SEM examination of human erythrocytes in uncoated bloodstains on stone: use of conventional as environmental-like SEM in a soft biological tissue (and hard inorganic material)

Summary

Although nowadays the so-called environmental scanning electron microscopes (ESEMs) allow the observation of the samples without metal or carbon coating, many conventional scanning electron microscopes (SEMs) are still in use. On the other hand, the presence of erythrocytes (red blood cells, RBCs) in a smear is considered a blood confirmation. Such a presence has been previously reported even in Lower Stone Age implements. In previous works, I have reported several studies dealing with cytomorphology of RBCs in bloodstains using scanning electron microscopy with standard specimen preparation procedures, i.e. via coating the samples before SEM analysis. In order to explore the potential of conventional SEM as environmental-like SEM in haemotaphonomical studies, two alkaline (limestone) and two acid (flint) rock fragments were smeared with human blood from a male and a female. The bloodstains obtained in this way were then air dried indoors and stored into a non-hermetic plastic box. Afterwards, the smears and their rock substrates were examined directly without coating, via secondary electrons, using a JEOL JSM-6400 scanning electron microscope. Satisfactory results reveal the capability of a conventional SEM to work in secondary-electron mode as an environmental-like SEM on these kinds of biological and inorganic materials, and probably in many other biological and non-biological samples.