Department of Physics, Chalmers University of Technology , S-412 96 Göteborg, Sweden.
School of Science and Technology, Örebro University , S-701 82 Örebro, Sweden.
ACS Nano. 2017 Oct 24;11(10):10053-10061. doi: 10.1021/acsnano.7b04302. Epub 2017 Sep 20.
Plasmonic gold nanorods are prime candidates for a variety of biomedical, spectroscopy, data storage, and sensing applications. It was recently shown that gold nanorods optically trapped by a focused circularly polarized laser beam can function as extremely efficient nanoscopic rotary motors. The system holds promise for applications ranging from nanofluidic flow control and nanorobotics to biomolecular actuation and analysis. However, to fully exploit this potential, one needs to be able to control and understand heating effects associated with laser trapping. We investigated photothermal heating of individual rotating gold nanorods by simultaneously probing their localized surface plasmon resonance spectrum and rotational Brownian dynamics over extended periods of time. The data reveal an extremely slow nanoparticle reshaping process, involving migration of the order of a few hundred atoms per minute, for moderate laser powers and a trapping wavelength close to plasmon resonance. The plasmon spectroscopy and Brownian analysis allows for separate temperature estimates based on the refractive index and the viscosity of the water surrounding a trapped nanorod. We show that both measurements yield similar effective temperatures, which correspond to the actual temperature at a distance of the order 10-15 nm from the particle surface. Our results shed light on photothermal processes on the nanoscale and will be useful in evaluating the applicability and performance of nanorod motors and optically heated nanoparticles for a variety of applications.
等离子体金纳米棒是各种生物医学、光谱学、数据存储和传感应用的首选候选材料。最近有人指出，被聚焦的圆偏振激光束光学捕获的金纳米棒可以作为非常高效的纳米级旋转马达。该系统有望应用于从纳米流体流动控制和纳米机器人技术到生物分子驱动和分析等各个领域。然而，为了充分利用这一潜力，人们需要能够控制和理解与激光捕获相关的加热效应。我们通过同时探测单个旋转金纳米棒的局域表面等离子体共振光谱和旋转布朗动力学，研究了它们的光热加热。实验数据揭示了一种非常缓慢的纳米颗粒重塑过程，涉及到每分钟数百个原子的迁移，对于中等激光功率和接近等离子体共振的捕获波长。等离子体光谱学和布朗分析允许根据周围水的折射率和粘度进行单独的温度估计，这些温度估计基于被捕获的纳米棒。我们表明，这两种测量方法都得到了相似的有效温度，这些有效温度对应于距离粒子表面约 10-15nm 处的实际温度。我们的研究结果阐明了纳米尺度上的光热过程，对于评估纳米棒马达和光热加热纳米颗粒在各种应用中的适用性和性能将非常有用。
