The present invention provides a device 10 for generating a non-thermal gaseous plasma which may be a flow of gas plasma in the form of a gas plasma plume emitted from the device. The device comprises a gas capsule, or pressure vessel, 12 for holding a gas or gases 14 under pressure and forming a flow of gas through a plasma generator 16 to an applicator 18 when released from the capsule. Gas released from the gas capsule is energised in the reaction generator to form a gas plasma.The device has a housing 28 for the plasma generator 16, a battery 116 and a signal generator 58 for energising the plasma generator. The gas capsule 12 docks with the housing 28. The device is adapted to be hand-held, typically by the gas capsule 12, and operated to allow it to be used for instance for cleaning and whitening teeth.