Silica bead packed microchips

To provide a stable and reproducible solid phase, the silica beads that were packed into glass microchips should be immobilized. This was achieved by using... 

Another method for the analysis of sexual assault evidence exploits the differential physical and chemical properties of sperm and epithelial cells to result in a cell separation, from which DNA can be extracted from each population independently. In this simple method, the epithelial cells settle to the bottom of the microchip inlet reservoir more rapidly than the sperm cells (as a result of their size and density). By subsequently invoking flow in the microchannel, sperm cells are swept from the inlet to the outlet reservoir, where they can be either collected for subsequent analysis or packed up against a silica bead/sol-gel bed for DNA extraction (Figure 37.1a). Efficient separation of a mixture of sperm and epithelial cells has been demonstrated via short tandem repeat... 

In a more direct translation of current macroscale, silica-based, SPE protocols other, microchip-based purification systems have focused on utilizing a packed silica-bead bed or silica sol-gel matrix solid phase for purification. This type of extraction was first miniaturized in a capillary format, to demonstrate the utility of the proposed method in the microscale, by Tian et al., who utilized a 500 nL capillary-based chamber packed with silica particles to establish that PCR-amplifiable DNA (with 80-90% of proteins removed during the load and wash steps) could be obtained from white blood cells with high extraction efficiencies (70%). This demonstrated the feasibility of incorporating such silica-based column purification methods into microfabricated devices and the effectiveness of such methods for the purification of DNA from a wide variety of biological species (white blood cells, cultured cells, and whole blood). 

Using a different approach, Oleschuk et al. succeeded in packing octadecyl silica beads from a side channel into a specifically designed chamber of the microchip. 

Landers and colleagues have demonstrated [3, 4] a microchip-based DNA purification technique where DNA from biological samples such as blood has been isolated. The approach taken here was to maximize the surface area of interaction for DNA adsorption to the silica. Hence, silica beads of 10 pm diameter were packed into a microfabricated channel (Fig. 2) as a means to increase the silica-DNA interaction surface area. To pack the column, the silica beads are first introduced into the microfluidic channel and then the beads are immobilized within a solgel. In the silica particle/solgel hybrid approach... 

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