Luc Bousse | PubMed Health

PubMed2003

Analysis of plasmid samples on a microchip.

We have developed a LabChip-based plasmid assay that runs on the Agilent 2100 Bioanalyzer. The assay determines the sizes and relative concentrations of the multiple forms of plasmid samples. Twelve samples can be analyzed on each chip in an automated run lasting approximately 30min. By using a supercoiled DNA sizing standard of 2-16kb, the size of the analyzed plasmid can be determined. The resulting MW has a relative standard deviation (CV) <5% and error <5%. Plasmids from 2-8kb can be separated with resolution better than 1kb. Topological isoforms in a plasmid sample can also be separated. However, due to differential staining, the heterogeneity of plasmid samples can only be measured if the signal of each isomer peak can be calibrated with pure standards for every isomer form. For a typical plasmid preparation which predominately is in the supercoiled form, the normalized corrected peak area for the supercoiled form correlates with the plasmid concentration in a broad range of 1-100ng/microl. The measurement is semiquantitative with a CV lower than 20%. A number of applications of this assay on a Labchip will be shown.

Chemistry Techniques, Analytical↗

PubMed2002

Electroosmotic pumping in microchips with nonhomogeneous distribution of electrolytes.

A general equation to calculate the node pressure at a junction in a microfluidic network is presented. The node pressure is generated from both the hydrodynamic flow due to the external applied hydraulic pressures and the electrokinetic flow resulted from the applied electric field. Pure electroosmotic flow has a plug-flow profile and pressure flow has a parabolic flow profile. In a first order approximation, these two flows can be treated separately, and the total flow is the sum of the two. An externally applied pressure simply creates a constant offset in the node pressure as long as the flow resistances remain the same. In a nonhomogeneous microfluidic network, where the electrical resistivity or the electroosmotic mobility is not constant everywhere, the differences in electroosmotic flow in various sections of the network will create an electroosmotically induced pressure at the internal nodes. Our theoretical approach can easily be extended to networks with more than one internal node. One prediction of this theory is that any variation in electroosmotic mobility or solution resistivity in different network branches will generate a pressure, and can thus be used as a pump. As an example, we demonstrate electroosmotic pumping in a high-low buffer system.

Electrolytes↗