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A few words about making your grids more hydrophilic



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All SPI "electrodeposited" grids, that is, those grids made by electrodeposition methods (e.g. Cu, Ni, Au) should arrive in a highly hydrophilic state, not needing any particular further treatment. However, this is often times a matter of opinion and some grid users require grids that are even more hydrophilic that what would be experienced in the "as received" condition.

Just what it is that could be going on to make grids less hydrophilic than is desired is open to debate, however some of the reasons would include a) pick up of organics from the atmosphere, b) pick up of organics from the grid vial itself, and c) residues remaining from the manufacturing process. In any case, there are several different approaches that are used to increase the hydrophilic nature of TEM grids. These various methods and procedures taken by different researchers in different institutions, from around the world, all supposedly to accomplish the same end result, were gleaned, in part, from postings on the Microscopy ListServer, primarily a posting made on Nov. 21, 1997 by Prof. Robert R. Wise:

1] Pass the grids quickly over the flame from an alcohol lamp or disposable lighter. This has to be done quickly in order to not alter the grid itself or to even melt the fine bars, especially for the Slim Bar® style of grids.

2] Rinsing in acetone before use to remove adsorbed hydrocarbons.

3] Washing in 100% ethyl alcohol followed by washing with 100% in acetone.

4] Individual grids may also be cleaned by dipping (5 to 10 times) into 4% nitric acid and then dipping several times in water. Grids can be held with PTFE (polytetrafluoroethylene) coated tweezers to prevent metal from the tweezers from dissolving in the acid treatment.

5] Hold each grid, one at a time, with tweezers ( PTFE (polytetrafluoroethylene) coated recommended) into the mouth of a bottle of concentrated nitric acid, for one second. The fumes will render the grid hydrophilic without tarnishing (if copper).

6] Place the grids into a plasma etcher/cleaner for a few minutes which removes all organics causing the loss of hydrophilic characteristics.

7] Swirl the grids in a small amount of cleaning solution for about 30 seconds, rinse several times with distilled water, followed by a drying with a Buchner funnel and a piece of filter paper at the bottom. The grids seems to remain hydrophilic for "quite some time", perhaps days or weeks before needing another treatment.

8] Dip the grids, one at a time, into 0.1N HCl just prior to picking up sections, no further washing.

We don't know which method would end up working best for you! After having spoken to some number of persons worried about the hydrophilic nature of their grids, the one thing that is certain is that different workers see their own method to be infinitely "better" than any other method. We leave it to you to discover which method works best for you!


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