Residual charges in the stream ?

Dear Flowers,

I've had some troubles lately with our FACS Aria. It seems there's some residual charges
present in the stream which result in the stream significantly moving to the left once
the sorting plates are charged, even if no sort is occuring. You can imagine that under
such conditions it is impossible to sort.

I've been looking for the reason why this happens. I thought it could come from the
home-made PBS we are using, so I turned back to FACSFlow to make a few tests but the
stream kept acting the same way. I also noticed some sheath fluid going into the flow
cell due to capilarity when the nozzle tends to clog (but this does not always happen),
after carefully drying the flow cell the stream was unaffected by the charged sorting
plates anymore but, the next time the stream moved again to the left, the flow cell
was clean and completely dry.

When checking my nozzles under a microscope I also noticed that they were in a pretty bad
shape (even after a single week of use) and look like they were corroded by something. I
thought they were covered with a thin layer of gold, and gold should not be affected by
salts present in PBS. Unless, the high voltage used while sorting plus the salt
concentration in the sheath would create an elecrolysis like phenomenon at the nozzle
level which would finally result in this corrosion-like symptoms observed.

Does any of you observed the same phenomenon ? Any idea what may cause that residual
charge in the sheath ? And were it come from ? And what's "eating" my nozzles ?

Any suggestion is welcome.

Regards,


Fred

Frederic Grosjean PhD
Ludwig Institute for Cancer Research
Lausanne Branch
Chemin des Boveresses 155
1066 Epalinges
Switzerland
Tel. +41-21-692 59 67
Fax. +41-21-653 44 74
www.licr.org