High-sensitivity parallel SPR probes for refractive index and temperature sensing

In order to advance the surface plasmon resonance (SPR) sensing technique toward the near-infrared (NIR), we propose to use a semiconductor film called TiO₂ to modulate the SPR effect. The results show that TiO₂ film can shift the SPR characteristic wavelength to the NIR and display higher sensing sensitivity than the visible band. The degree of redshift is positively correlated with the thickness of the semiconductor film. In addition, this work analyzes the physical mechanism by which TiO₂ modulates the SPR effect and proposes a dual-probe sensing system with a parallel structure. The system operates with a 400–1700 nm bandwidth for refractive index (RI) and temperature sensing. The simulation and experimental results of the sensing system show consistency. The experimental results show that the characteristic wavelength of the RI probe shifts in the visible range with a maximum RI sensitivity of 12800 nm/RIU and a detection range of 1.333–1.420 RI; the characteristic wavelength of the temperature probe shifts in the NIR with a maximum temperature sensitivity of 6.4 nm/℃ and a detection range of 0–100 °C. The test results also show that the sensing system has good stability in a short period. The method of using semiconductor film to modulate the SPR effect successfully promotes the extension of SPR sensing technology to the infrared wavelength band, and the parallel probe structure breaks through the narrow-band limitation faced by traditional multiparameter sensing, which provides value for the study of wide-range measurements of fiber optic sensors.