Nano-Confined Polymer Structures for Protein Binding

Abstract

Stimulated emission depletion lithography (STED-lithography), a further development of multiphoton polymerization (MPP) lithography, belongs to the most promising methods for 2D and 3D structuring of polymer scaffolds with structure sizes in the nanometer range. Already in the early developmental stages of STED-microscopy, it was pointed out that a nano-confined effective point-spread function (PSF) can be applied to spatially confine photo-chemical reactions to sub-diffraction volumes. In optical STED-lithography, one laser pulse excites photo-initiators for radical polymerization and a second donut-shaped laser beam locally inhibits these starter molecules in the outer rim of the PSF. This confinement of the excitation volume leads to a restriction of the size of the polymerized structures. Such a STED-based approach facilitates the creation of structures with sizes below the limits of conventional MPP. Currently, feature sizes as small as 55 nm and a resolution of 120 nm of adjacent lines can be achieved.We use stimulated emission depletion (STED) lithography for the assembly of polymeric structures down to several nanometers in any desired geometry. Protein adhesive photoresists allow manufacturing of nano-confined, protein functionalized structures. The structures show good biocompatibility and allow an easy biofunctionalization with proteins down to a single protein level. Furthermore, we use STED-lithography to create 3D compound structures of different acrylate polymers with distinct properties. A µm-sized protein repellent scaffold consists of multi-photon lithography (MPP) fabricated features, carrying STED-lithography written sub-100 nm protein-binding sites.Combining STED lithography with fluorescence microscopy allows us to produce well characterized, biocompatible structures, applicable to biological assays.