High sensitivity mercury ion fiber optic sensor based on Mach–Zehnder interference

Abstract This paper proposes a novel optical fiber sensor for highly sensitive Hg 2+ detection based on Mach–Zehnder interference (MZI) structure and thiophene–chitosan hydrogel (TCH). We obtained the MZI structure by splicing the coreless fiber (CLF), thin core fiber, and CLF. And then, we etched the thin-core optical fiber cladding and assembled the TCH to produce a Hg 2+ sensitive sensor. According to theoretical derivation and experimental verification, the detection sensitivity of the sensor to Hg 2+ can reach 1.008 × 10 11 mol l −1 , and the detection limit is 5 × 10 −13 mol l −1 . The sensor also has performance stability within 24 h for concentration measurement, with an average standard deviation of 3.2 × 10 −13 mol l −1 within an hour of observation. In addition, the sensor has the advantages of specificity, simple preparation, and low cost, and it is suitable for monitoring the concentration of Hg 2+ in complex water systems.