Highly sensitive and Rapid detection of mercury in water using functionalized etched fiber Bragg grating sensors

An effective optical method has been proposed using cysteine conjugated naphthalene diimide (CNC) bolaamphiphile functionalised etched Fiber Bragg grating (eFBG) sensor for selective and rapid detection of mercury (Hg2+) in drinking water. The sensor responds with a Bragg wavelength shift (Delta lambda B) to the thiol-Hg2+ coordination interaction between CNC and Hg2+. The thiol-Hg2+ interaction was initially studied by UV absorbance studies (bulk solutions) of CNC with increased concentrations of Hg2+ (600 nM to 3 mu M). The study displayed a linear relationship with the limit of detection (LOD) of 100 nM, which is below the world health organisation (WHO) standards for drinking water (22 nM). To enhance the LOD, the CNC was coated onto the eFBG sensor using two coating protocols (dip and spin coating) followed by Hg2+ detection. The dip (spin) coated sensor displayed a dynamic-range from 1 pM to 1 mu M (1 pM to 10 nM) and LOD of 1 pM. The sensor's repeatability (maximum error of 13.2 picometers) and specificity in the presence of other interfering metals like Pb2+, Cu2+, Na2+ and Cd2+ has been determined. The sensor can be developed into a highly sensitive, selective, portable, real-time, on-site Hg2+ optical probe for drinking water.