Multi-walled carbon nanotubes (MWCNTs) films have been fabricated by using plasma-enhanced chemical vapour deposition (PECVD) system onto Cr-Au patterned alumina substrates, provided with 3 nm thick Fe growth-catalyst, for NO2 and NH3 gas sensing applications, at sensor temperature in the range of 100-250°C. Nanoclusters of noble metals surface-catalysts (Au and Pt) have been sputtered on the surface of MWCNTs to enhance the gas sensitivity with respect to unfunctionalised carbon nanotube films. It was found that the gas sensitivity of Pt- and Au-functionalised MWCNTs gas sensors significantly improved by a factor up to an order of magnitude through a spillover effect for NH3 and NO2 gas detection, respectively. The NH3 and NO2 gas molecules act as electron-donor and electron-acceptor species respectively doping the unfunctionalised and Pt- and Au-modified MWCNTs, which have p-type …