Figure 2.
Retaining packed beads in microchannels. (A) Two-weir design, showing weir heights in relation to channel depth and particle size. Electroosmotic flow is driven by walls and by free silanol groups on particles. Solvent flow direction is indicated for a preconcentration step. (B) Two-side etching/alignment protocol. Two prefabricated plates were aligned and thermally bonded. On the right is a drawing of the cross section of a packed chip with its dimensions. (C) Photopolymerized frits retaining 3-µm-diameter beads. (D) The keystone effect. A suspension of particles is flowed toward the taper by vacuum. At the taper, the density of the particles increases, and these first particles act as “keystones”, blocking the others and allowing the packed segment to grow. Adapted and reproduced from Refs. 82–85, with permission from ACS and Wiley.