H.W. Baac, J.G. Ok, A. Maxwell, K.T. Lee, Y.C. Chen, A.J. Hart, Z. Xu, E. Yoon, L.J. Guo. Carbon nanotube optoacoustic lens for focused ultrasound generation and high-precision targeted therapy. Scientific Reports 2:989, 2012. [http://dx.doi.org/10.1038/srep00989]
We demonstrate a new optical approach to generate high-frequency (>15 MHz) and high-amplitude focused ultrasound, which can be used for non-invasive ultrasound therapy. A nano-composite film of carbon nanotubes (CNTs) and elastomeric polymer is formed on concave lenses, and used as an efficient optoacoustic source due to the high optical absorption of the CNTs and rapid heat transfer to the polymer upon excitation by pulsed laser irradiation. The CNT-coated lenses can generate unprecedented optoacoustic pressures of >50 MPa in peak positive on a tight focal spot of 75 um in lateral and 400 um in axial widths. This pressure amplitude is remarkably high in this frequency regime, producing pronounced shock effects and non-thermal pulsed cavitation at the focal zone. We demonstrate that the optoacoustic lens can be used for micro-scale ultrasonic fragmentation of solid materials and a single-cell surgery in terms of removing the cells from substrates and neighboring cells.