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. A fiber optics sensor based on the structure of no-core fiber/few-mode fiber coated with a smart hydrogel membrane/no-core fiber, cascading a fiber Bragg grating for temperature monitoring was developed to detect the concentration of Pb2+ in aqueous solution. It is the first time that a phase-modulated fiber sensor is used to measure the concentration of Pb2+ in aqueous solution. When the concentration of Pb2+ changes, the specific adsorption of the hydroxyethyl methacrylate crosslinked hydrogel on Pb2+ will change the refractive index of the sensing membrane, and will shift the interference fringe of the sensor in optical spectrum. The process is simple and friendly to environment, and does not produce any harmful substance. The fiber sensor with high sensitivity of 8.155 × 105nm/(mol/L) and the estimated detection limit of Pb2+ concentration of 2.452 × 10−8 mol/L at the spectral resolution of 0.02 nm. The sensor has the advantages of high concentration resolution, low cost, remote detection ability, etc. It has good application prospect in the detection of Pb2+ concentration.