Sci. Rep. 2, 989 (2012)

Credit: © 2012 NPG

Intense, focused ultrasound is highly demanded for many applications in biomedical therapy and ablation treatment. Today's ultrasound technology relies on low-frequency piezoelectric transducers and can produce focal spots that are typically >2 mm wide and >10 mm long. Now, Hyoung Won Baac and co-workers from the University of Michigan in the USA have demonstrated a way to generate intense, high-frequency (>15 MHz) focused ultrasound. Their optoacoustic source exploits a nanocomposite film made of multiwalled carbon nanotubes (CNTs) and an elastomeric polymer formed on a 6-mm-diameter concave lens. Thanks to the high optical absorption of the CNTs and the efficient energy-conversion process of the CNT–polymer composite, the CNT-coated lenses directly enable acoustic focusing and generate an optoacoustic pressure of over 50 MPa in a tight focal spot measuring 75 μm × 400 μm. The team observed strong shock effects and non-thermal pulsed cavitation when using the lens. They then applied the approach to fragment solid materials and single-cell surgery, thus proving it to be a flexible, controllable and precise tool for the ultrasonic therapy of cells, blood vessels and tissues.