Manipulation of deformable particles in optical and flow fields

光镊在许多物理领域无处不在，应用范围从单分子生物物理学到复杂结构和机器的纳米组装。在光镊中，聚焦的激光束用于施加和测量皮科到纳牛顿范围内的力。产生的光学力的大小和方向取决于激光束的形状和颗粒的几何形状，近年来已经开发了几种技术来评估这些。非保守运动是光镊中感兴趣的一个领域，其起因于存在通过系统的光动量流的事实，并且捕获起因于动力学力的平衡。这导致了最近对新行为的观察，例如光学翼[1]。光镊与微流控器件的耦合开辟了一系列新的可能性;流体和光动量的结合预示着许多新的应用，包括新的力转换机制，光学分选技术和光学驱动的微机械。微流体装置通常用于涉及在流体中运输细胞的芯片实验室类型的应用中。例如，红细胞相对柔韧，当它们通过血管和其他狭窄通道运输时会变形。它们也可以用光学镊子变形，这可能构成医疗诊断设备的基础[2]。除了光学拉伸器的特殊情况外，还没有对被光学捕获时变形的粒子进行过分析研究[3]。成形光场与流场中可变形可捕获颗粒的组合开辟了新应用的有趣可能性，并提供了研究光-物质相互作用的基本方面的机会，包括著名的Abraham-Minkowski争议[4]。这个博士项目的目的是开发计算模型，用于计算流场中不规则和可变形颗粒的捕获行为，并将这些应用于流场中细胞、胶束和更刚性的非球形结构的捕获。它将建立在该小组以前的工作基础上，特别是将离散偶极近似用于轻物质相互作用[5]与布朗动力学模拟相结合，以捕获流体动力学行为。该项目将利用最新的计算技术，作为布里斯托大学超级计算机蓝水晶的一部分。将有机会与经验主义者合作，并进行实验工作，探索模型的预测。[1]小斯沃茨兰德GA等人，Nature Photonics 5：48-51（2011）. [2]Agrawal R，et al.，科学报告6：15873（2016）。[3]Guck，J等人，Biophys. J.，81：767-784（2001）。[4]Pfeifer，RNC，等人，现代物理学评论。79：1197-1216（2007）。[5]Simpson，SH等，Optics Express，19：16526-16541（2011）。

Optical tweezers are ubiquitous in many fields of physics, with applications ranging from single molecule biophysics to nano-assembly of complex structures and machines. In optical tweezers, focussed laser beams are used to apply and measure forces in the pico- to nano-Newton range. The magnitude and direction of the optical forces generated depend on the laser beam shape and particle geometry, and several techniques have been developed in recent years for evaluating these. Non-conservative motion is an area of interest in optical tweezers, which arises from the fact that there is a flow of optical momentum through the system and trapping arises from a balance of dynamical forces. This has led to recent observations of novel behaviour such as the optical wing [1]. The coupling of optical tweezers with microfluidic devices opens up a range of novel possibilities; the combination of fluid and optical momentum should herald many new applications including novel force transduction mechanisms, optical sorting techniques and optically-driven micro-machines.The introduction of deformable particles introduces further degrees of freedom, and hence of control, to the system. Microfluidic devices are often used in lab-on-a-chip type applications involving the transport of cells in a fluid. Red blood cells, for example, are relatively flexible and deform as they are transported through blood vessels and other narrow channels. They may also be deformed with optical tweezers, and this may form the basis of a medical diagnostic device [2]. Particles which deform while being optically trapped have not been studied analytically, except in the special case of the optical stretcher [3]. The combination of shaped optical fields with deformable trappable particles in a flow field opens up intriguing possibilities of new applications, as well as providing opportunities to study fundamental aspects of the light-matter interaction, including the well-known Abraham-Minkowski controversy [4].The aim of this PhD project will be to develop computational models for calculating the trapping behaviour of irregular and deformable particles in flow fields, and apply these to the trapping of cells, micelles and more rigid non-spherical structures in flow fields. It will build on previous work in the group, in particular combining use of the discrete dipole approximation for light-matter interactions [5] with Brownian dynamics simulations to capture the hydrodynamic behaviour. The project will exploit the latest computing technology available as part of the Bristol University super-computer, BlueCrystal. There will be opportunities both to collaborate with experi-mentalists, and to undertake experimental work, to explore the predictions of the models.[1] Swartzlander Jr., GA, et al., Nature Photonics 5: 48-51 (2011).[2] Agrawal R, et al., Scientific Reports 6: 15873 (2016).[3] Guck, J, et al., Biophys. J., 81: 767-784 (2001).[4] Pfeifer, RNC, et al., Reviews of Modern Physics. 79: 1197-1216 (2007).[5] Simpson, SH, et al., Optics Express, 19:16526-16541 (2011).