Optical fibre turn-on sensor for the detection of mercury based on immobilized fluorophore

An optical fibre turn-on fluorescent sensor for the detection of mercury ions has been developed based on the use of immobilized organic fluorophore Rhod-5N. When the fibre was only used to deliver excitation laser and collection signal by dipping it into the mixture solution of the fluorophore and mercury ions, the detection limit was found to be as low as 0.3 ppb in aqueous solution, which is 10 times lower than that previously reported with both excitation source and fluorescence delivered by free space. For the fibre tip sensor with the fluorophore functionalized onto the fibre tip using a silica sol-gel film, it was found that higher Rhod-5N concentrations result in a more sensitive fluorescent response but a higher detection limit of 25 ppb in filtered river water. The portable features of this fibre probe are promising for online remote monitoring of mercury ions in water.