Sensitivity-enhanced fiber-optic surface plasmon resonance sensor utilizing Cu/WS2/PAAG composite film for pH measurement

In this paper, we reported a composite optical fiber probe structure based on a Cu/WS2 coated surface plasmon resonance (SPR) coreless fiber and a microfiber Fiber Bragg Grating (FBG), which can be used for the simultaneous detection of pH and temperature by assembling Polyacrylamide Gel (PAAG) film and Polydimethylsiloxane (PDMS) coating, respectively. The simulation and experimental results show that WS2 nanofilm can effectively enhance the refractive index (RI) sensitivity of 50 nm-Cu film coated optical fiber SPR probe. Due to the swelling ratio of PAAG is regulated by the pH of liquid solution, the sensitivity of pH detection can reach − 4.42 nm/pH in the pH range of 1–9. The temperature response of the pH probe is one of the main factors leading to the pH detection error, and the experimental result is as high as 76.60 pm/°C in the range of 20–60 °C. The temperature sensitivity of the FBG can be increased from 10.4 pm/°C to 85.67 pm/°C by chemical corrosion and covering PDMS coating for temperature compensation.