Light-driven nanodrones based on optical spin-orbit locking

我们能否设计出多功能的纳米物体，其典型尺寸为可见光的几个波长，只需用圆偏振的非聚焦光束照射，就能以纳米精度在三维液体中推进和操纵它们？在目前的项目中，我们将利用量身定制的等离子体纳米结构，即所谓的等离子体纳米马达，来开发这种能力。等离子体纳米马达被设计成具有强烈依赖于入射光子自旋的定向共振散射，类似于光学自旋轨道锁定。我们将采用一整套这样的等离子体纳米马达，放置在微小的透明固体支架上。通过它们的排列和驱动模式，可以实现所有必要的自由度，如向前向后，左右，上下，偏航，俯仰，最终还有滚转，这些自由度将完全控制和反馈稳定-非常类似于多功能宏观多旋翼无人机。反馈稳定将提供很大程度上抵消布朗运动的可能性，从而使纳米级精确驱动成为可能。我们的方法将提供一种通用的方法来控制波长大小的飞行器在液体环境中的运动——所谓的纳米无人机——它可以结合不同的功能，比如除了负责推进和转向的部分之外，还有一个探测部分。这为新型实验提供了基础，例如，在生命科学中，在表面或活细胞内进行调查和操作，或用于运输和处理附着在这种纳米无人机上的功能性货物。特别是，对所有自由度的纳米级精确控制将最终为进行扫描探针型实验提供平台，例如液固界面的尖端增强光谱或施加可控的局部力。

Can we devise multi-functional nano-objects with typical dimensions of a few wavelengths of visible light that can be propelled and steered in liquids in 3D with nanometer precision just by illuminating them with unfocused light beams of circular polarization? In the present project we will develop such capability by making use of tailor-made plasmonic nano-structures, so-called plasmonic nanomotors. Plasmonic nanomotors are designed to exhibit directional resonant scattering that depends strongly on the incident photon spin, similar as in optical spin-orbit locking. We will employ a whole set of such plasmonic nanomotors positioned on microscopic transparent solid supports. By means of their arrangement and actuation pattern it will be possible to implement all necessary degrees of freedom, like forward-backward, left-right, up-down, yaw, pitch, and eventually also roll, which shall be fully controlled and feedback-stabilized – much similar as in the versatile macroscopic multirotor drones. Feedback stabilization will provide the possibility to largely counter-act Brownian motion and thereby will enable nanometer-precise actuation. Our approach will provide a general method to control the movement of wavelength-sized vehicles in liquid environments – so-called nanodrones - that may combine different functionalities, such as a probing section in addition to a section responsible for propulsion and steering. This provides the basis for novel types of experiments, e.g. in the life sciences for investigations and manipulations at the surface or within living cells, or for the transport and processing of functional cargo attached to such nanodrones. In particular, nanometer-precise control of all degrees of freedom will finally provide a platform to perform scanning-probe-type experiments, e.g. tip-enhanced spectroscopy of liquid-solid interfaces or to exert controlled local forces.