Iodide ions concentration sensing using polymer-tipped optical fiber

The concentration of iodide (I − ) ions was determined by a fluorescence quenching method; a polymer-tipped optical fiber (PTOF) was used as the sensing head. The polymer tip, made by a free-radical photopolymerization method, combined the advantages of high sensitivity of the tapered fiber with a flexible and simple fabrication process. A sol–gel encapsulated fluorescein, used as the fluorescence indicator, was dip coated on the surface of the PTOF. Experimental results indicate that the backscatter fluorescence intensity collected by PTOF is 9.60 times higher than that of the flat-cut fiber. When the I − ions concentration changed from 6 to 36 mM, the backscatter fluorescence intensity collected by PTOF decreased linearly with a response time of 2 s. We demonstrate a method that can detect remote ion concentration with high repeatability, with stability, and which is simple to carry out. This method can be used in applications such as chemical production and water quality monitoring.