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Photophysical Behavior of a Dimeric Cyanine Dye (BOBO‐1) Within Cationic Liposomes
Author(s) -
Madeira Catarina,
Fedorov Aleksander,
AiresBarros M. Raquel,
Prieto Manuel,
Loura Luís M. S.
Publication year - 2005
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2005-03-16-ra-464
Subject(s) - cyanine , fluorescence , cationic polymerization , chemistry , cationic liposome , quantum yield , photochemistry , agarose gel electrophoresis , dna , fluorescence anisotropy , liposome , analytical chemistry (journal) , chromatography , transfection , physics , optics , organic chemistry , biochemistry , gene
This study is aimed at establishing optimal conditions for the use of 2,2′‐[1,3‐propanediylbis[(dimethyliminio)‐3,1‐propanediyl‐1(4H)‐pyridinyl‐4‐ylidenemethy‐lidyne]]bis[3‐methyl]‐tetraiodide (BOBO‐1) as a fluorescent probe in the characterization of lipid/DNA complexes (lipoplexes). The fluorescence spectra, anisotropy, fluorescence lifetimes and fluorescence quantum yields of this dimeric cyanine dye in plasmid DNA (2694 base pairs) with and without cationic liposomes (1,2‐dioleoyl‐3‐trimethylammonium‐propane [DO‐TAP]), are reported. The photophysical behavior of the dye in the absence of lipid was studied for several dye/DNA ratios using both supercoiled and relaxed plasmid. At dye/DNA ratios (d/b) below 0.01 the fluorescence intensity increases linearly, whereas lifetime and anisotropy values of the dye are constant (τ¯∼ 2.5 ns and 〈 r 〉= 0.20). By agarose gel electrophoresis it was verified that up to d/b = 0.01 DNA conformation is not considerably modified, whereas for d/b = 0.05–0.06 a single heavy band appears on the gel. For these and higher dye/DNA ratios the fluorescence intensity, anisotropy and average lifetime values decrease with an increase in BOBO‐1 concentration. When cationic liposomes are added to the BOBO‐1/DNA complex, an additional effect is noticed: The difference in the environment probed by BOBO‐1 bound to DNA leads to a decrease in quantum yield and average lifetime values, and a redshift is apparent in the emission spectrum. For fluorescence measurements including energy transfer (FRET), a d/b ratio of 0.01 seems to be adequate because no considerable change on DNA conformation is detected, a considerable fluorescent signal is still measured after lipoplex formation, and energy migration is not efficient.