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

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

Separation of platelets from other blood cells in continuous-flow by dielectrophoresis field-flow-fractionation

We present a microfluidic device capable of separating platelets from other blood cells in continuous flow using dielectrophoresis field-flow-fractionation. The use of hydrodynamic focusing in combination with the application of a dielectrophoretic force allows the separation of platelets from red blood cells due to their size difference. The theoretical cell trajectory has been calculated by numerical simulations of the electrical field and flow speed, and is in agreement with the experimental results. The proposed device uses the so-called "liquid electrodes" design and can be used with low applied voltages, as low as 10 V(pp). The obtained separation is very efficient, the device being able to achieve a very high purity of platelets of 98.8% with less than 2% cell loss. Its low-voltage operation makes it particularly suitable for point-of-care applications. It could further be used for the separation of other cell types based on their size difference, as well as in combination with other sorting techniques to separate multiple cell populations from each other. (C) 2011 American Institute of Physics

Continuous flow cell trapping and hybridoma-cell production on-chip using "liquid electrodes"

This paper reports on a new microfluidic chip designed for cell electrofusion. A pair of cells is brought into close contact by means of opposite dielectrophoretic forces and they are subsequently fused by applying a short electrical pulse

Dielectrophoresis-based particle exchanger for the manipulation and surface functionalization of particles

We present a microfluidic device where micro- and nanoparticles can be continuously functionalized in flow. This device relies on an element called particle exchanger, which allows for particles to be taken from one medium and exposed to some reagent while minimizing mixing of the two liquids. In the exchanger, two liquids are brought in contact and particles are pushed from one to the other by the application of a dielectrophoretic force. We determined the maximum flow velocity at which all the particles are exchanged for a range of particle sizes. We also present a simple theory that accounts for the behaviour of the device when the particle size is scaled. Diffusion mixing in the exchanger is also evaluated. Finally, we demonstrate particle functionalization within the microfluidic device by coupling a fluorescent tag to avidin-modified 880 nm particles. The concept presented in this paper has been developed for synthesis of modified particles but is also applicable to on-chip bead-based chemistry or cellular biology

Rapid, Sensitive and Real-Time Multiplexing Platform for the Analysis of Protein and Nucleic-Acid Biomarkers

We describe a multiplexing technology, named Evalution, based on novel digitally encoded microparticles in microfluidic channels. Quantitative multiplexing is becoming increasingly important for research and routine clinical diagnostics, but fast, easy-to-use, flexible and highly reproducible technologies are needed to leverage the advantages of multiplexing. The presented technology has been tailored to ensure (i) short assay times and high reproducibility thanks to reaction-limited binding regime, (ii) dynamic control of assay conditions and real-time binding monitoring allowing optimization of multiple parameters within a single assay run, (iii) compatibility with various immunoassay formats such as coflowing the samples and detection antibodies simultaneously and hence simplifying workflows, (iv) analyte quantification based on initial binding rates leading to increased system dynamic range and (v) high sensitivity via enhanced fluorescence collection. These key features are demonstrated with assays for proteins and nucleic acids showing the versatility of this technology

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