Light-Activated Micromotors in Air Propelled by Thermal Convection

Micromotors are an attractive cutting-edge technology that exhibit controllable motion in response to chemical reactions or external stimuli. These nature-inspired materials are widely explored for use in environmental remediation, and drug delivery, other emerging applications. Until now, the micromotors field is restricted to applications in aqueous environments, as achieving controllable motion in air while overcoming gravity remains a significant challenge. Herein, for the first time, to our knowledge, we introduce a system capable of overcoming gravity to achieve light-induced thermal convective motion in air, driven by near-infrared light excitation. The micromotors are composed of spiky, pollen-like ZnO microparticles coated with gold nanoparticles, which interact photothermally with the NIR light, generating a thermal gradient that induces propulsion of the micromotor system. Lanthanide-doped upconverting nanoparticles are deposited onto the micromotor surface to enable nanothermometric monitoring of surface temperature, providing critical information needed to describe the system's thermal behavior in air. This micromotor platform provides a versatile approach to overcome gravity and induce a controllable movement in a gaseous matrix, opening new opportunities to develop proof-of-concepts and applications using this aerodynamic micromotor approach.