A four-electrode system for measurement of bilayer lipid membrane capacitance

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Abstract
A four-electrode capacitance-to-period converter designed for capacitance measurements of bilayer lipid membranes is described. The capacitance measurement consists of cyclically charging and discharging the measured capacitance with a constant current, regarding its absolute value. The voltage of the studied capacitor is triangularly shaped. The cycle duration is proportional to the input capacitance. Capacitance measurement with a four-electrode system makes it possible to reduce considerably the errors caused by electrode and electrolyte impedance. It is possible to use high-resistance microelectrodes. The system makes it possible to measure the capacitance at an imposed polarization potential; the voltage oscillates about that value during the measurement. This makes it possible to measure the membrane capacitance as a function of polarization potential. An example is cited of using the capacitance-to-period converter in a computer-controlled measuring system.