A novel hybrid long period fiber grating-diffusive gradient in thin films sensor system for the detection of mercury (II) ions in water

This paper presents the detection of mercury (II) ions based on a novel hybrid Long Period Fiber Grating (LPFG)-Diffusive Gradient in Thin Films (DGT) sensor system. The fundamental design of the hybrid sensor combines the features of a gold nanoparticles-coated LPFG embedded within a DGT structure. The main function of the DGT structure is to overcome the weakness of LPFG sensor by providing a durable housing for the protection of the fiber sensor, thereby allowing near real-time, in situ as well as long-term monitoring of mercury (II) ions in water. Experiments were conducted with mercury (II) solutions with concentrations ranging from 0.5 ppm to 10.0 ppm in order to study the sensing ability of the hybrid sensor. The performance of this hybrid sensor was then compared with an open structure sensor, in which the membrane filter and gel layers of DGT device were not included. Results showed that the response rate of the hybrid structure was lower than the open structure, i.e., 0.0049- and 0.0078-a.u./min, respectively in 2.0 ppm mercury (II) solution. This has proven that the presence of the structure of DGT has prolonged the movement of the mercury (II) ions towards the innermost Polyelectrolyte-Gold nanoparticles (PE-AuNP) coated LPFG sensor. Furthermore, the brittle LPFG sensor was well protected by the DGT structure. This mechanism makes the proposed LPFG-DGT sensor system suitable to be used for long-term and near real-time monitoring of water bodies due to the prolonged lifespan.