Acoustic tweezers can position ti...(movement. The particle or cell will stop...)

If the sound comes from two parallel sound sources facing each other, the troughs form a line or series of lines. If the sound sources are at right angles to each other, the troughs form an evenly spaced set of rows and columns like a checkerboard. Here too, the particles are pushed until they reach the location where the sound is no longer moving.

The acoustic tweezers are manufactured by fabricating an interdigital transducer onto a piezoelectric chip surface. These transducers are the source of the sound. Next, using standard photolithography, microchannels are fabricated in which a small amount of liquid with the cells or particles can move around freely. These microchannels were bonded to the chip to create the area for particle movement.

To test their device, the researchers, who include Jinjie Shi, Daniel Ahmed and Sz-Chin Steven Lin, graduate students, engineering science and mechanics; Xiaole Mao, graduate student in bioengineering, and Aitan Lawit, undergraduate in engineering science and mechanics, used Dragon Green fluorescent polystyrene beads about 1.9 micrometers in diameter. They then used cows red blood cells and the single cell bacteria E. coli to test the acoustic tweezers.

"The results verify the versatility of our technique as the two groups of cells differ significantly in both shape (spherical beads vs. rod-shaped E. coli) and size," the researchers reported in a recent issue of Lab on a Chip. They note that the patterning performance is independent of the particle's electrical, magnetic and optical properties.

"Most cells or particles patterned in a few seconds," said Huang. "The energy used is very low and the acoustic tweezers should not damage cells at all. Because they have different properties, the acoustic tweezers could also separate live from dead cells, or different types of particles."

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