Light-induced actuating nanotransducers

Abstract

Nanoactuators and nanomachines have long been sought after, but key bottlenecks remain. Forces at submicrometer scales are weak and slow, control is hard to achieve, and power cannot be reliably supplied. Despite the increasing complexity of nanodevices such as DNA origami and molecular machines, rapid mechanical operations are not yet possible. Here, we bind temperature-responsive polymers to charged Au nanoparticles, storing elastic energy that can be rapidly released under light control for repeatable isotropic nanoactuation. Optically heating above a critical temperature Tc = 32 °C using plasmonic absorption of an incident laser causes the coatings to expel water and collapse within a microsecond to the nanoscale, millions of times faster than the base polymer. This triggers a controllable number of nanoparticles to tightly bind in clusters. Surprisingly, by cooling below Tc their strong van der Waals attraction is overcome as the polymer expands, exerting nanoscale forces of several nN. This large force depends on van der Waals attractions between Au cores being very large in the collapsed polymer state, setting up a tightly compressed polymer spring which can be triggered into the inflated state. Our insights lead toward rational design of diverse colloidal nanomachines.