Two-dimensional cell trapping by ultrasound microbeam

The availability of sound beams with its beamwidth approaching cell size is extremely important in order to apply the droplet trapping method to cellular manipulation in the Mie regime (cell diameter > wavelength). This can be achieved at frequencies higher than 100 MHz. We thus call ultrasound beams in the frequency range from 100 MHz to a few GHz as ultrasound microbeams. A zinc oxide (ZnO) transducer that is designed and fabricated to transmit a 200 MHz focused sound beam is employed to immobilize a 10 m leukemia cell (K-562) within the trap. The cell is transversely displaced from the trap center. Lateral displacement and trajectory of the trapped cell location are measured in a two-dimensional domain, validating the retracting cell motion. The potential of this technique for studying cellular adhesion between white blood cells and endothelial cells is discussed, suggesting its capability as a single cell manipulator.