A comparison of mass measurements with the stem using the wet-film technique with and without polylysine treatment

Abstract

The wet film technique of injection of a specimen into a drop on a thin carbon film (for eventual freeze-drying and mass analysis in the STEM) has been described and shown to give a uniform background and, in general, good biological preservation of specimens. However, an occasional specimen either does not absorb well or is of necessity very dilute. Many specimens absorb to polylysine-treated grids nearly 10-fold better than to thin C alone. We describe here our adaptation of the polylysine treatment originally described by Williams, and our finding that polylysine-treated thin C does not give significantly worse errors in mass measurements than thin C alone.To prepare a specimen, thin C is floated off cleaved NaCl onto a dish of water. Grids covered with holey film are dropped onto the thin C. A grid is picked up, inverted and washed with water, buffer, specimen, buffer. For poly lysine grids, after washing with water, 5 μl of 10 μg/ml poly lysine is injected for 1 minute.