Trap profiles of projector based optoelectronic tweezers (OET) with HeLa cells

In this paper we present trap profile measurements for HeLa cells in Optoelectronic Tweezers (OET) based on a data projector. The data projector is used as a light source to illuminate amorphous Si creating virtual electrodes which are used to trap particles through dielectrophoresis. We show that although the trap stiffness is typically greater at the edges of the optical spot it is possible to create a trap with constant trap stiffness by reducing the trap's size until it is similar to the object being trapped. We have successfully created a trap for HeLa cells with a constant trap stiffness of 3 x 10(-6) Nm-1 (capable of moving the cell up to 50 microms-1) with a 12 microm diameter trap. We also calculate the depth of the potential well that the cell will experience due to the trap and find that it to be 1.6 x 10(-16)J (4 x 10(4) kBT).