In article <173C51009FS86.PET101 at ukcc.uky.edu>, PET101 at ukcc.uky.edu says:
>>I've been making indium electrodes for extracellular recording, but I'm having
>trouble with the plating...What is a good resistance to use to get a nice, even
>coating when plating the indium with gold and then platinum black? How long
>does it usually take to get a good plating of both the gold and platinum?
>pet101 at ukcc.uky.edu
I was beginning to think I was the only one in the world with that
problem. I seem to have fixed it - managing to hold a units for
up to 8 hours now. Where are you trying to record from ? If it's
crest cells in the medulla, then welcome to insanity land. For these
cells you need plated ball diameters of around 3-4 microns and a
resistance of 3-10 megohms. For all other cells, especially midbrain
ones it seems, any sort of ball seems to work.
Anyways, to answer the question. The resistance and times for plating
depends on the concentrations of your solutions, and their purity. Pure
gold chloride is pure crap - you need to make a gold cyanide solution or
buy one from a supplier. Using pure gold chloride never seems to give
smooth round balls. I have a .7% stock AuCn solution which is diluted
to 8-10 parts water. I get a good round 2-3 micron ball from plating
for 15 seconds over 55 megohms. The platinum plating is the critical
stage - this is where the resistance of your electrode plumets with only
a small amount of plating. I use a .4% platinum chloride solution. Make
sure this is not too old; it is also very light sensitive so wrap the
container in foil. For sufficient plating - barely detectable under the
microscope - I plate for 1 1/2 to 2 seconds over 85 megohms.
All in all it begins with alot of trial and error. I have heaps of
helpful hints and also some very detailed protocols if you would
EMAIL me at halstead at sbsu1.auckland.ac.nz
This reminds me - anyone using indium electrodes - could you please
email me with details of what cells your recording from and the key
features of your electrodes - like ball diameter and resistance. I
want to build up a database and put it on WWW and FTP. A good description
of the cells anatomy would be well appretiated.