Bacteriography

I recently found a couple of articles which caught my interest, both on roles bacteria can play in electronics. The first has to do with a method to form semiconductor-like structures on a sheet of graphene. Graphene is an excellent conductor but in sheet form but conducts more or less equally in all directions. So the first problem is to be able pattern structures onto the graphene to create preferred directions.

Researchers at the University of Illinois knew that wrinkles in the graphene layer will reduce conductivity across the wrinkle but stretching and releasing a sheet gives little control on scale or location for wrinkles. Thinking very creatively, they placed a drop of a nutrient solution containing bacterius subtillis (a bacterium found in soil) on the sheet, then ran a current through the sheet which causes these bacteria to align in the direction of the field. They then built a layer of graphene over the whole sheet (and bacteria) and cooked the lot in vacuum at 250[SUP]o[/SUP]C. That causes the bacteria to dehydrate and wrinkle, which apparently they do to a form with a height of 7-10nm and very precise wrinkle spacing of 33nm, causing the upper layer of graphene to wrinkle correspondingly.

The achieves the desired directionality of conductivity, but misses the mark on giving band-gap characteristics to the graphene structure, which apparently would require a wrinkle spacing of 5nm or less. Researchers hope that a different type of bacteria may be more obliging. The work obviously has a way to go before any of this becomes practical, not least in first releasing the upper (wrinkled) layer of graphene from the lower layer and the desiccated bacteria.

Meanwhile, the Office of Naval Research has been working on creating nanowires built from a part of a bacterium. Geobacter (a bacterium found in river mud) produces very thin (1.5nm) protein filaments which are electrically conducting and help support the respiration of the organism through connection to metallic oxides. Natural conductivity is very low but can be improved by multiple orders of magnitude by fiddling with the amino acid sequence in these protein chains. These nano-wires can now be synthesized independently from the bacterium. Again, don’t bother looking for KickStarter campaigns just yet, though there is now a site independent of the ONR dedicated to reporting progress in this area.

You can learn more about creating wrinkle structure on graphene HERE and the ONR project on nanowires HERE. The independent site is HERE.

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