An ionic liquid-based ratio fluorescent sensor for real-time visual monitoring of trace Hg2+

As a brand probe material, functional ionic liquids (ILs) have already been successfully employed in the detections of many targets, however, few of them focused on the real-time visual monitoring of trace Hg2+, one of the most representative heavy metal ions. Herein, we report a novel ratio fluorescent sensor using facile mixture of [RDB] [P66614] IL and 7-hydroxycoumarin (HDC) for the on-site monitoring of Hg2+ ignoring background interferences. To utilize and enhance the affinity characteristics of rhodamine B for Hg2+, it was first covalently linked onto the anion of IL and further mixed with HDC to construct a novel ratio fluorescent sensor for the achievement of self-calibration. Furthermore, this novel sensor showed a rapid and obvious color rendering performance from light white to opera pink even towards trace mercury(Ⅱ) in the range of 0.1–50 nM and could be further used even in common real samples such as waste water, urine, human plasma et. al. Most importantly, the sensor could be assembled into a paper sensor for the on-site visual monitoring of trace Hg2+ ranging from 10 to 400 nM only taking 2 s, which enable to meet requirements for mercury(Ⅱ) limitations of WHO (30 nM) and EPA (10 nM).