Electrical Noise in Micropipettes

Metallic microelectrodes have the advantage over glass micropipettes that they produce lower amounts of electrical noise. Gesteland et al. (1959) have shown that noise in metal microelectrodes is approximately that for a pure resistance that is. 

T = temperature of electrode, °K R = real part of the electrode impedance, fi A/ = frequency band passed by the electrode, Hz 

For a typical metal microelectrode, the rms (root-mean-square) noise voltage for the audio band of frequencies is of the order of 60 /iV for a 10-MQ electrode at room temperature. 

Fluid-filled glass micropipettes are inherently more noisy than their metal counterparts. In addition to feTRA/ noise associated with the metal-electrolyte connector in the stem, we must deal with ionic flow. Ion flow occurs between the electrolyte in the lumen and the external electrolyte of the medium in which the electrode is placed. Ion movement depends upon tip size, ion concentrations in the two electrolytes, current in the electrode, pressure differentials, and other factors. It is a complex problem and not amenable to easy theoretical treatment. In general, the smaller the tip diameter, the lower the noise figure for glass electrodes. Little ionic flow occurs in pipettes with tips 1 /x diameter. 

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