Optical fiber sensor based on magneto-plasmonic features of Ag-Co nanostructure for ppm ammonium detection in aqueous solutions

Magneto-plasmonic nanocomposite deposition enables fiber optic sensors to detect water pollution caused by chemical contaminants of ammonium that is harmful to human and aquatic organisms as well. In this study, Ag-Co nanocomposite was deposited on unclad multimode glass fiber to distinguish the ammonium concentration in the aqueous medium. Prior to the fabrication of the fiber probe, for finding the stronger surface plasmon resonance (SPR) effect, Ag-Co nanocomposite (which had different structures) was deposited on the glass prism. The maximum SPR shift of 7.16° was observed by varying the ammonium concentration from 0 to 80 ppm, when Ag was deposited as the outer layer and Co acted as the inner layer. The working principle of the sensor was based on manipulating the analyte viscosity with the magnetization of Co nanolayer exposed to the external magnetic field and adjusting the SPR conditions via the interaction of different ammonium concentrations with the Ag layer. Spectral wavelength and the intensity interrogation technique in the visible region confirmed the detection of ammonium in the solution with sensitivity, response time, limit of detection (LOD), and recovery time of 0.131 nm/ppm, 17 s, 2.9 ppm, and 12 s, respectively. These features together with a high selectivity make the proposed sensor a potential candidate for determining the environmental pollution, controlling the industrial safety requirements, and accurately measuring the water quality in daily life.