Magnetic Au Nanoparticles on Archaeal S-Layer Ghosts as Templates

Abstract

Cell-ghosts representing empty cells of the archaeon Sulfolobus acidocaldarius, consisting only of their highly ordered and unusually stable outermost proteinaceous surface layer (S-layer), were used as templates for Au nanoparticles fabrication. The properties of these archaeal Au nanoparticles differ significantly from those produced earlier by us onto bacterial S-layer sheets. The archaeal Au nanoparticles, with a size of about 2.5 nm, consist exclusively of metallic Au(0), while those produced on the bacterial S-layer had a size of about 4 nm and represented a mixture of Au(0) and Au(III) in the ratio of 40 to 60 %. The most impressive feature of the archaeal Au nanoparticles is that they are strongly paramagnetic, in contrast to the bacterial ones and also to bulk gold. SQUID magnetometry and XMCD measurements demonstrated that the archaeal Au nanoparticles possess a rather large magnetic moment of about 0.1μB/atom. HR-TEM-EDX analysis revealed that the archaeal Au nanoparticles are linked to the sulfur atoms of the thiol groups of the amino acid cysteine, characteristic only for archaeal S-layers. This is the first study demonstrating the formation of such unusually strong magnetic Au nanoparticles on a non-modified archaeal S-layer.