Detection of biomacromolecules with fluorescent light-up probes
The emission properties of selected benzo[b]quinolizinium (acridizinium) derivatives in the presence of double-stranded DNA and proteins are presented. Spectrophotometric studies and linear dichroism (LD) spectroscopic experiments reveal that benzo[b]quinolizinium derivatives bind to DNA, mainly by intercalation. In contrast to the 9-aminobenzo[b]quinolizinium, which exhibits a moderate emission quantum yield in water, the 6-aminobenzo[b]quinolizinium ion as well as N-phenyl-9-aminobenzo[b]quinolizinium derivatives are almost nonfluorescent. The low intrinsic fluorescence quantum yields of the latter compounds are caused by conformational changes in the excited state, as shown by a linear double-logarithmic plot of the emission quantum yield vs. the solvent viscosity. Most notably, the fluorescence intensities of these dyes increase significantly by a factor of 10 to 50 upon addition of double-stranded DNA or proteins such as human serum albumin (HSA) or chicken egg albumin (CEA). Thus, these compounds exhibit ideal properties to be used as DNA- or protein-sensitive light-up probes.