High speed laser manipulation of on-chip fabricated microstructures by replacing solution inside microfluidic channel

The on-chip fabrication and manipulation of microstructures are expected to be applied for single cell analysis system such as cell manipulation and measurement tools. In this paper, we previously present a methodology for fabricating and assembling microstructures inside a microfluidic channel. By the illumination of patterned UV-ray through the mask under a microscope, microstructures with arbitrary shape are made of the photo-crosslinkable resin inside microfluidic device. The microstructures are fabricated at the desired place inside microfluidic channel and manipulated by optical tweezers. Based on the technique which can manipulate multiple points simultaneously by high-speed scanning of a single laser with galvanometer mirror, a rotational microstructure made of a microgear and a rotation axis is assembled and rotated. We also report two methods of solution replacement inside microfluidic channel which reduces viscosity of solvent in order to improve manipulation performance. By adjusting the concentration of photo-crosslinkable resin and replacing solution components, the viscosity of solvent inside channel can be changed. The manipulation speed of the rotational microstructure increases when the viscosity of solvent decreases, because the viscosity resistance for the movement of microstructure is weaker inside lower viscosity solvent. We fabricate rotational microstructures inside lower viscosity solvent and evaluate the movement efficiency compared with microstructures inside former high viscosity solvent.