Wang Hanwei, Chen Yun-Sheng, Zhao Yang
Department of Electrical and Computer Engineering, University of Illinois Urbana-Champaign, Urbana, IL, USA.
Micro and Nanotechnology Laboratory, University of Illinois Urbana-Champaign, Urbana, IL, USA.
Photoacoustics. 2022 Nov 14;28:100425. doi: 10.1016/j.pacs.2022.100425. eCollection 2022 Dec.
Understanding the mechanism of photoacoustic generation at the nanoscale is key to developing more efficient photoacoustic devices and agents. Unlike the far-field photoacoustic effect that has been well employed in imaging, the near-field profile leads to a complex wave-tissue interaction but is understudied. Here we show that the spatiotemporal profile of the near-field photoacoustic waves can be shaped by laser pulses, anisotropy, and the spatial arrangement of nanostructure(s). Using a gold nanorod as an example, we discovered that the near-field photoacoustic amplitude in the short axis is ∼75 % stronger than the long axis, and the anisotropic spatial distribution converges to an isotropic spherical wave at ∼50 nm away from the nanorod's surface. We further extend the model to asymmetric gold nanostructures by arranging isotropic nanoparticles anisotropically with broken symmetry to achieve a precisely controlled near-field photoacoustic "focus" largely within an acoustic wavelength.
了解纳米尺度下光声产生的机制是开发更高效光声设备和试剂的关键。与已在成像中得到充分应用的远场光声效应不同，近场分布会导致复杂的波 - 组织相互作用，但目前研究较少。在此我们表明，近场光声波的时空分布可由激光脉冲、各向异性以及纳米结构的空间排列来塑造。以金纳米棒为例，我们发现短轴方向的近场光声振幅比长轴方向强约75%，并且各向异性的空间分布在距纳米棒表面约50纳米处收敛为各向同性的球面波。我们通过将各向同性纳米颗粒以破缺对称性的方式进行各向异性排列，进一步将该模型扩展到不对称金纳米结构，从而在很大程度上在一个声波波长范围内实现精确控制的近场光声“焦点”。
