Dielectrophoretic trapping in microwells for manipulation of single cells and small aggregates of particles.

In this work we present a novel concept of active microwells based on cylindrical wells able to vertically trap and control single particles by means of negative dielectrophoresis. The device is fabricated by drilling through holes on a polyimide substrate with copper-gold or aluminum metals, forming three annular electrodes within the well. A channel under the device provides a fluid flow filling the microwell by capillarity. Particles are delivered from the top by a microdispenser and applying sinusoidal signals to the electrodes at frequencies ranging from 100kHz to 1.5MHz and amplitudes between 2V and 7V they are successfully trapped and levitated at the level of the central electrode in the middle of microwells with a diameter of 125mum. By changing signal phases, other configurations are also enabled to load particles in the well or eject them from the bottom. The extension to an array of microwells is presented and design rules are described for routing electrode connections and setting signal parameters. K562 cells cultured with Ara-C 1000nM were successfully trapped and controlled in physiological media. Polystyrene beads were also levitated in water and were used for experimental measurements on minimum amplitudes and phase differences in the signals required to levitate beads, confirming the results obtained by simulation.