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Investigation of protein-ligand interactions in physiological conditions is crucial for better understanding of biochemistry because the binding stoichiometry and conformations of complexes in biological processes, such as various types of regulation and transportation, could reveal key pathways in organisms. Nanoelectrospray ionization mass spectrometry is widely used in studies of biological processes and systems biology. However, non-volatile salts in biological fluid may adversely interfere with nanoelectrospray ionization mass spectrometry. In this study, the previously developed method of induced nanoelectrospray ionization was used to facilitate in situ desalting of protein in solutions with high concentrations of non-volatile salts, and direct investigation of protein-ligand interactions for the first time. In situ desalting occurred at the tip of emitters within a short period lasting for a few to tens of milliseconds, enabling the maintenance of nativelike conditions compatible with mass spectrometry measurements. Induced nanoelectrospray ionization was driven by pulsed potential and exhibited microelectrophoresis effect in each spray cycle, which is not observed in conventional nanoelectrospray ionization because the continuous spray procedure is driven by direct current. Microelectrophoresis caused desalting through micron-sized spray emitters (1–20 μm), as confirmed experimentally with proteins in 100 mM NaCl solution. The method developed in this study has been further illustrated as a potential option for fast and direct identification of protein-ligand (small molecules or metal ions) interactions in complex samples. The results of this study demonstrate that the newly developed method may represent a reliable approach for investigations of proteins and protein complexes in biological samples.

An online combination of isotachophoresis (ITP) and capillary zone electrophoresis (CZE) was employed on a microchip with a column-coupling technology for the determination of homocysteine in various body fluids. ITP with its high concentration ability was used as a sample pretreatment and injection technique for CZE, which facilitated the rapid and sensitive determination of homocysteine. The resolution of the analyte from other constituents present in real complex samples was enhanced by discrete spacers, which were added to the injected sample. A solid-phase microextraction (SPME) pretreatment technique based on silver- and barium-form resins was used prior to the ITP-CZE analysis to remove high concentrations of chloride and sulfate naturally present in the analyzed samples. The combination of the micropretreatment and microelectrophoresis techniques facilitated the determination of trace concentrations of homocysteine in samples of urine and saliva

A number of new membrane anchors based on water-soluble aminoglycerides with geraniol fragments have been synthesized. A biomimetic approach was used based on the design of meroterpenes structurally similar to archaeal lipids. Turbidimetry and laser Doppler microelectrophoresis showed that the synthesized compounds were incorporated into unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles.

As a bioactive and functional polysaccharide, sea cucumber fucoidan has received increasing attention. Chain conformation and physicochemical properties of fucoidan extracted from Thelenota ananas (Ta-FUC) was investigated by utilizing HPSEC-MALLS-Visc-RI, microelectrophoresis and steady shear measurements. The conformation parameter α s (0.61 ± 0.02), the Mark-Houwink-Kuhn-Sakurada exponent α η (0.92 ± 0.01), α h (0.64 ± 0.01) and the Smidsrod-Haug stiffness parameter B (0.036 ± 0.010) consistently manifested that Ta-FUC adopted a semi-flexible coil conformation in NaCl solution. Based on a wormlike cylinder model, stiffness parameters, including persistence length q (13.27 ± 0.80 nm) and cylinder diameter d (0.79 nm), were calculated. This polysaccharide demonstrated shear-thinning rheological behaviour, and critical concentration from dilute to semidilute concentration regime was determined as 3.6 mg/ml. Ta-FUC exhibited as a negative polyelectrolyte in wide pH and ionic strength ranges. These molecular characteristics and physicochemical properties would facilitate further application of Ta-FUC as a functional ingredient in food.

Equilibria between the membranes of erythrocytes as well as thrombocytes and solution ions in fatal accidental hypothermia were analyzed using a theoretical four-equilibria model. The model was developed to determinate parameters characterizing cell membrane-surrounding ion interactions: the total surface concentrations of both acidic and basic groups C A, C B, and association constants K AH, K BOH. Knowledge of these parameters was necessary to calculate the theoretical values of surface charge density. The model was validated by curve-fitting the experimental data points to simulated data generated by the model. The experimental and theoretical surface charge density values agree at pH 2-8, at higher pH the deviation was observed.

Reported values for the acid dissociation constant (p K a) of the saturated fatty acids show a wide range, depending on their method of measurement. Although the p K a values of the shorter chain saturated fatty acids are generally recognised to be approximately 4.5–5.0, p K a values for the longer chain fatty acids have been reported to be much higher, up to pH 10. It is the purpose of this study to investigate the values of p K a measured using microelectrophoresis for saturated fatty acids with chain lengths between C10 and C18. This returned an average p K a value of 4.0 for these saturated fatty acids. By the method of measurement, this value should be considered as the surface p K a value as opposed to bulk p K a values. The graphs of mobility vs. pH showed isoelectric points between 2 and 3, with the existence of positive surfaces on the particles of fatty acids confirmed. Some examples of the relevance of p K a values for saturated fatty acids in the flotation of non-sulphide minerals have also been given.

Lauric arginate (LAE), a cationic surfactant, is a highly potent food-grade antimicrobial that is active against a wide range of food pathogens and spoilage organisms. In compositionally complex environments, the antimicrobial activity of cationic LAE is likely to be impacted by its interactions with anionic components. The purpose of this study was to characterize the interactions between cationic LAE and an anionic biopolymer (high methoxyl pectin, HMP) using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. ITC and ME measurements indicated that LAE bound to pectin, while turbidity measurements indicated that the complexes formed could be either soluble or insoluble depending on solution composition. In the absence of pectin, the critical micelle concentration (CMC) of LAE determined by ITC at 25 °C was 0.21% (w/v). The amount of LAE bound per unit amount of pectin decreased with increasing pectin concentration (from 1.5 to 0.5 g/g for 0.05 to 0.5 wt % pecti...

The influence of the lysozyme and serum albumin in their native and amyloid forms on the electrokinetic behavior of the negatively charged uni- and multilamellar liposomes from the zwitterionic lipid phosphatidylcholine and anionic lipid cardiolipin has been investigated using the microelectrophoresis technique. The zeta - potential, the surface electrostatic potential and surface charge density of the lipid vesicles have been determined upon varying the lipid-to-protein molar ratio. The complex dependencies of the electrophoretic mobility on the protein concentration and reversal of the surface charge observed for the multilamellar vesicles have been explained by the multilayer protein adsorption on the liposomal surface. It has been found that the native and fibrillar proteins differ in their ability to modify the charge state of the model membranes.

Following systemic administration, liposomes are covered by a 'corona' of proteins, and preserving the surface functionality is challenging. Coating the liposome surface with polyethylene glycol (PEG) is the most widely used anti-opsonization strategy, but it cannot fully preclude protein adsorption. To date, protein binding has been studied following in vitro incubation to predict the fate of liposomes in vivo, while dynamic incubation mimicking in vivo conditions remains largely unexplored. The main aim of this investigation was to determine whether shear stress, produced by physiologically relevant dynamic flow, could influence the liposome-protein corona. The corona of circulating PEGylated liposome was thoroughly compared with that formed by incubation in vitro. Systematic comparison in terms of size, surface charge and quantitative composition was made by dynamic light scattering, microelectrophoresis and nano-liquid chromatography tandem mass spectrometry (nanoLC-MS/MS). Size of coronas formed under static vs. dynamic incubation did not appreciably differ from each other. On the other side, the corona of circulating liposomes was more negatively charged than its static counterpart. Of note, the variety of protein species in the corona formed in a dynamic flow was significantly wider. Collectively, these results demonstrated that the corona of circulating PEGylated liposomes can be considerably different from that formed in a static fluid. This seems to be a key factor to predict the biological activity of a liposomal formulation in a physiological environment.

Wetting properties of colloid silica binders modified by addition of surfactants were investigated. Perfluorononanoic, an anionic surfactant, the nonionic fluorinated surfactant Zonyl FSO-100, the nonionic commercial surfactant Rokafenol, and their mixtures were studied. As a model silica binder, a 30% colloid dispersion of SiO2 in water was used, which was compared with the commercial binder Sizol, also based on colloid silica. The size of particles in these dispersions was determined by dynamic light scattering and by the atomic force microscopy imaging of particles deposited on mica. The zeta potential of particles was measured by microelectrophoresis. The dynamic surface tension and contact angles of binders on a paraffin substrate was determined by drop shape analysis. Our investigations showed that the Zonyl-FSO surfactant and its mixture with Rokafenol effectively reduced the dynamic contact angle to a value of 18°. Such low contact angles represent a significant improvement in comparison with comm...

The effects of dissolved oxygen tension during bacterial growth and acclimation on the cell surface properties and biochemical composition of the bacterial pathogens Escherichia coli O157:H7 and Yersinia enterocolitica are characterized. Three experimental techniques are used in an effort to understand the influence of bacterial growth and acclimation conditions on cell surface charge and the composition of the bacterial cell: (i) electrophoretic mobility measurements; (ii) potentiometric titration; and (iii) ATR-FTIR spectroscopy. Potentiometric titration data analyzed using chemical speciation software are related to measured electrophoretic mobilities at the pH of interest. Titration of bacterial cells is used to identify the major proton-active functional groups and the overall concentration of these cell surface ligands at the cell membrane. Analysis of titration data shows notable differences between strains and conditions, confirming the appropriateness of this tool for an overall charge characterization. ATR-FTIR spectroscopy of whole cells is used to further characterize the bacterial biochemical composition and macromolecular structures that might be involved in the development of the net surficial charge of the organisms examined. The evaluation of the integrated intensities of HPO(2)(-) and carbohydrate absorption bands in the IR spectra reveals clear differences between growth protocols. Taken together, the three techniques seem to indicate that the dissolved oxygen tension during cell growth or acclimation can noticeably influence the expression of cell surface molecules and the measurable cell surface charge, though in a strain-dependent fashion.

The peculiarities of frog erythrocyte electrophoretic mobility, coupled to the seasonal course of temperatures, have been studied. At the periods of anabiosis and of burst of hemopoiesis, in the vascular bed there increases the portion of functionally young erythrocytes (up to 22%) with increased values of the cell membrane surface charge. Preparation to winter is accompanied by a rise of the number of circulating functionally worn-down blood cells (up to 60%) with low values of the superficial charge and low mobility in electrical field. Use of the cell microelectrophoresis method of evaluation of seasonal activity of frog erythrocytes allows obtaining objective data about the cellular surface charge and its depending functional cell activity without submitting the erythrocytes to modifying actions.

Organic soils or peat represent an accumulation of disintegrated plant remains which have been preserved under condition of incomplete aeration and high water content. In order to develop a fundamental understanding of electroosmotic phenomena in peat, initially microelectrophoresis studies were carried out to conceptualize the electrokinetic phenomena. Then electroosmosis experiments were conducted on rigid cube samples containing 0.0001 M NaCl-water saturated peat. The open-anode and open-cathode systems were employed to the soil samples. Distilled Water (DW) were used as anolyte and catholyte. The experiments were carried out via applications of diffrent DC electrical potentials. The results of microelectrophoresis study showed changes of zeta potential due to the effect of HCl and NaOH. The correlations between zeta potential and pH were found. The negative charge of peat is high pH dependent and the surface charge was dropped to zero at pH around 3. The high degree of decomposition resulted in the higher zeta potential in peat. It was also experimentally found that the electroosmotic flow in peat is feasible. The direction of electroosmotic flows were from the anode to cathode.

Nanocapsules containing hinokitiol (HKL) were prepared by an emulsion-diffusion method. In an emulsification step in preparing nanocapsules, cetyltrimethylamonium chloride (CTAC) was employed as a cationic emulsifier, Poly(epsilon-caprolactone) (PCL) was use as a wall material and HKL dissolved in octylsalicylate (OS) was used as a core material. The submicron-sized nanoparticle was observed on a TEM. The size ranged 55-234 nm and the mean diameters were 223 nm, which were determined by a dynamic light scattering method. According to the results of pH-dependent microelectrophoresis, the absolute value of the surface potential of the nanocapsules was greater than 20 mV. The nanocapsules were colloidally stable over the pH range of 3-11. The nanocapsules were included in two kinds of preparations, namely shampoo and hair tonic, and the preparations were applied every day for 3 weeks on the clipped backs of 6 week-old mouse (C57BL/6) to investigate the hair growth-promoting effect. The degree of hair growth was evaluated by image-analysing the photographs of the backs and, in parallel, by the histological observation of the formation and the growth of hair or hair bulbs. The results were compared with those of commercially available Minoxidil solution (3%). Phosphate buffered saline was used as a control. The in vivo hair growth-promoting effects of the two preparations were comparable to those of Minoxidil solution. These results are in a good agreement with the histological and structural changes of follicles of the model animals, of which skins were treated with either the testing samples or the control in the same way the experiments of in vivo hair growth promotion were performed.

Aims: Microelectrophoresis allows the detection of DNA bands using minimal amounts of sample in a short time, but commonly requires the use of special equipment which is not available in all laboratories. This fact has limited the application of this technique in microbiology despite its advantages. In this work, we describe a new approach to perform gel microelectrophoresis, named high-speed gel microelectrophoresis (HSGME), and its application for rapid detection of bacteria, protozoa and viruses in clinical, vegetal and environmental samples. Methods and Results: Aliquots of 0·4–1 μl of PCR product were loaded in 2 cm 1% agarose microgels and electrophoresed at high voltage (125 V cm−1) in conventional submarine horizontal mini-slabs. By using HSGME, single-DNA bands obtained after specific-PCR useful in diagnosis of different diseases caused by micro-organisms were detected in 5 min. Conclusions: HSGME is a rapid and easy procedure applicable to detection of microbial genes, which is carried out using conventional equipment and thus can be performed in any research and diagnostic laboratory. Significance and Impact of the Study: The performance of HSGME saves up to 90% time, material and energy costs, as well as laboratory hazardous wastes including carcinogenic agents used for visualizing DNA bands.

The purpose of this study was to compare the ability of electroacoustic (EA) and microelectrophoresis (ME) techniques for monitoring the adsorption of an anionic polysaccharide onto the surfaces of oppositely charged protein-coated oil droplets. The zeta-potential values determined by the EA technique were in excellent agreement with those determined by the ME technique. Both techniques were able to monitor the adsorption of pectin onto the surfaces of beta-lactoglobulin-coated droplets as a function of pectin concentration and pH. The major advantage of the EA technique was that it could be carried out in situ without having to dilute the emulsions, so that the equilibrium between adsorbed and non-adsorbed polyelectrolyte was not disturbed by dilution. Nevertheless, the good agreement between the zeta-potential values determined by the EA and ME techniques suggested that emulsion dilution did not cause an appreciable change in polysaccharide partitioning for the system used in this study. In summary, the EA technique appears to be a powerful means of monitoring polyelectrolyte adsorption in concentrated colloidal dispersions.

In this work, the pore structural parameters and size exclusion properties of LiChrospher strong cation-exchange and reverse phase restricted access materials (RAM) are analysed. The molecular weight size exclusion limit for polystyrenes was found to be about 17.7 kDa, while for standard proteins, the molecular weight size exclusion limit was higher, at approximately 25 kDa. The average pore diameter on a volume basis calculated from the pore network model changes from 8.5 nm (native LiChrospher) to 8.6 nm (diol derivative) to 8.2 nm (sulphonic acid derivative) to 6.9 nm ( n -octadecyl derivative). Additional characterisations were performed on restricted access materials with nitrogen sorption at 77 K, water adsorption at 25 °C, intrusion–extrusion of water (in order to evaluate the hydrophobic properties of the pores of the hydrophobic RAM), and zeta potential measurements by microelectrophoresis. For peptide analysis out of the biofluids, the strong cation-exchange functionality seems to be particularly suitable mainly because of the high loadability of the strong cation-exchange restricted access material (SCX-RAM) and the fact that one can work under non-denaturing conditions to perform effective chromatographic separations. For bacitracin, the dynamic capacity of the SCX-RAM columns does not reach its maximum value in the analysed range. For lysozyme, the dynamic capacity reaches a value of 0.08 mg/ml of column volume before column is overloaded. Additionally, the proper column operating conditions that lead to the total effective working time of the RAM column to be equal to approximately 500 injections (depending on the type of sample), is comprehensively described. The SCX-RAM column was used in the same system analysing urine samples for the period of 1 month (∼150 injections) with run-to-run reproducibility below 5% RSD and below 10% RSD for the relative fractions.

Biogenic microcapsules comprised of l-α-dimyristoyl phosphatitic acid (DMPA)/human serum albumin (HSA) were prepared by stepwise adsorption of DMPA/HSA multilayers onto charged colloids and subsequent dissolution of the colloidal cores. The properties of both lipid/protein modified particles and the hollow capsules were characterized by microelectrophoresis, scanning electron microscopy, transmission electron microscopy, confocal laser scanning microscopy, and scanning force microscopy, respectively. Single particle light scattering together with small-angle X-ray scattering measurements revealed that DMPA forms a bilayer structure on the HSA surface. A combination of HSA and DMPA on hollow capsules is proposed as a biomimetic membrane model.

The zeta potential (ζ) of 2-vol% and 10-vol% suspensions of a commercial α-alumina has been measured using the electroacoustic technique and found to be in good agreement with values reported previously from microelectrophoresis measurements. An increasingly negative ζ value was observed through semiautomatic addition of solutions of a ammonium salt of poly(methacrylic acid). The point of complete surface coverage was inferred from simultaneous conductivity measurements. The average particle size obtained from the electroacoustic dynamic mobility spectrum showed the effect of coagulation near the isoelectric point. The expected correlations among ζ, the viscosity, and the sedimentation volume were observed. The results illustrate the efficacy of the electroacoustic technique for examining colloidal dispersions.

The influence of the solvent (methanol-ethanol mixtures) on the electrokinetic behavior of polystyrene latices with sulfate groups was studied (methanol content was increased by 0.2 at a constant KBr concentration of 1 mM). Viscosity, density, and dielectric constant (eta, rho, and epsilon) were determined at experimental conditions. Two latices (with different surface charge densities and sizes) were used. Electrophoresis measurements were used for dilute dispersions. Streaming current and hydrodynamic permeability were measured for porous plugs. Linear trends in the electrokinetic measurements were observed in the whole molar fraction range. The experimental data obtained from different techniques allow determining the zeta potential according to a well-established classical relationship. The results obtained were analyzed on the basis of the solvent mixture properties and the electrical interface behavior. In addition, permeability data provided valuable information to interpret effects at the solid-liquid interface of the porous plug.

A recently developed high temperature microelectrophoresis cell was employed for ζ-potential measurements at the rutile/aqueous solution interface over a wide range of pH at temperatures of25, 120, and 200 °C. Water, 0.001 mol kg - 1 NaCl(aq), and 0.01 mol kg - 1 NaCl(aq) solutions were tested at these temperatures. The desired pH values were attained by adding either HCl(aq) or NaOH(aq). The obtained experimental data allowed us to estimate isoelectric point pH values (pH i e p ) of 5.26 (′0.45) at 25 \ C,5.13 (′0.37) at 120 °C, and 4.50 (′0.55) at 200 °C. This decrease in pH i e p values with increasing temperature agrees with the decease in point of zero net proton charge (pH z n c p ) pH values (as determined by potentiometric titration) observed for similar rutile powders in our previous studies. ζ-potential data were combined with the proton charge results and rationalized using a surface complexation modeling approach. Modeling results indicate that ζ-potentials are expressed at a distance that is generally equal to (within error) the so-called diffuse double layer thickness (κ - 1 ).

The relatively new technique of Sedimentation/Steric Field-Flow Fractionation (Sd/St FFF) is a simple, fast, and accurate method for the size separation and characterization of starch granules. In the present work, the Sd/St FFF technique was used for the calculation of the mass ratios of the A-large and B-small granules from barley and wheat starch samples. The mass ratios were obtained from the distribution curves of the starch samples at various pH and ionic strength of the suspending medium, in the presence or the absence of the surfactant FL-70. The influence of the suspension pH and ionic strength on the mass ratios of A- and B-granules is discussed in relation to the zeta potentials of the particles, which were measured by a microelectrophoresis apparatus.

The adsorption and depletion of the anionic polymer poly(styrene sulfonate) (PSS) on fresh human red blood cells (RBC) were investigated by measuring RBC electrophoretic mobility as a function of polymer molecular mass (48-2610 kDa), ionic strength (15 and 150 mM NaCl) and polymer concentration (

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.

Emerging need for large-scale, high-resolution analysis of biopolymers, such as DNA sequencing polymerase chain reaction, (PCR) product sizing, single nucleotide polymorphism (SNP) hunting and analysis of protein molecules necessitated the development of automated and high-throughput gel electrophoresis based methods enabling rapid, high-performance separations in a wide molecular weight range. Scaling down electric field mediated separation processes supports higher throughput due to the applicability of higher voltages, thus speeding up analysis time. Indeed, efforts in miniaturization resulted in faster, easier, less costly and more convenient analyses, fulfilling the needs of the emerging biotechnology industry for microscale and massively parallel assays. The two primary approaches in miniaturizing electrophoresis dimensions are the capillary and microslab formats. This latter one evolved towards ultrathin-layer gel electrophoresis which is, except from the thickness of the separation platform, slightly in the upper side of the scale, resulting in considerably easier handling. Ultrathin-layer gel electrophoresis combines the advantages of conventional slab-gel electrophoresis (multilane format) and capillary gel electrophoresis (rapid, high-efficiency separations). It is readily automated, automatic versions of it have been extensively used for large-scale DNA sequencing in the Human Genome Project and more recently became popular in high throughput DNA fragment analysis. Ultrathin-layer techniques are the first step towards the wider use of electrophoresis microchips in perfecting a user-friendly interface between the user and the microdevice.

Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme−polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. Ho...

A series of commercial and experimental water-based ferrofluids was analyzed by capillary electrophoresis (CE) coupled with diode array UV–visible detection. The ferrofluids examined include a neutral dextran–iron oxide colloid, a cationic iron oxide colloid and four negatively charged ferrofluids. The effects of pH, ionic strength and applied voltage on the electropherograms were monitored. The electrophoretic mobility of the iron oxide particles was calculated from the CE data and compared to the corresponding values obtained from microelectrophoresis. Capillary electrophoresis provides a new, efficient and sensitive method to characterize ferrofluids in terms of surface charge, electrophoretic mobility and the level of purity.

Cryptosporidium parvum is a protozoan parasite associated with waterborne outbreaks of diarrhoeal disease. The life cycle of this parasite includes the production of a spheroidal oocyst that is of 4–6 microns in diameter. The thickness of the oocyst wall and its capacity to strongly adhere to both organic and inorganic surfaces are features of the oocysts which could be attributed to its survival in the environment for extended periods. Hence, the need to study their surface chemistry in the aqueous environment. The surface charging properties of the intact C. parvum oocysts were derived from microelectrophoresis measurements on these robust biological species. The ζ potentials of Cryptosporidium oocysts were measured in a range of inorganic electrolyte solutions and in solutions of a multivalent cationic surfactant. The surface potential of the oocyst was found to be pH dependent, with an isoelectric point in mM NaCl of ∼2, suggesting the presence of surface carboxylate groups associated with glycoproteins or phosphate groups. The area/charge for the fully ionised oocysts was found to be ∼80 nm 2 , corresponding to a total maximum charge of 1.6×10 −13 C per oocyst. The effect of a highly charged novel cage surfactant known as CS12 on the Cryptosporidium oocyst surface potential provided valuable insight into its uptake and possible surface activity. Uptake of CS12 was detected at concentrations as low as 2×10 −8 M. At ∼2×10 −5 M CS12 the oocyst surface was uncharged and became positively charged at higher concentrations. These findings suggest that there could be improvements to current concentration methods by manipulation of the surface charge.

Chlorpromazine penetration into the lipid core of the membrane was demonstrated through measurements on lipid monolayers (surface pressure and surface potential). The surface pressure measurements allow us to calculate the intrinsic binding constant (partition coefficient) for the lipid−Chlorpromazine interaction. This latter value is in correct agreement with the obtained results by electrophoretic mobilities measurements on liposomes.

The study was aimed at investigating the role of asphaltenes as stabilizers for totuene-in-water miniemulsions. These miniemulsions were prepared with sodium laurylsulphate and cetyl alcohol. To confirm the amphoteric nature of the asphaltenes: 1) they were adsorbed on fluorite and their electrophoretic mobility was measured using a microelectrophoresis cell and; 2) interfacial tension measurements were carried out using a tensiometer. The experiments reported here use the electrosonic analysis (ESA) method and were carried out on the ESA-8000 Analysis System (Matec) It was experimentally observed that there is a direct relationship between the ESA Potential and the asphaltenes content in the miniemulsions. The pH influence on the ESA Potential of the alphaltenes-containing miniemulsions was investigated as welt A theoretical explanation for both phenomena is provided. To our knowledge, this is the first published attempt to determine the influence of asphaltenes on toluene-in-water emulsions sta...

The aims of this study are to optimize conditions for the preparation, stabilization, and harvesting of heparin/gelatin microcapsules prepared by complex coacervation. Microelectrophoresis and dry coacervate weight were used to determine the optimum conditions of pH and ionic strength for maximum heparin/gelatin coacervate yield. Heparin/gelatin microcapsules were formed by complex coacervation in the presence and absence of poly(1-vinyl-2-pyrrolidone) (PVP), which was used as a stabilizer. The microcapsules were collected using a spray-drying technique. Microcapsule particle size was analyzed using an AccuSizer optical sizer. Optimized conditions for maximum coacervate yield were pH 2.6, ionic strength 10 mM, and a 1:2 heparin/gelatin A ratio. PVP stabilized the heparin/gelatin coacervate droplets and reduced droplet aggregation during spray-drying. The mean particle diameter of the spray-dried coacervate droplets was lower in the presence of PVP and was unaffected by PVP concentration (in the range 0.5-2.0% w/w). Heparin/gelatin microcapsules, prepared under conditions optimized for maximum coacervate yield, were stabilized without the use of chemical cross-linking agents. Stabilization was achieved by a combination of the addition of PVP and spray-drying.

We here report an antibody functionalized microimmunoprecipitation (μIP) method used for enrich lowabundant post-translational modified (PTM) proteins. The device is a fabricated by inert, nontoxic and disposable polydimethylsiloxane (PDMS) using a silane-based chemical modification protocol, which yield an antibody-terminated PDMS surfaces. In this study, the μIP device is specifically designed for purification of carbonylated protein, a representative example here to illustrate the potential applications for any other PTMs, which could be immuno-tagged by specific antibodies. The test model- in vitro oxidized Bovine Serum Albumin (BSA) was first derivitized by dinitrophenylhydrazide (DNPH) and then captured by the anti-DNP immobilized on this μIP device. The surface functional group mapping was systematically analyzed and validated by fluorescence microscopy. Quantitative study of DNP-derivatized carbonylated protein capture recovery and elution efficiency of the device was also studied. We also envision that this proteome enrichment μIP device can be assembled with other lab-on-a-chip components, such as microelectrophoresis or micro-chromatographic devices for follow-up protein analysis. This selective enrichment of modified proteins greatly facilitates the study of low abundant protein biomarkers discovery.

Measurements of zeta potential (microelectrophoresis) and surface charge (polyelectrolyte titration) were performed on natural rubber latex with the addition of anion-active tensides of the fatty acid type. The negative zeta potential showed a monotonous rise with increasing tenside concentration for decanate, while a maximum was observed for laurate, myristate, and palmitate. The surface charge increased monotonously. A comparison with direct adsorption measurements showed that zeta potential measurements allow a simple determination of optimal tenside concentration, and that the mentioned maximum is related to the saturation concentration of the tenside.

Microelectrophoresis measurements have been made on haematite and on quartz particles equilibrated with and dispersed in two different river waters; a basic hard water obtained from the Sherston Avon (SA) and an acidic soft water obtained from Whitray Beck (WB). Information concerning the reversibility of surface-modifying adsorption processes has been obtained from studies of the effects of extensive washing of river-water-equilibrated particles with distilled water and with indifferent electrolyte solutions. Additional information concerning the influences of specific river water constituents on the oxide surface properties has been obtained from electrokinetic studies of particles dispersed in synthetic electrolyte solutions. The results obtained indicate that in the case of haematite, the surface electrical properties are controlled by a combination of inorganic cation and organic anion interactions with the particle surfaces. Whilst adsorbed cation species were found to be readily and completely removed from the particle surfaces by washing the particles with simple electrolyte solutions, adsorbed organic anion materials were found to be held far more tenaciously. This evidence suggests that the combined effects of cation and anion species on the surface electrical properties of haematite dispersed in these river waters arises either by the adsorption of these species at different surface sites or by adsorbed anions providing surface sites for cation species. Organic anion interactions with haematite particles appear to occur to essentially the same extent in the different river waters in spite of the significantly different pH values (pH ≈ 8.4 for SA pH ≈ 5.5 for WB) and humic concentrations (3 mg dm −3 for SA, 7 mg dm −3 for WB) of the two waters. In the case of quartz particles, surface interactions with organic anion species present in the river waters are of negligible importance with regard to modification of the surface electrical properties. The quartz surface properties appear to be determined essentially by interactions with inorganic cations, principally Ca 2+ and Mg 2+ in the basic SA water, and additionally, Al species in the acidic WB water.

Chitosan microspheres were prepared by a novel precipitation process using sodium sulfate as precipitant. Low, medium, and high molecular weight chitosan was chosen for the formulation of microspheres. The extent of precipitation was controlled by the concentration of sodium sulfate and monitored by turbidity measurement. The amount of sodium sulfate required for the preparation of the microspheres depended on the molecular weight of chitosan. The particle size was determined by photon correlation spectroscopy (PCS) and centrifugal sedimentation. The morphological characteristics were examined using a scanning electron microscope (SEM). The surface charge was measured by microelectrophoresis. After preparation the loading property with various anti-inflammatory drugs was investigated using spectrophotometry. The influence of surface adsorption on the drug modification was controlled by differential scanning calorimetry (DSC). Drug liberation was tested in vitro using side-by-side diffusion cells with a dialysis membrane made of cellulose acetate. The highest loading (up to 30.5% relative to the polymer mass) was achieved with prednisolone sodium phosphate (PSP). The adsorbed drug was present in an amorphous form. The drug release from the microspheres was dependent on the drug-polymer ratio.

Perfluorocarbon liquid emulsion systems were prepared containing lecithin, mixtures of synthetic phospholipids, cholesterol, cholesterol oleate and Pluronic F68 as emulsifiers. Attempts were made to correlate the stability of the various emulsion systems with their interfacial tension and charge properties. Due to batch to batch variability in the composition of natural egg yolk lecithin, a standard phospholipid mixture was formulated to represent lecithin in these studies. This standard mixture was composed of synthetic analogs of the major molecular species present in lecithin (dioleoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylethanolamine). Egg yolk lecithin and Pluronic F68 were studied for comparison with the standard phospholipid mixture. Analogs of the minor phospholipid species present in lecithin and other surfactant systems were investigated as additives to the standard phospholipid mixture as follows: phosphatidic acid, phosphatidylinositol, phosphatidylserine lysophosphatidylcholine, lysophosphatidylethanolamine, cholesterol, cholesterol oleate and Pluronic F68. Dynamic interfacial tension was determined using a Teflon Wilhelmy plate method (these data were reported in a previous publication). Interfacial charge was determined by microelectrophoresis of the emulsion droplets. Emulsions were prepared using an ultrasonic probe. Emulsion stability was determined by droplet size analysis as a function of time using photon correlation spectroscopy and Coulter analysis. Both thermal stability kinetic studies and sterilization stability studies were conducted. A novel method of assessment of emulsion stability is reported, involving the assignment of points to each emulsion system based on various droplet size parameters.

The effect of heavy metal ions (Cu2+, Ni2+) on the electrokinetic properties of S. cerevisiae was investigated by microelectrophoresis. The uptake of metal ions is associated with a change in surface charge on the cell surface. Increasing pH results in the cell surface being more negatively charged. Also, the change in the electrophoretic mobility in the presence of multi-ions is not simply due to the change in the metal concentration of the solutions, but is also dependent on the metal species involved.

A capillary-based microelectrophoresis platform for fast serial analysis of single cells is described. In this system, the capillary remains fixed and a two-channel flow system is used to rapidly switch the buffer surrounding the capillary inlet from a physiological buffer to an electrophoretic buffer. Single cells are retained in the physiologic-buffer channel utilizing an array of cell microwells patterned into the channel floor. The defined addresses of the cells on the array enable the sequential delivery of individual cells to the inlet of the capillary, where a focused laser pulse lyses the cell. The cell chamber is moved along a preordained route so that the inlet of the capillary is located in the electrophoresis buffer for separation and the physiological buffer during cell sampling. The throughput of the current system is limited by peak overlap between successive samples. Key characterizations of this system including the fluid flow rates, the cell array dimensions, and laser energies were performed. To demonstrate this system, 28 cells loaded with Oregon green and fluorescein were serially analyzed in under 16 min, a rate of 1.8 cells/min.

The electrokinetic properties of gold particles dispersed in aqueous inorganic electrolyte solutions have been studied using the technique of microelectrophoresis. Results obtained for dispersions formed from vacuum-evaporated metal indicate that electrical charge development at the “pristine” surface of gold in contact with aqueous solutions arises from the presence of a surface oxide layer. The influence of halide ions on the electrokinetic properties of these particles is consistent with metal—halide interactions involving both ligand exchange and specific anion adsorption. Evidence has been obtained which indicates that in the case of dispersions formed by citrate reduction of chloroauric acid, strongly adsorbed citrate ions modify the metal surface and inhibit interactions with halide species.

Electroacoustic potentials are measured for toluene in water miniemulsions stabilized by cetyl alcohol (CA) and 10 mM sodium lauryl sulfate (SLS). The general trend with increasing CA concentration is a sharp drop in the potential up to 20 mM CA, after which the potential remains relatively constant as the CA concentration is further increased. The general trends in the electrokinetic sonic amplitude (ESA) and ζ-potential calculated ESA agree with the ζ-potential determined with microelectrophoresis for o/w miniemulsions prepared at several CA concentrations. However, the magnitude of the electroacoustic ζ-potential is two to three times lower than that of the electrophoretic ζ-potential. Dilution experiments show that the dynamic mobility varies linearly with the dispersion concentration, indicating that particle-particle interactions cancel in the electroacoustic field. The magnitude of the ζ-potential calculated from the dynamic mobility extrapolated to infinite dilution remains lower than that of the electrophoretic ζ-potential. Similar behavior is observed for a monodisperse polystyrene latex.

Association of Carbopol 934P and Carbopol 1342 (a hydrophobic modified Carbopol resin) with phospholipid vesicles was assessed by photon correlation spectroscopy and microelectrophoresis at pH 7.4 and 5. The precorneal clearance of the polymer-coated vesicles was compared to that of uncoated vesicles by lacrimal dacryoscintigraphy in the rabbit. The mucoadhesive polymer-coated vesicles demonstrated significantly enhanced precorneal retention compared to noncoated vesicles only at pH 5 (P less than 0.005). The entrapment and subsequent release of tropicamide from Carbopol 1342-coated and uncoated liposomes were determined in vitro together with an in vivo evaluation of the vesicles formulated at the lower pH. Mucoadhesive polymer-coated vesicles failed to increase significantly the bioavailability of the entrapped tropicamide compared to uncoated vesicles and aqueous solution.

From microelectrophoretic measurements on multilamellar liposomes as a function of lipid composition and pH of the medium, the pH dependence of the ζ-potential was found to be the same for liposomes in both the absence and presence of insulin. For liposomes without insulin, it is concluded that dicetyl phosphate (DCP) is incorporated at the external surface of bilayers consisting of phosphatidylcholine and cholesterol. Furthermore, the apparent pKa for the -PO4H group of DCP in liposomes was 4.5. On the other hand, insulin entrapped in liposomes did not affect the ζ-potential of liposomes. The amount of entrapped insulin solution was the same as that of entrapped calcein solution, the latter being known to be distributed in the internal aqueous compartment of liposomes. By means of incubating the mixed solution of empty liposomes and insulin, the equilibrium constant for adsorption (k) and the amount of insulin adsorbed to liposomes at saturation (X∞) could be determined from Langmuir plots. The present data suggest that the polar regions of the insulin molecule do not occur at the liposomal surface. This may be the result of the interaction between insulin and liposomes being hydrophobic in nature.

The binding of dextran sulfate to phospholipid liposomes was investigated by microelectrophoresis experiments. The polyanion binds to neutral phospholipid liposomes (DMPC and PE) only in the presence of Ca2+. If positively charged stearylamine is incorporated in the vesicles dextran sulfate is bound without Ca2+. Negatively charged phospholipids as PS do not bind dextran sulfate, even in the presence of millimolar concentrations of Ca2+. The adsorption of dextran sulfate results in an aggregation of vesicles due to a bridging mechanism. In all cases the aggregation is followed by a disaggregation toward higher dextran sulfate concentrations. The disaggregation process starts at polymer concentrations smaller than the concentration of the onset of saturation of the adsorption. By use of the probe dilution method a fusion of small DMPC and DMPC/PE vesicles in the presence of Ca2+ and dextran sulfate was found.

The mechanism of adsorption of molybdates on the surface of γ-alumina was investigated by use of adsorption equilibrium experiments, potentiometric titrations, microelectrophoresis and UV/VIS spectroscopy. From the experimental results and the theoretical analysis of the isotherms it was concluded that Mo VI deposition was done by adsorption of the Mo x O y z − ions on energetically equivalent and distinct sites of the inner Helmholtz plane (IHP) of the double layer on the surface of the γ-alumina particles suspended in the aqueous medium. The creation of these sites was mainly attributed to the presence of the protonated surface hydroxyls of γ-alumina and not to the neutral hydroxyls. Analysis of the adsorption isotherms suggested that considerable lateral interactions are exerted between the adsorbed Mo x O y z − ions, resulting in the formation of Mo x O y z − … Mo x O y z − … oligomers in the IHP. It is proposed that these polymeric ions are deposited on the surface in the drying step.

The electrophoretic mobility of nitrofurantoin (based on the microelectrophoresis method) has been studied in dilute dispersions of the drug. Specifically, the effect of NaCl, CaCl2 and AlCl3, pH, and a thickener, Carbopol 934, was determined. The electrophoretic mobility (μ) increases in absolute terms when the pH is raised between 3 and 9, although μ remains negative in this pH range. The variation of absolute mobility (|μ|) with NaCl concentration shows a pronounced maximum for a concentration of about 10−4 M. However, when the concentration of CaCl2 in the medium is increased, |μ| decreases steadily. The effect of AlCl3 concentration on the mobility is markedly influenced by the pH of the dispersing medium although a general trend is observed for μ to become more positive with increasing concentration of the salt. Finally, Carbopol 934 appears to impart an extra negative charge to the nitrofurantoin surface, since higher negative mobilities were measured in the presence of the polymer.

Shewanella strains have previously been studied with regard to their cell surface ultrastructure and LPS composition. They have now been further characterized with respect to their surface physicochemistry and ability to adhere to haematite. The surfaces of the Shewanella strains were found to be electronegative and hydrophilic, and these properties could be correlated with LPS composition or the presence of capsular polysaccharides. Strains expressing rough LPS with no capsule were more hydrophobic and electronegative than those possessing smooth LPS or capsules. By combining different approaches, such as contact-angle measurement, hydrophilic/hydrophobic chromatography, microelectrophoresis, adhesion assays and calculation of interaction energies, it was shown that electrostatic interactions predominate over hydrophobic interactions at the cell–iron oxide interface. Bacterial adhesion to haematite was significantly reduced in strains expressing smooth LPS or a capsule. These findings remained true for Shewanella strains grown under either aerobic or anaerobic conditions, although the surfaces of anaerobic cells appeared to be less electronegative and more hydrophilic than those of aerobic cells.

We present a novel approach for label-free concentration measurement of a specific protein in a solution. The technique combines optical tweezers and microelectrophoresis to establish the electrophoretic mobility of a single microparticle suspended in the solution. From this mobility measurement, the amount of adsorbed protein on the particle is derived. Using this method, we determine the concentration of avidin in a buffer solution. After calibration of the setup, which accounts for electro-osmotic flow in the measurement device, the mobilities of both bare and biotinylated microspheres are measured as a function of the avidin concentration in the mixture. Two types of surface adsorption are identified: the biotinylated particles show specific adsorption, resulting from the binding of avidin molecules with biotin, at low avidin concentrations (below 0.04 μg/ml) while at concentrations of several μg/ml non-specific on both types of particles is observed. These two adsorption mechanisms are incorporated i...

We present a new method for simplified low-quantity DNA loading onto microelectrophoresis devices. The method is based on combined solid-phase extraction, purification, and transport of DNA reversibly bound on paramagnetic microspheres. DNA is adsorbed onto the microspheres, captured with a magnetized permalloy wire, and then directly injected as a highly focused sample plug into the separation channel. This method circumvents both the minimum volume requirement of pipettors (since only solid beads are transported) and the timing complications of double-T microfluidic injection. Injections from Sanger samples of100 pg total suspended weight match the signal strength of our previous conventional injections at10-times the starting DNA sample. Sequencing traces show a resolution that matches or exceeds double-T injections. A kinetic model reproduces the time-dependence of the injection signals and proves that total nonidealities in the method produce injection-broadened plugs of approximately 1-s duration. The method should be broadly extendable to DNA and protein separations in both microdevice and capillary electrophoresis.