Highly sensitive and selective fiber-optic modal interferometric sensor for detecting trace mercury ion in aqueous solution

A novel type of fiber-optic mercury ion (Hg 2+) sensor was prepared by coating poly (N-ethyl-4-vinylpyridinium chloride) (P4VP·HCl) and poly (sodium-p-styrenesulfonate) (PSS) ultrathin film on the surface of a thin-core fiber modal interferometer (TCFMI) with layer-by-layer (LbL) electrostatic self-assembly method. The fabricated TCFMI Hg 2+ sensor exhibits a high selectivity to Hg 2+ and its detection limit and response time are 10 -9 M and 30 s, respectively. The LbL electrostatic self-assembly process is monitored with a quartz crystal microbalance (QCM) and UV-vis spectroscopy for film growth. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used to characterize the morphology of the ultrathin film. Both demonstrated nanoporous film, which is helpful in shortening the response time of the TCFMI Hg 2+ sensor.