Selective self-assembly of biogenic silica assisted by layer-by-layer deposition and inkjet printing

Nature is an inspirational source of silica structures that possess unique optical properties. A few classes of organisms fabricate metal oxides with nanoscale features by a bottom-up self assembly process. In particular, diatoms are a prolific class of single-celled algae that possess silica shells or "frustules" with intricate submicron scale features, including two-dimensional pore arrays. During frustule development, membrane-bound transporters actively take actively up the soluble silicon in the form of Si(OH)4. Once inside the cell, Si(OH)4 is converted to nanostructured silica by protein-mediated condensation reaction within the silicon deposition vesicle, an organelle which serves as the mold for frustule development. Recently, it has been shown that intact diatom frustules can act as 2D photonic crystals and optical sensor platforms for the detection of organic vapors. Techniques to assemble and pattern these microorganisms at large scale is needed to take advantage of these nanostructured silica for device applications such as sensors, photonic crystals and electroluminescence devices. In this work, individual shells of the diatom Coscinodiscus self-assembled into a rectangular array on a glass surface which possessed a polyelectrolyte multilayer patterned through inkjet printing. This patterned thin film possessed hierarchical order with nanostructure provided by the diatom biosilica. The process used two polyelectrolytes with opposite electric potentials to control the surface charge of the substrate. The fine features of the diatom frustules were perfectly preserved due to the mild conditions of the deposition process. This technique has the potential to enable large-scale device applications which harness the unique properties of functionalized diatom biosilica.