Magnetic Au Nanoparticles on Archaeal S-layer Ghosts as Templates

Gold nanoparticles with a size of 2.5 nm were produced using the SlaA-layer ghosts of the archaeon Sulfolobus acidocaldarius as a template. These archaeal bio-Au nanoparticles differ significantly from those of the bacterial bio-Au nanoparticles produced on the S-layer of Bacillus sphaericus. The archaeal Au nanoparticles consist exclusively of Au(0), while the bacterial ones represent a mixture of Au(0) and Au(III). The most impressive feature of the archaeal Au nanoparticles is that they are paramagnetic, in contrast to the bacterial ones and also to bulk gold. As demonstrated by SQUID magnetometry, the archaeal bio-Au possess an unusually large magnetic moment of about 0.1 µB/Au atom. HR-TEM combined with EDX analysis revealed that the archaeal Au nanoparticles are linked to sulfur atoms. The latter originate from the thiol groups of the cystein amino acid residues which are characteristic for the SlaA-layer of S. acidocaldarius but absent in the S-layer of B. sphaericus.