their histological appearance or sorting pattern in mixed shaker culture. The results indicate that the neuraminidase- and ribonuclease-susceptible groups at the periphery of embryonic neural retina cells play a role in some aspects of cell contact behaviour in ways other than reduction in net negative surface charge.

Caenorhabditis briggsae: Electron microscope analysis of changes in negative surface charge density of the outer cuticular membrane

The negative surface charge density of the outer cuticular membrane of Caenorhabditis briggsae was visualized by use of cationized ferritin. When grown axenically in a medium which contained liver extract, the net negative surface charge density was significantly less in nematodes 21–24 days old than in nematodes 6–7 days old. Nematodes grown in heattreated medium, in which liver enzyme activities were presumably inactivated, did not show lower surface charge densities at 21 days. These findings indicate that the decrease in net negative surface charge was caused by a receptor-destroying enzyme present in the liver extract. The relation of the membrane charge changes observed in vitro to those which might occur in nature is discussed. Further studies showed that the negative charges are evenly distributed over the surface of the nematode except in the tail area, where they are lower.

Interaction of polynucleotides with cultured mammalian cells: II. Cell surface charge density and RNA uptake

This report describes the uptake of high molecular weight RNA by Ehrlich ascites tumor cells treated with enzymes and polycations which reduce cell net negative surface charge density. Enzyme treatment had little effect on RNA uptake, but treatment with poly- L-lysine resulted in increased binding and uptake of RNA. Present data indicate that decreased cell surface charge, increased availability of positive surface sites, and cell death, all contribute to increased RNA uptake. The individual contributions of these factors has been partially resolved. A possible mechanism for polyanion uptake by cells is proposed.