Investigation of two-photon fluorescence of DNA-dye complexes

Preliminary results of the investigation of two-photon excited fluorescence of acridine orange (AO) and ethidium bromide (EB) in complexes with DNA are presented. Spectrofluorometer based on picosecond Nd:YAG laser was used far investigations on two-photon (1064 nm, 1 mJ, 40 ps) and one-photon (532 and 355 nm) excitation. Highly purified DNA from beef spleen and AO, EB were used at the concentration of: AO- 15 mu M, EB- 12 mu M, DNA- 2-15 mu g/ml. The spectra of two-photon excited fluorescence of AO, EB and their complexes with DNA as well as kinetics of the intensification of dye's two-photon fluorescence during their interactions with DNA in dependence on DNA concentration were obtained. The intensity of fluorescence of AO and EB was increased maximum 2.4 and 8 times correspondingly. During the one-photon excitation corresponding values were for: AO-2.5 time and EB- 10 time. The difference in the intensification of EB fluorescence connected with the difference of the change of one-photon and two-photon absorption coefficients during the interaction of the dye with DNA.