Microfluidics systems

Miniaturisation of various devices and systems has become a popular trend in many areas of modern nanotechnology such as microelectronics, optics, etc. In particular, this is very important in creating chemical or electrochemical sensors where the amount of sample required for the analysis is a critical parameter and must be minimized. In this work we will focus on a micrometric channel flow system. We will call such miniaturised flow cells microfluidic systems , i.e. cells with one or more dimensions being of the order of a few microns. Such microfluidic channels have kinetic and analytical properties which can be finely tuned as a function of the hydrodynamic flow. However, presently, there is no simple and direct method to monitor the corresponding flows in. situ. 

Ross D, Gaitan M, Locascio LE (2001) Temperature measurement in microfluidic systems using a temperature-dependent fluorescent dye. Anal Chem 73 4117-4123 Sammarco TS, Bums MA (1999) ThermocapiUary pumping of discrete drops in microfabricated analysis devices. AlChE J 45 350-366... 

Gas flows are encountered in many microsystems like micro-motors, micro-turbines, micro-sensors, and microfluidic systems in the presence of air or gas environment. Since the ratio of surface area to volume increases in such microsystems, surface forces become dominant over the body forces, and gas flows have great affects on the performance and reliability of many microdevices. 

Moorthy, j., Beebe, D. )., Organic and biometric designs for microfluidic systems. Anal. Chem. 75, 7 (2003) 293-301. 

The focus of the examples given in this chapter is clearly on micro reactors for chemical processing in contrast to p-TAS or Lab-Chip systems for bioanalytical applications. In the latter microfluidic systems, the fluidic requirements are somehow different from those in micro reactors. Typically, throughput plays only a minor role in p-TAS systems, in contrast to micro reactors, where often the goal is to achieve a maximum molar flux per unit volume of a specific product. Moreover, flow control plays a much greater role in p-TAS systems than in micro reactors. In... 

The Navier-Stokes equation and the enthalpy equation are coupled in a complex way even in the case of incompressible fluids, since in general the viscosity is a function of temperature. There are, however, many situations in which such interdependencies can be neglected. As an example, the temperature variation in a microfluidic system might be so small that the viscosity can be assumed to be constant. In such cases the velocity field can be determined independently from the temperature field. When inserting the computed velocity field into Eq. (77) and expressing the energy density e by the temperature T, a linear equahon in T is... 

In a wider sense, the Hantzsch synthesis is a further example for evaluating the potenhal of microfluidic systems for high-throughput screening [9]. 

Schwesinger, K., Erank, T, A modular microfluid system with an integrated micromixer, in Proceedings of the MME 95, pp. 144-147, Copenhagen (1995). 

H., A modular microfluid system with an integrated micromixer, J. Micromech. 

Jackman, R. J., Floyd, T. M., Ghodssi, R., Schmidt, M.A., Jensen, K. F., Microfluidic systems with on-line UV detection fabricated in photodefinable epoxy, J. Micromech. Microeng. 11 (2001) 263-269. 

SCHWESINGER, N., FRANK, T., WURMUS, H., A modular microfluidic system with an integrated micromixer, J. Micromech. Microeng. 6 (1996) 99-102. 

For high-speed FLIM applications, including real-time imaging of biological tissue using endoscopes or macroscopes, as well as for imaging live cell dynamics and microfluidic systems, we have... 

Anderson J.R., Chiu D.T., Jackman R.J., Chemiavskaya O., McDonald J.C., Wu H.K., Whitesides S.H., Whitesides G.M., Fabrication of topologically complex three-dimensional microfluidic systems in PDMS by rapid prototyping, Anal. Chem. 2000 72 3158-3164. 

Taylor M.T., Belgrader P., Furman B.J., Pourahmadi F., Kovacs G.T.A., Northrup M.A., Lysing bacterial spores by sonication through a flexible interface in a microfluidic system, Anal. Chem. 2001 73 492-496. 

Lion N, Rohner TC, Dayon L et al (2003) Microfluidic systems in proteomics. Electrophoresis 24 3533-3562... 

Apart from immunoassays, enzyme assays can also be used to detect certain substrates in a clinical diagnostic setting. The benefits of performing enzymatic assays on microchips are the analytical power and minimal reagent use in microfluidic systems combined with the selectivity and amplification factors that come with biocatalysis. 

There are three types of mass transport processes within a microfluidic system convection, diffusion, and immigration. Much more common are mixtures of three types of mass transport. It is essential to design a well-controlled transport scheme for the microsystem. Convection can be generated by different forces, such as capillary effect, thermal difference, gravity, a pressurized air bladder, the centripetal forces in a spinning disk, mechanical and electroosmotic pumps, in the microsystem. The mechanical and electroosmotic pumps are often used for transport in a microfluidic system due to their convenience, and will be further discussed in section 11.5.2. The migration is a direct transport of molecules in response to an electric field. In most cases, the moving... 

D.C. Duffy, H.L. Gillis, J. Lin, N.F. Sheppard Jr, and G.J. Kellogg, Microfabricated centrifugal microfluidic systems characterization and multiple enzymatic assays. Anal. Chem. 71, 4669-4678... 

J. Gao, J.D. Xu, L.E. Locascio, and C.S. Lee, Integrated microfluidic system enabling protein digestion, peptide separation, and protein identification. Anal. Chem. 73, 2648-2655 (2001). 

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