Spirolactone and spirothiolactone rhodamine-pyrene probes for detection of Hg2 + with different sensing properties and its application in living cells

• Spirolactone and spirothiolactone rhodamine-pyrene probes, PyRbS and PyRbO were synthesized.
• The two probes showed colorimetric and fluorimetric response to Hg2 + ion with high sensitivity and selectivity in a short time.
• PyRbS could be used as a ratiometric probe and could monitor intracellular Hg2 + levels with low cytotoxicity.

Two new rhodamine B-based fluorescent probes PyRbS and PyRbO containing pyrene moiety were designed and synthesized. Both of the probes showed colorimetric and fluorometric sensing abilities for Hg2 + with high selectivity over other metal ions. The binding analysis using Job's plot suggested 1:1 stoichiometry for the complexes formed for Hg2 +. Compared with PyRbO, the PyRbS showed higher selectivity and sensitivity due to the thiophilic property of Hg2 + ion. The PyRbS exhibited the linear fluorescence quenching to Hg2 + in the range of 0.3 to 4.8 μM (λex = 365 nm) and 0.3 to 5.4 μM (λex = 515 nm), and the detection limit was 0.72 μM. Moreover, ratiometric changes of PyRbS with Hg2 + in absorption spectrum were observed, which could not be obtained in the combination of PyRbO with Hg2 +. In addition, the methyl thiazolyl tetrazolium (MTT) assay demonstrated that RbPyS had low cytotoxicity and was successfully used to monitor intracellular Hg2 + levels in living cells.

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