Abstract:
The confirmed identification of suspected body fluids can be very informative in a criminal investigation. Body fluids can indicate what crimes took place, and can corroborate an alleged suspect’s or witness’ description of events. Currently, the Institute of Environmental Science and Research Ltd. (ESR Ltd.) uses CellTyper messenger ribonucleic acid (mRNA) analysis to identify body fluids. Messenger RNA is an intermediary molecule, bridging the gap between deoxyribonucleic acid (DNA) and protein formation in body cells. Some mRNAs are body-‐fluid specific, and analysing the presence or absence of these mRNAs can identify a substance as a particular body fluid. There are a small number of difficulties with the mRNA system: RNA is relatively unstable, and thus is vulnerable to degradation by the methods used to transfer the potential body fluid stain from the substrate for analysis. Similarly DNA removal methods may be destructive to RNA; however all genomic DNA needs to be removed from the sample to avoid false positives; the sensitivity of the multiplex of body fluid primers may not be optimum. This work attempted to enhance the CellTyper system by managing these difficulties. Currently, body fluid stains are swabbed with sterile water, which leads to degradation of RNA and subsequently inaccurate results. Sterile water, a 70% ethanol solution and a commercially available swabbing solution were compared, and it was discovered that a solution of 70% ethanol and 30% sterile water was the most effective for swabbing body fluid stains for mRNA analysis. It was found that genomic DNA removal can be enhanced by the addition of a second application of resin containing paramagnetic beads, as part of the DNA IQ™ system, and by incubating the sample with DNAse treatment at 37°C as part of ReliaPrep™ RNA purification. For individual body fluids, the multiplex system appears to be sensitive enough for use in body fluid identification. In body fluid mixtures where a major body fluid is present, it is difficult to amplify body fluids without over-‐amplifying the major component using the multiplex system. The multiplex may be used as a screening tool, then body fluid-‐specific duplexes may be used for confirmation.