Nanostructuring of surfaces for biosensing and other "nano" applications

Many bacteria are covered with a protein envelope. These surface layer (s-layer) proteins are closely attached and anchored to the secondary cell wall polymer. The proteins used in our group derive from strains of Lysinibacillus species isolated from a uranium mining waste pile near Johanngeorgenstadt, Saxony, Germany. Once purified the disassembled S-layer keep the ability of self-organizing and self-assembling on interfaces. In vitro they form a paracrystalline protein lattice with defined pores and cavities as it can be naturally found on the bacterial surface. These protein sheets either coil up to tube-like structures or attach to surfaces. In addition to the self- assembling and organizing properties these proteins can bind high amounts of heavy metals. The ability to form monomolecular layers at interfaces qualifies them as tool for nano-patterning of surfaces. We are able to cover various surfaces with these proteins with nearly full coverage. This is possible due to recrystallization of monomers on polyelectrolyte coated surfaces. The recrystallization process can be monitored by AFM. AFM-images show the periodic nature of the protein lattice. The monomolecular character of the attached protein lattice was proven during the growth and afterwards by nanolithographic removal of the proteins. Different functional groups of the proteins are provided as binding sites for modifications such as crosslinking of molecules or binding or nucleation of inorganic particles. Therefore the lattice is a perfect immobilization matrix for different compounds as well as the assembly of sensory surfaces. A recently started project aims the development of a sensor for the optical readout of a chemical signal.
The efficient metal binding combined with the periodic alignment is used in other applications to create nanoparticles with a narrow size distribution. Currently we are optimizing the composition of the particles for photocatalysis. The high metal binding capacity itself turns the proteins into a promising material for filtering solutions as it is naturally used by the bacteria.