Microchip fabrication

Now for some practical examples of how phase diagrams are used. In the first, a typical design problem, we find out how solders are chosen for different uses. In the second we look at the high-technology area of microchip fabrication and study the production, by zone refining, of ultra-pure silicon. And lastly, for some light-hearted relief, we find out how bubble-free ice is made for up-market cocktails. 

Zant, V. R, Microchip Fabrication A Practical Guide to Semiconductor Processing, 4th ed., McGraw-Hill Companies, Inc., 2000. 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

Microchips fabrication with integrated tips can result in improved spray repeatability and efficiency since alignment and dead volume are not a critical issue anymore. However, production of fine and robust nanospray emitters as an integral part of a microdevice is not trivial, and highly specialized microfabrication procedures are required. Microfluidic devices with integrated ESI tips have been produced for infusion experiments, but to date, no microchips with such a design was fabricated for CE separation prior to MS detection. 

Plasma etching is a well-established technology for microchip fabrication, involving the removal of silicon with a beam of fluorine atoms generated by high energy electrical excitation of simple fluorocarbons, notahly carbon tetrafluoridc, chlorotrifluoromethanc. trifluorometh-... 

W.K.T. Coltro, J.A.F. da Silva, H.D.T. da Silva, E.M. Richter, R. Furlan, L. Angnes, C.L. do Lago, L.H. Mazo and E. Carrilho, Electrophoresis microchip fabricated by a direct-printing process with end-channel am-perometric detection, Electrophoresis, 25 (2004) 3832-3839. 

Figure 2.13 Schematic diagram of NCE microchip fabrication by improved ULIGA process [76].

FIGURE 7.35 (a) Initial mass spectrum obtained from PMMA microchip device. The mass spectrum is characterized by a substantial chemical noise background most likely due to residual developer solution present in the microchannels, (b) Electrospray mass spectrum obtained with 10 pM angiotensin I (in 50 50 MeOH/H20 containing 1% acetic acid) after the PMMA microchip has been washed with 50 50 MeOH/H20. The simple solvent wash completely eliminates the residual chemical contamination arising from the microchip fabrication step [200]. Reprinted with permission from the American Chemical Society. 

Chen, J., M. Wabuyele, H. Chen, D. Patterson, M. Hupert, H. Shadpour, D. Nikitopoulos, and S.A. Soper. Electrokinetically synchronized polymerase chain reaction microchip fabricated in polycarbonate. Anal Chem. 2005, 77(2), 658-666... 

Fig. 4.7. Plastic microchip fabricated by hot embossing (Photograph courtesy...

FIGURE 10.2 A diagram illustrating the processes involved in microchip fabrication using standard... 

FIGURE 41.4 Examples of electrophoresis microchip fabricated in PT. (A) Microdevice with cupper tape electrodes (a) positioned externally over the channel for C D measurements. Point b is a representation for the solution reservoirs. (Reprinted from do Lago, C.L., Silva, H.D.T., Neves, C.A., Brito-Neto, J.G.A. and Fracassi da Silva, J.A., Anal. Chem., 75, 3853, 2003. With permission.) (B) Microdevice layout for end-channel amperometric detection. S, SW, and b represent, sample, sample waste, and buffer reservoirs, respectively. (Reprinted from do Lago, C.L., et al.. Anal. Chem., 75, 3853, 2003. and Coltro, W.K.T., et al.. Electrophoresis, 25, 3832, 2004. With permission.)... 

Richter et al. have used this process to produce electrodes (see Figure 41.5) for EC detection in CE. These Au-CDtrodes were used first in a home-made CE system, in which an electrophoretic separation of iodide, ascorbic acid, dipyrone, and acetaminophen was successfully performed. Au-CDtrodes were later applied to an electrophoresis microchip fabricated with PT, where the effectiveness of the proposed system was demonstrated with a separation of iodide and ascorbic acid. A series of 10 repetitive injections obtained in a conventional CE-EC system and one electropherogram obtained in miniaturized system are shown in Figure 41.6. 

While one of the limitations of LIF detection is that few target molecules exhibit native fluorescence, especially biologically relevant proteins and DNA of clinical interest, several different labeling approaches both on- and off-chip have been demonstrated. For the former, the microchip fabrication steps provide the ability to incorporate additional structures into the design, in many cases without adding more steps (or cost) to the fabrication process. Examples include the additional channels and reaction chambers used to perform both precolumn" and postcolumn" labeling of amino acids. 

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