Microbial synthesis and the characterization of metal-substituted magnetites

The use of bacteria as a novel biotechnology to facilitate the production o f nanoparticles is in its infancy. We describe a bacterially mediated elect rochemical process in which metal (Co, Cr, or Ni)-substituted magnetite pow ders were synthesized by iron(III)-reducing bacteria under anaerobic condit ions. Amorphous Fe(III) oxyhydroxides plus soluble metal species (Co. Cr, N i) comprise the electron acceptor and hydrogen or simple organics comprise the electron donor. The microbial processes produced copious amount of nm-s ized, metal-substituted magnetite crystals. Chemical analysis and X-ray pow der diffraction analysis showed that metals such as Co, Cr, and Ni were sub stituted into biologically facilitated magnetites. These results suggest th at the bacteria may be viewed as a nonspecific source of electrons at a pot ential that can be calculated or surmised based on the underlying thermodyn amics. Microbially facilitated synthesis of the metal-substituted magnetite s at near ambient temperatures may expand the possible use of the specializ ed ferromagnetic particles. (C) 2001 Elsevier Science Ltd. All rights reser ved.