Optofluidic control of the dispersion of nanoscale dumbbells

Previous research has shown that gold nanoparticles immersed in water in an optical vortex lattice formed by the perpendicular intersection of two standing light waves with a \pi/2 rad phase difference will experience enhanced dispersion that scales with the intensity of the incident laser. We show that flexible nanoscale dumbbells (created by attaching two such gold particles by means of a polymer chain) in the same field display different types of motion depending on the chain length and field intensity. We have not disregarded the secondary optical forces due to light scattering. The dumbbells may disperse, rotate or remain trapped. For some values of the parameters, the (enhanced) dispersion possesses a displacement distribution with exponential tails, making the motion anomalous, though Brownian.