Glass microelectrode tip capacitance: its measurement and a method for its reduction.
The frequency response of input amplifiers used for measurement of bioelectric signals from small cells is severely limited by the resistance and capacitance of the fine glass microelectrodes which are required for these measurements. A significant improvement in the frequency response can be realized by employing the technique of input capacitance neutralization. This capacitance neutralization, however, is incomplete since: (1) the bandwidth of the input amplifier is finite; and (2) a fraction of the electrode capacitance is isolated from the amplifier input by a part of the electrode resistance and cannot be compensated. It is therefore desirable to ensure that the electrode capacitance is as low as possible before neutralization. A method is discussed for measuring and predicting the distributed capacitance of the microelectrode and a technique is described for coating the outside of the electrode near the tip with a substance which can lower the electrode capacitance per unit length by as much as 7-fold. The significance of the improved frequency response of the input amplifier that this technique provides is discussed in light of recent advances in intracellular single electrode voltage clamp technique.
D000818:Animals; D002468:Cell Physiological Phenomena; D004553:Electric Conductivity; D008722:Methods; D008839:Microelectrodes