Today's ultrasound machines are a long way beyond just checking out babies in the womb--they're used to break up kidney stones, ease sore muscles and more. Now, with a new nanotube lens, they can also serve as an invisible sonic knife.
Though targeted ultrasound is useful, it can be unwieldy, with a relatively large focal area. Aim a beam of sound at a kidney stone and you'll likely hit the centimeter-sized object, but better precision--like hitting a cholesterol deposit in a blood vessel, or a specific clump of cancer cells--is hard to achieve. To improve matters, University of Michigan researchers turned to nanotubes and started with light instead of sound.
First Jay Guo and colleagues coated a specially designed optoacoustic lens, used to convert laser light into high-amplitude sound waves, with a layer of carbon nanotubes. The nanotubes absorb the laser light and grow warm as a result. The second layer was a rubbery synthetic material that expands when it gets warm. This serves as an amplifier. To produce the ultrasonic waves, Guo and his colleagues pulsed laser light through the 6-millimeter lens, which converted the optical energy into sonic energy. The graphene absorbed the laser's heat and the amplifier boosted the signal. The result were sound waves with a frequency 10,000 times the hearing capability of humans.
What's more, the waves were super-focused--the researchers controlled their target range from around 6 to 15 microns up to 300 to 400 μm.
Where other ultrasonic therapy uses heat to provide a stimulus, this one creates shockwaves that force pressure toward a target. Its superfine focus can blast away anything from blood clots to tumor growth--all non-invasively. In tests, Guo and colleagues detached a single cancer cell from an ovary and blasted a 150-micron hole in an artificial kidney stone. They say this type of ultra-precise ultrasound can be a new way to deliver drugs, fight cancer or even perform cosmetic surgery.
A paper describing their methods is published in Nature Scientific Reports. They plan to present their work at the upcoming SPIE Photonics West meeting in San Francisco.
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