Microfluidic Systems :: essays research papers

Microfluidic SystemsThe set market availability of porous tissue layers with cylindrical pores of 15-200 nm and a thickness of 6-10 m facilitates the development of three dimensional analytical unit performance devices on an attaLiter scale. By employing these membranes as gates at the interface of cardinal go through microfluidic channels, the rate and direction of the fluid ex vary can be controlled with electrical potential, polarity, solution loft strength or diameter of the nanocapillary1. The microfluidic channels, fancied by soft lithography, have been used for a decade. Dr. Paul W. Bohn, centennial Professor of Chemical Sciences at the University of Illinois at Urbana-Champaign, sees the advance to multilayered liquid chromatography as a key step in the development of micro heart analysis systems (TAS), which would involve such new applications as injection, collection, mixing, switching and detection. deep he has been studying the analyte responses to various cons traints applied to the system and its deviations in appearance from that of a similar system on the macro scale. Microfluidic channels be a convenient and durable means of fluid transport do of poly(dimethylsiloxane) (PDMS), a common polymer with non-polar side groups. PDMS is durable, highly flexible and elastic, oxygen leaky and very hydrophobic2. It also has negative surface indict density at pH 81. The method of soft lithography allows for rapid deposition of complex crossed two dimensional fluid pathways on a silicon wafer.The membrane containing these nanopores is a 6 10 micron thick polycarbonate nuclear 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 twine of 15 200 nm. The size of these pores are of the same order 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 sufficient to metamorphose the interaction between the solution and the nanopore. By merely changing the concentration, the genius of the flow induced by electrical potential can 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 basic pH of the system