Control of diffusion of nanoparticles in an optical vortex lattice

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 π/2rad 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.

Nanometer-precision linear sorting with synchronized optofluidic dual barriers

The past two decades have witnessed the revolutionary development of optical trapping of nanoparticles, most of which deal with trapping stiffness larger than 10^-8 N/m. In this conventional regime, however, it remains a formidable challenge to sort out sub-50-nm nanoparticles with single-nanometer precision, isolating us from a rich flatland with advanced applications of micromanipulation. With an insightfully established roadmap of damping, the synchronization between optical force and flow drag force can be coordinated to attempt the loosely overdamped realm (stiffness, 10^-10 to 10^-8 N/m), which has been challenging. This paper intuitively demonstrates the remarkable functionality to sort out single gold nanoparticles with radii ranging from 30 to 50 nm, as well as 100- and 150-nm polystyrene nanoparticles, with single nanometer precision. The quasi-Bessel optical profile and the loosely overdamped potential wells in the microchannel enable those aforementioned nanoparticles to be separated, positioned, and microscopically oscillated. This work reveals an unprecedentedly meaningful damping scenario that enriches our fundamental understanding of particle kinetics in intriguing optical systems, and offers new opportunities for tumor targeting, intracellular imaging, and sorting small particles such as viruses and DNA.