Determination of effective charge of small ions, polyelectrolytes and nanoparticles by capillary electrophoresis

Determination of physicochemical parameters of (bio)molecules and (bio)particles by capillary electromigration methods

The review provides an overview of recent developments and applications of capillary electromigration (CE) methods for the determination of important physicochemical parameters of various (bio)molecules and (bio)particles. These parameters include actual and limiting (absolute) ionic mobilities, effective electrophoretic mobilities, effective charges, isoelectric points, electrokinetic potentials, hydrodynamic radii, diffusion coefficients, relative molecular masses, acidity (ionization) constants, binding constants and stoichiometry of (bio)molecular complexes, changes of Gibbs free energy, enthalpy and entropy and rate constants of chemical reactions and interactions, retention factors and partition and distribution coefficients. For the determination of these parameters, the following CE methods are employed: zone electrophoresis in a free solution or in sieving media, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography. In the individual sections, the procedures for the determination of the above parameters by the particular CE methods are described.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Taylor dispersion analysis of metallic-based nanoparticles - A short review

Taylor dispersion analysis (TDA) is an interesting tool for nanoparticle (NP) size determination, feasible using simple capillary electrophoresis apparatus. Based upon the radial diffusion of analytes upon a laminar stream, the diffusion coefficient of species is easily estimable. Moreover, TDA is generally more adequate than conventional dynamic light scattering methodologies as it is less dependent on the polydispersity of the sample, leading to accurate measurement and reliable results. This review provides every paper mentioning the use of TDA for metallic-based NPs size determination. Diverse strategies for the detection of metallic NPs (like UV-visible and inductively coupled plasma-mass spectrometry - ICP-MS - for instance) and interpretation of the Taylorgrams are discussed. Based upon the literature, advices on future prospects are also indicated, especially for the comparison of TDA results with other classical techniques.

Size and Charge Characterization of Lipid Nanoparticles for mRNA Vaccines

Messenger RNA vaccines have come into the spotlight as a promising and adaptive alternative to conventional vaccine approaches. The efficacy of mRNA vaccines relies on the ability of mRNA to reach the cytoplasm of cells, where it can be translated into proteins of interest, allowing it to trigger the immune response. However, unprotected mRNA is unstable and susceptible to degradation by exo- and endonucleases, and its negative charges are electrostatically repulsed by the anionic cell membranes. Therefore, mRNA needs a delivery system that protects the nucleic acid from degradation and allows it to enter into the cells. Lipid nanoparticles (LNPs) represent a nonviral leading vector for mRNA delivery. Physicochemical parameters of LNPs, including their size and their charge, directly impact their in vivo behavior and, therefore, their cellular internalization. In this work, Taylor dispersion analysis (TDA) was used as a new methodology for the characterization of the size and polydispersity of LNPs, and capillary electrophoresis (CE) was used for the determination of LNP global charge. The results obtained were compared with those obtained by dynamic light scattering (DLS) and laser Doppler electrophoresis (LDE).

Multistable interaction between a spherical Brownian particle and an air-water interface

We report the measurement of the interaction energy between a charged Brownian polystyrene particle and an air-water interface. The interaction potential is obtained from the Boltzmann equation by tracking particle interface distance with a specifically designed Dual-Wave Reflection Interference Microscopy (DW-RIM) setup. The particle has two equilibrium positions located at few hundreds of nanometers from the interface. The farthest position is well accounted by a DLVO model complemented by gravity. The closest one, not predicted by current models, more frequently appears in water solutions at relatively high ions concentrations, when electrostatic interaction is screened out. It is accompanied by a frozen rotational diffusion dynamics that suggests an interacting potential dependent on particle orientation and stresses the decisive role played by particle surface heterogeneities. Building up on both such experimental results, the important role of air nanobubbles pinned on the particle interface is discussed.

Structure and effective charge characterization of proteins by a mobility capillary electrophoresis based method

Measuring the conformations and effective charges of proteins in solution is critical for investigating protein bioactivity, but their rapid analysis remains a challenging problem. Here we report a mobility capillary electrophoresis (MCE) based method for the rapid analysis of protein stereo-structures and effective charges in different solution environments. With the capability of mixture separation, MCE measures the hydrodynamic radius of a protein through Taylor dispersion analysis and its effective charge through ion mobility analysis. The experimental results acquired from MCE are then utilized to restrain molecular dynamics simulations, so that the most probable conformation of that protein can be obtained. As proof-of-concept demonstrations, the charge states and structures of five proteins were analyzed under close to native environments. The conformation transitions and charge state variations of bovine serum albumin and lysozyme under different pH conditions were also investigated. This method is promising for high-throughput protein analysis, which could potentially be coupled with mass spectrometry for investigating protein stereo-structures and functions in top-down proteomics.

Characterization of hydrosoluble fraction and oligomers in poly(vinylidene chloride) latexes by capillary electrophoresis using electrophoretic mobility modeling

The characterization of hydrosoluble oligomers in latexes is an important topic in emulsion polymerization since oligomers are suspected to be responsible for latex destabilization. In this work, the hydrosoluble fraction of poly(vinylidene chloride) latexes synthesized by emulsion polymerization of three monomers (acrylic acid, methyl acrylate, vinylidene chloride) was characterized by capillary electrophoresis (CE). CE using direct UV detection permitted to estimate residual monomers and surfactants concentrations contained in the latexes serums. Water soluble oligomers, polymerization initiator (persulfate) and other inorganic anions were detected by indirect UV detection. The oligomers content in the dry extract of serum was estimated to be about 6% (% m/m) represented mainly by 9 different compounds belonging to 3 different families. Using a semi-empirical electrophoretic mobility modeling, the charge number of these oligomers was estimated to be -2 and the molar masses were estimated in the range of ∼300-550 g.mol^-1. Oligomer samples obtained by surfactant-free polymerization, with different initial monomers proportions, provided qualitatively 14 different oligomers, including the 9 oligomers previously detected in the serums. Finally, the latex was characterized (electrophoretic mobility and zeta potential) using its serum as a background electrolyte. This approach could be very useful to study the behavior of the latexes, and possibly destabilization effect, in analytical conditions very close to its real environment / applications.

Determination of the Exact Particle Radius Distribution for Silica Nanoparticles via Capillary Electrophoresis and Modeling the Electrophoretic Mobility with a Modified Analytic Approximation

In this study, we use aqueous dispersions of amorphous silica nanoparticles of various sizes to investigate whether electropherograms recorded from capillary electrophoresis experiments can be converted directly into exact number-based particle radius distributions, provided that there is a relaxation effect-based size selectivity of the electrophoretic mobility and provided that the electrokinetic potential ζ of the particles can be regarded to be homogeneous over the surface of the particles, independent of the particle size. The results of this conversion procedure are compared with number-based particle radius distributions obtained from a large set of transmission electron microscopy (TEM) data. For this specific example, it is shown that the modified analytic approximation developed by Ohshima adequately describes the mobility-dependent relaxation effect and the electrophoretic mobility of the particle as a function of the reduced hydrodynamic radius and electrokinetic potential, which is a prerequisite for the presented procedure. Simultaneously, we confirmed that for the given Debye length/particle diameter ratio the electrokinetic surface charge density can be regarded to be size-invariant (including spherical geometry and planar limiting case). It is shown that the accuracy of the results of the developed method is comparable to that gained by a large set of TEM data, which is important when a precise description of the particle size distribution is needed to deduce conclusions regarding the underlying mechanism(s) of particle growth. The values obtained for the dispersion (width) of the distribution show only a small negative deviation, when compared with the TEM data (4-16%).

On the ionic strength dependence of the electrophoretic mobility: From 2D to 3D slope-plots

Determining the charge and the nature (small ion, nanoparticle, or polyelectrolyte) of an unknown solute from its electrophoretic characteristics remains a challenging issue. In this work, we demonstrate that, if the knowledge of the effective electrophoretic mobility (μ_ep ) at a given ionic strength is not sufficient to characterize a given solute, the combination of this parameter with (i) the relative decrease of the electrophoretic mobility with the ionic strength (S), and (ii) the hydrodynamic radius (R_h ), is sufficient (in most cases) to deduce the nature of the solute and its charge. These three parameters are experimentally accessible by CZE and Taylor dispersion analysis performed on the same instrumentation. 3D representation of the three aforementioned parameters (μ_ep ; S and R_h ) is proposed to visualize the differences in the electrophoretic behavior between solutes according to their charge and nature. Surprisingly, such 3D slope plot in the case of small ions and nanoparticles looks like a "whale-tail," while polyelectrolyte contour plot represents a rather simple and monotonous map that is independent of solute size. This work also sets how to estimate the effective charge of a solute from a given experimental (S,Rh,μ ep 5 mM ) triplet, which is not possible to obtain unambiguously with only (Rh,μ ep 5 mM ) or (S,μ ep 5 mM ) doublet, where μ ep 5 mM is the effective electrophoretic mobility at 5 mM ionic strength.

Size-based characterization of nanoparticle mixtures by the inline coupling of capillary electrophoresis to Taylor dispersion analysis

Separation of closely related nanoparticles is still a challenging issue for the characterization of complex mixtures for industrial/research applications or regulatory purposes. In this work, the remarkable separating performances of CE were complemented with the absolute size-based determination provided by Taylor dispersion analysis (TDA) for the characterization of nanoparticle mixtures. The inline hyphenation of CE to TDA was successfully implemented for the baseline separation followed by a size-based characterization of a bimodal mixture containing two closely size-related nanolatexes (70nm and 56nm radii). A pixel sensor UV area imager providing three detection points along the capillary was used for a differential measurement of the peak broadening during the Taylor dispersion step. Comparison of this new technique with dynamic light scattering and hydrodynamic chromatography is also discussed.

Simple and robust monitoring of ethanol fermentations by capillary electrophoresis

Free-solution capillary electrophoresis (CE), or capillary zone electrophoresis, with direct UV detection was used for the first time for the determination of mono- and disaccharides, sugar alcohols, and ethanol in fermentation broths. Sample preparation proved to be minimal: no derivatization or specific sample purification was needed. The CE conditions can be adapted to the type of fermentation by simply altering the background electrolyte (BGE). KOH (130 mM) or NaOH (130 mM) as the BGE led to the fastest analysis time when monitoring simple fermentations. A mixture of 65 mM NaOH and 65 mM LiOH led to a 19% improvement in resolution for a complex mixture of carbohydrates. Quantification of a simple carbohydrate fermentation by CE showed values in close agreement with that of high-performance anion exchange chromatography and high-performance liquid chromatography (HPLC) on a cation exchange resin. For complex fermentations, quantification of carbohydrates by HPLC and CE led to similar results, whereas CE requires an injection volume of only 10-20 nL. Analysis of an ethanol fermentation of hydrolyzed plant fiber demonstrated the robustness of the separation and detection of carbohydrates, as well as ethanol. Ethanol determination is achieved by coupling the CE method to pressure mobilization, using the same instrument and the same sample.

Recent developments in capillary and microchip electroseparations of peptides (2011-2013)

The review presents a comprehensive survey of recent developments and applications of capillary and microchip electroseparation methods (zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography) for analysis, isolation, purification, and physicochemical and biochemical characterization of peptides. Advances in the investigation of electromigration properties of peptides, in the methodology of their analysis, including sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, as well as in detection of peptides, are presented. New developments in particular CE and CEC modes are reported and several types of their applications to peptide analysis are described: conventional qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC techniques to provide relevant physicochemical characteristics of peptides are demonstrated.

Correlation between the charge of polymer particles in solution and in the gas phase investigated by zeta-potential measurements and electrospray ionization mass spectrometry

The relationship between the effective charge of polymer nanoparticles (PNP) in solution and the charge states of ionized particles produced in the gas phase by electrospray ionization was investigated. Charge detection mass spectrometry was used to measure both the mass and charge of individual electrosprayed ions. The effective charges extracted from the measured zeta-potential of PNPs in solution are partially correlated with the average values of charge of PNPs in the gas phase. The correlation between the magnitude of charging of PNPs ions produced in the gas phase with the PNPs surface charge in solution demonstrates that the mass spectrometry-based analysis described in this work is an alternative and promising way for a fast and systematic characterization of charges on colloidal particles.

Size and charge characterization of polymeric drug delivery systems by Taylor dispersion analysis and capillary electrophoresis

In this work, Taylor dispersion analysis and capillary electrophoresis were used to characterize the size and charge of polymeric drug delivery nanogels based on polyglutamate chains grafted with hydrophobic groups of vitamin E. The hydrophobic vitamin E groups self-associate in water to form small hydrophobic nanodomains that can incorporate small drugs or therapeutic proteins. Taylor dispersion analysis is well suited to determine the weight average hydrodynamic radius of nanomaterials and to get information on the size polydispersity of polymeric samples. The effective charge was determined either from electrophoretic mobility and hydrodynamic radius using electrophoretic modeling (three different approaches were compared), or by indirect UV detection in capillary electrophoresis. The influence of vitamin E hydrophobicity on the polymer effective charge has been studied. The presence of vitamin E leads to a drastic decrease in polymer effective charge in comparison to non-modified polyglutamate. Finally, the electrophoretic behavior of polyglutamate backbone grafted with hydrophobic vitamin E (pGVE) nanogels according to the ionic strength was investigated using the recently proposed slope plot approach. It was deduced that the pGVE nanogels behave electrophoretically as polyelectrolytes which is in good agreement with the high water content of the nanogels.

How Can Nanotechnology Help to Repair the Body? Advances in Cardiac, Skin, Bone, Cartilage and Nerve Tissue Regeneration

Nanotechnologists have become involved in regenerative medicine via creation of biomaterials and nanostructures with potential clinical implications. Their aim is to develop systems that can mimic, reinforce or even create in vivo tissue repair strategies. In fact, in the last decade, important advances in the field of tissue engineering, cell therapy and cell delivery have already been achieved. In this review, we will delve into the latest research advances and discuss whether cell and/or tissue repair devices are a possibility. Focusing on the application of nanotechnology in tissue engineering research, this review highlights recent advances in the application of nano-engineered scaffolds designed to replace or restore the followed tissues: (i) skin; (ii) cartilage; (iii) bone; (iv) nerve; and (v) cardiac.