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Laser Microdissection as a Technique to Resolve Mixtures and Improve the Analysis of Difficult Evidence Samples

NCJ Number
Date Published
October 2008
95 pages
The research reported here focused on the further investigation of the various aspects and benefits of laser microdissection (LM), which has proven to be an effective method for cell mixture separations in the forensic laboratory while improving the collection and DNA analysis associated with low copy number (LCN) samples.
This work found that the swabbing of substrates followed by a cellulose-aided elution increased the number of cells recovered for LM slide preparation. The QIAamp Micro Extraction kit was found to be efficient and reliable for extracting low-level samples collected by LM. Amplification results indicate that the Applied Biosystems AmpFlSTR MiniFiler kit is the optimal choice for amplifying LCN samples collected with LM instruments. Additional research was also completed on the cellular separation of problematic sample mixtures. Although sperm and epithelial cell sexual-assault mixtures can easily be separated based upon morphological differences, combinations of the same cell type are more difficult to separate. For such problematic samples, a protocol was developed that is capable of successfully separating male/female cellular mixtures of similar morphology by using chromosome X/Y FISH (fluorescent in situ hybridization) probing. In the course of performing these LM evaluations, the Pix Cell and Zeiss PALM Microbeam instruments were assessed in order to determine optimal processing protocols. They proved to be suitable for LCN and mixture evidence processing. By applying the findings of this research, forensic labs can now successfully and efficiently resolve various LCN sample mixtures by incorporating FISH, LM, and optimized elution/extraction/amplification methods into their standard operating protocols. 26 figures, 13 tables, 25 references, and a listing of 6 publications that disseminate research findings

Date Published: October 1, 2008