A novel sensor for detecting PM_(2.5) concentration based on refractive index sensing of a photonic crystal fiber

摘要

A novel sensor for detecting participate matter 2.5 (PM_(2.5), particles with a diameter smaller than 2.5 μm) concentration in environment air is presented by using modal interference in a photonic crystal fiber (PCF). The sensor is composed of a single mode-multimode-PCF-multimode-single mode optical fiber, and the corresponding polypyrrole (PPy) sensing nanofilm with a light-inducing characteristic is synthesized onto the outside surface of a PCF in-situ by an interfacial ploymerization method. The experimental result shows that the thickness of the sensing film is within the range of 100~150 nm by a scanning electron microscope. When the sensor is placed in PM_(2.5) air flow, the PM_(2.5) particles are absorbed onto the surface of a PPy sensing film due to a light-inducing electrostatic effect, resulting in the refractive index (RI) change of a sensing film. For PM_(2.5) air flow with a concentration of 55 μg/m~3 and a sampling time of 30 min, the characteristic wavelength of the interference spectra has a blue shift with 1 nm. After turning off the light source, the characteristic wavelength of the sensor is back to the initial value owing to no light-inducing electrostatic effect and the PM_(2.5) particles desorbing. The sensor has a good reversibility.