Microfabricated structures

Folch, A., Mezzour, S., During, M., Hurtado, O., Toner, M., Muller, R., Stacks of microfabricated structures as scaffolds for cell culture and tissue engineering. Biomed. Microdevices 2000, 2(3), 207-214. 

Burns MA, Mastrangelo CH, Sammarco TS, Man FP, Webster JR, Johnsons BN, et al. Microfabricated structures for integrated DNA analysis. Proc Natl Acad Sci U S A 1996 93 5556-61. 

Figure 8F-1 Layout of a microfabricated structure for combining FIA with a capillary electrophoretic separation, (a) Two glass plates are used in a sandwich structure. The upper plate contains the channel structure (30 p,m wide by 10 p.m deep), and the lower plate contains platinum electrodes for controlling the flow, (b) Samples are injected, mixed with reagents, and carried to a detector. An electrophoretic separation can also be achieved if desired. Detectors have been conductivity, electrochemical, and fluorescence. (Modified from A. Manz, J. C. Fettinger, E. Veipoorte, H. Ludi, H. M. Widmer, and D. J. Harrison, Trends in Analytical Chemistry (TRAC), 1991,10, 144, with permission from Elsevier Science.)...

Ferrari and co-workers examined the feasibility of using microfabiicated silicon nanochannels for immunoisolation. A suspension of cells was placed between two microfabricated structures with nanopor-ous membranes to fabricate an immunoisolation biocapsule. Characterization of diffusion through the nanoporous membranes demonstrated that 18nm channels did not completely block IgG but did provide adequate immunoprotection (immunoprotected cells remained functional in vitro in a medium containing immune factors for more than two weeks, while unprotected cells ceased to function within two days). A major application of biocapsules containing nanochannels is immunoisolation of transplanted cells for the treatment of hormonal and biochemical deficiency diseases, such as diabetes. 

FIGURE 17 Microfabricated structured catalyst packing inside a microchannel [31]. (Adapted with permission from Elsevier.)... 

A first interest of MS when used in combination with microfabricated structures, or at the outlet of microfluidic devices, is the match in the volume of liquid handled. A typical MS analysis requires less than 1 pL of liquid, for ESI-MS as well as for MALDI-MS techniques. When working with a continuous flow of liquid and ESI-MS, the MS performance is even more enhanced for flow rates down to 50-100 nL min-1 the lower the flow rate, the better the MS analysis. This flow-rate range corresponds to flow-rate values observed in microfluidic devices. Consequently, the technique of MS is easily scalable and exhibits an enhanced response when the sample size is decreased. This is not the case for instance for other detection techniques, such as UV absorbance or amperometry these two techniques require large detection area or volume, which is the opposite of the quest of microfluidics. This first advantage of MS compared to other technique goes together with its high sensitivity. 

The term pTAS is sometimes interchanged with lab-on-a-chip (LOG), more often when the manipulation of fluids is involved. pTAS and LOG range in size from a few microns to a few millimetres. The technique of pTAS is interdisciplinary it combines the advantages of chemical sensors and the resolving power of modem benchtop analytical systems and is constantly evolving. The main advantage of pTAS is integration of the entire separation process onto one analytical microdevice, so early efforts focused on micropumps and valves to manipulate fluids inside a microfabricated structure. In such a fluid-based pTAS,... 

Washizu, M., Kurosawa, O., 1990. Electrostatic manipulation of DNA in microfabricated structures. IEEE Trans. Ind. Appl. 26, 1165—1172. 

Microfabrication techniques allow the patterning of large arrays of complex features down to the micrometer scale, without the cost associated with high-precision manufacturing. Figure 2 shows examples of silicon microfabricated structures for fuel cells, ranging from meso- to nanoscale. Photolithography can be used to transpose microchannel shapes or other microstructures on... 

Frisbie, C.D., Martin, J.R., Duff, R.R. Jr., Wrighton, M.S. (1992) Use of high lateral resolution secondary-ion mass spectrometry to characterize self-assembled monolayers on microfabricated structures. J. Am. Chem. Soc., 114, 7142-7145. 

FIGURE 33-13 Layout ol a microfabricated structure for FIA. Microfluidic channels are shown in blue, and control channels (pumps and valves) are shown in black, (a) Peristaltic pump, (b) infection valve, (c) mixing and reaction chamber, (d) sample selector. Slue circles indicate fluid reservoirs (1 and 2). samples (3), carrier (4), reactant (5). and waste (6). The entire structure is 2.0 cm by 2.0 can. (From A. M. Leach. A. R. Wheeler, and R. N. Zare, Ansi. Chem.. 2003, 75,967.)... 

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