For the period January 2006 to December 2007, Web of Science reports ∼4800 hits on capillary electrophoresis (CE) including 410 reviews. Because of the prominence of CE techniques in bioanalysis, we decided make them the focus of this review and selected 200 hundred papers representing advances in this field. The selected papers cover advances in CE theory, instrumentation, and methodologies that are specific to various analytes of biological origin or relevance. The group of analytes includes nucleic acids, proteins and peptides, carbohydrates, lipids, single cells, and bioparticles. In addition, we have included advances in the use of CE to define functional assays or to investigate biomolecular interactions. The use of microfabricated devices for CE analysis was not included because this is already covered in other review.

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Capillary electrophoresis in bioanalysis.

Sodium dodecyl sulfate-induced rapid gelation of silk fibroin

Impedance analysis of adherent cells after in situ electroporation: Non-invasive monitoring during intracellular manipulations

pH Dependence of Charge Multipole Moments in Proteins

Negative electrophoretic mobilities of oil in water are widely interpreted in terms of adsorption of hydroxide leading to negative surface charge. Challenging this traditional view, an increasing body of evidence suggests surface depletion of hydroxide and surface accumulation of hydronium leading to a positive surface charge. We present results from molecular dynamics (MD) simulations showing electrophoretic mobilities of oil in water with the same sign and magnitude as in experiment but in the absence of ions. The underlying mechanism involves interfacial roughness leading to gradients in dielectric permittivity in field direction and, thus, local elevation of the applied electric field. Although all molecules have zero net charge, their partial charges are distributed non-uniformly such that oil exhibits negative and water positive excess charge in regions of high field intensities; this induces a net force on the oil or the water against or in field direction, respectively. Our results indicate that deducing net charges from electrophoretic mobilities as widely done can be misleading. Our findings suggest that pH dependent electrophoretic mobilities in experiment being negative above and positive below pH 2.5 arise from a competition between the negative mobility of the ion-free interface and the positive mobility from adsorbed hydronium ions.

Electrophoresis of neutral oil in water.

We derive a simple formula for the free solution electrophoretic mobility of protein by including both molecular shape and charge distribution effects. The molecular shape of protein is described by a deformed sphere model, while the charge distribution is represented in terms of net charge, charge dipole, and charge quadrupole. The deformed sphere model approximates the radial coordinate of the protein surface as a simple quadratic equation based on the atomic coordinate data. Charge dipole does not affect the mobility of protein. Combined with the quadratic coefficients of the surface equation, charge quadrupole affects the mobility. When the charge quadrupole contribution is negligible, the mobility equation simplifies to the Henry equation in which the sphere radius is replaced with the hydrodynamic radius of protein. The deformed sphere model predicts correctly the hydrodynamic radius of protein from the atomic coordinate data. The hydrodynamic radius is not the radius of sphere of equal volume but the effective radius that correlates with the translational diffusivity of protein. To illustrate the utility of our mobility equation we study the electrophoresis of lysozyme and compare our results with previously published works.

Seung Tae Kang

Papers

Electrophoretic mobility equation for protein with molecular shape and charge multipole effects.