Pb2+ fiber optic sensor based on smart hydrogel coated Mach-Zehnder interferometer

•A new fiber optic sensor with high sensitivity (8.155 × 105 nm/(mol/L)) is proposed to detect Pb2+ concentration.•It is the first time that a phase-modulated fiber sensor is used to measure the concentration of Pb2+ in aqueous solution.•The estimated minimum detection limit is 2.452 × 10−8 mol/L at the spectral resolution of 0.02 nm.•The structure of the fiber optic sensor is simple, and the synthesis method of lead-ion sensitive hydrogel is easy and low cost.