TABLE OF CONTENTS Because of their versatility, electric field-based techniques are the most widely used for bioanalyses, not only for the separation of biological objects through the well-known electrophoresis-derived techniques but also for the handling and micromanipulation of particles, cells, or even biomolecules through dielectrophoresis. We'll review in this chapter the principles of these techniques with their use, their limitations, and their foreseen applications. With the transfer of microfabrication techniques to this field and the advent of the lab-on-a-chip approach, particularly well suited to many of these experiments, new original tracks are now opened for potential developments. Although we certainly do not pretend to make an exhaustive list of these new routes, we will try to give a few examples illustrative of this approach.
Quite generically, objects dispersed in water bear a surface charge. The origin of this charge is diverse: It may come from the natural ionization of some of these colloids (e. g., proteins) that give them a net charge depending on the pH of the solution, but other phenomena such as the adsorption of charged ions or the intrinsic ionic nature of some of these particles may come into play.
However, it is important to remember that a charged particle should never be considered naked in the solvent. It is always surrounded by counter-ions, so that its global charge is strictly zero (electroneutrality). Because of the thermal agitation, this layer of counter-ions is diffuse.
Electrophoresis consists of applying to these charged objects a direct external...
