Light hybrid micro/nano-robots: From propulsion to functional signals

Untethered motile micro/nanorobots (MNRs) that can operate in hard-to-reach small space and perform noninvasive tasks in cellular level hold bright future in healthcare, nanomanufacturing, biosensing, and environmental remediation. Light, as a flexible encoding method with tunable freedom of intensity, wavelength, polarization, and propagation direction, endows unique spatial-temporal precision and dexterity to the manipulation of MNRs. Meanwhile, light has been extensively investigated as functional signals in bioimaging, phototherapy, as well as photoelectrochemical reactions. The hybridization of light and other actuation method ushers in novel MNRs with broadened design space, improved controllability, and advanced functionality. In this review, the fundamental mechanisms of light-driven MNRs will be revisited. On top of it, light hybrid systems, coupling with magnetic, electric, chemical, or ultrasound field, will be reviewed, with light for propulsion or as functional signal. The rational hybridization of multiple stimulus in MNRs not only promises simple combination of two driving forces, but more importantly, motivates rethinking of light-driven MNRs for unprecedented applications.