In this paper, we investigate the sensitivity and selectivity of lead sulphide colloidal quantum dots (CQDs) gas sensor. The benefits of CQDs, compared to commercial bulk sensor gas, are a large surface/volume ratio, a lower operating temperature, an easy deposition process and a precise control of dimensions to increase sensor sensitivity. The sensor is based on a chemo-resistive device with an active layer composed by PbS CQDs deposited on interdigitated metal contacts with a ligand exchange treatment. The sensor performance are validated on different gas pollutants (NO 2 , NO, CO 2 and CO) for increasing gas concentrations and times. The sensor shows high selectivity towards NO and NO 2 against CO and CO 2 at room temperature.