Abstract:
Microengines have shown promise for a variety of applications in nanotechnology, mi- crofluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics re- mains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the equilibrium point between optical and thermal forces. By using circularly polarized light, we can transfer angular momentum to the particle breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam, while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibili- ties for their utilization in a wide range of applications, encompassing microscale transport, sensing, and actuation.

Link to article at ACS Photonics:
https://pubs.acs.org/doi/10.1021/acsphotonics.3c00630