Microelectrophoresis Research Articles

The biomolecular corona of gold nanoparticles in a controlled microfluidic environment.

Nanoparticles (NPs) exposed to biological media are coated by proteins and other biomolecules forming a biomolecular corona (BC) on the particle surface. Recent studies have shown that shear stress as that created by laminar fluid flow generates more complex coronas with systematic changes in composition with respect to counterparts formed under static incubation. However, in most studies reported so far, dynamic environments have been produced by peristaltic pumps and comparing experimental results appears challenging. On the other side, generating shear stress by microfluidic devices could help to remove user variability and ensure better reproducibility of experimental data. This study was therefore aimed at exploring formation of NP-BC in a microfluidic environment. To this end, 100 nm gold nanoparticles and human plasma (HP) were used as models for nano-formulation and biological medium. We injected gold nanoparticles and HP in each of the islets of a remote-controlled microfluidic cartridge. Static incubation was used as a reference. BC-decorated NPs were thoroughly characterized by dynamic light scattering (DLS), micro-electrophoresis (ME), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and nano-liquid chromatography tandem mass spectrometry (nano-LC MS/MS). By varying the incubation time from 30 s to 2.5 min we demonstrate that BC is already determined by the earliest exposure time point and does not appreciably evolve in time. DLS and ME results demonstrate that the BC formed in a microfluidic chip is thicker and more negatively charged than its counterpart formed under static incubation. SDS-PAGE and nano-LC MS/MS revealed that the incubation procedure had a major effect on BC composition. As an example, immunoglobulins are the most abundant plasma proteins of the BC generated in a microfluidic environment (relative protein abundance ∼30%), while tissue leakage proteins (relative protein abundance ∼26%) are the most enriched proteins when the BC is formed upon static incubation. Potential implications in emerging biomedical research arenas are discussed.

Correction to "Analysis of the Interactions of a Cationic Surfactant (Lauric Arginate) with an Anionic Biopolymer (Pectin): Isothermal Titration Calorimetry, Light Scattering, and Microelectrophoresis".

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 degrees 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 % pectin) and with increasing temperature (from 1.7 to 1.3 g/g for 15 to 40 degrees C). The binding contribution to the LAE-pectin interaction was exothermic and was attributed to electrostatic attraction between the cationic surfactant and anionic biopolymer. This study demonstrates that lauric arginate can form either soluble or insoluble complexes with anionic biopolymers depending on the composition of the system.

Interaction of cationic antimicrobial (ɛ-polylysine) with food-grade biopolymers: Dextran, chitosan, carrageenan, alginate, and pectin

The cationic biopolymer ε-polylysine (ε-PL) is a food-grade antimicrobial that is highly effective against food pathogens and spoilage organisms. In compositionally complex environments, the antimicrobial activity of cationic ε-PL is likely to be impacted by its interactions with other charged species. The purpose of this study was to characterize the interactions of cationic ε-PL with various food grade biopolymers with different charge characteristics: anionic (carrageenan, alginate, pectin), neutral (dextran), and cationic (chitosan). Isothermal titration calorimetry (ITC), micro-electrophoresis (ME) and turbidity measurements were used to characterize the interactions and the nature of any aggregates formed. Our measurements suggested that there was little interaction or complex formation between cationic ε-PL and cationic or neutral biopolymers, but that strong electrostatic interactions and complex formation occurred between cationic ε-PL and anionic biopolymers. The solubility of the aggregates formed depended on biopolymer type and the mass ratio of biopolymers to ε-PL. The results of this study have important implications for the application of ε-PL in compositionally complex systems.

Cationic Antimicrobial (ε-Polylysine)–Anionic Polysaccharide (Pectin) Interactions: Influence of Polymer Charge on Physical Stability and Antimicrobial Efficacy

The cationic biopolymer ε-polylysine (ε-PL) is a potent food-grade antimicrobial that is highly effective against a range of food pathogens and spoilage organisms. In compositionally complex systems such as foods and beverages, cationic ε-PL molecules may associate with anionic substances, leading to increased turbidity, sediment formation, and reduced antimicrobial activity. This study therefore characterized the interactions between cationic ε-PL and anionic pectins with different degrees of esterification (DE) and then investigated the influence of these interactions on the antimicrobial efficacy of ε-PL. The nature of the interactions was characterized using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. High (DE 61%), medium (DE 51%), and low (DE 42%) methoxyl pectins interacted with ε-PL molecules through electrostatic forces, forming either soluble or insoluble complexes with various electrical charges, depending on the relative mass ratio of pectin and ε-PL. The interaction of pectin with ε-PL increased as the negative charge density on the pectin molecules increased, that is, with decreasing DE. The antimicrobial efficacy of ε-PL against two acid-resistant spoilage yeasts (Zygosaccharomyces bailii and Saccharomyces cerevisiae) decreased progressively in the presence of increasing levels of all three pectins. Nevertheless, the low DE pectin decreased the antimicrobial efficacy of ε-PL much more dramatically, likely due to strong electrostatic binding of ε-PL onto low DE pectin molecules reducing its interaction with anionic microbe surfaces. This study provides knowledge that will facilitate the rational application of ε-PL as an antimicrobial in complex food systems.

Interactions of a Cationic Antimicrobial (ε-Polylysine) with an Anionic Biopolymer (Pectin): An Isothermal Titration Calorimetry, Microelectrophoresis, and Turbidity Study

ε-Polylysine (ε-PL) is a food-grade cationic antimicrobial that is highly effective against a range of food pathogens and spoilage organisms. In compositionally complex environments, like those found in most foods and beverages, the antimicrobial activity of cationic ε-PL is likely to be impacted by its interactions with anionic components. The purpose of this study was to characterize the interactions between cationic ε-polylysine and an anionic biopolymer (high methoxyl pectin, HMP) using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. ITC and ME measurements indicated that ε-PL bound to pectin, while turbidity measurements indicated that the complexes formed could be either soluble or insoluble depending on solution composition. Ionic strength and pH were also shown to affect the interactions significantly, highlighting their electrostatic origin. This study demonstrates that ε-PL can form either soluble or insoluble complexes with anionic biopolymers depending on the composition of the system. Our study provides basic knowledge that will facilitate the more rational application of ε-PL in complex food systems.

Analysis of the Interactions of a Cationic Surfactant (Lauric Arginate) with an Anionic Biopolymer (Pectin): Isothermal Titration Calorimetry, Light Scattering, and Microelectrophoresis

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 degrees 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 % pectin) and with increasing temperature (from 1.7 to 1.3 g/g for 15 to 40 degrees C). The binding contribution to the LAE-pectin interaction was exothermic and was attributed to electrostatic attraction between the cationic surfactant and anionic biopolymer. This study demonstrates that lauric arginate can form either soluble or insoluble complexes with anionic biopolymers depending on the composition of the system.

In Situ Electroacoustic Monitoring of Polyelectrolyte Adsorption onto Protein-Coated Oil Droplets

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.

Capillary Electrophoresis Measurements of Electrophoretic Mobility for Colloidal Particles of Biological Interest.

The electrophoretic mobilities of three bacterial strains were investigated by capillary electrophoresis (CE) and were compared with results obtained by microelectrophoresis (ME). The CE measurements yielded bimodal electropherograms for two of the strains, thus illustrating for the first time that surface charge variations within a monoclonal population can be probed by CE. Intrapopulation variations were not detected by ME. The mobilities of three chemically distinct types of latex microspheres were also measured. Differences between the mean mobilities obtained by CE and ME were not statistically significant (P </= 0.50); the standard deviations of the CE measurements were typically 2 to 10 times smaller than those obtained by comparable ME measurements. The reproducibility of CE permitted batch-to-batch mobility variations to be probed for the bacteria (one of the strains exhibited such variations), and aggregation was evident in one of the latex suspensions. These effects were not measurable with ME.

Submicron particles in the rhine river—I. Physico-chemical characterization

This paper describes a complete sampling, fractionation and characterization scheme for submicrometer particles isolated from the Rhine River. Decreasing particle size fractions were obtained by means of gravitational sedimentation, cascade centrifugation/ultracentrifugation and cascade filtration. These size fractions were analyzed by photon correlation spectroscopy (PCS), micro-electrophoresis (ME), transmission electron microscopy (TEM), light scattering (LS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and total organic carbon (TOC), which gave complementary results concerning the nature of the particles. The data indicated that submicron particles contribute only a small proportion of the total particle mass and volume, but an important proportion of the total particle number. Moreover, their specific surface area may be quite large. Associations of submicrometer particles with organic macromolecules and fibrils, which may have maintained such particles in suspension, were observed.

Surface characterization of some TiO2-based pigments. Part 3.—Coating of the pigments

Titanium dioxide (TiO2) pigments, subjected to different coating processes, have been characterized by microelectrophoresis (MEP), high-resolution transmission electron microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FTIR). MEP and HRTEM measurements are in excellent agreement with the FTIR data, to which they add useful complementary information. Among the FTIR measurements, the adsorption of pyridine yields vital information on the composition and thermal stability of the surface layer. The coating overlayer complete in all cases examined, and none of the ions introduced in the TiO2 phase (e.g. the photostabilizing Zn2+) is present in the surface layer after the coating process.Pre-coating with TiO2 from titanyl sulfate produces a porous overlayer of scale-like anatase crystallites. The vacuum thermal stability of the TiO2 overlayer is quite low. Coating with alumina yields a thick, homogeneous, and amorphous overlayer, whose chemical nature depends on the coating procedure. When derived from Na aluminate, it is an amorphous Al hydrate (similar to boehmite), but contains some Al3+ surface ions in a quasi-tetrahedral co-ordination. However, when derived from aluminium sulfate, it is an amorphous aluminium basic sulfate, ionic and highly hydrated. The alumina overlayers of both types are quite unstable towards vacuum thermal treatments. Coating with silica yields an amorphous overlayer of variable thickness of regular hydrated silica, with no mixed TiO2–SiO2 phases. The SiO2 layer is chemically stable towards vacuum thermal treatments at high temperatures, whereas the hydration degree and the texture (surface area and porosity) are irreversibly modified.