Direct Electron-Beam Nanopatterning of Teflon AF Surfaces for Site-Selective Formation of Molecular Phospholipid Films

Abstract

Teflon AF is a family of amorphous copolymers containing fluoroethylene and dioxole groups. Its splendid properties such as low surface energy, high optical transmission, chemical resistance and low autofluorescence, have made it a desirable surface for the fast generation of molecular phospholipid films, which are being evaluated for biosensing and single molecule spectroscopy. The possibility of confinement of chemical species to a surface-adhered 2-dimesional film, while keeping them mobile within the structure, circumvents many problems of volume-based flow systems (Czolkos et al. 2011). Patterning the Teflon AF by common photolithography is limited to a few specialized processes with micrometer resolution, and it is still difficult to get nano-structured Teflon AF surfaces. It has been shown that a thin film of Teflon AF can be directly patterned by electron beam lithography without the need of further chemical development (Karre et al., 2009), where degradation of the fluorinated dioxole groups by electron beam radiation changes the hydrophobicity of the exposed area.We have established that electron beam-exposed Teflon AF features far lower hydrophobicity, effectively preventing the spreading of phospholipid monolayers. By taking advantage of this functional difference, we established a nanostructuring protocol by means of electron beam frame exposure around a desired nano-scale region. The frame exposure outlines desired surface areas of high hydrophobicity by a region of low hydrophobicity, confining the lipids in the framed surface areas. The method represents an effective nanopatterning strategy for a specialized surface application, the controlled formation of self-assembled molecularly thin films, which we are developing into a new platform for single molecule studies.