Rhodamine B Hydrazide Revisited: Chemodosimetric Hg-selective Signaling Behavior in Aqueous Environments

The well-known Cu-selective chemodosimetric behavior of rhodamine B hydrazide was successfully switched to selectivity for Hg. The fluorescence signaling is remarkably selective toward Hg ions compared to other common biologically and environmentally important metal ions, including Cu ions. The detection limit was 0.2 μM in an acetate-buffered aqueous 10% methanol solution at pH 5. The OFF-ON type of signaling is due to the selective Hg-induced hydrolysis of the lactam ring of the hydrazide as has been reported for the standard Cu-signaling process of the same compound. A simple change in medium resulted in clear switching of selective signaling from Cu to Hg, which extends the applicability of the easily accessible hydrazide derivative.