A Microfluidic Diluter Based on Pulse Width Flow Modulation

Journal article, 2009

We demonstrate that pulse width flow modulation (PWFM) can be used to design fasts accurate, and precise multi-stage 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) mu m) with corresponding hydraulic resistance variances of similar to 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 Ca2+ concentration on a phospholipid bilayer spreading from a membrane reservoir onto a SiO2 surface. This is one of many possible applications where flexible concentration control is desirable.