Bioinspired nanocomposites based on self-assembling bacterial surface layer proteins

Bio-inorganic materials are very attractive for a variety of technical applications. The use of self-assembling proteins as part of such a hybrid material is an attractive approach for the development of such materials. Especially the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].
In a current project we use monolayers of the S-layer protein of Lysinibacillus sphaericus for the construction of sensory layers. These S-layers are functionalized by aptamers (oligonucleotides) that work as receptor and two different fluorophores working as donor/acceptor for detection. Appropriate excitation/emission spectra and closest proximity of the fluorophores permit FRET. The binding of the analyte to the aptamer should influence the fluorescence, ideally causing the interruption of the FRET.
In other projects we used the S-layers for the formation of (photo)catalytic layers. In this approach S-layers work as template for the bioinspired formation of (photo)catalytic particles such as Pd or ZnO. Size, crystallinity, distribution and morphology of the particles are influenced by the proteinaceous template.
These examples demonstrate the high potential of the S-layers for various applications.

[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
[3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244