Electron Beam-Based Methods for Bioforensic Investigations

Forensic investigations of biological attacks or incidents use physical evidence as well as genomics-based evidence to establish the places involved and the processes used to develop and to disperse a biological attack agent. The electron beam analysis techniques of SEM and (S)TEM have been invaluable tools that can be applied to the analysis of bioforensic samples. These tools provide both morphological and elemental information with high resolution and high elemental sensitivity to elucidate important signatures for forensic attribution from biological and chemical agents. The SEM is an important tool as samples do not require extensive preparation and thus much information about the morphology and the chemistry of the sample can be learned quickly. The SEM is capable of very high-resolution imaging (subnanometer has been demonstrated in some cases) and can provide elemental analysis of regions as small as fractions of a micrometer. These capabilities make the SEM the logical first choice for analysis of unknown solid biological or chemical materials. The (S)TEM is used when more detailed morphological or elemental information is needed, particularly at smaller length scales. Although typical samples for (S)TEM must be electron transparent or about 100 nm thick or less, some fine powders may be imaged directly. Preparation of thin samples for (S)TEM can be somewhat time-consuming, and the potential for contamination with fixatives and contrast stains must be constantly kept in mind. Use of thin samples in the (S)TEM allows extremely high-resolution imaging and microanalysis to be performed and important details of the sample to be revealed. © 2011 Elsevier Inc. All rights reserved.