The image above shows a schematic cross-section of the trapping device. Cells or particles are transported to the ultrasonic transducers by a pressure dirven flow through the microfluidic channels. As the transducers are activated the cells are drawn to a pressure minima in the centre of the channel by the force field generated by the acoustic standing wave.

The image to the left is a fluorescent image of acoustically trapped neurol stem cells. The cell cluster was trapped and tested for viability after 15 minutes of continous ultrasonic radiation. All cells responded well to the viability test.

To ensure a high trapping yield hydrodynamic focusing is used in the particle inlet to direct the particles directly to the center of the transducer where the force field is strongest. A short video-clip showing trapping of hydrodynamically focused microbeads can be found here.

Publications

Norris J.V., Evander M., Horsman-Hall K.M., Nilsson J., Laurell T., Landers J.P., Acoustic Differential Extraction for Forensic Analysis of Sexual Assault Evidence, Analytical Chemistry, 2009, 81, 6089-6095

M. Evander, L. Johansson, T. Lilliehorn, J. Piskur, M. Lindvall , S. Johansson, M. Almqvist, T. Laurell  and J. Nilsson, Non-invasive acoustic cell trapping in a microfluidic perfusion system for on-line bioassays, Analytical Chemistry, 2007, 79, 2984-2991

Lilliehorn T., Simu U., Nilsson M., Almqvist M., Stepinski T., Laurell T., Nilsson J., Johansson S., Trapping of microparticles in the nearfield of an ultrasonic transducer, Ultrasonics 43(5) (2005) 289-299

Lilliehorn T., Nilsson M., Simu U.,Johansson S., Almqvist M., Nilsson J., Laurell T., Dynamic arraying of microbeads for bioassays in microfluidic, Sensors and Actuators B: Chemical, 2005, 106, 2, 851-858

Almqvist M, Torndahl M, Nilsson M, Lilliehorn T, Characterization of micromachined ultrasonic transducers using light diffraction tomography, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control,2005, 52 (12): 2298-2302