On-chip microplasma discharge devices capable of producing light, including ultraviolet light, capable of detecting atomic and molecular gas, and capable of detecting atomic and molecular contaminants in water samples. The on-chip microplasma discharge devices utilize nanoparticles or magnets to tune or confine microplasma discharges generated by electrodes delivering a voltage to the device. Selective control of the gaseous pressure at a value between atmospheric pressure and a vacuum pressure allows for further refinement of gas or contaminant detection, or for further tuning of the wavelength of the light to be produced.