(111i) Fabrication of Nanopatterned Dots of Proteins by Particle Lithography

We have developed a general method to fabricate nanometer to micrometer sized dots of proteins on glass and silicon substrates by particle lithography. In this technique a colloidal suspension of beads (1, 2, 5, 10 or 20 μm) is dispersed onto a clean glass or silicon substrate. As the solvent evaporates attractive capillary forces between the colloidal particles causes them to form a self-assembled monolayer on the substrate. The monolayer of beads is then used as a mask to graft poly(ethylene glycol) silanes (PEG-Si) into the interstitial space between the beads. Following bead removal the unexposed sites on the substrate can then be filled with protein. Atomic Force Microscopy has measured the height of the grafted PEG-Si layer to be ~ 2nm, while the diameter of the protein structures varied from 200 nm to 5 μm, depending upon the size of bead utilized. Advantages of this technique are that it does not require expensive microfabrication equipment and that dot patterns of a variety of proteins (fibrinogen, albumin or IgG) can be made. These substrates should be extremely useful in investigating the effects of ligand spatial geometry on cell adhesion.