Easy preservation protocol for SEM-EDX analysis of skin specimens in forensic context

Abstract

Summary The use of scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) is routinely used by scientific police and increasingly described on biological samples in forensic context. However, the pre-analytical conditions of such analyses are not standardised in forensic context and each operator designs its own protocol depending on his practice. Using SEM-EDS on unprepared samples can be destructive but above all encounters technical problems. In the judiciary system, using non-destructive techniques (or less destructive as possible) is attractive to allow reiterate analyses or complementary techniques. So, in this study we try to design a SEM-EDX pre-analytical protocol for hydrated biological samples considering forensic requirement. We tested a protocol with five fragments of the legs of pigs on which a sharp wound was produced. Samples were fixed in 4% formalin for 7 days then dehydrated with absolute ethanol over 48 hours. Samples were dried in ambient air for 24 hours and analysed with SEM-EDS. Anatomo-pathologic examination was performed afterward. Samples were then stored again for 7 days with the same protocol before being examined again. Particle detection was possible without any technical problems on each analysis. This protocol allows reiterated SEM-EDS analyses and anatomo-pathologic examination afterward. This technique is easy to enforce and cheap, and no adaptation of forensic practice is required. Such a protocol is a prerequisite to the spread of EDS analysis use in French forensic practice.