Abstract
Microbial production of nano-sized particles has a demonstrated capacity to make highly crystalline pure phase magnetite or with some substitution of Fe by Co, Ni, Cr, Mn, Zn or the rare earths. Microbial production of magnetic nanoparticles can be achieved in large quantities and at low cost. Over 1 kg (wet weight) of Zn-substituted magnetite (nominal composition of Zn0.6Fe2.4O4) has been recovered from 30 L fermentations. Transmission electron microscopy (TEM) was used to confirm that this mass produced extracellular magnetites exhibited good mono-dispersity. TEM results also showed a highly reproducible particle size and corroborated average crystallite size (ACS) of 13.1 � 0.8 nm determined through X-ray diffraction (N=7) at a 99 % confidence level. Based on scale-up experiments performed using a 35 L reactor, the increase in ACS reproducibility may be attributed to an increase of electron donor input, availability of divalent substitution metal ions and less ferrous ions in the case of substituted magnetite, increased reactor volume overcoming differences in each batch, or a combination of the above. While costs of commercial nanometer sized magnetite (25-50 nm) may cost $500/kg, microbial production is likely capable of producing 5-90 nm pure or substituted magnetites at a fraction of the cost of traditional chemical synthesis. While there are numerous approaches for the synthesis of nanoparticles, bacterial fermentation of magnetite or metal-substituted magnetite may represent an advantageous manufacturing technology with respect to yield, reproducibility and scalable synthesis with low costs at low energy input.
