title: Probing the charge-transfer dynamics in DNA at the single-molecule level.
abstract: Photoinduced charge-transfer fluorescence quenching of a fluorescent dye produces the nonemissive charge-separated state, and subsequent charge recombination makes the reaction reversible. While the information available from the photoinduced charge-transfer process provides the basis for monitoring the microenvironment around the fluorescent dyes and such monitoring is particularly important in live-cell imaging and DNA diagnosis, the information obtainable from the charge recombination process is usually overlooked. When looking at fluorescence emitted from each single fluorescent dye, photoinduced charge-transfer, charge-migration, and charge recombination cause a "blinking" of the fluorescence, in which the charge-recombination rate or the lifetime of the charge-separated state (τ) is supposed to be reflected in the duration of the off time during the single-molecule-level fluorescence measurement. Herein, based on our recently developed method for the direct observation of charge migration in DNA, we utilized DNA as a platform for spectroscopic investigations of charge-recombination dynamics for several fluorescent dyes: TAMRA, ATTO 655, and Alexa 532, which are used in single-molecule fluorescence measurements. Charge recombination dynamics were observed by transient absorption measurements, demonstrating that these fluorescent dyes can be used to monitor the charge-separation and charge-recombination events. Fluorescence correlation spectroscopy (FCS) of ATTO 655 modified DNA allowed the successful measurement of the charge-recombination dynamics in DNA at the single-molecule level. Utilizing the injected charge just like a pulse of sound, such as a "ping" in active sonar systems, information about the DNA sequence surrounding the fluorescent dye was read out by measuring the time it takes for the charge to return.
authors.affiliation: The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan. kiyohiko@sanken.osaka-u.ac.jp
authors.forename: Kiyohiko
authors.initials: K
authors.lastname: Kawai
authors.forename: Eri
authors.initials: E
authors.lastname: Matsutani
authors.forename: Atsushi
authors.initials: A
authors.lastname: Maruyama
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Majima
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D004579:Electron Transport; D005456:Fluorescent Dyes / Q000737:chemistry; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D055668:Photochemical Processes; D020641:Polymorphism, Single Nucleotide; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D004247:DNA