The development of sensitive graphene-based surface acoustic wave sensors for NO₂ detection at room temperature

Bilayer graphene (Bl-Gr) and sulphur-doped graphene (S-Gr) have been integrated with LiTaO₃ surface acustic wave (SAW) sensors to enhance the performance of NO₂ detection at room temperature. The sensitivity of the Bl-Gr SAW sensors toward NO₂, measured at room temperature, was 0.29º/ppm, with a limit of detection of 0.068 ppm. The S-Gr SAW sensors showed 0.19º/ppm sensitivity and a limit of detection of 0.140 ppm. The origin of these high sensitivities was attributed to the mass loading and elastic effects of the graphene-based sensing materials, with surface changes caused by the absorption of the NO₂ molecules on the sensing films. Although there are no significant differences regarding the sensitivity and detection limit of the two types of sensors, the measurements in the presence of interferent gases and various humidity conditions outlined much better selectivity and sensing performances towards NO₂ gas for the Bl-Gr SAW sensors.