title: Influence of DNA adsorption and DNA/cationic surfactant coadsorption on the interaction forces between hydrophobic surfaces.
abstract: The forces between hydrophobic surfaces with physisorbed DNA are markedly and irreversibly altered by exposure to DNA/cetyltrimethylammonium bromide (CTAB) mixtures. In this colloidal probe atomic force microscopy study of the interactions between a hydrophobic polystyrene particle and an octadecyltrimethylethoxysilane-modified mica surface in sodium bromide solutions, we measure distinct changes in colloidal forces depending on the existence and state of an adsorbed layer of DNA or CTAB-DNA complexes. For bare hydrophobic surfaces, a monotonically attractive approach curve and very large adhesion are observed. When DNA is adsorbed at low bulk concentrations, a long-range repulsive force dominates the approach, but on retraction some adhesion persists and DNA bridging is clearly observed. When the DNA solution is replaced with a CTAB-DNA mixture at relative low CTAB concentration, the length scale of the repulsive force decreases, the adhesion due to hydrophobic interactions greatly decreases, and bridging events disappear. Finally, when the surface is rinsed with NaBr solution, the length scale of the repulsive interaction increases modestly, and only a very tiny adhesion remains. These pronounced changes in the force behavior are consistent with CTAB-induced DNA compaction accompanied by increased DNA adsorption, both of which are partially irreversible.
authors.affiliation: Department of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-22100, Lund, Sweden.
authors.forename: Alan D
authors.initials: AD
authors.lastname: Braem
authors.forename: José
authors.initials: J
authors.lastname: Campos-Terán
authors.forename: Björn
authors.initials: B
authors.lastname: Lindman
mesh_terms: D000327:Adsorption; D000818:Animals; D002412:Cations / Q000737:chemistry; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008297:Male; D018625:Microscopy, Atomic Force; D012474:Salmon; D012680:Sensitivity and Specificity; D013094:Spermatozoa / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D002412:Cations; D002593:Cetrimonium Compounds; D013501:Surface-Active Agents; D004247:DNA; D000077286:Cetrimonium