title: Surface-directed and ethanol-induced DNA condensation on mica.
abstract: The adsorption of lambda-phage DNA onto mica was investigated with atomic force microscopy. We found that the morphologies depended on the solvent conditions in the sample preparation procedure. Flat-lying networks of hybridized single-stranded DNA were obtained if ultrapure water was used. If buffered conditions are maintained during the whole of the preparation procedure, single double-stranded DNA molecules are adsorbed. The adsorbed double-stranded DNA molecules subsequently can be condensed in situ on the surface by a brief rinse with anhydrous ethanol in the presence of divalent magnesium cations. The majority of these surface-directed and ethanol-induced condensed structures are toroids, but a small fraction of rods also has been observed. Analysis of the height and lateral dimensions shows that the toroids are single-molecular and disk-like with a height of one to two DNA diameters. The thin toroid morphology appears to be a general phenomenon of surface-directed condensation, irrespective of the nature of the condensing ligands and the specific surface interaction.
authors.affiliation: National University of Singapore, Department of Physics, 2 Science Drive 3, Singapore 117542.
authors.forename: Ce
authors.initials: C
authors.lastname: Zhang
authors.forename: Johan R C
authors.initials: JR
authors.lastname: van der Maarel
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002413:Cations, Divalent; D004247:DNA / Q000737:chemistry / Q000648:ultrastructure; D000431:Ethanol / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry; D018625:Microscopy, Atomic Force; D009690:Nucleic Acid Conformation; D012997:Solvents / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D002413:Cations, Divalent; D012997:Solvents; D014867:Water; D000431:Ethanol; D004247:DNA; D008274:Magnesium; C011934:mica