The use of charged polymers for supporting films for the electron microscopy of macromolecules
The use of charged polymers for making substrate films was originally described (Birbeck and Stacey, 1958) for the examination of deoxyribosenucleic acid (DNA) molecules. It was found that when DNA was dried down on to conventional substrate films (formvar or collodion) the molecules would not adhere to the film but instead were deposited in a large mass at the centre of the drying drops. By using films made of a co-polymer of styrene and vinyl pyridine, it was found that the molecules could be made to adhere to the film and remain separated from each other. The particular co-polymer chosen was one which possesses positive charges on the pyridine groups to attract the negatively charged DNA molecules Films of these co-polymers may be made by stripping from a glass slide in a manner similar to that used for formvar, and the films are mechanically strong and stable in the microscope.
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