On-chip label-free protein analysis with downstream electrodes

Published on July 29th, 2019

Authors: Kadi L. Saar, Yingbo Zhang, Thomas Müller, Challa P. Kumar, Sean Devenish, Andrew Lynn, Urszula Łapińska, Xiaoting Yang, Sara Linsed and Tuomas P. J. Knowles.

Lab Chip, 2018, 18, 162-170. DOI: 10.1039/C7LC00797C



The ability to apply highly controlled electric fields within microfluidic devices is valuable as a basis for preparative and analytical processes. A challenge encountered in the context of such approaches in conductive media, including aqueous buffers, is the generation of electrolysis products at the electrode/liquid interface which can lead to contamination, perturb fluid flows and generally interfere with the measurement process.

Here, they address this challenge by designing a single layer microfluidic device architecture where the electric potential is applied outside and downstream of the microfluidic device while the field is propagated back to the chip via the use of a co-flowing highly conductive electrolyte solution that forms a stable interface at the separation region of the device. The co-flowing electrolyte ensures that all the generated electrolysis products, including Joule heat and gaseous products, are flowed away from the chip without coming into contact with the analytes while the single layer fabrication process where all the structures are defined lithographically allows producing the devices in a simple yet highly reproducible manner.

They demonstrate that by allowing stable and effective application of electric fields in excess of 100 V cm-1, the described platform provides the basis for rapid separation of heterogeneous mixtures of proteins and protein complexes directly in their native buffers as well as for the simultaneous quantification of their charge states. They illustrate this by probing the interactions in a mixture of an amyloid forming protein, amyloid-β, and a molecular chaperone, Brichos, known to inhibit the process of amyloid formation. The availability of a platform for applying stable electric fields and its compatibility with single-layer soft-lithography processes opens up the possibility of separating and analyzing a wide range of molecules on chip, including those with similar electrophoretic mobilities.

Figure 1: Schematic of the device used in this study. (A) The electrophoresis chamber is connected to a co-flowing electrolyte solution (3M KCl) via narrow perpendicular channels that control the mass transfer of the electrolyte to the electrophoresis chamber forming a thin sheet of electrolyte at the edges of the chamber (inserts (i), (ii); visualized via the addition of trace amounts of bovine serum albumin). The electric field is applied from metal clips at the outlets of the electrolyte channels and it propagates to the electrophoresis channel along with the flowing electrolyte solution. (B) The co-flowing electrolyte solution transports the electrolysis products away from the chip while simultaneously propagating the electric field in the direction opposite to the flow back into the device.

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