Reactive μCP on Ultrathin Block Copolymer Films: Investigation of the μCP Mechanism and Applications to Sub-μm (Bio)Molecular Patterning

Abstract

In this chapter, three different, complementary lithographic approaches to produce chemical patterns on ultrathin polystyrene-b-poly(t-butyl acrylate) (PS₆₉₀-b-PtBA₁₂₁₀) films are introduced, which can be expanded to obtain patterns of biomolecules with (sub)micrometer feature sizes. In this chapter, three different, complementary lithographic approaches to produce chemical patterns on ultrathin polystyrene-b-poly(t-butyl acrylate) (PS₆₉₀-b-PtBA₁₂₁₀) films are introduced, which can be expanded to obtain patterns of biomolecules with (sub)micrometer feature sizes. In approach (A), PS₆₉₀-b-PtBA₁₂₁₀ films were homogeneously hydrolyzed and subsequently functionalized with (N-hydroxysuccinimide) (NHS). Two types of molecules, fluoresceinamine and BSA, were patterned and covalently bound on the activated polymer films in sequential direct molecular transfer steps using reactive μCP. NHS functionalized polymer films were also patterned with PEG₅₀₀NH₂ by reactive μCP in approach (B). The PEG layer was used as antifouling layer to prevent the non-specific adsorption of (bio)molecules in the subsequent covalent coupling step of fluoresceinamine and bovine serum albumin (BSA) carried out in solution. The area selective immobilization was also successfully demonstrated for 25mer probe DNA, as shown by the fluorescence microscopic detection of the hybridization of dye-labeled target DNA. In approach (C), the polymer films were locally hydrolyzed with trifluoroacetic acid that was locally applied on the films using acid-soaked poly(dimethyl siloxane) (PDMS) stamps. A detailed study of the reactive μCP mechanism led to the conclusion that ink spreading and diffusion must be controlled for faithful pattern transfer, in particular on the sub-micrometer level. In addition, it was found that patterns with micrometer scale dimensions could be fabricated by using stamps with >10 μm dimensions by controlling the spreading of trifluoroacetic acid. Thus, ultrahigh density patterns can be conveniently fabricated.