SPI Supplies® TEM Grid Collection
Special grid cleaning procedures
Grids fresh out of the vial from SPI Supplies are pre-cleaned and are meant
to be used as is, out of the vial, and without the need for further cleaning.
Contamination, when it is present, is very minute in amounts, and tends to
be organic in nature, possibly residues from the production process.
Color of the grids:
The dark, reddish color we associate with copper is actually copper oxide.
Freshly exposed copper, without this oxide layer, is almost pink in color.
There are small, theoretical advantages to removing the "native" oxide,
mostly in the area of contact resistance, but the treatment lasts only a
very short time before the oxide forms again. You can preserve the pink
color by storing the material in some non-aqueous solvent, like alcohol, at
least for a while. Maybe some users might see some benefit from such storage,
but for most, the only end result would be to make the grids thinner.
The SPI Supplies copper grids do have applied a layer (of molecular dimensions in
thickness) that serves as a passivation layer to prevent or at least reduce
the tendency of the copper surface to oxidize and tarnish. The decision to
clean or not clean is determined on the basis of whether a) this layer could
interfere in some way with a reaction being carried out on the grid or
b) additional wettability is desired, since removal of the layer makes the
grids more hydrophilic. But we are talking only about copper grids and we
are not talking about Ni or Au grids.
How necessary is it to subject copper grids to these kinds of procedures?
For the copper grids purchased from SPI Supplies, it is our position that
these kinds of cleaning procedures should not be necessary at all. We
believe that for most people, if the grids were used right out of the vial,
the results they get would be indistinguishable from what they would achieve
using a cleaning procedure. The exception to this statement would be if the
grids are very old, and we know that some people do "discover" ancient grids
in a drawer that have been hidden from view for years and years.
So when doing procedures that demand the complete absence of any such
contamination, or discoloration, or when additional wetting characteristics
are desired, we can offer the following cleaning protocol:
- Place the grids to be cleaned in a clean 100 ml beaker
- Cover the grids with glacial acetic acid, approximately 20cc. It seems
like the GAA is effective against the organics but does not react with the
metal of the grid itself.
- Clean the grids in this acid, using an ultrasonic cleaner, for 5-10 minutes.
- Rinse in 100% acetone until the smell of the acetic acid is gone.
- Do a final rinse in 100% ethyl alcohol and pipette the alcohol off the
remaining liquid.
- Quickly invert the beaker and stand it over a glass petri dish that has
a clean Whatman filter paper on its surface. Surface tension will keep the
grids "attached" to the now inverted bottom of the beaker, when inverted
(e.g. turned up-side-down).
- Place the entire system in a small lab oven at 60°C for an hour or
more. The grids will fall on to the filter paper.
- Cover the bottom of the glass with a top. The grids will keep without
father cleaning until they are all used up. There is some preference for a
glass petri dish because there is less static charge.
Further comments:
There are of course many different cleaning procedures, and some users of
grids swear by their own method almost religiously! We ourselves like the
above described acetic acid method because it seems to not change at all the
"dullness" of the "dull" side of the grids. Some use a 10% HCl solution for
this grid cleaning step. It is a bit faster, but it can also result in loss
of the dull vs. shinny side discrimination.
A third method would be the use of 5% nitric acid (HNO3)
for about 5 minutes. We know that the anti-tarnish or passivation layer
that is applied to copper grids will be removed after 2-5 minutes of
treatment at the above concentration.
Nickel and Gold Grids:
We really don't believe that these grids require any kind of cleaning, and
again, unless they have been stored some very long number of years, should
in general not even show evidence of visual discoloration. We know that
some workers doing immunogold work believe that a thorough cleaning in
purified acetone will enhance the outcome of their results but we are not
aware of anyone who has actually published documentation that such treatment
really does improve results.
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Tuesday February 09, 2010
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