Microfabricated fluidic devices Microfluidics

FIGURE 7.41 Picture of the microfabricated fluidic device integrated with a standard MALDI-TOF sample plate. Because of the self-activating character of the microfluidic device, the system can be introduced into the MALDI ionization chamber without any wire or tube for the sample introduction and the flow control [820]. Reprinted with permission from the American Chemical Society. 

Many individually microfabricated fluidic devices have been demonstrated and even marketed commercially. As sample volumes become smaller, and the analysis of individual cells or molecules is desired, the research instra-mentation itself decreases in size and new methods of interconnection and assembly are required. Microfluidic corrponents must often first be assembled from smaller subunits (e. g., channels, actuators) and then further assembled together to form microfluidic systems and instrumen-... 

The deep reactive ion etching (DRIE) technique, first presented in the mid- to late 1990s, facilitated the fabrication of numerous innovative microsystems, especially power-MEMS systems. Since most MEMS devices involve some form of lithography-based microfabrication, the use of flat substrates is required. Often, these flat substrates involve the use of DRIE methods and result in structures characterized by extrusion of two-dimensional features into the third dimension as illustrated in Fig. 2. Therefore, microfluidic components are often limited in their geometrical appearance, which precludes full three-dimensional shapes commonly found in many large-scale fluidic devices such as pumps hydrofoils, turbine blades and vanes, mixers, etc. 

Behavior of the fluids in the microfabricated channels are different from those in the millimeter scale channels. Miniaturization of micro flow devices opens a new research field, microfluidics which represents the behavior of the fluid in the micro channel [8]. Since the Reynolds number in the micro channel is usually below 200, the flow is laminar and special design concepts are necessary for the fluidic elements of mixers, reaction coils etc. in the pTAS. Some components of flow switches and fluid filters were developed using laminar flow behavior. 

The ability to fill a device with many different fluids in different channels and chambers allows for the implementation of a simple and robust geometric method of metering solutions. The principle behind this scheme is to set up a geometry in which two microfluidic chambers may be primed with different solutions and connected via a fluidic interface that is controlled by a microfabricated valve (Fig. 11.4). With a central interface valve closed, the two chambers are first deadend filled with two different solutions using the POP technique. Once both chambers have been completely filled, containment valves are actuated, isolating the chambers from the rest of the chip. The interface valve is then opened, creating a... 

Alternatively, Foret et al. - have devised a microfabricated device that incorporated a sample injection loop, a separation channel for CE, lEF, or chromatography, and a liquid junction MS interface. The samples were loaded sequentially from a microtiter plate with the aid of an electropneumatic distributor, and microfluidic manipulations on the chip were accomplished with electrokinetic and pressure fluidic control. The sequential CE-ESI-MS analysis of protein tryptic digests is shown in Figure 53.25. 

Figure 10 illuminates this simple process. The reverse 3D structure is first prepared by microfabrication techniques as a mold. Then, a prepolymer with cross-link is cast onto the mold. After the polymer is well cured by heat or UV, the 3D polymer structure is produced by peeling off the polymer structure from the mold. To construct a microfluidic device, bonding the 3D polymer structure with a substrate is the next step to seal the fluidic channels and reservoirs. 

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