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Adhesion of particulate specimens to support films for electron microscopy: a model system for assessing the surface properties of support films, and its application to chromatin particles
Author(s) -
Woodcock C. L. F.,
Frado LL. Y.,
Green G. R.,
Einck L.
Publication year - 1981
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1981.tb01214.x
Subject(s) - adhesion , surface charge , materials science , ionic bonding , ionic strength , scanning electron microscope , adhesive , chemical engineering , electron microscope , particle (ecology) , nanotechnology , composite material , chemistry , ion , aqueous solution , organic chemistry , optics , physics , oceanography , layer (electronics) , geology , engineering
SUMMARY Silica microspheres bearing a known surface charge were used to test the adhesive properties of support films and support film treatments commonly used in the electron microscopy of particulate specimens. Adhesion was strongly correlated with surface charge, negatively charged microspheres binding well only to positively charged support films and vice versa in solutions of low ionic strength. This charge dependency could be overcome by increasing the ionic strength to about 100 mmol with monovalent cations; under these conditions, it was not necessary to provide an oppositely charged film surface to obtain adhesion. Chromatin particles (nucleosomes) which have a net negative charge, behaved very much like the negatively charged silica with respect to adhesion, confirming that the microspheres provided an accurate indication of support film surface properties. The chromatin particles showed dramatic structural changes under conditions when adhesion was either poor, or very strong, indicating the need for careful selection of binding conditions for delicate biological specimens. A new and simple method for pretreating carbon films to improve adhesion was developed, and a preliminary account of this technique is presented.