Raphaël Tornay

Wide channel dielectrophoresis-based particle exchanger with electrophoretic diffusion compensation

We present here a microfluidic device for the chemical modification of particles. In order to alleviate diffusive mixing issues beads are pushed from a starting buffer to a reagent over a wide channel by an array of shifted electrodes. We also show that the effect of reagent diffusion can be compensated by electrophoretic forces.

Electrical Detection and Ejection of Beads in a One-Cell-Per-Drop Microdispenser

We present developments on a one-cell-per-drop microdispenser for cell-based assays. This device has been designed to detect individual cells inside a microfluidic channel and eject them in nanoliter-size droplets with the advantage of dispensing a precise number of cells at a given spot on a receptor slide. Detection of beads or cells is based on the electrical measurement of a small section of the microfluidic channel. The detection triggers the opening of a valve and consequently the ejection of a droplet containing the cell. We demonstrate electrical detection and controlled ejection of beads, and we introduce the dispenser robot for arraying of cell-containing droplets.

A virtual valve for smooth contamination-free flow switching

We present a channel geometry that allows for clean switching between different inlets of a microchip without any contamination of the inlets or the downstream flow. We drive this virtual valve with a pneumatic pressure setup that minimizes disturbance of the downstream flow during the switching procedure by simultaneous variation of the pressures applied to the different inlets. We assess the efficiency of the setup by spectroscopic measurement of downstream dye concentrations, and demonstrate its practical utility by sequentially constructing multiple layers of alginate hydrogel. The method is potentially useful for a whole series of further applications, such as changing perfusion liquids for cell culture and cell analysis, metering, chemical-reaction initiation and multi-sample chromatography, to name a few.