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Acoustic tweezers are useful in biology experiments

One of the biggest challenges in moving tiny objects like single cells is moving them accurately without damaging the living cell. Techniques that work for moving tiny beads or other objects involve optical tweezers, but this method could kill live cells.

Optical tweezers on the other hand are large and expensive devices. Researchers at Penn State, however, have developed acoustic tweezers that are smaller than a dime and can be fabricated onto a chip using standard chip making techniques.

The acoustic tweezers can be used to position many tiny objects like cells simultaneously. The objects are placed equidistant from each other either in parallel lines or on a grid. The most useful method for biological applications would be the grid configuration. The researchers say scientists could use this configuration to place stem cells on a grid for testing or to place skin cells on a grid to grow new skin.

"Current methods for moving individual cells or tiny beads include such devices as optical tweezers, which require a lot of energy and could damage or even kill live cells," said Tony Jun Huang, assistant professor of engineering science and mechanics. "Acoustic tweezers are much smaller than optical tweezers and use 500,000 times less energy."

He continued saying, "Acoustic tweezers are not just useful in biology. They can be used in physics, chemistry, and materials science to create patterns of nanoparticles for coatings or to etch surfaces."

The acoustic tweezers work by creating a standing surface acoustic wave. If the two acoustic sound sources are aimed at each other, a series of lines is formed where objects align. If aimed at right angles to each other a line or series of lines are formed creating a checkerboard effect. The tweezers are made by fabricating an interdigital transducer onto a piezoelectric chip surface. These transducers are the source of the sound. The researchers tested the acoustic tweezers using cow red blood cells and a single E. coli bacteria cell.

"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," Noted the researchers.

"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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Interdigital Transducer (IDT)
By EEeng on 9/1/2009 5:34:07 PM , Rating: 2

These is surface acoustic wave (SAW) device and an IDT is the standard means of excitation on a piezoelectric substrate. There are something like 19 of these devices in an average cellular phone and they used to perform filtering and signal processing by constructive and destructive mechanical interference. Basically the material stretches or compresses in the presence of an electric field. Staggered capacitive "fingers" with correct dimensions create a Rayleigh wave(similar to displacements in an earthquake) at the surface of the material. Think of extremely tiny earthquake wave crests pushing relatively massive cells around on a plate.

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