title: Fluorescence quenching studies of potential-dependent DNA reorientation dynamics at glassy carbon electrode surfaces.
abstract: The potential-dependent reorientation dynamics of double-stranded DNA (ds-DNA) attached to planar glassy carbon electrode (GCE) surfaces were investigated. The orientation state of surface-bound ds-DNA was followed by monitoring the fluorescence from a 6-carboxyfluorescein (FAM6) fluorophore covalently linked to the distal end of the DNA. Positive potentials (i.e., +0.2 V vs open circuit potential, OCP) caused the ds-DNA to align parallel to the electrode surface, resulting in strong dipole-electrode quenching of FAM6 fluorescence. Switching of the GCE potential to negative values (i.e., -0.2 V vs OCP) caused the ds-DNA to reorient perpendicular to the electrode surface, with a concomitant increase in FAM6 fluorescence. In addition to the very fast (submilliseconds) dynamics of the initial reorientation process, slow (0.1-0.9 s) relaxation of FAM6 fluorescence to intermediate levels was also observed after potential switching. These dynamics have not been previously described in the literature. They are too slow to be explained by double layer charging, and chronoamperometry data showed no evidence of such effects. Both the amplitude and rate of the dynamics were found to depend upon buffer concentration, and ds-DNA length, demonstrating a dependence on the double layer field. The dynamics are concluded to arise from previously undetected complexities in the mechanism of potential-dependent ds-DNA reorientation. The possible origins of these dynamics are discussed. A better understanding of these dynamics will lead to improved models for potential-dependent ds-DNA reorientation at electrode surfaces and will facilitate the development of advanced electrochemical devices for detection of target DNAs.
authors.affiliation: Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Li
authors.forename: Chenchen
authors.initials: C
authors.lastname: Cui
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Higgins
authors.forename: Jun
authors.initials: J
authors.lastname: Li
mesh_terms: D001483:Base Sequence; D002021:Buffers; D002244:Carbon / Q000737:chemistry*; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D004566:Electrodes; D004735:Energy Transfer; D007700:Kinetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D013050:Spectrometry, Fluorescence; D013499:Surface Properties
chemical_list: D002021:Buffers; D002244:Carbon; D004247:DNA