Etched FBG-Based Optical Fiber Sensor for Hg²+ Ion Detection in Aqueous Solution

This letter demonstrates an optical fiber sensor employing chitosan-caped gold nanoparticle (Au-NPs) coated on etched FBG (EFBG) for the label-free detection of Hg2+ in an aqueous solution. The Bragg wavelength of proposed optical fiber is monitored at different Hg2+ concentrations in water for the experimental investigation of sensor characteristics. The sensor responds linearly over a range of 1–10 ppb mercury concentration, with a sensitivity of 101.7pm/ppb. The limit of detection (LOD) of the proposed sensor is 0.07 ppb, well within the World Health Organization’s (WHO) acceptable limit of 2 ppb for safe drinking water.