Synthesis of metal nanoparticles using bacterial surface layers (S-layers) as biological templates

The regular structured paracrystalline surface layers (S-layers), which are one of the most common surface structures found in bacteria and archaea, are promising biological templates for the production of metal nanoclusters. Most of them are composed of protein monomers with the ability to self assemble in two-dimensional arrays. They possess regularly arranged pores of identical size that enable the exchange of ions and small molecules between the living cells and their environment.
In the present work the purified S-layer sheets of the uranium mining waste pile isolate B. sphaericus JG-A12 were used as biological template to produce Pd, Au, and Pt nanoparticles of a size of 0.8-1 nm. Such metal nanoparticles may have strongly altered properties compared to their bulk counterparts making them interesting for the development of new materials and applications in the field of catalysis. The deposition of metal nanoclusters was performed via a two step process, consisting of biosorption by exposition of the S-layer proteins to a hydrolyzed solution of metal salt (I) and of metal reduction (II) by the addition of a strong reducing agent. The interaction of Pd(II) with the S-layer of B. sphaericus JG-A12 and the formed Pd-nanoclusters were analyzed using EXAFS-spectroscopy and ATR-FT-IR-spectroscopy. The analyses demonstrated the complexation of Pd(II) to carboxyl groups. The metal nanoclusters were investigated using EXAFS spectroscopy and SQUID magnetometry. The Pd and Pt nanoclusters reveal interesting magnetic properties in a wide temperature and magnetic field range.