Heavy metal thunder: Protein can be switched on to conduct electricity like a metal

When pushing the boundaries of discovery, sometimes even the most experienced of scientists can get a surprise jolt from a completely unpredictable result.

That was the case for ASU Regents' Professor and biophysicist Stuart Lindsay, who has spent his career building new microscopes that have become the eyes of nanotechnology and next-generation, rapid and low-cost DNA and amino acid readers to make precision medicine more of a reality.

In the process, Lindsay's research team has learned a thing or two about how single molecules behave when tethered between a pair of electrodes, which is the foundation for how his DNA readers work.

The technology, called recognition tunneling, threads single molecules down a nanopore like a thread through the eye of a needle.

As they go down the nano-rabbit hole, electrodes measure the electrical properties of these single DNA or amino acid molecules to determine their sequence identity.

Having spent a considerable amount of time building DNA and amino readers, the thought was to give whole proteins a try. "The technological goal here was, can we use our technology to electronically detect whole proteins," said Lindsay.

But, about four years ago, Lindsay's research team got a lab result that even he couldn't quite believe.

As with most scientific surprises, it goes against all conventional wisdom.

"What we've done here is to use our recognition tunneling to measure the electrical conductance of intact proteins. The thought was, that if you can specifically trap a whole protein between a pair of electrodes, you would have a label-free electronic reader."

The potential to have a nanotechnology device sensitive enough to identify a single protein molecule could become a powerful new diagnostic tool in medicine.

But the building blocks in every cell, proteins, were thought to behave electrically as inert organic blobs. Electronically, they were thought to act as insulators, just like putting a piece of plastic over a metal wire.

"There is just a large amount of swept under the rug data on the electrical properties of proteins," said Lindsay. "There is one camp who dismiss these claims. There is another camp that says proteins are incredible electrical conductors. And never the twain shall meet, just like American politics."

So four years ago, one of his graduate students at the time, Yanan Zhao, gave the protein challenge. He had tethered a protein between two electrodes, turned up the voltage, and voila! The protein started performing like a metal, with a wild and "remarkably high electronic conductance."

"If it's true, it's amazing," said Lindsay.

Now, after years of trying to disprove the results himself and trying to account for every potential wrong avenue or detour, his research group has published their new findings in the advanced online edition of the Institute of Physics journal Nano Futures.

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