ION-SENSITIVE MICROELECTRODE SYSTEM WITH SHORT RESPONSE-TIME

The measurement of changes in ion activity (e.g., pH) in neurons requi res fine tip-sized double-barreled microelectrodes: one channel being equipped with an ion-selective liquid membrane, the other used for mea surement of the membrane potential. The limited bandwidth and the diff ering transfer functions for electrical and ionic signals necessitate frequency response linearization networks to ensure that the output si gnal of the electrode is a faithful image of the input signal. We have developed a linearization network to ensure a rapid response time for ion-sensitive microelectrodes. To test the response characteristic we have developed a test system that allows the pH at the electrode tip to be changed within 1 ms. Application of these techniques to electrod es of 1 mu m tip diameter results in a 90% response time to a pH step of similar to 60 ms and of similar to 2 ms with electrodes with 20 mu m tip.