Rotary nanomotors are man-made objects, about the size of a virus particle, that are able to spin like tiny propellers. The energy that drives this motion could come from chemical reactions in the solution where the motor is operated or from an external source, for example visible light. One vision for the far future is that such motors might be used as ultra small robots that could perform diverse operations. It might, for example, be possible to couple artificial nanomotors to biological molecules to study or influence their behavior or use them for delivering drugs to the body. A more realistic scenario for the near future might be to use artificial nanomotors as model systems for better understanding of mechanical motion at the nanoscale or for controlled experiments on single cells in a culture medium.
In their feature article in Advanced Functional Materials, Prof. Mikael Käll and Dr. Lei Shao from Chalmers University of Technology, Sweden, highlight recent investigations of how to use gold nanoparticles as efficient rotary nanomotors propelled by circularly polarized laser light. These particles are characterized by a particular optical phenomenon, a so-called surface plasmon resonance, which can be utilized to drive the particles to rotate at record speeds in liquids (2.5 million rpm in water). Moreover, the particles are easy to make, and they can also be used as ultrasensitive optical molecular sensors at the nanoscale. Käll and Shao discuss the driving mechanism, the rotation performance, the stochastic Brownian properties and the photothermal effects that are important for this field of research. They then discuss possible sensing applications, indicating their advantages and limitations, and they point out some open questions and possible future research directions that may improve the performance and extend the range of applications of the plasmonic rotary nanomotors. This paper is recognized as a "hot paper" and "highly cited paper" by Web of Science. Besides this work, interested readers are suggested to read other related works by the authors and their collaborators (see the links below).