Dark-field electron microscopy of unstained biological materials embedded in Nanoplast

Extremely thin sections of unstained materials (beef liver catalase, double-stranded calf thymus DNA, horse spleen ferritin and mammalian skeletal muscle), embedded in the water-soluble melamine resin Nanoplast FB101, were studied by dark-field electron microscopy and electron spectroscopic imaging. While ferritin molecules so recorded show 0.4 and 0.9 nm lattice fringes within the crystalline iron core, double-stranded DNA shows a helical repeat with a spacing of 3.4 nm. The gain in resolution of structural detail reported here is probably due mainly to the reduced section thickness as compared to traditional thin-sectioning techniques. As we reported earlier (Frösch & Westphal, 1984), melamine resins can be sectioned extremely thinly (less than 10 nm) and observed without a supporting film, making them especially suitable for dark-field electron microscopy.