title: Direct measurement of hydrogen bonding in DNA nucleotide bases by atomic force microscopy.
abstract: We have used self-assembled purines and pyrimidines on planar gold surfaces and on gold-coated atomic force microscope (AFM) tips to directly probe intermolecular hydrogen bonds. Electron spectroscopy for chemical analysis (ESCA) and thermal programmed desorption (TPD) measurements of the molecular layers suggested monolayer coverage and a desorption energy of about 25 kcal/mol. Experiments were performed under water, with all four DNA bases immobilized on AFM tips and flat surfaces. Directional hydrogen-bonding interaction between the tip molecules and the surface molecules could be measured only when opposite base-pair coatings were used. The directional interactions were inhibited by excess nucleotide base in solution. Nondirectional van der Waals forces were present in all other cases. Forces as low as two interacting base pairs have been measured. With coated AFM tips, surface chemistry-sensitive recognition atomic force microscopy can be performed.
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle 98195, USA.
authors.forename: T
authors.initials: T
authors.lastname: Boland
authors.forename: B D
authors.initials: BD
authors.lastname: Ratner
mesh_terms: D000225:Adenine / Q000737:chemistry*; D001482:Base Composition; D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D006046:Gold; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D018625:Microscopy, Atomic Force; D013941:Thymine / Q000737:chemistry*
chemical_list: D006147:Guanine; D006046:Gold; D003596:Cytosine; D004247:DNA; D000225:Adenine; D013941:Thymine