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Plasmonic antennas are well-known and extremely powerful platforms for optical spectroscopy, sensing, and manipulation of molecules and nanoparticles. However, resistive antenna losses, resulting in highly localized photothermal heat generation, may significantly compromise their applicability. Here we investigate how the interplay between plasmon-enhanced optical and thermal forces affects the dynamics of nanocolloids diffusing in close proximity to gold bowtie nanoantennas. The study is based on an anti-Stokes thermometry technique that can measure the internal antenna temperature with an accuracy of ∼5 K over an extended temperature range. We argue that Kapitza resistances have a significant impact on the local thermal landscape, causing an interface temperature discontinuity of up to ∼20% of the total photothermal temperature increase of the antenna studied. We then use the bowties as plasmonic optical tweezers and quantify how the antenna temperature influences the motion and distribution of nearby fluorescent colloids. We find that colloidal particle motion within the plasmonic trap is primarily dictated by a competition between enhanced optical forces and enhanced heating, resulting in a surprising insensitivity to the specific resonance properties of the antenna. Furthermore, we find that thermophoretic forces inhibit diffusion of particles toward the antenna and drive the formation of a thermal depletion shell that extends several microns. The study highlights the importance of thermal management at the nanoscale and points to both neglected problems and new opportunities associated with plasmonic photothermal effects in the context of nanoscale manipulation and analysis.

The prospect of self-propelled artificial machines small enough to navigate within biological matter has fascinated and inspired researchers and the public alike since the dawn of nanotechnology. Despite many obstacles toward the realization of such devices, impressive progress on the development of its basic building block, the nanomotor, has been made over the past decade. Here, we review this emerging area with a focus on inorganic nanomotors driven or activated by light. We outline the distinct challenges and opportunities that differentiate nanomotors from micromotors based on a discussion of how stochastic forces influence the active motion of small particles. We introduce the relevant light–matter interactions and discuss how these can be utilized to classify nanomotors into three broad classes: nanomotors driven by optical momentum transfer, photothermal heating, and photocatalysis, respectively. On the basis of this classification, we then summarize and discuss the diverse body of nanomotor literature. We finally give a brief outlook on future challenges and possibilities in this rapidly evolving research area.

Nanostructured dielectric metasurfaces offer unprecedented opportunities to manipulate light by imprinting an arbitrary phase-gradient on an impinging wavefront. 1 This has resulted in the realization of a range of flat analogs to classical optical components like lenses, waveplates and axicons. 2-6 However, the change in linear and angular optical momentum 7 associated with phase manipulation also results in previously unexploited forces acting on the metasurface itself. Here, we show that these optomechanical effects can be utilized to construct optical metavehicles -microscopic particles that can travel long distances under low-power plane-wave illumination while being steered through the polarization of the incident light. We demonstrate movement in complex patterns, self-correcting motion, and an application as transport vehicles for microscopic cargo, including unicellular organisms. The abundance of possible optical metasurfaces attests to the prospect of developing a wide variety of metavehicles with specialized functional behavior.One of the most distinguishing features of optical metasurfaces is their ability to simultaneously manipulate a wave's propagation direction and polarization despite being sub-wavelength in thickness. This results in an exchange of linear and angular momentum between light and matter and, by virtue of Newton's third law, optical forces and torques acting on the metasurface. Two main challenges need to be overcome in order to exploit this phenomenon for the practical realization of microparticles capable of movement and steering in a plane-wave light field (Figure 1). First, the microparticle should contain a metasurface that efficiently bends light towards a