Geometry and surface - assisted micro flow discretization ∗

This paper presents a micro flow discretization system that autonomously digitizes continuous liquid flow into nanoliter segments. Powered by the interactions between liquid flow and micro-channels, the discretization process does not consume any electricity or require any external control. In the prototype demonstration, the discretizer is made of PDMS microfluidic channels with desired geometries and surface properties. Employing a novel self-aligned masking process followed by oxygen plasma treatment to pattern the three-dimensional channel surfaces, the areas exposed to plasma are converted from naturally hydrophobic into hydrophilic while the others covered by the mask remain hydrophobic. With the assistance of channel geometries and hydrophobic/hydrophilic surface patterns, continuous water flow has been split by interfacial forces into segments with controllable and pre-determined volumes from 15 to 35 nl. As such, this autonomous flow discretizer could serve a new class of metering and manipulation schemes for microfluidic applications including drug delivery and lab-on-a-chip. (Some figures in this article are in colour only in the electronic version)