title: A microfluidic diluter based on pulse width flow modulation.
abstract: We demonstrate that pulse width flow modulation (PWFM) can be used to design fast, accurate, and precise multistage dilution modules for microfluidic devices. The PWFM stage unit presented here yields 10-fold dilution, but several PWFM stages can be connected in series to yield higher-order dilutions. We have combined two stages in a device thus capable of diluting up to 100-fold, and we have experimentally determined a set of rules that can be conveniently utilized to design multistage diluters. Microfabrication with resist-based molds yielded geometrical channel height variances of 7% (22.9(16) microm) with corresponding hydraulic resistance variances of approximately 20%. Pulsing frequencies, channel lengths, and flow pressures can be chosen within a wide range to establish the desired diluter properties. Finally, we illustrate the benefits of on-chip dilution in an example application where we investigate the effect of the Ca(2+) concentration on a phospholipid bilayer spreading from a membrane reservoir onto a SiO(2) surface. This is one of many possible applications where flexible concentration control is desirable.
authors.affiliation: Department of Chemical and Biological Engineering, and Microtechnology Centre (MC2), Chalmers University of Technology, SE-412 96, Göteborg, Sweden.
authors.forename: Alar
authors.initials: A
authors.lastname: Ainla
authors.forename: Irep
authors.initials: I
authors.lastname: Gözen
authors.forename: Owe
authors.initials: O
authors.lastname: Orwar
authors.forename: Aldo
authors.initials: A
authors.lastname: Jesorka
mesh_terms: D002118:Calcium / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D007201:Indicator Dilution Techniques / Q000295:instrumentation*; D008051:Lipid Bilayers / Q000378:metabolism; D044085:Microfluidics / Q000295:instrumentation* / Q000379:methods; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D012822:Silicon Dioxide; D002118:Calcium