Mark T Tuominen | PubMed Health

PubMed2005

Direct control of the magnetic interaction between iron oxide nanoparticles through dendrimer-mediated self-assembly.

Cationic superparamagnetic iron oxide nanoparticles were assembled using a series of anionic polyamidoamine dendrimers. The resulting assemblies featured systematically increasing average interparticle spacing over a 2.4 nm range with increasing dendrimer generation. This increase in spacing modulated the collective magnetic behavior by effective lowering of the dipolar coupling between particles. The results obtained in these studies deviate from the predicted dependence of collective behavior on interparticle spacing, suggesting that a dense assembly of magnetically "free" particles can exist with a surprisingly small space between particles.

Journal Article↗

PubMed2005

Extracellular electron transfer via microbial nanowires.

Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.

Biotechnology↗