X-rays can propel and visualize colloids

Abstract

Light-powered wireless manipulation of small objects in fluids has been of interest for biomedical and environmental applications. Although many clever techniques employing UV-Vis-NIR light have been devised, new methods that hold greater penetrating power deep into medium are still in demand. Here, we report on a method that exploits hard X-rays to propel half-metal coated Janus microparticles in aqueous environment. Using a full-field transmission X-ray microscope (TXM), we simultaneously trigger and visualize the propulsive motion of the Janus particles. Our real-time observation discovers that the propulsive motion follows bubble growth by radiolysis of water on the particle under X-ray irradiation. Furthermore, the dependence of propulsion speed on radiation dose enables manipulation of the particles by instant variation of X-ray pulses. This work could suggest interesting approaches to operate micro/nanoswimmers under whole-body medical imaging.