A micropit for biological cell positioning

Dielectrophoresis (DEP) may be used to trap or to move biological cells. Automated position control of cells has been proposed to eliminate operator dependent experimental parameter variations and increase throughput of labour intensive laboratory procedures such as couplet fusion for mammalian cloning or plant hybridisation, and cell sorting. However, the use of DEP in laboratory procedures is often precluded due to the relatively high complexity of microfabricated apparatus. A simple two layer microchip was fabricated and demonstrated to position cells. Thin film interdigitated titanium electrodes (300 nm thick, 250 ¿m wide and 250 ¿m apart) were deposited on a solid borosilicate glass substrate. They were coated with a film of insulating photosensitive resist AZ1518. Circular holes (¿micropits¿) measuring 5, 10, 20, and 40 ¿m in diameter were fabricated above the electrodes. Saccharomyces cerevisiae (bakers yeast) cells were dispensed onto the microchip. Positive and negative dielectrophoresis were used to position cells resting on the surface of the micropit array. After patterning with positive DEP, a rinse was used to create small islands of cells. The experimental results were accompanied by a 2D numerical simulation of the micropit device to determine the influence of pit height and diameter on the DEP force.