Microfluidic Systems :: essays research papers

Microfluidic SystemsThe ready market availability of porous membranes with cylindrical pores of 15-200 nm and a thickness of 6-10 m facilitates the development of three dimensional analytical building block operation devices on an attaLiter scale. By employing these membranes as gates at the user interface of two crossed smallfluidic convey, the rate and direction of the fluid exchange tramp be controlled with electrical potential, polarity, solution ionic strength or diameter of the nanocapillary1. The microfluidic channels, fabricated by soft lithography, have been used for a decade. Dr. capital of Minnesota W. Bohn, Centennial Professor of Chemical Sciences at the University of Illinois at Urbana-Champaign, sees the advance to multilayered semiliquid chromatography as a key step in the development of micro total analysis systems (TAS), which would involve such new applications as injection, collection, mixing, transmutation and detection. Recently he has been studying the analyte responses to various constraints applied to the system and its deviations in behavior from that of a similar system on the macro scale. Microfluidic channels are a convenient and durable means of fluid apotheosis made of poly(dimethylsiloxane) (PDMS), a common polymer with non-polar side groups. PDMS is durable, highly flexible and elastic, group O permeable and very hydrophobic2. It also has negative step to the fore charge meanness at pH 81. The method of soft lithography allows for rapid deposition of involved crossed two dimensional fluid pathways on a atomic number 14 wafer.The membrane containing these nanopores is a 6 10 micron thick polycarbonate thermonuclear track-etched membrane (PCTE) that has been coated with poly(vinylpyrrolidone) (PVP) to make it hydrophilic. This coating results in a pH of 8 in the system3. The pores in the membrane are cylindrical and of diameters in the range of 15 200 nm. The size of these pores are of the same set up of magnitude of the Debye length (-1) of the ionic interactions in solution (1 nm -1 50 nm) when the ionic strength is in the millimmolar range1. The small physical character of the nanopore allows for a change in ionic strength of the solution to be commensurate to alter the interaction between the solution and the nanopore. By merely ever-changing the concentration, the nature of the flow induced by electrical potential passel be switched between electrophoresis and electro osmosis1. The direction of the flow can be controlled by the size of the nanopore. At large pore sizes, the negative surface charge density on the microfluidic channel caused by the slightly canonical pH of the system