A novel low-cost gas sensor for CO2 detection using polymer-coated fiber Bragg grating

•The polymer-coated FBG sensor is the first to realize CO2 detection based on tensile effects.•The PES coating is fabricated by low-temperature spin coating and high-temperature curing.•The low-cost sensor shows high sensitivity and excellent selectivity to CO2.•An over-concentration alarm system for on-line monitoring of CO2 is demonstrated. The realization of detection of carbon dioxide (CO2) is important for environmental protection. A critical challenge is how to fabricate low-cost fiber Bragg grating (FBG) sensor. Here, a new type of polyether sulfone (PES)-coated FBG sensor for CO2 detection is reported to address this challenge. The PES coating exhibits volume dilation in CO2 exposure and can transfer the stress to the grating, causing changes of the period and the refractive index of the grating. The uniform and smooth PES coating is critical for the repeatability and reliability of the sensor, which is realized through the low-temperature spin coating and high-temperature curing. The influence factors and the performance of the FBG sensor were investigated. The maximum Bragg wavelength shift is positively related to coating thickness and negatively related to temperature. The PES-coated FBG sensor possesses good selectivity to CO2 and the minimum response time is 3.27 min. The limit of detection (LOD) can be down to 0.78 % for CO2 detection. Finally, an over-concentration alarm system for on-line CO2 monitoring was developed. The outstanding features of the PES-coated FBG sensor with low-cost and simple fabrication process provide widely prospect in applications.