Numerical investigation of Au-silane functionalised optical fibre sensor for volatile organic compounds biomarker (VOCs) detection

Abstract

A numerical modelling to theoretically investigate and analyse the characteristic of the surface functionalised optical fibre based sensor to detect volatile organic compounds (VOCs) biomarker is introduced in this paper. A 125-micron diameter of coreless silica fibre (CSF) connected to single-mode fibre (SMF) at both ends to achieve a structure of SMF-CSF-SMG is proposed to detect VOCs biomarkers for diabetes such as acetone and isopropanol. The coreless fibre region is considered to be a sensing region where the multimode interference (MMI) occurs having a higher light interaction at the interface between the fibre and sensing medium which leads to the enhancement of sensitivity. The sensing region undergoes surface functionalisation with Au-silane for the sensor to be selectively detect VOCs biomarker with electrostatic absorption. The length of the sensing region is numerically optimised to achieve a reimaging distance where the highest possible of coupling efficiency occurs and the maximum output signal can be obtained. Coupling efficiency spectra at different volume fractions of gold nanoparticles with various acetone and isopropanol concentrations are also presented. A sensitivity of the Au-silane functionalised optical fibre sensor is achieved by using the analysis of wavelength shift interrogation. The results show the spectra undergoes red-shift phenomenon in the near-infrared region (NIR) when concentrations of acetone and isopropanol are increased. The functionalisation of Au-silane on the optical fibre sensor provides a higher sensitivity compared to the unfunctionalised sensor as it shows more dramatic shifts of absorption spectra when there is a change in VOCs biomarker concentration.