Imaging different interactions of mercury and silver with live cells by a designed fluorescence probe rhodamine B selenolactone.

Rhodamine B selenolactone has been designed, synthesized, and characterized as a new fluorescent probe for imaging both Hg(2+) and Ag(+) in live cells to better understand their distinct toxicities to organisms. The probe is designed based on the fact that selenium has a strong affinity for mercury and silver, and is constructed by incorporating a Se atom into the spirocyclic structure of rhodamine. It exhibits a rapid and specific spectroscopic off-on response to Hg(2+) and Ag(+) instead of other species, with detection limits of 23 nM Hg(2+) and 52 nM Ag(+). Moreover, the probe is membrane-permeable, and can react with Ag(+) even in the presence of Cl(-) because of the higher affinity of Se than Cl(-) for Ag(+), which makes it of potential use for imaging not only Hg(2+) but also Ag(+) in live cells. This applicability has been demonstrated by imaging Hg(2+) and Ag(+) in Hela cells. It is observed that the reaction of Ag(+) with the probe inside the cells occurs much slower than that of Hg(2+), which is ascribed to the high concentration of cellular chloride ions inhibiting the formation of sufficient free Ag(+). The present finding is helpful to get an insight into the different interaction mechanism of Hg(2+) and Ag(+) with cells, and more applications of the probe may be expected for studying the behaviors of Hg(2+) and Ag(+) in various biosystems.