High-Performance Colorimetric Room-Temperature NO2 Sensing Using Spin-Coated Graphene/Polyelectrolyte Reflecting Film

Nitrogen dioxide (NO₂) is a colorless, flammable, and dangerous gas even at very low concentrations. To date, quantitative analysis of NO₂ concentrations have been made using conventional techniques (e.g., electrochemical method). In light of the energy and time consumption involved in such applications, efforts have been made to develop new detection methods that are more sensitive and sustainable. At this point, structural color-based sensing shows great advantages because of its sensitive, visualized, and reproducible response. In this study, graphene oxide/polystyrene sulfonate (GO/PSS) optical films were designed and prepared to evaluate the potential usage for the effective detection of NO₂. The uniform GO/PSS thin films were fabricated by the spin-coating-assisted layer-by-layer assembly method. The resulting colorful films exhibited ultrafast response, obvious optical shifts, and good reversibility within the visible range toward NO₂. The concentration-dependent NO₂ sensing characteristics and selectivity were investigated as well. The dynamic study showed that the absorption/desorption time was 200/200 ms and the detection limit was 1.0 ppm at room temperature. The sensing mechanism was investigated and verified by computer simulations. Such ultrasensitive and colorimetric properties of GO/PSS films may enable many potential applications such as disposable sensors for health and environmental monitoring.