Bead-packed microchannels

Adding additional surface. Whilst a high ratio of surface to volume is inherent in an empty/open micro-channel, this characteristic may be further pronounced by packing micro-beads in the channel (He et al. 2004). The introduction of beads within microchannels can introduce some practical difficulties, but a number of successful applications using this type of methodology have been described (He et al. 2004 Nikbin and Watts 2004). 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

DNA extraction has been achieved using silica beads (5 pm), which were packed in a glass microchannel and held by a sol-gel [913]. This method provided more reproducible extraction than a previous method in which extraction was performed without physically fixing the beads in microchambers [639]. 

Fig. 9.7.8 (a) Diagrammatic rendering of fritless method of packing a microchannel with beads, using the keystone effect for self-damming by first beads to become blocked at the channel constriction. 

Another type of solid support for capture antibody is microbeads. Beads coated with antibodies are packed in the microchannel with a dam or cage structure. Bead format is considerably superior to... 

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... 

Microsphere-packed glass microchip Trypsin Covalent linking Class microchannels packed with immobilized trypsin gel beads performed efficient proteolysis in 12 min [82]... 

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