Abstract: A gas sensor and a method of fabrication wherein the sensor includes a polymer fiber substrate and a metal oxide nanoshell. The nanoshell is deposited on the substrate using magnetron sputtering deposition. The sensor can be designed to detect specific gases, such as NO2 or NH3, by using different metal oxides such as tin oxide or zinc oxide. The polymer fiber substrate can be a cellulose acetate substrate prepared by electrospinning. The method for making the sensor involves electrospinning polymeric fibers, depositing a metal oxide on the fibers to produce a nanoshell, and heating the fibers and oxide in air to remove the fibers. The gas sensor uses the nanoshell for the transduction process.