MASTER THESIS Biomimetic potential of sponge ... - IAP/TU Wien

On the subject of spicule inspired nanostructures many different approaches have been
pursued. Cha and colleagues (2000) soon after their discovery of the silicatein controlled
synthesis of spicules reported the successful synthesis of silica structures by a biomimetic
approach. In the mineralization process, silicatein was replaced by a synthetic peptide
(consisting of cysteine and lysine) that catalyzed the deposition of regular silica rods.
It has been found out that for the efficient deposition of silica two amino acids in the
sequence of silicatein were crucial (Zhou et al., 1999). The identification of this essential
feature of silicatein helped researchers to find simple chemical compounds that catalyze the
formation of silica structures. In this line of research, Park and Choi (2010) used small simple
molecules, an amino acid derivative and a surfactant, to catalyze the formation of
individually separated microspheres at near-neutral pH.
A different approach in nanotechnology is the use of (recombinant) silicatein to catalyze
the deposition of other metal oxides than silica. Conceptually, it is not clear whether this
classifies as biomimetics because the naturally occurring enzyme is used directly, and no
abstraction is being made at that level. However, as stated by André and co-workers (2012),
the emulation of the chemistry behind natural mineralization processes is indispensable for
the use of known biomineralization agents like silicatein in technological processes. Thus, at
the scale of chemical conditions relevant for the mineralization process some degree of
abstraction is recognizable.
Examples of successful attempts to use silicatein, immobilized on synthetic surfaces, for
mineralization of metal oxides include the formation of layered titania (TiO 2 ) and zirconia
(ZrO 2 ) (Tahir et al., 2005) and the formation of gallium oxide (GaOH ⁄ Ga 2 O 3 ) nanocrystals on
filaments (Kisailus et al., 2005). In the examples presented here, the absence of alkali and
acid (near-neutral pH) was stressed as distinctive to previous protocols for the synthesis of
similar compounds. André and colleagues (2011) went one step further by including not only
silicatein, but also silintaphin (a protein interacting with silicatein in vivo) that enhanced the
deposition of the metal oxide used. Specifically, TiO 2 nanorods were coated with silicatein
and silintaphin and subsequently catalyzed the deposition of either zirconia or silica.
Irrespective of the assembled molecules, there have been identified two key features of
the polycondensation reaction by silicatein or a biomimetic analogue. The hydrolysis of the
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