Electrical detection of ppb region NO 2 using Mg-porphyrin-modified graphene field-effect transistors.

The trace detection of NO 2 through small sensors is essential for air quality measurement and the health field; however, small sensors based on electrical devices cannot detect NO 2 with the desired selectivity and quantitativity in the parts per billion (ppb) concentration region. In this study, we fabricated metalloporphyrin-modified graphene field-effect transistors (FETs). Mg-, Ni-, Cu-, and Co-porphyrins were deposited on the graphene FETs, and the transfer characteristics were measured. With the introduction of NO 2 in the ppb concentration region, the FETs of pristine graphene and Ni-, Cu-, and Co-porphyrin-modified graphene showed an insufficient response, whereas the Mg-porphyrin-modified graphene exhibited large voltage shifts in the transport characteristics. This indicates that Mg-porphyrin acts as an adsorption site for NO 2 molecules. An analysis of the Dirac-point voltage shifts with the introduction of NO 2 indicates that the shifts were well-fitted with the Langmuir adsorption isotherm model, and the limit of detection for NO 2 was found to be 0.3 ppb in N 2 . The relationship between the mobility and the Dirac-point voltage shift with the NO 2 concentration shows that the complex of NO 2 and Mg-porphyrin behaves as a point-like charge impurity. Moreover, the Mg-porphyrin-modified graphene FETs show less response to other gases (O 2 , H 2 , acetic acid, trimethylamine, methanol, and hexane), thus indicating high sensitivity for NO 2 detection. Furthermore, we successfully demonstrated the quantitative detection of NO 2 in air, which is near the environmental standards. In conclusion, the results of the Mg-porphyrin-modified graphene FETs enable a rapid, easy, and selective detectability.