Imaging of single uncoated DNA molecules by scanning tunneling microscopy.
TLDR
A mechanism that explains the magnitude of the tunneling currents measured in DNA is proposed, which suggests a general method by which large insulating molecules can be rendered conductive.Abstract:
Scanning tunneling microscope images of DNA molecules absorbed onto highly oriented pyrolytic graphite have been obtained. Three methods of deposition and sample preparation have been utilized. In the first method, a highly concentrated solution of DNA is sonicated, and a drop is deposited on freshly cleaved graphite. Under these conditions, the molecules tend to align in a parallel fashion, forming liquid-crystalline phases. In the second method, a solution of DNA is deposited directly on the graphite surface without sonication. In this case, ammonium acetate, a volatile salt, is used to decrease the amount of the residual salt crystals left after drying. In the third method, a solution containing lysed phage particles and DNA is adsorbed onto a graphite surface. The molecules are seen either isolated or in small bundles. The values of height, periodicity, and thickness observed and the handedness of the molecules are consistent with those expected for DNA. In all cases, the molecules were identified by their characteristic periodic structure and because, at higher magnification, no graphite-like structure was detectable on the surface of the molecules. Often the DNA molecules appear to adsorb in areas of the graphite that have many steps and defects. A mechanism that explains the magnitude of the tunneling currents measured in DNA is proposed. This mechanism, in turn, suggests a general method by which large insulating molecules can be rendered conductive.read more
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Graphite: a mimic for DNA and other biomolecules in scanning tunneling microscope studies
Carol R. Clemmer,Thomas P. Beebe +1 more
TL;DR: These images illustrate features previously thought to be due to biological molecules, such as periodicity and meandering of "molecules" over steps, that can no longer be used to distinguish real molecules from features of the native substrate.
Journal ArticleDOI
Atomic-scale imaging of DNA using scanning tunnelling microscopy.
TL;DR: Atomic-resolution imaging of duplex DNA is described and the potential of the STM for characterization of large biomolecular structures is demonstrated, but additional development will be required to make such high resolution imaging of DNA and other large molecules routine.
Journal ArticleDOI
A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite
Wing-Tat Pong,Colm Durkan +1 more
TL;DR: In this paper, the authors review the discovery of graphite superlattices, the observation of the associated properties, and the research efforts on this subject and make an effort to envision the future experimental and theoretical research possibilities to unveil the mystery of this anomaly of scanning tunnelling microscopy.
Journal ArticleDOI
Images of single-stranded nucleic acids by scanning tunnelling microscopy.
David Dunlap,Carlos Bustamante +1 more
TL;DR: The micrographs demonstrate the potential application of scanning tunnelling microscopy in structural studies of nucleic acids and provide evidence that it could be used to sequence DNA.
Journal ArticleDOI
Mutation-based detection and monitoring of cell-free tumor DNA in peripheral blood of cancer patients
L Benesova,Barbora Belsanova,Stepan Suchanek,Marta Kopeckova,Petra Minarikova,Ludmila Lipska,Miroslav Levy,V. Visokai,Miroslav Zavoral,Marek Minarik +9 more
TL;DR: Apart from conventional mutation detection approaches, several dedicated techniques have been presented to detect low levels of cfDNA in an excess of nontumorous (nonmutated) DNA, including real-time polymerase chain reaction (PCR), "BEAMing" (beads, emulsion, amplification, and magnetics), and denaturing capillary electrophoresis.