PRION proteins are virtually indestructible. So why not use this property to make strong-yet-ultrathin wires for delicate nanoscale electronic devices of the future? Susan Lindquist and a team at the Whitehead Institute in Cambridge, Massachusetts are doing just that.
Prions are familiar to many people as the misfolded proteins that induce other proteins to change shape, triggering a chain reaction that leads to deadly diseases such as BSE in cows and variant CJD in humans. But Lindquist and her team are experimenting with a harmless type of prion, obtained by genetically engineering bacteria so that they produce prions from the yeast Saccharomyces cerevisiae. The yeast prion has the same physical property as other prions, but it does not cause disease. With activists already getting worried about the threats some nanotechnologies could pose to society, that鈥檚 an important point.
The prions start out looking like wiggly worms with no particular form or structure but soon some of them start aligning themselves into a highly ordered, tightly packed structure or 鈥渘ucleus鈥�. This nucleus then forces the other proteins to fall into line, and they assemble themselves into fibres about 10 nanometres in diameter and up to 100 micrometres long. The process can take up to 50 hours.
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Each prion fibre has millions of proteins and has exceptional strength, says Lindquist. 鈥淭hey are as tough as can be. You can boil them, denature them or put them in organic solvents,鈥� she says. To take advantage of this toughness the team decided to turn the nanofibres into conducting wires by adding gold nanoparticles that are chemically attracted to certain sites on a prion fibre.
Then they added gold and silver to the nanoparticles so that they grew into beads, until the beads touched end-to-end. They ended up with a metal wire on a prion fibre substrate barely 100 nanometres in diameter, which can carry current and has the same conductance as gold.
In the future, Lindquist plans to attach the protein nucleus that triggers the formation of nanofibres to electrodes in a nanocircuit. This will allow the wires to be grown in situ, she hopes, allowing intricate-but-tough circuits to be created. New sensors are possible, too, if the prions are engineered so that other proteins, perhaps with chemical-sensing capabilities, project outwards from the fibres.