Rapid fabrication of micro- and nanoscale patterns by replica moulding from diatom biosilica

Diatoms are single-celled micro-algae that possess an exoskeleton (called frustule) comprised of diverse and highly ordered 3D porous silica structures and that hold considerable promise for biological or biomimetic fabrication of nanostructured materials and devices. We have used, for the first time, a soft lithographic approach of replica molding to replicate porous diatom structures into polymers. Two centric diatom species, Coscinodiscus sp., Thalassiosira eccentrica cultured in our laboratory were used as masters for replication. In the first step, replica molding onto soft and elastic polymer using poly(dimethylsiloxane) PDMS produced a negative replica of the diatom frustule. These PDMS replicas were then used as a mold to fabricate the positive polymer replicas of diatoms using a mercaptol ester type UV curable polymer (NOA 60). Fabricated polymer replicas were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). In all cases, diatom micro- and nanoscale porous structures were successfully transferred with high precision into polymer replicas. Such an accomplishment effectively demonstrates the potential for using diatoms as blueprints for rapid and simple fabrication of polymer nanostructures. The prepared replicas were used as diffraction gratings and as nanowells to hold polymeric nanoparticles effectively demonstrating the functional properties of these biomimetic structures.D. Losic, J. G. Mitchell, R. Lal, and N. H. Voelcke

Interfacing the nanostructured biosilica microshells of the marinediatom Coscinodiscus wailesii with biological matter

Biosilicified nanostructured microshells from the marine diatom Coscinodiscus wailesii have been properly functionalised to bind a molecular probe which specifically recognises a target analyte. The chemical modification process has been characterised by Fourier transformed infrared spectroscopy. Fluorescence measurements demonstrate that the antibodies we used, even if linked to the amorphous silica surface of C. wailesii microshells, still efficiently recognise their antigens. These low cost and largely available natural materials can be thus used as transducers elements for optical biosensors or as targeting microcapsules for drug deliver

Particle morphology dependent superhydrophobicity in treated diatomaceous earth/polystyrene coatings

Superhydrophobic surfaces have been prepared from three different types of diatomaceous earth (DE) particles treated with 3-(heptafluoroisopropoxy)propyltrimethoxysilane (HFIP-TMS) and low molecular mass polystyrene. The untreated particles, consisting of CelTix DE (disk shape), DiaFil DE (rod shape) and EcoFlat DE (irregular), were studied using particle size analysis, bulk density, pore volume and surface area analysis (via Brunauer–Emmett–Teller, BET, methods). The treated particles were characterized with thermogravimetric analysis (TGA), contact angles, scanning electron microscopy, profilometry, and FTIR spectroscopy. The minimum amount of silane coupling agent on the DE surfaces required to obtain superhydrophobicity of the particles was determined and found to be dependent on the particle morphology. In the coatings made from different particles with 2.4 wt% HFIP-TMS, the minimum amounts of treated particles (loadings) for superhydrophobicity was determined with the less dense CelTix DE requiring about 30 wt%, DiaFil DE requiring about 40 wt%, and EcoFlat DE each requiring about 60 wt% loading of treated particles

Directed assembly of nanoparticles to isolated diatom valves using the non-wetting characteristics after pyrolysis

A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is presented. After pyrolysis, the valves exhibit incomplete wetting due to their characteristic T-shaped profiles as a prerequisite for a regioselective coupling reaction. A micromanipulation system allows for precise handling and their immobilization onto an adhesive substrate and manipulation into arrays