title: The structure of DNA by direct imaging.
abstract: The structure of DNA was determined in 1953 by x-ray fiber diffraction. Several attempts have been made to obtain a direct image of DNA with alternative techniques. The direct image is intended to allow a quantitative evaluation of all relevant characteristic lengths present in a molecule. A direct image of DNA, which is different from diffraction in the reciprocal space, is difficult to obtain for two main reasons: the intrinsic very low contrast of the elements that form the molecule and the difficulty of preparing the sample while preserving its pristine shape and size. We show that through a preparation procedure compatible with the DNA physiological conditions, a direct image of a single suspended DNA molecule can be obtained. In the image, all relevant lengths of A-form DNA are measurable. A high-resolution transmission electron microscope that operates at 80 keV with an ultimate resolution of 1.5 Å was used for this experiment. Direct imaging of a single molecule can be used as a method to address biological problems that require knowledge at the single-molecule level, given that the average information obtained by x-ray diffraction of crystals or fibers is not sufficient for detailed structure determination, or when crystals cannot be obtained from biological molecules or are not sufficient in understanding multiple protein configurations.
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Monica
authors.initials: M
authors.lastname: Marini
authors.affiliation: NABLA Lab, BESE Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Manola
authors.initials: M
authors.lastname: Moretti
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Tania
authors.initials: T
authors.lastname: Limongi
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Marco
authors.initials: M
authors.lastname: Allione
authors.affiliation: NABLA Lab, BESE Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Genovese
authors.affiliation: Imaging and Characterization Core Lab, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Sergei
authors.initials: S
authors.lastname: Lopatin
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Luca
authors.initials: L
authors.lastname: Tirinato
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Gobind
authors.initials: G
authors.lastname: Das
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Bruno
authors.initials: B
authors.lastname: Torre
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Giugni
authors.affiliation: Bio Nanotechnology and Engineering for Medicine (BIONEM), Department of Experimental and Clinical Medicine, University of Magna Graecia, Viale Europa, Germaneto, 88100 Catanzaro, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Gentile
authors.affiliation: Bio Nanotechnology and Engineering for Medicine (BIONEM), Department of Experimental and Clinical Medicine, University of Magna Graecia, Viale Europa, Germaneto, 88100 Catanzaro, Italy.
authors.forename: Patrizio
authors.initials: P
authors.lastname: Candeloro
authors.affiliation: SMILEs Lab, Physical Science and Engineering (PSE) and Biological and Environmental Science and Engineering (BESE) Divisions, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia. ; Bio Nanotechnology and Engineering for Medicine (BIONEM), Department of Experimental and Clinical Medicine, University of Magna Graecia, Viale Europa, Germaneto, 88100 Catanzaro, Italy.
authors.forename: Enzo
authors.initials: E
authors.lastname: Di Fabrizio
keywords: A-DNA; HRTEM; direct imaging; single molecule imaging; structural study; superhydrophobic surfaces