Wireless EEG electrode design
You can't transmit the voltage of an electrode, because that does not exist: a voltage is always between two points, so you need at least two electrodes connected to your transmitter. In practice you need three to cancel out the 'common mode' noise.

To transmit the signal, you must first filter it (to remove the ever-present 50 or 60 Hz), amplify it (to bring it in the range of the A/D converter), the convert it to digital and finally transmit it. This is doable (for someone who can design such circuits, which is far from trivial), but there is not that much advantage over a wired version.