AJP - Cell Physiology, Vol 249, Issue 5 514-C521, Copyright © 1985 by American Physiological Society
Submicron tip breakage and silanization control improve ion-selective microelectrodes
S. Tripathi, N. Morgunov and E. L. Boulpaep
Probable causes of failure of otherwise well-constructed liquid
ion-exchanger (LIE) micro-electrodes of average tip size less than 0.15
micron were examined. The problem could be attributed to two major
variables, both localized at the tip: partial tip occlusion during
fabrication prevents the generation of an electromotive force (small or
absent slope and/or selectivity, high resistance); or poor hydrophobicity
of the tip permits water to displace the resin from the tip (small or
absent slope and/or selectivity and low electrode resistance). Controlled
dry tip breakage on paper coated with glassine to final tip sizes well
below 0.5 micron (confirmed by scanning electron microscopy) improves the
yield of usable electrodes severalfold. Adequate silanization of the tip
and consequent retention of resin at the tip can be predicted from the
contact angles observed at the glass-LIE-backfilling solution interface.
Satisfactory silanization can be achieved despite high ambient humidity. No
evidence of shunting of Na+-LIE microelectrodes by the glass wall was seen.
In the isolated perfused proximal tubule of Ambystoma tigrinum, the mean
intracellular Na+ activity recorded by broken-tip electrodes (13.7 +/- 1.9
meq, n = 4) was similar to that recorded by intact electrodes (15.5 +/- 1.1
meq, n = 31).
