Plasmonic Nanomachines: Creating Local Potential Gradients and Motions.

Humanity has developed a wide range of physical machines engineered to perform work for specific purposes while emphasizing controllability and upscaling. Recently, a growing aspiration has emerged to construct minuscule mechanical systems, often enabled by a microscopic, bottom-up understanding of nature. As biological systems inherently function at sub-micrometer scales, artificial nanoscale machines have attracted increasing attention as a route to achieve nature-like synthetic and functional precision. Among the possible strategies to activate and drive such systems, light stands out as a highly efficient and versatile energy source that can interact strongly with plasmonic nanomaterials. Owing to strong optical responses, efficient photothermal conversion, and catalytic activity, plasmonic nanostructures can transduce light energy into spatially confined optical, thermal, and chemical gradients, which in turn generate nanoscale mechanical motions. This Perspective highlights the designing principles for these plasmonic nanomachines and fundamental physics behind plasmonically driven force generation and motion, while focusing on approaches that localize energy inputs via material integration. We further explore how energetic and geometric asymmetries provide directional forces that enable translational and rotational motions, guiding movement along targeted trajectories. This framework lays a foundation for advancing autonomous, optically addressable plasmonic nanomachines, overcoming key challenges and opening avenues for nanomachinery and nanorobotics.