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I have found that sonicating a ceramic nozzle tip will usually clear a
clog, except when it doesn't. It has been suggested that enzymatic
cleaning may work even better. Figuring that these clogs are from DNA and
protein from lysed cells, we tried a DNase and proteinase K digestion.
We incubated with DNase I first using about 1000U of enzyme in the supplied
buffer (0.1 mol/l Na acetate, 5mmol/l Mg+, pH 5.0) at 37=BA for 1 hour.
We followed with proteinase K at about 100 ug/ml in a buffer of 10mM Tris,
1mmol/l Ca+ at pH 7.8, also for one hour. This can be heated to 50=BA ,
which might help to clean things as well.
You can rinse with detergent, followed by water, after each incubation.
Remember that these enzymes require Ca+ or Mg+ (no EDTA). Also, I do the
DNase first, since residual proteinase K will inactivate it. Sometimes,
I'll sonicate for a minute or two after each incubation as well. It sure
seems to get rid of the most stubborn clogs.
One more thing; it's a good idea to sonicate with the business end (tip) of
the nozzle facing up. This allows crud to fall out as well as keep from
chipping the tip.
While I'm here, special thanks to Steve and Paul for maintaining this
forum. I find myself reading it every day. It's a great way to
communicate and learn, and continues the helpful tradition of cytometrists
worldwide.
Hank Pletcher
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