A simple and pH-independent and ultrasensitive fluorescent probe for the rapid detection of Hg2+

Development of fluorescent probes for Hg2+ has become a hot topic in modern chemical research due to its high toxicity. In this paper, we for the first time report the synthesis and application of a thioether spirocyclic rhodamine B derivative (TR) as an efficient fluorescent probe for Hg2+. TR was synthesized using a simple procedure under mild condition. By employing a thioether spirocycle instead of classic spirolactam as recognition unit, our proposed probe TR is acidity-insensitive, and exhibits a pH-independent and ultrasensitive response to Hg2+. The probe works well within a wide pH range from 3.5 to 11.5, and exhibits a 350-fold fluorescence enhancement upon 0.5 equiv of Hg2+ triggered, with a detection limit of 2.5 nM estimated for Hg2+. In virtue of the strong thiophilic characteristic of Hg2+, the response of the probe to Hg2+ is instantaneous and highly selective, which make it favorable for cellular Hg2+ imaging applications. It has been preliminarily used for highly sensitive monitoring of Hg2+ level in living cells with satisfying resolution, demonstrating its value of the practical applications in biological systems.