Light Sci. Appl. 7, 105 (2018)

Recent simulations predict that dissimilar particle dimers can experience a net force that is transverse to the direction of the illuminating light and may be exploited for optically driven nanomotor applications. Now, Yuval Yifat and colleagues in Chicago have directly confirmed the effect and have measured the net forces in asymmetric nanoparticle dimers excited by plane waves. A continuous-wave Ti:sapphire laser (790 nm wavelength) illuminated a mixture of ~150-nm-diameter and ~180-nm-diameter Ag nanoparticles in a 3.4-μm-radius optical ring-trap and the positions of the particles were tracked. Both homodimer and heterodimer pairs were investigated. The anticipated optically driven motion was confirmed for heterodimers that were sufficiently close for optical coupling to occur (separations less than 1.2 μm) and is attributed to an asymmetric scattering pattern. The team hopes that asymmetric nanoparticle assemblies can actually be used as active colloids and optically driven ‘nanoswimmers’ that may be useful in soft condensed-matter and biophysics research.