title: Anionic polyelectrolyte adsorption on mica mediated by multivalent cations: a solution to DNA imaging by atomic force microscopy under high ionic strengths.
abstract: Adsorption of DNA molecules on mica, a highly negatively charged surface, mediated by divalent or trivalent cations is considered. By analyzing atomic force microscope (AFM) images of DNA molecules adsorbed on mica, phase diagrams of DNA molecules interacting with a mica surface are established in terms of concentrations of monovalent salt (NaCl) and divalent (MgCl2) or multivalent (spermidine, cobalt hexamine) salts. These diagrams show two transitions between nonadsorption and adsorption. The first one arises when the concentration of multivalent counterions is larger than a limit value, which is not sensitive to the monovalent salt concentration. The second transition is due to the binding competition between monovalent and multivalent counterions. In addition, we develop a model of polyelectrolyte adsorption on like-charged surfaces with multivalent counterions. This model shows that the correlations of the multivalent counterions at the interface between DNA and mica play a critical role. Furthermore, it appears that DNA adsorption takes place when the energy gain in counterion correlations overcomes an energy barrier. This barrier is induced by the entropy loss in confining DNA in a thin adsorbed layer, the entropy loss in the interpenetration of the clouds of mica and DNA counterions, and the electrostatic repulsion between DNA and mica. The analysis of the experimental results provides an estimation of this energy barrier. We then discuss some important issues, including DNA adsorption under physiological conditions.
authors.affiliation: Laboratoire Structure et Reconnaissance des Biomolécules, EA 3637, Université d'Evry, Rue du Père Jarlan, 91025 Evry Cedex, France. d.pastre@iut.univ-evry.fr
authors.forename: David
authors.initials: D
authors.lastname: Pastré
authors.forename: Loïc
authors.initials: L
authors.lastname: Hamon
authors.forename: Fabrice
authors.initials: F
authors.lastname: Landousy
authors.forename: Isabelle
authors.initials: I
authors.lastname: Sorel
authors.forename: Marie-Odile
authors.initials: MO
authors.lastname: David
authors.forename: Alain
authors.initials: A
authors.lastname: Zozime
authors.forename: Eric
authors.initials: E
authors.lastname: Le Cam
authors.forename: Olivier
authors.initials: O
authors.lastname: Piétrement
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods; D009994:Osmolar Concentration; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000538:Aluminum Silicates; D000838:Anions; D002412:Cations; D004573:Electrolytes; D011108:Polymers; D012996:Solutions; D012965:Sodium Chloride; D004247:DNA; C011934:mica