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Automated Dielectrophoretic Separation of Heterogeneous Cell Populations

Javier L. Prieto, Jami Nourse, Jente Lu, Lisa Flanagan and Abraham P. Lee

Dielectrophoresis (DEP) has shown promising results as a tool for the separation and trapping of cells. These results are specially relevant in some applications such as the isolation of stem cells from their differentiated progeny where the lack of unique surface markers make traditional methods challenging. As an alternative DEP is a non-invasive method that avoids the use of surface markers. Varying electric fields at different frequencies interact differently with cells with different electric phenotypes allowing for their separation and selective trapping based on the cell polarizability.

Here we present an automated DEP cell trapping and cell separation device for the characterization and enrichment of heterogeneous cell populations. The device consists of an inlet, where an initial mixture of cells is loaded, connected to a main channel with three multiplexed DEP trapping regions. Each region is intersected by a dedicated perpendicular collection channel leading to three separated wells. Loading and unloading of cells are easily done by conventional methods such as pipetting. The fabrication of the device is done using soft lithography and bonding together two layers of poly(dimethyl) siloxane (PDMS) to a glass slide with patterned Ti-Au electrodes. Flow direction is controlled by the use of pneumatic valves that occlude the collection channels during cell trapping and separate the different regions during cell recovery.

Trapping cycles consisting of a trapping step, a washing step and a collection step is automated and controlled through a LabView interface. The user can setup the different parameters such as number of trapping cycles, duration of each step, frequencies of each trapping zone and flow rates. Operation of the entire platform is therefore simplified and reduced to loading and unloading of the cells and parameter setting through a graphical interface.

In order to prove the ability of the system to enrich different cell populations, two different mixed populations were used, the first consisting of mouse NSPCs and neurons while the second contained mouse NSPCs and astrocytes. A low frequency of 100 kHz and a higher frequency of 1 Mhz and an amplitude of 8 Vpp were used for trapping in the different regions. By staining the different populations we could determine after separation an enrichment of cells of up to 10-20% depending on frequency and cell type. This platform has the potential to automate the separation and enrichment of different cells types where differences in electrical phenotypes are apparent.

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