Transpiration-based micropump for delivering continuous ultra-low flow rates

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Abstract
In this paper we describe the design, construction and operation of a micropump that delivers continuous, ultra-low flow velocities at ~100 μm s−1. The pumping concept is based on the commonly observed phenomenon of transpiration in plant leaves. A liquid meniscus is pinned inside a microchannel by selective hydrophobic patterning and the evaporation rate of the liquid at the meniscus is controlled. The controlled evaporative flux results in a regulated flow of the liquid from a reservoir to the meniscus. Using this technique, precise flow control (5 nl min−1) has been achieved in several channel geometries for extended periods of time (~2 h). Various factors affecting the performance of the pump were studied and theoretical predictions along with experimental results are presented. Such a micropump could find applications in emerging biological assays such as single-molecule studies of DNA and cell adhesion analyses.