Trace NO2 Detection in Ambient Air Using Co-Phthalocyanine-Modified Graphene Field-Effect Transistors

The sensitive detection of NO₂ in air is crucial for controlling environmental pollution and protecting public health. Therefore, a simple and sensitive method for detecting NO₂ must be developed. In this study, we fabricated phthalocyanine (Co, Cu, Ni, and H₂)-modified graphene field-effect transistors (FETs) for NO₂ detection at the parts-per-billion (ppb) level. Compared with other phthalocyanine-modified devices, the Co-phthalocyanine-modified graphene FET exhibited large voltage shifts in its transfer characteristics following the introduction of NO₂ gas at the ppb level. The Dirac-point voltage shifts observed at each NO₂ concentration tested were well fitted to the Langmuir adsorption isotherm, indicating that the Co-phthalocyanine-modified graphene FET was capable of quantitatively detecting NO₂ at concentrations ranging from a few ppb to the sub-ppm level, corresponding to environmental standards. In addition, the Co-phthalocyanine-modified graphene FET demonstrated high selectivity for NO₂ and maintained excellent sensing characteristics even after repeated use. The NO₂-sensing performance of the Co-phthalocyanine-modified graphene FET was not significantly degraded in air (0–25% relative humidity (RH)), and the device could quantitatively detect NO₂ with high sensitivity even in 40% RH air. Considering these results, the Co-phthalocyanine-modified graphene FET could enable the highly sensitive detection of NO₂ at the ppb level in ambient air with humidity.