Cyanines as new fluorescent probes for DNA detection and two-photon excited bioimaging.

A series of cyanine fluorophores based on fused aromatics as an electron donor for DNA sensing and two-photon bioimaging were synthesized, among which the carbazole-based biscyanine exhibits high sensitivity and efficiency as a fluorescent light-up probe for dsDNA, which shows selective binding toward the AT-rich regions. The synergetic effect of the bischromophoric skeleton gives a several-fold enhancement in a two-photon absorption cross-section as well as a 25- to 100-fold enhancement in two-photon excited fluorescence upon dsDNA binding.