Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
Natural Sciences in General
Single molecule resolution in beam-sensitive, uncoated, noncrystalline materials has heretofore not been possible except in thin (≤150 Å) platinum-carbon (Pt-C) replicas, which are resistant to electron beam destruction. Previously, the granularity of metal film replicas limited their resolution to ≥20 Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low-angle 20° rotary, 45° unidirectional, and vertical 9.7 ± 1 Å Pt-C films deposited on mica under the same conditions were compared. Vertical replication had a 5 Å granularity, the highest resolution, and evenly coated the whole surface. A 45° replication had a 9.5 Å granularity, a slightly poorer resolution, and a discontinuous surface coating. The use of 20° rotary replication proved to be unsuitable for high-resolution imaging, with 20-25 Å granularity and resolution two to three times poorer. Vertical and 45° Pt-C replicas can visualize the deep-etched DNA helix and the 13.3 Å 32 helix of pectin in a gel. The DNA double helix, the complex structures of sol-gel glasses, Immobilon filters (polyvinylidene fluoride), a polymethacrylate plastic, the metal oxide surfaces of 440c stainless steel, and aluminum are illustrated. This high-resolution vertical Pt-C replica technique can image in the context of solutions, gels, or solids, single molecular chains 3-7 Å wide, their associations, and their conformation. Included in the present article are first time descriptions for removing replicas from metals and plastics and for making high-magnification photographic prints of normal contrast using a reversal rephotographic process.
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