Following the target of the NANOPOLY project, the objective of this project is to fabricate metamaterial-based resonators (namely split-ring resonators or SRRs) operating in the X band (8-12 GHz), and to deposit carbon nanotubes (CNTs) as a sensitive layer for the detection of carbon dioxide (CO2) over the SRRs, for applications in the domain of sensors for environmental pollution monitoring. The fabrication of SRR-based resonators with CNTs in the band stop configuration will allow the realization of gas sensors with high sensitivity. A resonator based on metamaterial with CNTs has a very narrow band, due to a high-quality factor Q and for this reason is very sensitive to any physical phenomenon that affects the materials of the resonator. Since the effect of recombining CO2 molecules with CNTs is a change in the conductivity of nanotubes (and, thus, a change in their dielectric permittivity), at microwaves it will be possible to observe a shift of the resonance frequency depending on the level of absorption. Thus, the obtained sensitivity of the proposed gas sensor will be higher than that of a classic sensor.