Channel etching

For flow at a given rate, the only way to significantly increase the heat transfer coefficient is to reduce the channel size, whose optimum can be calculated assuming a practical limit on the available pressure. Recourse to multiple channels, instead of continuous coolant flow over the entire back substrate surface, enables one to multiply the substrate area by a factor (jp, representing the total surface area of the channel walls which are in contact with fluid. Single-row micro-channels etched dir-... 

The active micro-channel cooling contains a cooling system centered on a microheat collector that is fabricated much in the same way as the chip. Heat collector usually has a dense amount of micro-channels etched into the surface that works to transfer heat to a fluid, which is circulated through the entire package. 

There are other, nonhydrogel, new materials for chromatographic and electrophoretic separations [7,8,103,164,199,214,377,407], Eor example, Volkmuth and Austin [407] proposed electrophoretic studies in microlithographic arrays of posts and channels etched into sihcon wafers. This material may be useful for studying fundamental transport characteristics of macromolecules in defined media, and many recent studies have been conducted to develop chromatography and electrophoresis on silicon wafers with micron-scale channels... 

Flockhart, S. M., Dhariwal, R. S., Experimental and numerical investigation into the flow characteristics of channels etched in (100) silicon, J. Fluids Eng. 120 (1998) 291-295. 

Operating temperature 200-350 °C Reaction channel (etched) width depth length 500 pm 80 pm 9.5 mm... 

Reactor type Chip micro reactor with multiple vertical injections in a main channel Micro-channels etch 146 pm 38 pm mask width etch depth... 

Some reviews [5-7] have appeared on NCE-electrospray ionization-mass spectrometry (NCE-ESI-MS) discussing various factors responsible for detection. Recently, Zamfir [8] reviewed sheathless interfacing in NCE-ESI-MS in which the authors discussed several issues related to sheathless interfaces. Feustel et al. [9] attempted to couple mass spectrometry with microfluidic devices in 1994. Other developments in mass spectroscopy have been made by different workers. McGruer and Karger [10] successfully interfaced a microchip with an electrospray mass spectrometer and achieved detection limits lower than 6x 10-8 mole for myoglobin. Ramsey and Ramsey [11] developed electrospray from small channels etched on glass planar substrates and tested its successful application in an ion trap mass spectrometer for tetrabutylammonium iodide as model compound. Desai et al. [12] reported an electrospray microdevice with an integrated particle filter on silicon nitride. 

Channel etching using HF was usually performed before bonding, but etching could also be achieved after glass bonding (for enlarging some channels) [120,121,671,1065]. 

FIGURE 2.6 SEM images of etched channels illustrating the dependence of the smoothness of the etched surface on the etching solution. (A) SEM image of the channel etched with a high concentration of buffered HF (32% HF buffered with a 1 1 ratio of HF to ammonium fluoride) (scale bar 150 pm). (B) SEM image of the channel etched with a low concentration of non-buffered HF solution (10% HF) (scale bar 100 pm) [125], Reprinted with permission from Elsevier Science. 

In some cases, drilled holes are created on the same plate where the channels are etched. To achieve this, the holes were drilled either on the channel plate, or on a plain plate with subsequent channel etching [13,134]. In the latter case, the photoresist can only be sprayed, rather than spin-coated on the drilled glass plate [134],... 

After channel etching and access-hole forming, the channel plate and cover plate are bonded. Thermal bonding is the major method used, though alternative schemes exist. All glass bonding methods are summarized in Table 2.5. 

Fused Quartz Channel Etching and Hole-Drilling... 

Whereas the previous example relies on a series of channels etched into the membrane, typical single-channel stochastic sensors can be created in a closely related way.91 For such sensors, usually one protein (e.g., a-hemolysin) is introduced into a lipid bilayer. However, the problem here is that lipid bilayers are rather fragile objects. As an alternative, Martin and coworkers embedded a single gold nanotube... 

The acrylamide-based monolith originally developed by Hjerten for CEC capillary columns was very recently used by the same group to fill a 30.6 cm long 40 mm wide serpentine channel etched in flat quartz substrate shown in Fig. 6.8 [33], The channel... 

Fig. 11.6. Cross-sectional schematic for (a) tri-layer TFT and (b) back-channel etch structure.

Figure 14 (A) Schematic of a chip for flow-through PCR. Three well-defined zones are kept at 95, 77, and 60°C by means of thermostated copper blocks. The sample is hydrostatically pumped through a single channel etched into the glass chip. The channel passing through the three temperature zones defines the thermal cycling process. (B) Layout of the device used in the study. The device has three inlets on one side of the device and an outlet on the opposite side. Only two inlets were used, one carrying the sample, the other bringing a constant buffer flow. The chip incorporates 20 identical cycles, except for the first one, which includes a threefold increase in DNA melting time. (Reprinted with permission from Ref. 98.)...

Microchip electrophoresis is a natural extension of CE, with the capillary replaced by a channel etched into a substrate and then covered with a cover plate to enclose the channel. The components necessary to carry out the electrophoresis including electrodes, buffer reservoirs, and sample reservoirs must be fabricated into the chip itself or designed into an interface that allows the macroscopic world access to the microscopic structures. The design, fabrication, and substrate materials of microchips are the important factors in determining what components can be fabricated into the device itself and what must be included in an interface as well as in determining what types of analyses can be carried out on a given device. 

Microchip reactors often contain a mixing part, such as a T-shaped or Y-shaped junction. A typical example is shown in Figure 7.2. A substrate solution and a reagent solution are introduced to inlets A and B, respectively, through holes in the cover plate. The inlet tubes are connected to the holes. The two solutions are combined at a Y junction and a reaction takes place in a reactor channel etched on the reactor plate. Then, a product solution comes out from outlet C on the cover plate. 

Several research groups implemented carbohydrate analysis on-chip with direct detection of underivatized sugar molecules. Electrochemical detection is the most attractive approach, as it offers reasonable sensitivity and selectivity, and it is ideally suited for microchip format. Schwarz et al. [203] developed amperometric detection of sugars using microfabricated copper electrode. They separated fructose, sucrose, and galactose in 70 s on a glass chip with 50-p,m wide and 20-p,m deep microchannel and double tee injection geometry. The detection was based on Teflon-coated platinum wire plated with copper and inserted in the end of the separation channel etched in a conical shape. The detection limit down to 1 JtM was achieved. Hebert and coworkers [204] reported an... 

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