protein nanowires | FrogHeart

A February 24, 2022 news item on phys.org describes research into using proteins as electrical conductors,

Proteins are among the most versatile and ubiquitous biomolecules on earth. Nature uses them for everything from building tissues to regulating metabolism to defending the body against disease.
Now, a new study shows that proteins have other, largely unexplored capabilities. Under the right conditions, they can act as tiny, current-carrying wires, useful for a range human-designed nanoelectronics.
….

A February 25, 2022 Arizona State University (ASU) news release (also on EurekAlert but published February 24, 2022), which originated the news item, delves further into the intricacies of nanoelectronics (Note: Links have been removed),

In new research appearing in the journal ACS Nano, Stuart Lindsay and his colleagues show that certain proteins can act as efficient electrical conductors. In fact, these tiny protein wires may have better conductance properties than similar nanowires composed of DNA [deoxyribonucleic acid], which have already met with considerable success for a host of human applications.
Professor Lindsay directs the Biodesign Center for Single-Molecule Biophysics. He is also professor with ASU’s Department of Physics and the School of Molecular Sciences.
Just as in the case of DNA, proteins offer many attractive properties for nanoscale electronics including stability, tunable conductance and vast information storage capacity. Although proteins had traditionally been regarded as poor conductors of electricity, all that recently changed when Lindsay and his colleagues demonstrated that a protein poised between a pair of electrodes could act as an efficient conductor of electrons.
The new research examines the phenomenon of electron transport through proteins in greater detail. The study results establish that over long distances, protein nanowires display better conductance properties than chemically-synthesized nanowires specifically designed to be conductors. In addition, proteins are self-organizing and allow for atomic-scale control of their constituent parts.
Synthetically designed protein nanowires could give rise to new ultra-tiny electronics, with potential applications for medical sensing and diagnostics, nanorobots to carry out search and destroy missions against diseases or in a new breed of ultra-tiny computer transistors. Lindsay is particularly interested in the potential of protein nanowires for use in new devices to carry out ultra-fast DNA and protein sequencing, an area in which he has already made significant strides.
In addition to their role in nanoelectronic devices, charge transport reactions are crucial in living systems for processes including respiration, metabolism and photosynthesis. Hence, research into transport properties through designed proteins may shed new light on how such processes operate within living organisms.
While proteins have many of the benefits of DNA for nanoelectronics in terms of electrical conductance and self-assembly, the expanded alphabet of 20 amino acids used to construct them offers an enhanced toolkit for nanoarchitects like Lindsay, when compared with just four nucleotides making up DNA.
Transit Authority
Though electron transport has been a focus of considerable research, the nature of the flow of electrons through proteins has remained something of a mystery. Broadly speaking, the process can occur through electron tunneling, a quantum effect occurring over very short distances or through the hopping of electrons along a peptide chain—in the case of proteins, a chain of amino acids.
One objective of the study was to determine which of these regimes seemed to be operating by making quantitative measurements of electrical conductance over different lengths of protein nanowire. The study also describes a mathematical model that can be used to calculate the molecular-electronic properties of proteins.
For the experiments, the researchers used protein segments in four nanometer increments, ranging from 4-20 nanometers in length. A gene was designed to produce these amino acid sequences from a DNA template, with the protein lengths then bonded together into longer molecules. A highly sensitive instrument known as a scanning tunneling microscope was used to make precise measurements of conductance as electron transport progressed through the protein nanowire.
The data show that conductance decreases over nanowire length in a manner consistent with hopping rather than tunneling behavior of the electrons. Specific aromatic amino acid residues, (six tyrosines and one tryptophan in each corkscrew twist of the protein), help guide the electrons along their path from point to point like successive stations along a train route. “The electron transport is sort of like skipping stone across water—the stone hasn’t got time to sink on each skip,” Lindsay says.
Wire wonders
While the conductance values of the protein nanowires decreased over distance, they did so more gradually than with conventional molecular wires specifically designed to be efficient conductors.
When the protein nanowires exceeded six nanometers in length, their conductance outperformed molecular nanowires, opening the door to their use in many new applications. The fact that they can be subtly designed and altered with atomic scale control and self-assembled from a gene template permits fine-tuned manipulations that far exceed what can currently be achieved with conventional transistor design.
One exciting possibility is using such protein nanowires to connect other components in a new suite of nanomachines. For example, nanowires could be used to connect an enzyme known as a DNA polymerase to electrodes, resulting in a device that could potentially sequence an entire human genome at low cost in under an hour. A similar approach could allow the integration of proteosomes into nanoelectronic devices able to read amino acids for protein sequencing.
“We are beginning now to understand the electron transport in these proteins. Once you have quantitative calculations, not only do you have great molecular electronic components, but you have a recipe for designing them,” Lindsay says. “If you think of the SPICE program that electrical engineers use to design circuits, there’s a glimmer now that you could get this for protein electronics.”

Here’s a link to and a citation for the paper,

Electronic Transport in Molecular Wires of Precisely Controlled Length Built from Modular Proteins by Bintian Zhang, Eathen Ryan, Xu Wang, Weisi Song, and Stuart Lindsay. ACS Nano 2022, 16, 1, 1671–1680 DOI: https://doi.org/10.1021/acsnano.1c10830 Publication Date:January 14, 2022 Copyright © 2022 American Chemical Society

This paper is behind a paywall.

Part of neuromorphic computing’s appeal is the promise of using less energy because, as it turns out, the human brain uses small amounts of energy very efficiently. A team of researchers at the University of Massachusetts at Amherst have developed function in the same range of voltages as the human brain. From an April 20, 2020 news item on ScienceDaily,

Only 10 years ago, scientists working on what they hoped would open a new frontier of neuromorphic computing could only dream of a device using miniature tools called memristors that would function/operate like real brain synapses.
But now a team at the University of Massachusetts Amherst has discovered, while on their way to better understanding protein nanowires, how to use these biological, electricity conducting filaments to make a neuromorphic memristor, or “memory transistor,” device. It runs extremely efficiently on very low power, as brains do, to carry signals between neurons. Details are in Nature Communications.

An April 20, 2020 University of Massachusetts at Amherst news release (also on EurekAlert), which originated the news items, dives into detail about how these researchers were able to achieve bio-voltages,

As first author Tianda Fu, a Ph.D. candidate in electrical and computer engineering, explains, one of the biggest hurdles to neuromorphic computing, and one that made it seem unreachable, is that most conventional computers operate at over 1 volt, while the brain sends signals called action potentials between neurons at around 80 millivolts – many times lower. Today, a decade after early experiments, memristor voltage has been achieved in the range similar to conventional computer, but getting below that seemed improbable, he adds.
Fu reports that using protein nanowires developed at UMass Amherst from the bacterium Geobacter by microbiologist and co-author Derek Lovely, he has now conducted experiments where memristors have reached neurological voltages. Those tests were carried out in the lab of electrical and computer engineering researcher and co-author Jun Yao.
Yao says, “This is the first time that a device can function at the same voltage level as the brain. People probably didn’t even dare to hope that we could create a device that is as power-efficient as the biological counterparts in a brain, but now we have realistic evidence of ultra-low power computing capabilities. It’s a concept breakthrough and we think it’s going to cause a lot of exploration in electronics that work in the biological voltage regime.”
Lovely points out that Geobacter’s electrically conductive protein nanowires offer many advantages over expensive silicon nanowires, which require toxic chemicals and high-energy processes to produce. Protein nanowires also are more stable in water or bodily fluids, an important feature for biomedical applications. For this work, the researchers shear nanowires off the bacteria so only the conductive protein is used, he adds.
Fu says that he and Yao had set out to put the purified nanowires through their paces, to see what they are capable of at different voltages, for example. They experimented with a pulsing on-off pattern of positive-negative charge sent through a tiny metal thread in a memristor, which creates an electrical switch.
They used a metal thread because protein nanowires facilitate metal reduction, changing metal ion reactivity and electron transfer properties. Lovely says this microbial ability is not surprising, because wild bacterial nanowires breathe and chemically reduce metals to get their energy the way we breathe oxygen.
As the on-off pulses create changes in the metal filaments, new branching and connections are created in the tiny device, which is 100 times smaller than the diameter of a human hair, Yao explains. It creates an effect similar to learning – new connections – in a real brain. He adds, “You can modulate the conductivity, or the plasticity of the nanowire-memristor synapse so it can emulate biological components for brain-inspired computing. Compared to a conventional computer, this device has a learning capability that is not software-based.”
Fu recalls, “In the first experiments we did, the nanowire performance was not satisfying, but it was enough for us to keep going.” Over two years, he saw improvement until one fateful day when his and Yao’s eyes were riveted by voltage measurements appearing on a computer screen.
“I remember the day we saw this great performance. We watched the computer as current voltage sweep was being measured. It kept doing down and down and we said to each other, ‘Wow, it’s working.’ It was very surprising and very encouraging.”
Fu, Yao, Lovely and colleagues plan to follow up this discovery with more research on mechanisms, and to “fully explore the chemistry, biology and electronics” of protein nanowires in memristors, Fu says, plus possible applications, which might include a device to monitor heart rate, for example. Yao adds, “This offers hope in the feasibility that one day this device can talk to actual neurons in biological systems.”

That last comment has me wondering about why you would want to have your device talk to actual neurons. For neuroprosthetics perhaps?

Here’s a link to and a citation for the paper,

Bioinspired bio-voltage memristors by Tianda Fu, Xiaomeng Liu, Hongyan Gao, Joy E. Ward, Xiaorong Liu, Bing Yin, Zhongrui Wang, Ye Zhuo, David J. F. Walker, J. Joshua Yang, Jianhan Chen, Derek R. Lovley & Jun Yao. Nature Communications volume 11, Article number: 1861 (2020) DOI: https://doi.org/10.1038/s41467-020-15759-y Published: 20 April 2020

This paper is open access.

There is an illustration of the work

FrogHeart

Commentary about nanotech, science policy and communication, society, and the arts

Tag Archives: protein nanowires

Protein wires for nanoelectronics

Neuromorphic computing with voltage usage comparable to human brains