In order to observe in real-time and to accurately measure the filling speed during the capillary process in planar microfluidic devices, we integrated a ruler in the silicon master structures, side by side with the channels, and replicated it into the elastomeric elements. The time dependence of the covered length (z, t) and of the filling rate (v, t) under different temperature and surface functionalization conditions was then exactly determined by optical microscopy. This allowed us to quantitatively assess the strong dependence of v on the process environmental conditions, and to discard in real-time the presence of impurities on employed substrates, thus allowing one to strongly improve the throughput of the microfluidic-based soft lithography for nanotechnology applications. © 2005 Elsevier B.V. All rights reserved.

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