Live wire: new research on nanoelectronics
Proteins are among the most versatile and ubiquitous biomolecules on earth. Nature uses them for everything from building tissue to regulating metabolism to defending the body against disease.
Now, a new study shows that proteins have other largely unexplored abilities. Under the right conditions, they can act as tiny current-carrying wires, useful for a range of man-made nanoelectronics.
In new research published 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 threads may have better conductance properties than similar nanowires composed of DNA, which have already found considerable success for a host of human applications.
Professor Lindsay directs the Biodesign Center for Single-Molecule Biophysics. He is also a professor in ASU’s Department of Physics and School of Molecular Sciences.
Just as with DNA, proteins offer many attractive properties for nanoscale electronics, including stability, tunable conductance, and vast information storage capacity. Although proteins have traditionally been thought of as poor conductors of electricity, that all changed recently when Lindsay and his colleagues demonstrated that a protein placed between a pair of electrodes could act as an efficient conductor of electrons.
The new research takes a closer look at the phenomenon of electron transport through proteins. The results of the study establish that over long distances, protein nanowires exhibit better conductance properties than chemically synthesized nanowires specifically designed to be conductors. Moreover, proteins self-organize and allow atomic-scale control of their components.
Synthetically engineered protein nanowires could give rise to new ultra-thin electronics, with potential applications in medical sensing and diagnosis, nanorobots to perform search-and-destroy missions against diseases, or in a new breed of transistors ultra-tiny computers. Lindsay is particularly interested in the potential of protein nanowires for use in new devices to perform ultra-fast DNA and protein sequencing, an area in which he has already made significant progress.
In addition to their role in nanoelectronic devices, charge transport reactions are crucial in living systems for processes such as respiration, metabolism, and photosynthesis. Therefore, research on transport properties through engineered proteins can shed new light on how these processes operate within living organisms.
While proteins have many of the advantages of DNA for nanoelectronics in terms of electrical conductance and self-assembly, the expanded alphabet of 20 amino acids used to build them offers an enhanced toolkit for nanoarchitects like Lindsay. , compared to only four nucleotides making up DNA.
Although electron transport has been the subject of considerable research, the nature of electron flow through proteins has remained a mystery. Broadly speaking, the process can occur by electron tunneling, a quantum effect occurring over very short distances, or by the jumping of electrons along a peptide chain – in the case of proteins, a chain of amino acids.
One of the goals of the study was to determine which of these regimes appeared to work by performing quantitative measurements of electrical conductance on different lengths of protein nanowires. The study also describes a mathematical model that can be used to calculate the electronic molecular properties of proteins.
For the experiments, the researchers used protein segments in four-nanometer increments, ranging from 4 to 20 nanometers in length. A gene was engineered to produce these amino acid sequences from a DNA template, with the lengths of proteins then strung 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 the conductance decreases along the length of the nanowire in a manner consistent with the jumping 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 electrons along their path from point to point, like successive stations along of a train journey. “Electron transport is a bit like jumping a stone over water – the stone doesn’t have time to sink with each jump,” Lindsay explains.
While the conductance values of the protein nanowires decreased with distance, they did so more gradually than with conventional molecular wires specifically designed to be efficient conductors.
When protein nanowires exceeded six nanometers in length, their conductance surpassed molecular nanowires, opening the door to their use in many new applications. The fact that they can be subtly designed and modified with atomic-scale control and self-assembled from a gene template allows for fine-tuned manipulations that far exceed what can currently be achieved with transistor design. conventional.
An interesting possibility is to use these protein nanowires to connect other components in a new suite of nanomachines. For example, nanowires could be used to connect an enzyme known as DNA polymerase to electrodes, resulting in a device that could potentially sequence an entire human genome at low cost in less than an hour. A similar approach could allow the integration of proteosomes into nanoelectronic devices capable of reading amino acids for protein sequencing.
“We are now beginning to understand electron transport in these proteins. Once you have quantitative calculations, not only do you have great molecular electronics, but you have a recipe for designing them,” says Lindsay. “If you think of the SPICE program that electrical engineers use to design circuits, there’s a glimmer now that you could get it for protein electronics.”
Researchers reveal why nanowires stick together
Bintian Zhang et al, Electronic transport in precisely controlled length molecular wires constructed from modular proteins, ACS Nano (2022). DOI: 10.1021/acsnano.1c10830
Arizona State University
Live Wire: New Research in Nanoelectronics (2022, February 24)
retrieved 24 February 2022
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