Colloidal quantum dots (CQDs) are emerging as ideal building blocks for the development of sensitive and low-cost gas sensors because of their large surface area and solution processability. So far, the construction of CQD gas sensor is limited to lab-scale, batch-processing methods such as spin coating. Here, we demonstrated highly sensitive and fast-response CQD gas sensors through a room-temperature spray-coating route in ambient air. Unlike the spin-coating process, a porous film morphology could be achieved by the spray-coating of ultrasmall PbS CQDs (4.0 nm in diameter) on the alumina ceramic substrates, possibly explaining their superior gas-sensing performance. Moreover, we investigated the effect of the dispersing solvent on the spray-coated PbS CQD films and found that organic solvents with lower boiling point were preferred in producing porous and sensitive CQD films. The response of the optimal gas sensors toward 50 ppm of NO2 at room temperature was high as 44, with response and recovery times short as 1 s and 28 s, respectively. The enhanced gas-sensing capabilities, coupled with the promise for mass production at room temperature, make the spray-coated CQD gas sensors very attractive in the future gas-sensing technology. (C) 2016 Elsevier B.V. All rights reserved.