Plasmonic micro-channel based highly sensitive biosensor in visible to mid-IR

A strong light coupling between core-guided mode and metal layer leads to the enhancement of plasmonic sensor performance significantly. In this work, a plasmonic metal coated micro-channel based surface plasmon resonance sensor is proposed where a micro-channel is introduced to increase the mode coupling by reducing the distance between the core and analyte channel. Gold (Au) is considered to coat the micro-channel and generate surface plasmon on the fiber surface. Titanium dioxide (TiO₂) is employed to stick the Au layer tightly with the silica which assists in shifting the sensing wavelength from visible to mid-IR region. The light-guiding and bio-sensing properties of the proposed D-shaped sensor performance is numerically investigated by employing the finite element method. The sensor obtained maximal wavelength and amplitude sensitivities of 1,21,000 nm/Refractive index unit (RIU) and 1,405 RIU⁻¹, respectively in the x-polarized mode. Moreover, the sensor exhibits an extremely high resolution of 8.26 × 10⁻⁷ RIU and the limit of detection (LOD) is 6.83 × 10⁻¹² RIU²/nm, respectively, in the wavelength interrogation technique. To the best of our knowledge, the proposed sensor shows the highest wavelength sensitivity, resolution and LOD when compared to the existing PCF based SPR sensors. Due to the extremely sensitive response, the proposed sensor will enhance the unknown analyte detection capability significantly. Furthermore, the broad sensing range of analyte refractive index (RI) variation from 1.33 to 1.44 makes the sensor suitable for biochemical as well as medical diagnostic applications.