Sorting, trapping, and shifting of microparticles with stagnation point flow on an optofluidic chip

This paper proposes an optofluidic chip for highly efficient and multipurpose microparticle manipulation including sorting, trapping, and shifting. The operating principles are based on the different optical forces exerted on the microparticles by controllable optical and fluidic conditions. The microparticles are confined by hydrodynamic focusing and conveyed to the optical active region, where the particles are slowed down by stagnation flow. Low velocity extends the acting time, allowing high-efficiency optical sorting by a laser of 500 mW power. Numerical simulations are utilized to optimize the fluidic conditions. Experiments have demonstrated the sorting of polystyrene particles with a diameter of 3.2 µm from those of 1.1 µm. In addition, we have realized the trapping of a single 3.2 µm particle with adjustable equilibrium positions. Velocity variation of the microparticles has been analyzed during the manipulation process. The proposed design presents an alternative to provide desirable sorting performance, target selectivity, throughput, and versatility of an integrated device in biomedical applications.