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Press release
Lab-on-a-chip: A micromixer to facilitate chemical and biochemical analyses | |||
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Paris, January 25, 2002 |
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we expect miniaturized analysis laboratories, small enough to fit onto a
one square centimeter chip, to be developed soon? Such "labs-on-chips"
would enable scientists to carry out chemical and biochemical analyses on
minute quantities of samples. Researchers from Harvard University and the
CNRS team of the "Laboratoire de physico-chimie théorique"
* (Laboratory of Theoretical Physico-Chemistry) have developed
a high-performance method that rapidly and efficiently mixes samples and
reagents at microscopic scales. The results of their work are published
in the January 25, 2002 issue of Science. A lab-on-a-chip that is easy to reproduce en masse, and which enables analysis to be carried out in just a few minutes on quantities of samples ranging from the picoliter to the nanoliter, would save the space of one or two rooms of a laboratory. Made of plastic, glass or silicon, such a chip would consist of networks of connected microchannels with a lateral dimension of approximately 10 microns. For example, the lab would make it possible to mix the sample with various reagents successively, and then to isolate, sort and detect the products of this reaction. The implementation of this technology at these very small scales requires the development of several basic devices, such as micropumps, microvalves, micromixers, etc. It is difficult to mix solutions in these miniature channels because there is no turbulence at such scales. When two channels join, the fluids flowing through them do not mix. Instead, they circulate side by side in the single channel that results from the joining of the two. Only the transfer of heat can ensure that mixing takes place. Generally speaking, however, heat transfer is too slow a process. Over the past few years, several protocols for the mixing essential to combining samples and reagents rapidly and efficiently have been put forward. These often involve microfabrication or a complex operation: irregularly shaped channels, three-dimensional networks of channels, and transversal channels activated through oscillation. The idea developed by Abraham Stroock (Harvard) and Armand Ajdari (CNRS) involves placing small-amplitude ridges on the floor of the channel, at 45° with respect to the long axis of the channel. This naturally generates a helical flow of the fluid. A more complicated pattern than the simple parallel ridges, using a staggered herringbone shape, even leads to a flow where the streamlines are successively stretched, separated and folded over. The resulting mix is chaotic while the fluid is being transported. Its efficiency is quantitatively demonstrated in the report. A complex flow geometry is thus obtained by simply engraving the floor of the channel. This process is extremely easy using the microfabrication techniques initially developed for electronic components. This solution could thus be integrated into many devices. The researchers are continuing to collaborate on the production of other microfluidic elements necessary to truly miniaturize the equipment used in chemical and biochemical detection and analysis. *UMR7083: Joint CNRS / ESPCI PARIS laboratory Reference: “Chaotic Mixer for Microchannels” published in Science, January 25, 2002. CNRS researcher
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