TiO 2 NP@HKUST-1 based D-typed multimode optical fibre sensor for nicotine detection at room temperature

In this paper, a nicotine-detecting nanocomposite TiO2NP@HKUST-1 was fabricated using titanium dioxide nanoparticles and a metal–organic framework (MOF) and coated on the surface of D-typed multimode fibre (MMF) for nicotine detection. Moreover, the spherical optical fibre serves as the excitation region of the high-order mode. The specific adsorption of nicotine alters the equivalent refractive index (RI) of TiO2NP@HKUST-1 films, resulting in a regular shift in the D-typed fibre interferometric spectrum. Experiments show that based on the demodulation of a spectrometer with a resolution of 0.02 nm, the detection limit (LOD) of this sensor can reach 0.08nM. On this basis, we proposed a speckle demodulation method based on machine learning, which further reduced the LOD of the sensor to 0.01nM with R2 = 99.97%. Studies show that different demodulation methods have their own advantages.