S-layers as multifunctional templates for nanotechnology

Surface-layer (S-layer) proteins are biomolecules which can self-assemble in aqueous solutions and on surfaces. Those polymers form highly ordered two dimensional structures with unit cell sizes of few nanometers. On surface of such protein polymers one can find a high amount of modifiable groups like COOH-, NH2- and OH-groups. The latter and its nanostructuring make S-layers a perfect platform for nanotechnology.
Therefore S-layers can work as biotemplate to build biosensors consisting of fluorescence dyes and aptamers. Thereby fluorescence dyes will work as signal transducer system by performing a Foerster Resonance Energy Transfer (FRET) between each other. Aptamers serve as receptor for one specific analyte. Analyte binding by the aptamer leads to a detectable signal change because of a disturbed FRET. An idealized design of such a biosensor is shown in Fig. 1a. In a recent published work a FRET-pair was chemically linked to S-layers and showed an energy transfer efficiency of 40 % [1]. In further work aptamers will be chemically linked to the S-layer-FRET-system to reach proof of concept.
Another application for those S-layer proteins can be the development of catalytic materials based on highly ordered nanoparticles. Thereby nanoparticles of platinum or palladium are synthesized in the pores of S-layers. Fig. 1b shows an idealized scheme. After removal of the organic matrix nanoparticles are arranged on the surface having a defined size and order. These materials can now work as catalysts for e.g. organic synthesis or metallization of polymers.