Sandwich Nanolayers Deposited on Curvedly Double-Polished Optical Fiber for Surface Plasmon Resonance Sensor of Simultaneous Dual-Parameter Detection

Cross-sensitivity reduces the reliability of ambient temperature (T) and refractive index (RI) detection during the process of photothermal therapy (PTT). Current dual-parameter sensors focus on RI and T measurement in spatially separated regions, limiting the advancement of PTT. To tackle this issue, we proposed a curvedly double-polished optical fiber surface plasmon resonance (SPR) sensor based on sandwich nanolayers of gold film–gold nanoparticle (AuNPs)–polydimethylsiloxane (PDMS), which successfully achieved simultaneous dual-parameter detection of refractive index (RI) and temperature (T) within a single spatial region. Fiber bending and polishing techniques deepen the effective penetration distance of the evanescent field, strengthening the coupling between light and electrons in metal layer. The sandwich nanolayers modulate the SPR location in response to the fluctuations of ambient RI and T. Simultaneous detection was achieved by monitoring dual SPR signals. Two typical curvedly double-polished structures, namely side-polished and front-polished, exhibited similar sensitivity but distinctive confinement loss. Key factors including polishing depth, bending radius, Au film, and PDMS thickness for sensing performance were explored. Under optimal conditions, the proposed side-polished and front-polished fiber SPR sensor achieved sensitivities of 1502 nm/RIU and 1.86 nm/°C, 1382 nm/RIU and 1.88 nm/°C, respectively. With a simple structure and high integrability, it provides a viable solution forin vivocyto-sensing and therapeutic applications.