A Slotted Air Hole-Based Circular Channel Sensor Internally Coated with Au-TiO₂ for Ultra-Wide Sensing Range with High Sensitivity

This study introduces an extremely sensitive internally coated circular channel biosensor that uses surface plasmon resonance (SPR) featuring a slotted air hole-based photonic crystal fiber (PCF) capable of sensing an ultra-wide variation in sample analyte refractive index (RI). Gold (Au) strips are selected as the plasmonic material due to their well-recognized reputation for being chemically stable, and a very thin layer of Titanium dioxide (TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) is coated to promote the adhesion of gold to silica. The analyte channels are positioned inside the silica structure to ensure better sensitivity. COMSOL Multiphysics software, built upon the finite element method (FEM), served here as a valuable tool for designing and investigating the influence of various initial geometric parameters on the biosensor’s sensing capabilities. The designed single-core PCF sensor provides a maximum wavelength sensitivity (WS) of $79000 \mathrm{~nm} /$ RIU, a maximum wavelength resolution (WR) of $1.27 \times 10^{-6}$ RIU, and an amplitude sensitivity (AS) of $343.14 \mathrm{RIU}^{-1}$. Additionally, this proposed sensor can detect the RI of an ultra-wide range of analytes, spanning from 1.17 to 1.41. The biosensor’s performance may also be used to detect organic molecules, straight-chain alkanes such as ethane, octane, and decane, as well as to monitor environmental contaminants, biochemical substances, and biomolecular interactions.