Painting with biomolecules at the nanoscale: biofunctionalization with tunable surface densities

We present a generic and flexible method to nanopattern biomolecules on surfaces. Carbon-containing nanofeatures are written at variable diameter and spacing by a focused electron beam on a poly(ethylene glycol) (PEG)-coated glass substrate. Proteins physisorb to the nanofeatures with remarkably high contrast factors of more than 1000 compared to the surrounding PEG surfaces. The biological activity of model proteins can be retained as shown by decorating avidin spots with biotinylated DNA, thereby underscoring the universality of the nano-biofunctionalized platform for the binding of other biotinylated ligands. In addition, biomolecule densities can be tuned over several orders of magnitude within the same array, as demonstrated by painting a microscale image with nanoscale pixels. We expect that these unique advantages open up entirely new ways to design biophysical experiments, for instance, on cells that respond to the nanoscale densities of activating molecules.