Detection of mercury in the 411-year-old beard hairs of the astronomer Tycho Brahe by elemental analysis in electron microscopy.

Hairs more than 400 years old of the famous astronomer Tycho Brahe were studied by electron microscopy to evaluate the hypothesis that Johannes Kepler murdered his teacher Brahe by mercury intoxication. The beard hairs showed a well-preserved ultrastructure with typical hair scales and melanosomes. The authors detected an accumulation of electron-dense granules of about 10 nm inside the outer hair scales, but not in the hair shaft and roots. At the places of these heavy-metal-containing granules they detected mercury besides other elements by energy dispersive X-ray analysis (EDX, Oxford, UK) in a field cathode scanning electron microscope (SEM, Gemini, Zeiss). The mercury-containing granules were found over the whole length of hairs, but only in the outer hair scales. Nevertheless, surface coatings of hairs were free of mercury. This distribution of mercury does not support the murder hypothesis, but could be related to precipitation of mercury dust from the air during long-term alchemistic activities.

Compositional contrast of uncoated fungal spores and stained section-face by low-loss backscattered electron imaging.

Comparative surface imaging was performed on uncoated fungal spores and stained section-face by field emission scanning electron microscopy with an in-column energy-selective backscattered electron detector. Epoxy resin thin sections (ca. 200 and 500 nm thick) of the osmicated and uranyl acetate/lead citrate-stained fungus were examined with the microscope. Topographical contrast was evident in secondary electron imaging by either a below-lens or an in-lens detector. Meanwhile, low-loss backscattered electron images showed mainly compositional contrast at low accelerating voltages (mostly below 1 kV). With attenuated topographical contrast, several different electron densities could be detected, exhibiting several levels of electron density even on a flat plane of spines. Minute differences in topography on epoxy resin sections as seen by secondary electron imaging represented the periphery of the fungal spores and hyphae. On the other hand, the compositional contrast could be retrieved from stained section-face in low-loss BSE imaging, revealing subcellular entities after contrast inversion. The resolution of low-loss BSE imaging was sufficient to resolve plasma membrane, and various types of vacuoles and vesicles. These results suggest that low-loss backscattered electron imaging could potentially provide compositional information to resolve surface chemical features of uncoated microbial cells and stained section-face with heterogeneous surface compositions.