title: Multiphoton excitation of fluorescent DNA base analogs.
abstract: Multiphoton excitation was used to investigate properties of the fluorescent DNA base analogs, 2-aminopurine (2AP) and 6-methylisoxanthopterin (6MI). 2-aminopurine, a fluorescent analog of adenine, was excited by three-photon absorption. Fluorescence correlation measurements were attempted to evaluate the feasibility of using three-photon excitation of 2AP for DNA-protein interaction studies. However, high excitation power and long integration times needed to acquire high signal-to-noise fluorescence correlation curves render three-photon excitation FCS of 2AP not very useful for studying DNA base dynamics. The fluorescence properties of 6-methylisoxanthopterin, a guanine analog, were investigated using two-photon excitation. The two-photon absorption cross-section of 6MI was estimated to be about 2.5 x 10(-50) cm(4)s (2.5 GM units) at 700 nm. The two-photon excitation spectrum was measured in the spectral region from 700 to 780 nm; in this region the shape of the two-photon excitation spectrum is very similar to the shape of single-photon excitation spectrum in the near-UV spectral region. Two-photon excitation of 6MI is suitable for fluorescence correlation measurements. Such measurements can be used to study DNA base dynamics and DNA-protein interactions over a broad range of time scales.
authors.affiliation: Arizona State University, Biodesign Institute, Department of Chemistry and Biochemistry and the Center for BioOptical Nanotechnology, Tempe, Arizona 85287-5201, USA. ekatilius@asu.edu
authors.forename: Evaldas
authors.initials: E
authors.lastname: Katilius
authors.forename: Neal W
authors.initials: NW
authors.lastname: Woodbury
mesh_terms: D015075:2-Aminopurine / Q000032:analysis*; D004247:DNA / Q000032:analysis*; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D009711:Nucleotides / Q000032:analysis*; D013050:Spectrometry, Fluorescence / Q000379:methods*; D014976:Xanthopterin / Q000031:analogs & derivatives* / Q000032:analysis
chemical_list: C483770:6-methylisoxanthopterin; D009711:Nucleotides; D015075:2-Aminopurine; D004247:DNA; D014976:Xanthopterin