Laser doppler electrophoresis using a diffusion barrier

Abstract

In one general aspect, an electrophoretic measurement method is disclosed that includes providing a vessel that holds a dispersant, providing a first electrode immersed in the dispersant, and providing a second electrode immersed in the dispersant. A sample is placed at a location within the dispersant between the first and second electrodes with the sample being separated from the electrodes, an alternating electric field is applied across the electrodes, and the sample is illuminated with temporally coherent light. A frequency shift is detected in light from the step of illuminating that has interacted with the sample during the step of applying an alternating electric field, and a property of the sample is derived based on results of the step of detecting.

Description

[0001]This application is a divisional of U.S. application Ser. No. 12 / 972,412, filed Dec. 17, 2010, which is herein incorporated by reference.FIELD OF THE INVENTION[0002]This invention relates to methods and apparatus for performing electrophoretic measurements, including laser Doppler electrophoresis measurements that use diffusion barriers.BACKGROUND OF THE INVENTION[0003]There are a number of techniques that have been used to measure the electrophoretic mobility of soft samples such as capillary zone electrophoresis, membrane confined steady state electrophoresis, the Tiselius apparatus, and electrophoretic light scattering, including Laser Doppler Electrophoresis (LDE). LDE measures mobility of particles by measuring particle motion under the application of an external electric field. Referring to FIG. 1, the particles 16 are dispersed in a buffer 14 and electrodes 24, 26 are immersed into the sample. The field is applied and at very high buffer conductivities and degradation o...

AI Technical Summary

Benefits of technology

[0008]Generally, this document describes a diffusion barrier concept, whereby a small volume of the sample itself (dispersed or otherwise) is introduced into a larger volume, that includes the electrodes, prefilled with dispersant only. The diffusion barrier is intended to isolate the sample from the electrode surface whilst maintaining electrical contact with the surface, via the buffer within which the sample is dispersed. The LDE measurement ideally occurs before the sample has migrated to the electrode or if an extended measurement duration is required then before the aggregates created at the electrodes have migrated back into the light scattering detection volume. The sample volumes are also, by default, then greatly reduced and since, ideally, the sample is not degraded at the electrode then significantly more measurements are available in order to properly optimize the measurement. It may also then be possible to retrieve the sample after the measurement, depending on the physical format of the sample cell. Whilst primarily aimed at protein or other soft samples, the technique can also be used to increase cell life by the reduction of blackening of the electrodes.

[0010]Systems according to the invention can be advantageous in that they can help to avoid the creation of aggregates in electrophoretic mobility measurements on protein samples. This can potentially reduce a source of errors in these measurements, because the aggregates can have very different mobilities from those of the native protein itself. And although some researchers have shown that the blackening of the electrodes does not affect the quality of the measurement, this blackening is extremely unsightly and the perception in the marketplace is that it indicates a ‘dirty’ and therefore unusable cell.

Problems solved by technology

The volumes typically associated with LDE can also be problematic due to high sample cost and the iterative nature of LDE measurement optimization.

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