In a nutshell, the process consists of placing a drop of specimen on a previously primed support film, removing the excess solution, and immediately immerse the grid with the specimen in liquified ethane. The ultimate goal is to produce a film of vitrified water which is thin enough to allow the passage of electrons, carrying information about the structure of the molecules embedded in the layer of water.

Of course, this is much easier said than done. To allow the passage of electrons to create an image, the layer of water has to be as thin as possible, with a maximum thickness of about 1um. For films this thin, evaporation is an extremely fast and catastrophic process, therefore the relative humidity has to be controlled well. Also, evaporation of water has the undesirable effect of increasing the salt concentration on the sample, which can interfere with the imaging, or in the worst of cases, destroy it altogether.

Liquified ethane is used to vitrify water, since the low heat capacity of liquid nitrogen makes it a poor cryogen, as it has a rather low heat capacity. In order to produce vitrified water, the sample has to be frozen in a microsecond scale, which also implies that only very thin specimens can be prepared successfully.

At the NYSBC we have two plungers. One is a home made apparatus, in which everything is done manually, while the other is a new Gatan CP3 system. Both of them are at the service of our users, and the staff can answer any questions about them.

Vitrobox	Gatan CP3