MICROINJECTION

[Stephen J. Moorman]

As a former patch clamp electrophysiologist, I can tell you that 
there are many things that influence leakage of a solution into or 
out of a pipette tip.  Including how much you fill the electrode in 
addition to tip size. Filling just the tip of the electrode will tend to 
result in media being sucked into the pipette.  Filling the electrode 
more than half way will tend to result in leakage into the media.