When putting a sample onto a TEM grid, or when treating that sample with some sort of negative stain (or even just a water rinse), there is often the annoying problem that the tips of the tweezers wick away all (or some) of the liquid. This means that inconsistent amounts of sample or stain are put onto grids (and that the amounts can effectively change over time as the wicking occurs). Such issues can impact the consistency of the staining, which is a real headache given how inconsistent negatives stains can be in the first place! Here are a couple of suggestions to prevent (or at least minimize) this problem:
Tricks for When Your Tweezers Eat Your Sample
Buy anti-capillary tweezers
Most EM supply companies sell anti-capillary tweezers that are specifically designed to handle this issue. Instead of the two tips forming very close parallel surfaces where liquids can wick between them by capillary action, the anti-capillary style of tweezers keeps the tips further apart and lessens the capillary action effect. Anti-capillary tweezers generally work quite well but do tend to be more expensive than regular tweezers. The biggest problem with anti-capillary tweezers is that if either of the tips get at all bent, their precise alignment can be so distorted that not only do they no longer function as anti-capillary tweezers, but they also won't even clamp a TEM grid securely. If you are gentle with your tweezers, this is not a problem (and the only thing to consider is the additional cost).
Treat the tips of your tweezers with something very hydrophobic
At the suggestion of Deb Kelley at the Virginia Tech Carilion Research Institute, several users of the Electron Microscopy Center (EMC) have recently begun using beeswax to prevent this problem. Beeswax is a chemically diverse mixture of fatty acid esters of long-chain (30+ carbon atoms) alcohols and other things like hydrocarbons, free acids, di- and triesters and their hydroxylated derivatives. This makes beeswax is a very hydrophobic natural product that can be used to coat the tweezer tips and that will repel any liquid that would normally be pulled between the tips by capillary action.
The key properties for this use of beeswax are that it is soft enough at room temperature to partially coat tweezer tips that are plunged into a block of it and that essentially none of its components are soluble in samples or stains (and so it does not interfere with the staining). Natural beeswax does not contain any of the small molecular weight dyes, stabilizers, etc. that are found in treated beeswax and that might transfer into the sample or the stains. Beeswax is sold commercially and small blocks are relatively inexpensive. One small block should essentially last forever.
The way to use the beeswax is simply to carefully plunge the tips of your tweezers into a block of it. The tips will eventually lose this hydrophobic coating and for consistency, this should probably be done immediately before using the tweezers. Coating can be repeated as often as seems necessary. If you want to test this approach, please contact David Morgan at email@example.com (who can supply you with a small amount of beeswax to try).
If you have other suggestions for dealing with this problem, please let the EMC staff know.