Dielectrophoresis-based continuous-flow particle microreactor

This thesis mainly deals with the integration of a microfluidic system for the extraction of micrometric and submicrometric particles from a solution. Traditional methods take from several minutes to hours to separate particles from a solution. Microfluidics allow for a more rapid separation, and in addition provide a way to control the duration of the exposition of the particles to a specific reagent. In the first device proposed in this dissertation (called simple exchanger) a microchannel carrying the particle solution overlaps over a short distance with a channel carrying the reagent. In this region the particles are pushed from one solution to the other by dielectrophoretic forces. They are created by an array of microelectrodes patterned on the side of the channel. Diffusion across the interface between the solutions causes molecules from the reagent stream to pollute the particle solution (and inversely). This effect is minimized by increasing the flow velocity in the overlap region. The maximum velocity applicable as well as diffusive mixing and a biochemical application of the device are presented in a first part. In a second part, new designs for the exchanger are proposed in order to prevent diffusive mixing. The first design relies on a massive enlargement of the channel as well as an intermediate buffer flow to keep the destination solution clean. The enlargement diminishes the relative effect of diffusion; the buffer flow "collects" the diffused molecules and is discarded. A second scheme relies on electrophoretic forces to pull charged reagents against diffusion, thereby decreasing diffusive mixing. In a final chapter a microfluidic device based on simple exchangers is used to probe the aggregation of nanoparticles to a biological target. Thanks to a well-controlled flow velocity in the channel and the given channel length the duration a single target is exposed to a nanoparticle solution is known. By exposing targets for different durations it is possible to follow the aggregation kinetics of the nanoparticles. This measurement is carried out for yeast cells and carboxylated nanoparticles. A Brownian dynamics simulation is finally used to outline a promotion of the aggregation due to the microchannel format. In the future, these devices could be used for various applications in the biotechnological domain, where a well-controlled, short duration of exposure of a small particle to a chemical is required.


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