Ultrafast holographic nanopatterning of biocatalytically formed silica

Abstract

Diatoms are of interest to the materials research community because of their ability to create highly complex and intricate silica structures under physiological conditions: what these single-cell organisms accomplish so elegantly in nature requires extreme laboratory conditions to duplicate-this is true for even the simplest of structures. Following the identification of polycationic peptides from the diatom Cylindrotheca fusiformis, simple silica nanospheres can now be synthesized in vitro from silanes at nearly neutral pH and at ambient temperatures and pressures. Here we describe a method for creating a hybrid organic/inorganic ordered nanostructure of silica spheres through the incorporation of a polycationic peptide (derived from the C. fusiformis silaffin-1 protein) into a polymer hologram created by two-photon-induced photopolymerization. When these peptide nanopatterned holographic structures are exposed to a silicic acid, an ordered array of silica nanospheres is deposited onto the clear polymer substrate. These structures exhibit a nearly fifty-fold increase in diffraction efficiency over a comparable polymer hologram without silica. This approach, combining the ease of processability of an organic polymer with the improved mechanical and optical properties of an inorganic material, could be of practical use for the fabrication of photonic devices.

Novel nanocomposites from spider silk–silica fusion (chimeric) proteins

“…Typically, for silica precipitation with or without the presence of proteins, 30 mM silicic acid was used, unless otherwise stated. Silica synthesis was carried out as described previously (11,12,14,15,44,45). The reaction mixture was allowed to condense for a desired period while aliquots at known time were taken for molybdosilicate kinetic assay (44).…”

“…Even though the lysine and serine groups are not posttranslationally modified in R5 peptide (unlike natural silaffins), this 19-aa unit is found to promote and regulate silica formation at neutral pH (under conditions that would not have been expected to generate silica). Specifically, the R5 peptide has been used to obtain spherical silica nanostructures by using various precursors (12,14,15) as well as structures with different morphologies, including arch shapes and elongated fibers (13).In the present article we describe a novel biomimetic nanocomposite approach to synthesize silica composites using fusion (chimeric) proteins. Fusion proteins have found applications in a wide spectrum of areas such as the biomedical field [including immunology, cancer research, and drug delivery (17-20)] and materials science [self-assembled materials (e.g., gels), quantum dot bioconjugates, sensors, and inorganic materials synthesis (21-27)].…”

“…Various proteins have been isolated from biosilicas, in particular, siliceous frustules of a few selected diatoms of which some low-molecular-weight proteins, known as silaffins, and some even lower molecular weight compounds, termed polyamines, have also been suggested to play a crucial role in silica formation (11). In vitro studies of silica formation have also been performed by using synthetic variants of the R5 peptide that derives from the repeating motif found in silaffin proteins (11)(12)(13)(14)(15)(16). Even though the lysine and serine groups are not posttranslationally modified in R5 peptide (unlike natural silaffins), this 19-aa unit is found to promote and regulate silica formation at neutral pH (under conditions that would not have been expected to generate silica).…”

“…Even though the lysine and serine groups are not posttranslationally modified in R5 peptide (unlike natural silaffins), this 19-aa unit is found to promote and regulate silica formation at neutral pH (under conditions that would not have been expected to generate silica). Specifically, the R5 peptide has been used to obtain spherical silica nanostructures by using various precursors (12,14,15) as well as structures with different morphologies, including arch shapes and elongated fibers (13).…”

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

“…These insights into biomineralization appear to be vastly important to control the sol-gel processing of silica. The use of short polypeptide sequences of a silaffin-1 precursor protein, rich in serine and lysine residues, has been utilized in the holographic patterning of silica [14]. Similarly the use of polypeptides and synthetic cationic polymers, and long-chain polyamines have demonstrated the ability to direct and control the deposition and morphology of silica [15][16][17].…”