Surfactant 0.05 tween 20

Polystyrene beads (PolySciences Inc., Warrington, PA) with the nominal mean diameter of 3, 6 and 10 μm (2.954 ± 0.052, 5.497 ± 0.168, and 9.977 ± 0.142 μm in exact size, respectively) and common baker's yeasts whose shape was spherical and diameter was about 5 μm were used as separation targets. Potassium chloride (KCl) aqueous solution was prepared with the purified water that was produced by passing it through an EASYpure water purification system (Thermo Fisher Scientific Inc., USA). Sample solutions were prepared by suspending particles in 1.16 M KCl aqueous solution or 0.155 M KCl solution with 20% urea (2.7 -4.2 × 10 6 particles mL -1 ), and supporting solutions consisted of 1.16 M KCl aqueous solution or 0.155 M KCl solution with 20% urea. The densities of the polystyrene particle and the solutions were kept almost equal in our experiments so that any influence of the gravitational force was neglected. A surfactant 0.05% Tween 20 (Sigma-Aldrich, Inc., St. Louis, MO) was added to solution to prevent non-specific adsorption both between particles and of particles on the microfluidic devise. The other regents were used as received.

Polystyrene (PS) beads with the nominal mean diameter of 3, 6 and 10 μm (2.954 ± 0.052, 5.497 ± 0.168, and 9.977 ± 0.142 μm in exact size, respectively), paper mulberry pollen (12 -13 μm) and ragweed pollen (19 -20 μm) were purchased from Polyscience, Inc. (Warrington, PA). Polypropylene (PP) beads were obtained from Seishin Enterprises Co., Ltd. (Tokyo, Japan). Potassium chloride (KCl) aqueous solution was prepared with the purified water that was produced by passing it through an EASYpure water purification system (Thermo Fisher Scientific Inc., Waltham, MA). Sample solutions were prepared by suspending particles in 1.16 M KCl aqueous solution or 0.116 M KCl solution with about 10 6 particles mL -1 for PS particles or the concentration that did not interfere with observation for PP particles and pollens, respectively. In the case of separation of PS and PP particles, a surfactant 0.05% Tween 20 (Sigma-Aldrich, Inc., St. Louis, MO) was added to the solution to prevent non-specific adsorption both between particles and of particles on the microfluidic device. The other reagents were used as received.