(37f) Using Proteins As Resolution Probes to Quantify Gradient Insulator-Based Dielectrophoresis

Dielectrophoresis (DEP) is an ideal technique for separation and concentration of small volume samples. Dielectrophoresis has typically been applied to particles or cells, but recently smaller analytes, such as proteins, have been targeted. Concentration of proteins by 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 are the proteins BSA (66 kDa) and streptavidin (60 kDa). Proteins of smaller molecular weights have been studied and manipulated using dielectrophoretic forces resulting in streaming (Electrophoresis, 2013, 34, 1085-1096). Here, we extend the range of explicit capture down to 14.3 kDa by capturing lysozyme from chicken egg white, trypsin inhibitor from soy, and other lower 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 difficulty in attempting to quantitatively assess dielectrophoretic capture is that particles are on the same length-scale as the capture zone and local electric field gradient. When a number of particles are captured, they alter the local field and interact with one another. Smaller analytes such as proteins more faithfully reflect the forces present in the channel since they cause less of a disturbance to the electric field lines. Here we present capture of proteins and use these capture events to analyze the forces present within the channel. Electrokinetic mobilities and dielectrophoretic mobilities are calculated and compared with more traditional methods and numerical simulations.