## 1 Introduction  
The rapid development of smart objects has led to the increased interest of sensor technologies to collect and exchange sensed data in real-time. With the development of nanotechnologies, the sensor efficiency and accuracy have been improved leading to a large extension of their application domains [1, 2]. Among a wide range of sensor applications, such as environmental monitoring or public safety, the development of sensor devices allowing monitoring of harmful greenhouse gases (GHGs) is of the utmost importance. GHGs need to be monitored in areas as diverse as the monitoring of industrial processes or personal tracking. Carbon monoxide (CO) is one of the GHGs. Its efficient detection and monitoring is essential and require the development of specific sensor devices, which must meet the following criteria: reliable, responsive, highly sensitive, miniaturized, low cost, and capable to operate on a large range of temperature, from ambient temperature (smart objects) to high temperatures (up to 600 \({}^{\circ}\)C for industrial combustion processes). Most of actual sensors are solid-state sensors based on the interaction of gas particles with surfaces and volumes. The electrochemical potential, the resistivity, the density, and/or the optical properties are altered upon gas adsorption. This alteration must be maximized to increase the detection. Common high-temperature GHG sensors are based on metal oxide materials working on the principle of the chemiresistor. For CO, the detection mechanism is based on the redox reaction between the gas species and the pre-adsorbed O\({}_{2}\) on the surface of metal oxide, affecting the depletion layer and thus resulting in the change of the conductivity of the material [3; 4; 5; 6; 7]. Metal oxide sensors based on SnO\({}_{2}\) material have been developed to monitor CO due to their relatively high sensitivity [8; 9]. Indeed, the detection of 5 ppm CO in few seconds at 300 \({}^{\circ}\)C has been demonstrated [10; 11]. Chemiresistor sensors based on titanium oxide (TiO\({}_{2}\))/lanthanum oxide (La\({}_{2}\)O\({}_{3}\)/CuO) have also demonstrated their capacities to selectively detect down to 500 ppm of CO against CH\({}_{4}\)[12] under 5% of O\({}_{2}\) up to 600 \({}^{\circ}\)C. However, these kinds of sensors can present a low selectivity (due to interferences with other gases), a drift of the sensor response and/or a poor recovery. CO-sensors based on Ga\({}_{2}\)O\({}_{3}\) thin films have also been developed, usually operating in the 400-600 \({}^{\circ}\)C temperature range. Comparing to SnO\({}_{2}\), Ga\({}_{2}\)O\({}_{3}\) gas sensors present faster response, faster recovery time and lower cross-sensitivity to humidity [13; 14; 15; 16]. The sensitivity and selectivity performances of these Ga\({}_{2}\)O\({}_{3}\) sensors have been improved by adjusting the oxygen vacancy concentration [17] or by using gold particles to catalyze the reaction between adsorbed oxygen on sensor surface and gas molecules by reducing their activation energy [18]. However, these sensors based on planar films present numerous drawbacks. Among them, the limited surface, where takes place the interactions between gas molecules and materials, results in limited sensor performances. These last decades, a new class of sensors based on 1D-nanostructures, such as nanowires (NWs) or nanorods (NRs), has appeared as a promising way to improve the sensing performances.