Fabrication and Surface Chemical Modification of Support Structures for Synthesis of Self-Assembled Bioinspired Nanoarchitectures

We have carried out the fabrication of several gold-patterned test array structures for studies of in vitro recrystallization using 2-dimensional surface-layer (“S-layer”) proteins. These test structures, patterned via e-beam lithography exposure of a poly(methylmethacrylate (PMMA) resist layer on silicon, are comprised of square features 25-300 nm in size and spaced 2-10 μm apart. Physical vapor deposition (PVD) and metal-lift methods were employed to create the final structures, which contain a ~40-45 nm thick layer of gold and a ~2 nm thick chromium adhesion layer. Tapping-mode atomic force microscopy (AFM) of the test structures was conducted in order to evaluate the dimensions and uniformity of the array features. These gold arrays, upon further chemical functionalization, will be used in future studies of site-directed S-layer protein self-assembly. Summary: Paracrystalline surface layer (“S-layer”) protein arrays are biological nanostructures that represent a surface feature common to almost all archaeal microorganisms [1]. S-layer lattices usually display oblique (p1, p2), square (p4), or hexagonal (p3, p6) lattice symmetries, and as a result of their crystalline nature, they display distinct classes of pores of identical size and morphologies. In addition to their highly ordered structure, one of the most interesting properties of S-layers is their ability to recrystallize into monolayer sheets at air-liquid, liquid-solid interfaces. This reassembly property is one of the key features that makes S-layer proteins especially promising as candidates for an emerging class of “bioinspired nanoarchitectures” with a broad range of potential applications in nanotechnology [2]. Success in this area will be achieved by the fabrication of novel types of chemically-modified surfaces conducive to the re-assembly of S-layer proteins. Through the fabrication of patterned silicon substrates using the various optical and electron-beam lithography tools at CNF, we are presently Fabrication and Surface Chemical Modification of Support Structures for Synthesis of Self-Assembled Bioinspired Nanoarchitectures CNF Project # 1306-05 Principal Investigator(s): Dr. Carl A. Batt investigating the possibility of manipulating the S-layer protein-surface interaction and, in effect, the ability to guide the formation of self-assembly nucleation sites, thus potentially creating large-area single-crystal domains with long-range order. In particular, we expect that genetically modified Slayers proteins created in our laboratory will initially become bound to the patterned sites (after appropriate surface chemical modification) and then spontaneously nucleate long-range single crystal growth. These adsorption sites (~100-10,000 square nm in size) are currently being manufactured within designated areas on standard wafer substrates so that highly ordered microscopic arrays of monocrystalline S-layer lattices will be obtained for use in further nanoparticle patterning studies. We have recently completed the fabrication of several gold-patterned test array structures for our in vitro S-layer reassembly studies. These test structures, patterned via e-beam lithography exposure of a poly(methylmethacrylate (PMMA) resist layer, are comprised of square features 25-300 nm in size and spaced 2-10 μm apart. Physical vapor deposition (PVD) and metal-liftoff methods were employed to create the final structures (~40-45 nm thick gold pads supported by a ~2 nm thick chromium adhesion layer). These test structures were analyzed by AFM in order to characterize the dimensions and uniformity of the array features. Efforts are currently underway to chemically modify the surfaces of these gold patterns in order to utilize them in future studies of site-directed S-layer protein self-assembly. References: [1] Sleytr, U.B., Schuster, B, and Pum, D. 2003. Nanotechnology and biomimetics with 2-D protein crystals. IEEE Eng Med Biol Mag. 22:140-50. [2] Bergkvist, M., Mark, S.S., Yang, X., Angert, E.R., and Batt, C.A.. 2004. Bionanofabrication of ordered nanoparticle arrays: Effect of particle properties and adsorption conditions. The Journal of Physical Chemistry B. 108:8241-8248.