Particle sorting by optical radiation pressure with low energy density

This paper presents the development of a microfluidic device for particle sorting using optical radiation pressure with low energy density. The need for efficient particle manipulation in the microchannel has led to the recent development of a couple of advanced techniques of particle manipulation. An optical approach to sort particles in a microchannel by the optical radiation pressure can provide non-contact and remote handling technique of manipulating the particles. We utilized a two-dimensionally focused laser beam, namely light sheet, for a light source to enable the optical-based particle sorting with low energy density leading less damage to the sample and device. A microfluidic device in this study consisted of the channel structure made of SU-8 between silicon substrate and PDMS lid. Since SU-8 has higher refractive index than other materials, the total reflection of the optical wave occurs to serve the channel walls as a waveguide leading the 2D focused laser beam with less scattering. Particle migration to the direction of light propagation was verified without any damage in the chip under an irradiation of a 2 W laser beam, which had enough strong power to damage the polymer chip using a spot, namely 3D focused beam. Reasonable agreement of our experimental results with theoretical prediction was also confirmed