Simple applications of microparticle transportation by tender optical scattering force

Hideharu Kotari, Masahiro Motosuke

This paper provides a novel application of the optical radiation pressure for microfluidic particle transportation without precise focusing or alignment of the laser beam to the device and target. An optical manipulation of particles in a microfluidic platform is highly exploited in life science or biomedical analysis using optical tweezers with the use of a gradient force of the optical radiation pressure. Our method utilizes the other term of the radiation pressure, namely scattering force, to manipulate particles in a microchannel. The migration distance of particle depends on the amount of light received by the particle. Therefore, particle movement with long retention distance can be achieved by large-area irradiation even with low energy density. In our experiments, two proof-of-concept microfluidic chips were designed and investigated; one was a lateral particle sorting using a monolithic microfluidic chip integrated with a planar SU-8 waveguide and beam expander, the other was a vertical sorting using a 10-cm-long polydimethylsiloxane channel with whole-area irradiation. Experimental results show that 1, 2 and 5 μm polystyrene beads can be transported by the optical scattering force and that particle migration is achieved with the irradiated energy density <10 mW/mm2. The present method has practical potential for simple and fuss-free use of the optical radiation pressure without spot focusing or precise alignment process of the laser beam and damage to the device and sample.

DOI