A new Hg2+-selective signaling system based on a thio-functionalized rhodamine B hydroxamic acid was
investigated. A thio-analogue of rhodamine B hydroxamic acid had a distinct Hg2+-selective signaling
behavior in aqueous solution, whereas its parent hydroxamic acid was completely unreactive toward
any metal ions. Selective chromogenic and fluorogenic signaling of Hg2+ by the thio-functionalized rhodamine
B hydroxamic acid in aqueous solution was possible with a detection limit of 1.0 106 M. Hg2+
determination based on paper test strips was conducted as a practical application.