A method to detect Hg2+ in vegetable via a “Turn–ON” Hg2+–Fluorescent sensor with a nanomolar sensitivity

[Display omitted] •New Hg2+-sensor based on NBD connected to thiophene was prepared.•Sensor exhibited the “Turn-ON” fluorescence enhancement with the D.L. of 3.9 ppb.•Sensor showed high selectivity toward Hg2+ in aqueous acetonitrile solutions.•Sensor was Hg2+ “visual-eye” detection by color change from orange to purple.•Sensor can apply for real samples (drinking water, HepG-2 cancer cells and vegetable). A new Hg2+ colorimetric and fluorescent sensor (NT) was synthesized. The chemical structure of the sensor consists of 7-nitrobenzo-2-oxa-1,3-diazolyl (NBD) fluorophore and the thiophene ionophore. In the presence of Hg2+, the change of color from orange to purple and the “OFF-ON” fluorescent change of sensor NT in 60 % aqueous acetonitrile solutions were observed. The detection limit of the sensor was 3.9 ppb, which was significantly lower than the permitted Hg2+ concentration in drinking water of WHO (6 ppb) and Hg2+ in edible fish of US EPA (0.55 ppm). In addition, the sensor was highly selective to Hg2+ compared to other metal ions in aqueous acetonitrile solutions. Detection of Hg2+ in drinking water, HepG2 cells and Napa cabbage stems by sensor NT were also demonstrated. Therefore, sensor NT was evidently practical for detection of Hg2+ in biological and environmental aqueous samples.