The technique they are referring to is FSCV (fast scan cyclic voltamatry). Im not sure about its use in humans but it's been around in rodent research for like thirty years. This paper was the one to introduce it I think (Millar J. and Barnett T. G., J. Neurosci. Methods. 1988).

Its also possible to measure other things using the same technique such as pH and adenosine but as I heard from colleagues that getting good signal to noise ratio in these preps is really difficult.