Tetracationic bis-triarylborane tetraynes as dual fluorescence and SERS sensors for DNA, RNA and proteins

We report herein two new dual luminescent and Raman (SERS)-active probes, able to sense submicromolar concentrations of DNA and protein in aqueous samples. Both analogues, characterized by a tetrayne linker connecting two triarylborane fluorophores, show high binding affinities and strong fluorescent and SERS re-sponses to ds-DNA, ds-RNA, and protein (BSA). Detailed studies revealed that both the neutral and tetracationic analogue bind to ds-DNA/RNA grooves and protein (BSA) with similar affinities, at variance to previous non -charged triarylboranes, which interacted only with BSA. The fluorimetric response upon binding to BSA was different to that observed for previous analogues; the tetracationic analogue emission was enhanced and the neutral analogue emission quenched, this selectivity being attributed to the difference in solvatochromism of the triarylborane fluorophore (charged vs neutral). The neutral dye did not show any SERS signal due to the lack of interaction with negatively charged Ag nanoparticles, stressing the importance of positive charge for the application of SERS sensing. The SERS signal of the tetrayne linker of the tetracationic analogue was shifted by-81 cm(-1) compared to that of the previously studied diyne analogue. The SERS signal intensity change was proportional to dye binding to ds-DNA, and completely quenched by nanomolar concentrations of BSA, such a specific response being attributed to the complete immersion of the dye within BSA.