Method for Manipulating Magnetic Particles in a Liquid Medium

Abstract

A method of mixing magnetic particles (3) in a reaction chamber (2) that is part of a microfluidic device and that contains the said particles in suspension, comprises the steps: (a) providing an electromagnetic means (1,1′,6,7) to generate magnetic field sequences having polarity and intensity that vary in time and a magnetic field gradient that covers the whole space of the said reaction chamber (2); (b) applying a first magnetic field sequence to separate or confine the particles (3) so the particles occupy a sub-volume in the volume of the reaction chamber (2); (c) injecting a defined volume of the said reagent in the reaction chamber; and (d) applying a second magnetic field sequence to leads the particles (3) to be homogenously distributed and dynamically moving over a substantial portion of the whole reaction chamber volume.

Description

REFERENCE TO RELATED APPLICATIONS [0001]This application claims benefit of International Application No. PCT / IB2007 / 052409 filed on 21 Jun. 2007, International Application No. PCT / IB2007 / 052410 filed on 21 Jun. 2007, International Application No. PCT / IB2006 / 052005 filed on 21 Jun. 2006, and International Application No. PCT / IB2006 / 054182 filed on 9 Nov. 2006, which are incorporated by reference herein.FIELD OF THE INVENTION [0002]The invention relates to a method of handling and mixing magnetic particles within a reaction chamber that is a part of a fluidic or microfluidic platform. More particularly, the invention concerns a method of handling magnetic particles in a way to improve the mixing of the particles with the surrounding liquids medium and where the liquids are automatically handled in a fluidic platform. Further, the invention relates to a method for conducting assays on a test sample containing specific biological or chemical substances using active biochemically surface...

AI Technical Summary

Benefits of technology

The present invention is a new magnetic device and magnetic pole geometry that allows for more efficient and controlled mixing of magnetic particles with a liquid flow. The device includes a reaction chamber with a cavity shape that matches the magnetic pole geometry, which creates a magnetic field gradient and a magnetic force to retain the particles in the chamber. A time-varying magnetic field is then applied to break down the aggregated chain-like structures formed by the particles. The new geometry allows for a more uniform mixing of the particles with the liquid flow.

Problems solved by technology

Indeed, as for any surface-based assay the reaction is strongly limited by the natural diffusion process, a strong steering and mixing is necessary to promote the affinity binding reaction between the ligand and the target substance.

However, with this method the magnetic field gradient will attract and confine the particles in a cavity region close to the walls of the container.

In such condition, the contact between the particles and the test medium is limited to the said cavity space which reduces the mixing efficiency.

In such conditions indeed, the particles can be moved while relatively separated from each other, which will potentially affect the mixing.

However, in this approach when one takes in consideration the whole duration of the particles handling process, the time during which the particles are relatively separated from each other is relatively short.

Moreover, during the mixing process the particles are not homogenously contacted with the sample volume in the test tube, which will in turn strongly limit the mixing efficiency.

This issue is more pronounced as the sample volume is large.

Consequently when these mechanical mixing approaches are compared with the “manual shaking of a test tube”, the reaction time and the performance are substantially similar if not lower, indicating that diffusion is still an important limiting factor.

This process limits the movement of the particles to a relatively small distance, significantly reducing the mixing efficiency between particles and the surrounding liquid medium.

In general, beyond the limited mixing capability of the state of the art magnetic particles technologies, mainly based on the concept of “bringing a magnet in the proximity of a test tube”, the integration and the automation of magnetic particles assay procedures are very complex, necessitating bulky robotic systems.

These limitations become all the more critical as the assay procedures are becoming more and more complex.

The major limitation of this “in flow mixing” approach is that the volume of the test medium that can be mixed with the particles is very small and the reaction time very short, limiting considerably the cases of its applicability.

However the so described flow-through approach suffers from a serious physical constraint since in order to be handled in an environment with continuous fluidic processing, the particles must be continuously exposed to a magnetic field.

Under such conditions the particles will stick together aid agglomerate thereby losing their main advantage: the particle surface that is in active contact with the fluid flow will be drastically reduced which will seriously compromise the assay performance.

Even demonstrating an important development in magnetic particles handling and mixing in a microfluidic environment, the approach disclosed in U.S. patent application 2005 / 208,464 suffers however from many practical limiting constraints.

First, as the particles are kept stationary and fixed in a narrow segment of the flow-through cell, the contact between the particles and the target substance is limited to that narrow region and for a very short time, which in practice makes such process difficult to set up.

Secondly, this approach is specifically adapted for handling and mixing magnetic particles under flow-through conditions in microfluidics environments, which make it not fully adapted for different assay conditions.

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