Ultralow Limit Detection of Sodium Ions by Optical Fiber Surface Plasmon Resonance With Ion Pair Exchange

The detection of trace sodium ions is important for environmental monitoring. This paper presents a fiber-optic surface plasmon resonance (SPR) sensor capable of ultra-sensitive sodium ion detection, which operates on the principle of ion pair exchange. A gold film is coated on the surface of tilted fiber Bragg gratings (TFBG) to excite SPR. And then, an ion-selective membrane is fabricated by spin-coating a mixture solution onto a gold film. This mixture, comprising tetrakis (3,5-bis(trifluoromethyl)phenyl) borate (TFPB), 2-nitrophenyl octyl ether (NPOE), methylene blue (MB), sodium ionophore III, and poly (vinyl chloride) (PVC), enables the adsorption and binding of sodium ions from the solution for trace sodium ion detection. The experimental results show that within the dynamic detection range of 10-16to 10-4M, the detection limit of the proposed sensor is 2.95×10-14M, and the detection time is less than 3 minutes.