Using Gradient Insulator-Based Dielectrophoresis To Concentrate Small Molecular Weight Proteins

Dielectrophoresis (DEP) has the potential to serve as a separation and concentration technique for small volume samples. Dielectrophoresis has typically been applied to particles or cells, but recently analytes with small molecular weights such as proteins, have been targeted. Protein dielectrophoresis has been demonstrated, with the first observations of protein DEP trapping about twenty years ago by Washizu et. al. (IEEE Trans. Ind. Appl., 1994, 30, 835-843). The smallest proteins to be captured thus far using techniques similar to ours are the proteins BSA at 66 kDa and streptavidin at 60 kDa.

Proteins of smaller molecular weights have been studied, and even successfully manipulated using dielectrophoresis resulting in streaming (Electrophoresis, 2013, 34, 1085-1096), but discrete isolation in a pseudo steady state has not been shown. Here, we extend the range of capture down to 14.3 kDa by capturing lysozyme from chicken egg white, along with other small molecular weight proteins.
Dielectrophoresis is carried out on a microfluidic device consisting of an insulating sawtooth-patterned microchannel such that an inhomogeneous electric field is induced in the channel when a DC potential is applied across the device. The gradient of dielectrophoretic forces in our device arises from the varying distances of each successive gate within the device: as the gates become narrower, the ratio of the dielectrophoretic force to the electrophoretic force increases. When the dielectrophoretic force is great enough to counteract all other forces a protein experiences within the channel, immobilization and concentration occurs.
One protein of great interest in the medical field is Aβ (1-40) amyloids. Aggregates of Aβ amyloid and other amyloids have been implicated in numerous human diseases, including Alzheimer’s disease.
While it is known that the fully-developed Aβ amyloid fibrils are related to this disease, recent research has suggested the smaller oligomers and protofibrils are more prevalent in disease pathogenesis and are more cytotoxic. The proteins for our research were chosen based on their small molecular weights such that their capture conditions might be comparable to small oligomers of Aβ amyloid proteins. Future work includes studying the behavior of small Aβ amyloid oligomers in our device.