Liu Changhong, Mi Chunting Chris, Li Ben Q
Shanghai Jiao Tong University, Shanghai 200240 China.
IEEE Trans Nanobioscience. 2008 Sep;7(3):206-14. doi: 10.1109/TNB.2008.2002284.
The unique optical characteristics of a gold nanoshell motivate the application of nanoshell-based hyperthermia in drug delivery and cancer treatment. However, most of our understanding on energy absorption and heat transfer is still focused on individual particles, which may not be accurate for nanoshell aggregates in a real application due to the strong optical interaction of nanoshells. This paper investigates the relationship between the optical interaction and the interparticle distance in the visible and near-infrared regions by means of a finite-difference time-domain (FDTD) method. The objective is to explore the energy transportation mechanism, which is critical for hyperthermia therapy. From the numerical simulation results of different forms of nanoshell aggregates, including individual nanoshells, 1-D chains, 2-D arrays, and 3-D clusters, it was found that the interparticle distance plays a crucial role from the maximal absorption point of view. The interparticle distance affects both field enhancement and surface plasmon resonance position. The accurate prediction of energy absorption also helps the way nanoshells are populated in the tumor cell so as to prevent heat damage to healthy tissues in clinic applications. In the case of 3-D clusters, the laser energy decays exponentially along the wave propagation, and the penetration depth greatly depends on the interparticle distance. The closer the nanoshells are placed, the shorter the penetration depth is. The maximal total length for the laser penetration through the shell of gold nanoparticles is about a few hundred to several nanometers. The actual penetration depth primarily depends not only on the interparticle distance, but also on the size of the nanoshells as well as other factors. Since the absorption energy is concentrated on the surface clusters of nanoparticles, heat transfer mechanisms in metal-nanoparticles-based hyperthermia will differ from that in other hyperthermia. The information obtained from this paper will serve as a basis for further study of heat transfer in metal-nanoparticles-based hyperthermia.
金纳米壳独特的光学特性促使基于纳米壳的热疗在药物递送和癌症治疗中得到应用。然而，我们目前对能量吸收和热传递的大多数理解仍集中在单个粒子上，由于纳米壳之间强烈的光学相互作用，这对于实际应用中的纳米壳聚集体可能并不准确。本文采用时域有限差分（FDTD）方法研究了可见光和近红外区域内光学相互作用与粒子间距离的关系。目的是探索能量传输机制，这对热疗至关重要。从不同形式的纳米壳聚集体（包括单个纳米壳、一维链、二维阵列和三维簇）的数值模拟结果发现，从最大吸收的角度来看，粒子间距离起着关键作用。粒子间距离既影响场增强，也影响表面等离子体共振位置。能量吸收的准确预测也有助于了解纳米壳在肿瘤细胞中的分布方式，从而在临床应用中防止对健康组织造成热损伤。在三维簇的情况下，激光能量沿波传播方向呈指数衰减，穿透深度很大程度上取决于粒子间距离。纳米壳放置得越近，穿透深度越短。激光穿透金纳米颗粒壳层的最大总长度约为几百到几纳米。实际穿透深度不仅主要取决于粒子间距离，还取决于纳米壳的尺寸以及其他因素。由于吸收能量集中在纳米颗粒的表面簇上，基于金属纳米颗粒的热疗中的热传递机制将与其他热疗不同。本文获得的信息将为进一步研究基于金属纳米颗粒的热疗中的热传递提供依据。
