Noble metal nanoparticles illuminated at their plasmonic resonance wavelength turn into heat nanosources. This phenomenon has prompted the development of numerous applications in science and technology. Simultaneous optical manipulation of such resonant nanoparticles could certainly extend the functionality and potential applications of optothermal tools. In this article, we experimentally demonstrate optical transport of single and multiple resonant nanoparticles (colloidal gold spheres of radius 200 nm) directed by tailored transverse phase-gradient forces propelling them around a 2D optical trap. We show how the phase-gradient force can be designed to efficiently change the speed of the nanoparticles. We have found that multiple hot nanoparticles assemble in the form of a quasi-stable group whose motion around the laser trap is also controlled by such optical propulsion forces. This assembly experiences a significant increase in the local temperature, which creates an optothermal convective fluid flow dragging tracer particles into the assembly. Thus, the created assembly is a moving heat source controlled by the propulsion force, enabling indirect control of fluid flows as a micro-optofluidic tool. The existence of these flows, probably caused by the temperature-induced Marangoni effect at the liquid water/superheated water interface, is confirmed by tracking free tracer particles migrating towards the assembly. We propose a straightforward method to control the assembly size, and therefore its temperature, by using a nonuniform optical propelling force that induces the splitting or merging of the group of nanoparticles. We envision further development of microscale optofluidic tools based on these achievements.

在等离子共振波长照射的贵金属纳米颗粒变成热纳米源。这种现象促使科学技术领域的众多应用得以发展。此类共振纳米粒子的同时光学操作当然可以扩展光热工具的功能和潜在应用。在本文中，我们通过实验证明了单个和多个共振纳米粒子（半径为200 nm的胶体金球）的光学传输，这些纳米粒子是由量身定制的横向相位梯度力推动它们围绕2D光学阱捕获的。我们展示了如何设计相梯度力来有效地改变纳米颗粒的速度。我们已经发现，多个热纳米颗粒以准稳定基团的形式组装，其围绕激光阱的运动也受到这种光学推进力的控制。该组件的局部温度显着升高，这会产生光热对流流体流，将示踪剂颗粒拖入组件。因此，所产生的组件是受推进力控制的移动热源，从而能够作为微光流体工具间接控制流体的流动。这些流动的存在，可能是由液态水/过热水界面处的温度引起的马兰戈尼效应引起的，可通过追踪向组件中迁移的游离示踪剂颗粒来确认。我们提出了一种简单的方法来控制组件的尺寸，从而控制其温度，通过使用不均匀的光学推动力，该力会引起纳米颗粒组的分裂或合并。我们基于这些成就，设想进一步开发微型光流体工具。