Fabrication of Porous Nanostructured Thin Films For Microfluidic and Microarray Applications

Abstract

ABSTRACTThe functionality of microfluidic and microassay devices could be enhanced through further development of porous engineered microstructures. New structural elements fabricated with porous nanostructured thin films deposited by the glancing angle deposition (GLAD) technique have been developed for these devices, and are reviewed here. With the GLAD technique, engineered structures such as vertical posts, slanted posts, helices, and square spirals can be directly grown inside microfluidic channels. A high surface area channel (517cm2/cm2) was made by depositing a silicon oxide porous film in glass microchannels (up to 4.5μm deep and 50μm wide). Similar channels were also fabricated by patterning channels in a photoresist-coated porous film. Self-sealed microchambers and channels were made by growing a SiO2 porous film on 14μm high silicon mesas (2.5×2.5μm, 7×7μm, and 25×25μm) and lines (2.5 to 50μm wide). Devices with channels containing periodic arrays of Si pillars with controllable porosity and architecture were fabricated with only one lithography and deposition cycle. The entire device was made by depositing a single GLAD porous film with areas of different porosity defining the channels. The channels, 200μm wide and 10.5μm deep, contained helical pillars with pore sizes ranging from 100nm-2μm, while a more dense nanofibrous helical film made up the remainder of the device. Fluid flow activated by negative pressure was demonstrated in this device, using both a dye solution and a 50nm microsphere solution. Material selection is not limited to silicon or silicon oxide, but may include a wide range of semiconductors, insulators and metals. A GLAD film was used to separate a test dye solution, demonstrating its potential for use in thin layer chromatography. The reported elements are suitable for a range of applications, including – but not limited to – chromatography, nano-assays and capillary electrophoresis.