Through-bond energy transfer based dyad and triad shape fluorescence “OFF-ON-OFF” probes for Hg2+ ions and their application in live HeLa cells and Zebrafish.

Two novel through-bond energy transfer (TBET) based naphthoquinone derivatives, R1 and R2, have been designed and synthesized with characteristics of a dyad (rhodamine-quinone) and a triad (rhodamine-quinone-rhodamine), respectively. Probes R1 and R2 selectively sense Hg 2+ ions over other common interference metal ions in aqueous-methanol medium with a broad pH range (6.0–8.0). By the combination of dual functions, (i.e., fluorescence off-on (rhodamine) and TBET off-on (through a conjugation linker) processes), the proposed TBET-probes exhibit very large pseudo-Stokes shifts, with a wavelength difference ≈210 nm, and high energy transfer efficiency for the detection of Hg 2+ with a detection limit of 41 nM. The fluorescence intensity of the triad ( R2 ) is nearly 2 orders of magnitude greater than that of the dyad R1 due to the existence of two rhodamine fragments. The OFF-ON fluorescence effect of the TBET cassettes regains the ON-OFF mode by subsequent addition of the I − ion. The optical restoring behavior of the R1 / R2 -Hg 2+ complex with I − could be potentially be applied as an INHIBIT molecular logic gate with the combination of YES and NOT functions. Finally, the Hg 2+ ion sensing ability of TBET probes R1 and R2 was utilized in a HeLa cell imaging application, and the probe R1 was used to monitor the Hg 2+ ion in live zebrafish. [ABSTRACT FROM AUTHOR]