The small interfacial area of microelectrodes results in low interfacial capacitance and a correspondingly small cell time constant, permitting measurements on the microsecond time scale. The current obtained at a microelectrode is generally in the nanoamp or picoamp range. These measurement conditions place rather severe demands on the measurement system, namely, the need for high gain and wide bandwidth at a reasonable signal-to-noise ratio. A potentiostat design based on a voltage follower circuit is described. The potentiostat can be constructed from inexpensive operational amplifiers and has a bandwidth of 10 kHz at 100 pA full scale (10 V output), 100 kHz at 10 nA full scale, and over 2 MHz at 1 μA (or more) full scale. Since the working electrode in this configuration is no longer at ground potential, a differential controller has been designed to control the potential difference between working and reference electrodes directly. © 1990.
