A microfluidic device for stepwise size-based capturing of suspended particles

In this paper, we report a new method for size-based capturing of suspended particles by a specially designed micro fluidic structure named 'vernier walls'. A number of particles in suspension can be captured based on their sizes by a series of gaps between the closest walls, one standing on the ceiling and the other on the bottom of a wide microfluidic channel. The dimensions of the gaps narrow stepwise along the flow direction with a fixed step size per gap, which can be determined according to the required capturing resolution. Particles are captured based on their sizes in a line along each of the gaps with their corresponding dimensions. A part of the wide channel works as a bypass area, where the gap is constant to avoid clogging, letting the excess number of particles go through the channel. To realize the proposed structure, a new device assembly method has also been developed adopting planar gear-shaped structures surrounding the microfluidic channel solely for the fine and easy alignment of the narrowing gaps. The performance of the present method was evaluated using a device designed and fabricated for size-based capturing with a 5 mu m resolution, and it was demonstrated that three kinds of particles with diameters from 10 to 26 mu m were successfully captured by size. Additionally, we confirmed that the capturing rate was no less than 20% under the experimental condition. The present method can be used as a basic tool for handling particles with certain ranges of sizes.