Dynamic Modulation of Dielectrophoretic Force Using Resonant Feedback*

Dielectrophoresis is the backbone of micromanipulation in lab-on-a-chip platforms. In such systems, once the electrodes are defined by fabrication the spatial profile of the dielectrophoretic force is fixed. Modification of the force profile entails refabrication of entire systems with the redesigned electrodes. To overcome this problem, we propose to connect the trap electrodes in series with an external resistor and an inductor to form a resonant RLC circuit. As a dielectrophoretically trapped droplet moves, it modifies the capacitance between the electrodes by inducing additional charges on them, which in turn shift the circuit resonance and the voltage across the electrodes to exert an additional feed-back force on the droplet. We show that by tuning the A.C. supply frequency and the circuit resistance the detuning and linewidth of the resonant circuit can be modulated to dynamically control the spatial profile of the dielectrophoretic force through the feed-back effect. The additional handles introduced by the resonant circuit allow to extend the trap range while ensuring that the trapped sample is not exposed to high electric fields at the stable trapping position, an extremely important criterion for the trapping of sensitive biochemical specimen.