The design and operation of a new type of single nucleation site electrode, the gas phase nucleation core (GPNC) electrode, is described in this paper. The GPNC is basically an artificial Harvey nucleus which is made on a microelectrode. It is experimentally shown that it is possible to generate monosized gas bubbles with a periodical evolution by this method. The gas bubble evolution process is monitored electrically by means of overpotential and impedance measurements as well as optically observed. It is concluded that a possible use of the devices could be as a surfactant concentration sensor.