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Using the NYSBC
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NMR Facility
X-Ray Facility
Protein Production Facility
Electron Crystallography Center
Plasma Cleaning (aka glow discharging)
| Plasma cleaning is a crucial -albeit largely dismissed as irrelevant- step in sample preparation of protein samples for electron microscopy. It consists of a rarified gas which is ionized by a high voltage source, which imparts them of energy, and as the ions collide, more of them are ionized, causing a cascade that is successfully used either to produce light (flurescent lights), or making some of them crash against a surface to be cleaned, etching thus the hydrocarbon impurities accumulated at the surface to be cleaned. Sustaining a plasma is difficult to do with a constant voltage, and therefore in almost all applications, an oscillating field such as one from a Tesla coil is used. There are some sophisticated plasma cleaners, which has very precise gas pressure controls, allowing a better control of the conditions used to clean the surfaces. In practice, what one sees is that as carbon film ages, it has the tendency to become more hydrophobic, probably due to the accumulation of hydrocarbons at the surface. Plasma cleaning removes the top level of carbon atoms from the surface, including the hydrocarbon contamination, leaving behind a fresh surface that tends to be quite hydrophilic and suitable for most applications involving frozen hydrated samples. The Gatan Solarus is a very easy model to use. It comes with a series of recipes for cleaning grids, holders, etc., and has inlets to use hydrogen, oxygen and argon. At the NYSBCÂ we have all of them, and the plasma cleaner produces suitably hydrophilic grids. For plasma cleaning in the presence of pentylamine, we have also a home made device that can be used. The Edwards evaporator can also be used for plasma cleaning by those users who wish to do so.
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