title: Atomic force microscopy reveals two phases in single stranded DNA self-assembled monolayers.
abstract: We have investigated the structure of single-stranded (ss) DNA self-assembled monolayers (SAMs) on gold by combining peak force tapping, Kelvin probe and phase contrast atomic force microscopy (AFM) techniques. The adhesion, surface potential and phase shift signals show heterogeneities in the DNA film structure at two levels: microscale and nanoscale; which cannot be clearly discerned in the topography. Firstly, there is multilayer aggregation covering less than 5% of the surface. The DNA multilayers seem to be ordered phases and their existence suggests that DNA end-to-end interaction can play a role in the self-assembly process. Secondly, we find the formation of two phases in the DNA monolayer, which differ both in surface energy and surface potential. We relate the two domains to differences in the packing density and in the ssDNA conformation. The discovered heterogeneities in ssDNA SAMs provide a new scenario in our vision of these relevant films that have direct consequences on their biological, chemical and physical properties.
authors.affiliation: Bionanomechanics Lab, Institute of Microelectronics of Madrid, CSIC, Isaac Newton 8 (PTM), Tres Cantos, 28760 Madrid, Spain.
authors.forename: Priscila M
authors.initials: PM
authors.lastname: Kosaka
authors.forename: Sheila
authors.initials: S
authors.lastname: González
authors.forename: Carmen M
authors.initials: CM
authors.lastname: Domínguez
authors.forename: Alfonso
authors.initials: A
authors.lastname: Cebollada
authors.forename: Alvaro
authors.initials: A
authors.lastname: San Paulo
authors.forename: Montserrat
authors.initials: M
authors.lastname: Calleja
authors.forename: Javier
authors.initials: J
authors.lastname: Tamayo
mesh_terms: D015342:DNA Probes / Q000737:chemistry; D004277:DNA, Single-Stranded / Q000737:chemistry*; D006046:Gold / Q000737:chemistry; D018625:Microscopy, Atomic Force; D055672:Static Electricity; D013696:Temperature
chemical_list: D015342:DNA Probes; D004277:DNA, Single-Stranded; D006046:Gold