基于片上高频超声辐射力系统的纳米颗粒操控研究

Periodic nano-structure plays a crucial role for the field of biosensor, and it can be used to observe the interaction of protein, polypeptide and cell because of special optical property of plasma resonance. And this material can be fabricated by the method of patterning and manipulation of nano-particles. Ultrasound, a carrier of energy, has radiation force on the particles in acoustic field. However, acoustic radiation force is closely related to the size of particle, thus the nano-particles are difficult to be controlled as a sharp decrease in acoustic radiation force. This project proposes to manipulate nano-particles by high-frequency (200 MHz) and micro-scale ultrasound device, explores the mechanism of nano-particle manipulation and investigates the acoustic radiation forces on nano-particles with complex structures. First of all, the simulation model of nano-particle structure and equivalent acoustic impedance was established which is based on the physical properties of nano-particle such as the density and acoustic velocity. Secondly, the algorithm of particle image velocimetry is used to calculate the movement of the nanoparticles to quantify the acoustic radiation force. Then the theoretical relationship between acoustic impedance and acoustic radiation force is investigated. Finally, periodic nano-material can be achieve by precise movement and periodic patterning of nanoparticles through the optimization of acoustic parameters (phase, frequency, amplitude). This project provides theoretical evidence for manipulation of nano-particles by ultrasound and develop a new method for the assembly, processing and development of periodic nano-materials.

周期性纳米结构具有等离子共振的特殊光学性质，可以实时观测蛋白质、多肽，甚至细胞间相互作用，在生物传感技术领域具有重大需求。因此通过对纳米颗粒排列、操控等操作实现周期性纳米材料制备具有重要意义。超声波携带有能量，会对声场中微粒产生辐射力的作用，辐射力的大小与粒径密切相关，对于纳米颗粒，声辐射力大幅下降，声波操控困难。本项目围绕高频（200 MHz）微尺度超声芯片操控纳米颗粒展开，理解纳米颗粒操控物理机制，探索复杂结构纳米颗粒在声场中受力特性。首先依据复杂结构纳米颗粒密度、声速等特性，建立纳米颗粒结构与等效声阻抗仿真模型。其次通过粒子图像测速算法表征纳米颗粒声场中的运动，量化其受到的超声辐射力，建立声阻抗与辐射力之间关系模型。最终利用可调制声场实现纳米颗粒精确移动和周期性排列，得到周期性纳米材料。本项目为超声操控纳米颗粒提供理论依据，为周期性纳米材料的组装与加工、新材料的研发提供了一种新方法。

纳米颗粒的排列和操控在纳米材料制备、分子工程、光子学、癌症的诊断和治疗、靶向药物递送方面具有重要意义。基于声辐射力的微粒子操纵由于具有无标记、高通量、穿透深度高等优点，受到越来越多的关注。然而，由于声辐射力与粒子的体积成正比，因此很难对纳米粒子进行操纵。并且，由于布朗运动的存在进一步提高了纳米颗粒操控的难度。在本项目中，我们利用高频声表面波芯片实现了对具有中空结构的金纳米笼颗粒的操控。理论和实验验证得到纳米颗粒的中空结构提高了其对超声辐射力的敏感性。基于声波干涉形成的复杂声场实现了对纳米金笼多尺度的排列。并且，基于相位调控技术实现纳米金笼任意轨迹的移动。结合纳米金笼的光热效应，激光照射可在微米范围内实现选择性温度升高，从而实现纳米颗粒排列区域内癌症细胞的选择性杀伤。另一方面本项目基于微流控装置，设计了具有均一粒径的微泡结构，基于稳态空化效应产生的辐射力实现了纳米颗粒的分选。最终，本项目提出一种基于圆柱壳层结构的声镊技术，用于捕获半径仅为波长400分之一的微粒，其捕获能力远高于驻波。其主要机制由于圆柱壳层结构的低频圆周波模式在结构表面形成了高度局域的声场，显著提高了超声辐射力，有望应用到纳米颗粒的操控中。