A series of novel dibenzothiophene-based two-photon fluorescent probes for cellular nucleus imaging

In this study, a series of novel dibenzothiophene-based two-photon excited fluorescence (TPEF) probes with excellent nuclear staining ability were prepared and investigated. The one-photon photophysical properties indicated these labels possessed UV absorption wavelength of 390-393 nm and quantum yields of 0.425-0.71. The two-photon photophysical performance exhibited two-photon absorption (TPA) cross-sections of 506-630 GM by excitation of femtosecond laser at a wavelength of 800 nm. 18-30-fold one-photon excited fluorescence (OPEF) enhancement and 300-450% TPEF increment binding with calf thymus DNA in Tris-HCl buffer solutions displayed obvious fluorescence “turn-on” effect. The co-localization studies showed mean co-localization coefficients of 0.88-0.94 by double-staining with commercial nuclear staining reagent DAPI in 3T3 cells, indicating accurate nuclear localization ability. The confocal fluorescence imaging displayed clear TPEF nuclear imaging. The staining penetration depth of 0-9 μm exhibited good membrane permeability and three dimensional imaging ability. The observation time of 1800 s and fluorescence decay amplitude of 8-10% within 300 s under persistent irradiation were achieved in TPEF imaging for nuclear labeling. The DNA binding mechanism was discussed as well.