Long-range and rapid trapping of nanoobjects via a combined optical-force and photothermal-convection effect

Optical tweezer is an important technique for capturing and manipulating micro and nano particles, with the advantages of non-contact and flexibility. However, optical force is a short-range force with a limited capture range and slow capture speed, making it unable to meet the demands for fast and large-range capture of micro and nano particles. In this article, a method called optical-force and photothermal-convection induced long-range and rapid trapping (OFPC-LRRT) is proposed for a long-range and fast capture of micro and nano particles in water environment. The method combines the advantages of optical force and the traction force generated by photothermal convection, and can quickly capture micro and nano particles at a speed of ∼300 μm/s within a large range (up to ∼30 μm) in solution on glass substrate. After the optical force captures gold nanoparticles, local heating creates bubbles, which causes a large-range fluid convection in the solution, and thus allows micro and nano particles to be transported along the streamlines to the region of focused laser spot. This method has the advantages of flexible operation and not being limited by the substrate, as well as the advantages of long-distance and high-efficiency capture via photothermal convection. It can be used for a wide range of applications such as cleaning micro and nano cavities, capturing micro and nano particles, and fabricating micro and nano structures.