Nanotechnology is revolutionizing various fields of research, including biotechnology and materials science. It is a cutting-edge technology that is opening up new and interesting possibilities for future developments in these fields and many others. One of the main focuses of research in the field at the moment is in the creation of stable materials that can construct useful structures at the atomic level.
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The field of nanotechnology traces its routes back to Richard Feynman’s 1959 lecture, “There’s plenty of room at the bottom.” One of Feynman’s inspirations was derived from the natural world. In a biological system, there are nanostructures and molecular machines that create molecular switches, information storage, synthetic machinery, and scaffold structures. By exploiting the experiences of nature, nanomolecular machines could possibly be created artificially in the lab.
Since those early days in the field of nanotechnology, several naturally occurring materials have been studied in depth for their potential applications. One particularly interesting target of this research is nucleic acids.
Nucleic acids: a potential target for creating nanostructures
Nucleic acids are currently the subject of research to create nanostructures due to their unique properties. One of the primary functions that nucleic acids show potential is as novel scaffold structures. One nucleic acid nanostructure that has scaffold potential is the double-helical DNA cube. This is a single molecular unit, which has the potential to form two and three-dimensional arrays with further modification.
Due to factors such as a definable base sequence, linear geometry, self-assembling properties, and simple and non-toxic replication, DNA is an attractive candidate for integration into nanoelectronics as a biological nanowire.
Forming aggregates by molecular self-assembly is a major goal of designers of nanoscale structures. Several methods for achieving this have been proposed.
G-quartet DNA research
One such structure that has been the subject of particular attention in oligonucleotide studies is the G-quartet (Guanine-quartet) DNA structure. These are formed in nucleic acids by guanine-rich sequences. Helical in nature, they contain guanine tetrads that can form from one, two, or four strands.
Custom synthesis of G-quartet structures is reliable and relatively inexpensive, making them ideal candidates for creating monomers that can undergo self-assembly, which is one of the aims of nanotechnology research. Formation of stable G-DNA superstructures limited to 4 or 5 repeats has been demonstrated for 3’ end self-complementary G4-DNA.
Guanine-quartet DNA structures have the potential for use in a wide range of nanotechnological applications due to these properties. One of these applications that are being looked at is the guanine nanowire (G-wire.)
G-wires: Creating superconductive nanowires from simple nucleotide sequences
G-wires are, simply, nanomolecular superconductive wires that are comprised of G-DNA structures. Whilst other research has been carried out into producing nanowires that have the capability of conducting electricity from other materials, including graphite and copper, guanine-quartet DNA structures show particular promise for this application due to their unique properties.
G-wire structure has been analyzed using atomic force microscopy (AFM.) One project focused on the Tetrahymena telomeric DNA sequence d[G4T2G4], which has been extensively studied with respect to G-wire formation. Whilst the structure of G-wires is still not fully understood, G-wire surfaces show a great deal of variety with several subtypes that even have variations within those subtypes. Clearly, understanding the variety of subtypes can give insight into how guanine nanowires behave.
Using a simple ten nucleotide sequence – d(GGGGTTGGGG) – G-4 DNA can be utilized to create self-assembling nanostructures, providing a simple, scalable process with minimal cost. Long, continuous monomolecular G-wires can be produced. G-wires can be constructed by composing single self‐folded poly(G) strands of thousands of bases.
G-wire DNA acts as an insulator. Studies have determined that the lower limit of resistance of G-wire DNA networks is in excess of 1 GΩ. By shadow-depositing metal contacts onto the top of the G-wire (one study used electron beam evaporated gold and argon sputtered gold), a highly conductive composite material can be achieved at the nanomolecular level.
G-wires: Potential applications
As they are relatively cheap and easy to synthesize, G-wires have the potential for a variety of uses. Current research is ongoing into their use as constituents of biosensors, including highly sensitive electrochemical biosensors for microRNA. There is also the potential for integration into paper-based systems and using G-wires as constituents of other nanomachines as an alternative to other forms of nanowire made from substances such as graphite and copper.
Guanine nanowires have been shown to be incredibly versatile nanomolecular structures, which in the future may become standard components of nanomachines carrying out a range of functions in biomedical studies, targeted drug delivery, and many more applications in a wide variety of industries.
Marsh, T.C and Henderson, E (1994) G-Wires: Self-Assembly of a Telomeric Oligonucleotide, d(GGGGTTGGGG), into Large Superstructures Biochemistry Vol. 33 Issue 35 pgs. 10718-10724 https://pubs.acs.org/doi/abs/10.1021/bi00201a020
Huang, Y.L et al. (2017) Amperometric biosensor for microRNA based on the use of tetrahedral DNA nanostructure probes and guanine nanowire amplification Michrochimica Acta Vol. 184 Issue 8 pgs. 2597-2604 https://link.springer.com/article/10.1007/s00604-017-2246-8
Bose, K et al. (2018) High-resolution AFM structure of DNA G-wires in aqueous solution Nature Communications 9 article number 1959 https://www.nature.com/articles/s41467-018-04016-y
Marsh, T.C. (1994) G-wires: The growth and characterization of a G4-DNA nanostructure Retrospective Theses and Dissertations, Iowa State University https://lib.dr.iastate.edu/rtd/11291
Vesenka, J et al. (2006) Analysis of G-wire conductivity AIP Conference Proceedings 859, 83-88 www.researchgate.net/.../234262828_Analysis_of_G-wire_DNA_conductivity
Kotlyar, A.B. et al. (2005) Long, Monomolecular Guanine-Based Nanowires Advanced Materials Vol. 17 Issue 15 pgs. 1901-1905 https://doi.org/10.1002/adma.200401997
Xu, Y. et al. (2018) Ultrasensitive and specific imaging of circulating microRNA based on split probe, exponential amplification, and topological guanine nanowires Sensors and Actuators B: Chemical Vol. 269 pgs. 158-163 https://www.sciencedirect.com/science/article/pii/S092540051830827X