A solid-state gas sensor functions by its recognition element exhibiting changes in a given property in response to changes in the concentration of an analyte in the gas phase. Common examples of recognition elements are metal oxides , polymers , carbon nanotubes , and metalorganic frameworks . The analyte adsorbs onto the recognition element and, through either physical or chemical interactions, alters some property of it (e.g., mass , electrical resistance , or color ). This change in property of the recognition element is converted by a transducer (e.g., a quartz crystal microbalance in the case of a gravimetric sensor) into an electrical signal that is subsequently used to infer the concentration of the analyte in the gas.