Cécile Goubault

Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces

When ligands and receptors are both attached on surfaces, because of the restriction of configurational freedom, their recognition kinetics may be substantially reduced as compared with freely diffusing species. In nature, this reduction may influence the efficiency of the capture and adhesion of circulating cells. Here we show that similar consequences are observed for colloids grafted with biomolecules that are used as probes for diagnostics. We exploit Brownian magnetic colloids that self-assemble into linear chains to show also that the resulting one-dimensional confinement considerably accelerates the recognition rate between grafted receptors and their ligands. We propose that because confinement significantly augments the colliding frequency, it also causes a large increase in the attempt frequency of the recognition. This work gives the basis of a rapid, homogeneous, and highly sensitive bioanalysis method.

Self-Assembled Magnetic Beads for Cell Sorting

We present an original matrix for cell sorting by affinity : magnetic beads self-organised into an array of columns. Data concerning the development of such matrices will be presented and the potential for cell sorting will be discussed.

Self-Assembled Magnetic Colloids for DNA Separations in Microfluidic Devices

We present a new approach to separations in microchannels, using superparamagnetic colloids as a self-organizing matrix. In a magnetic field, the colloidal suspension forms a 2-dimensional array of columns with urn-sized spacing. This rigid matrix reverts back to a low viscosity suspension when the field ceases, allowing easy replacement between runs. It is applied here to constant and pulsed-field electrophoresis of large duplex DNA molecules in an automated microfluidic system. Fragments ranging from 15–145.5 kilobase pairs were separated in about 10 mn. Single molecule epifluorescence microscopy was used to unravel the mechanisms responsible for these separations.