Contactless dielectrophoresis (cDEP) devices are a new adaptation of dielectrophoresis in which fluid electrodes, isolated from the main microfluidic channel by a thin membrane, provide the electric field gradients necessary to manipulate cells. This work presents a continuous sorting device which is the first cDEP design capable of exploiting the Clausius-Mossotti factor at frequencies where it is both positive and negative for mammalian cells. Experimental devices are fabricated using a cost effective technique which can achieve 50 μm feature sizes and does not require the use of a cleanroom or specialized equipment. An analytical model is developed to evaluate cDEP devices as a network of parallel resistor-capacitor pairs. Two theoretical devices are presented and evaluated using finite element methods to demonstrate the effect of geometry on the development of electric field gradients across a wide frequency spectrum. Finally, we present an experimental device capable of continuously sorting human leukemia cells from dilute blood samples. This is the first cDEP device designed to operate below 100 kHz resulting in successful manipulation of human leukemia cells, while in the background red blood cells are unaffected.
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