Force versus position profiles of HeLa cells trapped in phototransistor-based optoelectronic tweezers

Phototransistor-based Optoelectronic Tweezers (Ph-OET) enables optical manipulation of microscopic particles in physiological buffer solutions by creating electrical field gradients around them. A spatial light pattern is created by a DMD based projector focused through a microscope objective onto the phototransistor. In this paper we look into what differences there are in the trap stiffness profiles of HeLa cells trapped by Ph-OET compared to previous a-Si based OET devices. We find that the minimum trap size for a HeLa cell using a phototransistor with pixel pitch 10.35μm is 24.06μm in diameter which can move cells at 20μms-1 giving a trap stiffness of 8.38 x 10-7 Nm-1.