Other Pre-Concentration Methods

FIGURE 5.18 Illustration of the flow confinement concept. In microchannels, a sample flow is joined with a confinement flow (e.g., water or sample medium) in a perpendicular orientation. Under laminar flow conditions, no mixing occurs. The sample flow is confined into a thin layer of higher velocity. For immunoassay application, rabbit IgG is immobilized on a planar waveguide and Cy5-labeled anti-rabbit IgG is introduced as analyte in the sample flow [694]. Reprinted with permission from the American Chemical Society. 

H-Filtcr cartridge - lop view Detail H-Fitter channel - side view 

FIGURE 5.19 The H-filter cartridge was constructed on a polyester chip for blood cell removal. The inset illustrates the diffusive mass transfer. First, to prime the device (1) the pneumetic valve V2 was closed and blood sample placed in PI was pumped (via SI) to fill SL up to V2, and the receiver solution placed in P2 was pumped (via S2) to fill RL up to HI. (2) Then V2 is opened (VI is closed), the blood sample was pumped to reach HI (the start of the H-filter, see inset), and receiver solution was pumped from HI to H2, and the waste loop (WL) was back-filled (via S3) to H2. Second, to start the process of solution flow and diffusive mass transfer, solution pushing (via SI and S2) and pulling (via S3) was carried out. The products went to PR and blood cells (which diffused to a less extent) went straight to WL [596]. Reprinted with permission from Elsevier Science. 

The temperature gradient can also be achieved at the junction of two microchannels of two different cross-sectional areas in the presence of an electric field. Since there is a higher current density in the narrower channel than in the wider channel, it is hotter in the narrower channel [597]. 

A pressurization technique for stacking DNA before separation will be described in Chapter 9, section 9.4.3. 

---