Several microfluidic platforms incorporating cavities and channels have been designed and fabricated in silicon and fused silica. C4F8 and SF6 plasmas are used to etch reproducibly 400 μm features in silicon and 150 μm in fused silica. Hydrophilic surface characteristics allow capillary action without external pumping or electro-osmosis. Filling of poled cavities can be triggered by increasing temperature i.e. by tuning hydrophobicity of a channel. The pole structure can also be used for sieving particles of different size or elasticity. In this work, agarose beads trapped by poles were used for solid phase extraction. By covering the microfluidic features, filling is also achieved by cooling the substrate. Filling velocities of aqueous solutions have been observed to depend strongly on liquid composition, but also final treatment and roughness of silicon or silica surface. Mixing of two aqueous solutions can also be triggered by increasing temperature. Cavities with pre-immobilised substance can be filled simultaneously or, if necessary, sequentially. Various non-leaking 3D channel networks can be constructed by gluing, fusion or anodic bonding of many silicon or glass wafers including via holes. Integrating of electrical circuits for both silicon and silica is possible by standard IC technology.
|