Microfluidic valves based on superhydrophobic nanostructures and switchable thermosensitive surface for lab-on-a-chip (LOC) systems

This paper describes a novel valve concept using a nanostructured functional polymer surface. To prove the concept, two fully integrated microfluidic valves, one with a superhydrophobic polymer surface and the other with a switchable, thermosensitive polymer surface have been fabricated and tested. The passive valve with the superhydrophobic polymer surface selectively inhibits the flow of water-based reagents and passes aqueous solutions containing surfactants. In case of the thermosensitive valve, the switchable polymer surface becomes hydrophobic when heated to temperatures exceeding 65 °C, thus inhibiting the flow of water and becomes hydrophilic at room temperature, thus allowing the flow of water. The microchannels are fabricated by standard photolithography and wet etching techniques. The polymer surface for both the valves is fabricated using the layer-by-layer (LBL) deposition technique, in which multiple layers of polyelectrolytes are coated on a channel wall followed by silica nanoparticle treatment. For the thermosensitive valve, the polymer surface is further coated with the thermosensitive polymer poly(N-isopropylacrylamide) (PNIPAAm). The fabricated microfluidic valve was tested with liquids flowing in the microchannels under capillary action. It is shown that the valve selectively regulates the flow of test samples.