Frédéric Tessier

Theory of DNA electrophoresis: a look at some current challenges.

Although electrophoresis is one of the basic methods of the modern molecular biology laboratory, new ideas are being suggested at an accelerated rate, in large part because of the pressing demands of the biomedical community. Although we now have, at least for some methods, a fairly good theoretical understanding of the physical mechanisms that lead to the observed peak spacings, widths and shapes, this knowledge is often too qualitative to be used to guide further technical developments and improvements. In this article, we review some selected elements of the current state of our theoretical ignorance, focusing mostly on DNA electrophoresis, and we offer several suggestions for further theoretical investigations.

An exactly solvable Ogston model of gel electrophoresis: VIII. Nonconducting gel fibers, curved field lines, and the Nernst‐Einstein relation

In this article, we examine the low‐field electrophoretic migration of infinitely small analytes in dilute sieving media made of nonconducting gel fibers. Using an Ogston obstruction model, we show that the electrophoretic mobility is not affected by the presence of curved field lines. In other words, the Nernst‐Einstein relation between the mobility and the diffusion coefficient is valid regardless of the electrical properties of the gel fibers. Although this finding may greatly simplify the development of obstruction models of electrophoretic sieving, it also represents a critical test for any analytical or computational approach.

Deformation, Stretching, and Relaxation of Single‐Polymer Chains: Fundamentals and Examples

#From the forthcoming book, Soft Materials: Structure, and Dynamics, Marangoni, A. G. and Dutcher, J., Eds., Marcel Dekker, Inc., in press.

The Electroosmotic Flow (EOF)

Controlling and manipulating liquids and analytes at the sub-millimeter scale is a challenge that frequently requires new methods to be developed. Indeed, scaling-down of traditional macroscopic ideas often fails. For instance, pumping liquids using pressure differences is often impractical and counterproductive because the resulting parabolic flow profile deforms sample zones. As the size of the system shrinks, the surface-to-volume ratio increases and interfacial effects become dominant. This actually opens new possibilities since the phenomenon of electroosmotic flow (EOF), wherein a fluid is made to move relative to a stationary charged boundary, can then be exploited to design efficient microfluidic devices. In this chapter, we review the fundamental principles of EOF as well as some of the methods used to coat channel walls and reduce the impact of EOF in situations where it would be unfavorable for the device performance.

Effective molecular diffusion coefficient in a two-phase gel medium

We derive a mean-field expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free solvent inclusions, in terms of the homogeneous diffusion coefficients in the gel and in the solvent. Upon comparing with exact numerical lattice calculations, we find that our expression provides a remarkably accurate prediction for the effective diffusion coefficient, over a wide range of gel concentration and relative volume fraction of the two phases. Moreover, we extend our model to handle spatial variations of viscosity, thereby allowing us to treat cases where the solvent viscosity itself is inhomogeneous. This work provides robust grounds for the modeling and design of multiphase systems for specific applications, e.g., hydrogels as novel food agents or efficient drug-delivery platforms.