S-layer protein and carbon nanotube construction kit

Carbon nano tubes (CNTs) are cylindrical nano structures made of carbon atoms. Due to their outstanding mechanical and electrical properties, and thermal conductivity, they are already used as additives in various novel materials. Recently, CNTs have also been considered for several medical applications due to their small diameters and ability to penetrate cells and tissues. However, since CNTs are chemically inert and insoluble in water, they have to be chemically functionalized or coated with biomolecules to carry payloads or interact with the environment. Proteins bound to the surface of CNTs are preferred because they provide a better biocompatibility and offer functional groups for binding additional molecules. Nevertheless, their arrangement and density on the CNT surface and, consequently the availability of functional groups, varies considerably. An alternative approach to functionalize CNTs with an - additionally closed and precisely ordered - protein layer is offered by bacterial surface layer (S-layers) proteins which have already attracted much attention in the functionalization of surfaces as well as supporting structures for biomembranes. In a broad range of bacteria and archaea S-layer proteins cover the cells completely and may be considered as one of the most abundant biopolymers on earth. S-layer protein lattices show parameters in the nanometer range and offer surface chemical groups and genetically introduced biologically functional domains in precisely defined locations and orientation on their surfaces. Moreover, and highly relevant for this project too, is the natural capability of isolated S-layer proteins to self- assemble into monolayers in solution and at interfaces (e.g. on solid supports). The overall project aim is to conduct fundamental studies on the reassembly of S-layer proteins on CNTs and learn from nature how these new hybrid architectures may be used to make novel materials e.g. for biosensing. Key are the reassembly and binding properties of S-layer proteins which allow a highly specific and sensitive functionalization of the CNT surface. Moreover, novel hybrid organic- inorganic nano structures (e.g. nano containers for drug delivery) will become possible by using the S- layer coating as template in the biomineralization of silica, metals or other technologically important materials. Further on, it may also be assumed that the pores in the S-layer lattice will induce an ordered arrangement of metallic nanoparticles directly on the CNT surface and thus might lead to new electronic effects along the one-dimensional CNTs. Based on these few examples of an S-layer protein and CNTs construction kit, we would like to stress that our research, although longer term in nature, might lead to a new technology for the functionalization of carbon nanotube surfaces.

Carbon nanotubes (CNTs) are cylindrical nanostructures made purely of carbon atoms. Due to their outstanding mechanical and electrical properties, as well as thermal conductivity, carbon nanotubes are used as basic materials in nanotechnology. However, carbon nanotubes have also recently been looked at more closely for applications in medicine, as they can penetrate cells and tissues due to their small diameter. Since carbon nanotubes are chemically inert and do not dissolve in water, for example, their surface must be adapted chemically or by binding molecules so that they can interact with their environment. Various possibilities are known for this, but they often have the disadvantage that the so-called functionalization of the surface of the carbon nanotubes is usually only possible very irregularly or incompletely. A new way to functionalise carbon nanotubes is offered by S-layer proteins, which have already been used for a long time to modify surfaces in nanotechnology. S-layer proteins form two-dimensional lattices that completely enclose the cells of many bacterial strains and all archaea. Crucial for the application of S-layer proteins in nanotechnology and thus in this project is their property to form two-dimensional lattices again by themselves in solution and at interfaces, such as carbon nanotubes. The project objective was to investigate the recrystallization of S-layer proteins on carbon nanotubes and to apply the knowledge gained to the production of novel materials, such as for biosensors. This was successfully achieved with so-called S-layer fusion proteins, which allow a highly specific functionalization of the surface through genetically introduced functional groups. Building on this fundamental work, it was possible to develop novel hybrid structures, such as nano-containers for the transport of active substances, based on the biomineralization on S-layers. Crucial to the success of the project, however, was also the development of a completely new preparation protocol that also allows the coating of pristine carbon nanotubes. The carbon nanotubes coated with S-layer protein were stable for several months, which is extremely important for their technological use. It should also be mentioned that graphene, which consists of a single-layered honeycomb pattern of carbon atoms and is of utmost importance in nanotechnology today, could also be coated with S-layer proteins. By using different S-layer proteins and carbon nanotubes, it was possible to develop a construction kit that can be used in a wide range of applications in nanotechnology.