Ultrasensitive Chemiresistive Sensor for NO₂ Based on Oxidation of a Thiophene Polymer Bearing Oligoethylene Glycol Side Chains

Abstract

Nitrogen dioxide (NO2) is a potent greenhouse gas produced through the combustion of fossil fuels, posing significant threats to both the environment and human health. This study focuses on the development of a low-cost and highly sensitive NO2 sensor for improved public health and environmental protection. A chemiresistive NO2 sensor based on a thiophene polymer with oligoethylene glycol side chains (p­(g42T-TT)) is presented. The sensor operates on the principle of change in the electrical resistance of the sensing material upon exposure to NO2 gas. P­(g42T-TT) exhibits a high sensitivity to NO2 due to its high highest occupied molecular orbital (HOMO) level, making it susceptible to oxidation by NO2. The doping process was validated through UV–vis–NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The film morphology analysis using GIWAX and AFM techniques confirmed the partially crystallized structures in the NO2-doped p­(g42T-TT) film. The doped film exhibited a conductivity of 12 S/cm and a Seebeck coefficient of 1.6 μV/K, indicating the high doping level of p­(g42T-TT). The chemiresistive NO2 sensor was tested under various concentrations and showed an ultrahigh sensitivity with a response of 3.58 ± 2.38 × 100% at the 20 ppb level, which is among the highest reported sensitivity in conducting polymer (CP)-based chemiresistive NO2 sensors. The simplicity, flexibility, and high sensitivity of the p­(g42T-TT)-based chemiresistor make it a promising candidate for one-time use in NO2 sensing applications. These findings provide valuable insights for further advancements in chemiresistive gas sensor technologies.