Synthesis and magnetic characterization of microstructures prepared from microbial templates of differing morphology

In this study, we demonstrate the use of bacterial templates of differing morphology for the facile synthesis of magnetic micron-sized spheres, tetrads of spheres, filaments, and coils. These microstructures were synthesized by a platinum catalyzed electroless deposition of nickel under mild aqueous conditions using D. radiodurans, genetically elongated E. coli, and R. rubrum as templates, respectively. Analysis by SEM/EDS, TEM, and SQUID magnetometry indicates the formation of superparamagnetic metallic microfilaments, which possess a blocking temperature of ∼70 K with no observable exchange anisotropy. XPS analysis of the metallic microfilaments supports the presence of NiB, which is diamagnetic, thus supporting the hypothesis that the morphologically unique microbial templates are encapsulated within a biosurface-bound NiB shell that contains embedded nickel nanoparticles (12–20 nm). The use of microorganisms as templates, which may be recombinantly modified, may therefore serve as alternative means for magnetic microstructure and core–shell synthesis.