Acoustic Particle/Cell trapping

The Acoustic Trapping project is a collaboration with Uppsala University and the project is aimed at performing particle and cell trapping in a perfusion based microfluidic system. The technique will provide a platform for performing bioassays and cellassays in a non-contact way using ultrasonic standing waves. Each trapping site can be adressed separately through a fluidic network which enables on-line nanotitrations and multistep bioassays to be performed.

The trapping device consists of a PCB with miniaturised PZT-transducers, 600 x 600 µm cast in epoxy. Fluidic channels are etched in borosilicate glass and mounted on the PCB, creating fluidic channels passing over the transducers. when the transducers are activated, a standing wave forms between the transducer surfaces and the glass channel walls. In this standing waves, particles or cells will be trapped and can be retained while perfusing them with fluids suchs as analytes or cell media.

Trapped Cells

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.


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

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