Abstract:
It is common to encounter biological stains from blood, semen, saliva or mixed body fluids in forensic casework. Although a deoxyribonucleic acid (DNA) profile can be obtained from each to assist with the identification of the donor, it is often important to know not only where the sample came from, but also from what body fluid or tissue source the sample originated. Messenger ribonucleic acid (mRNA) profiling has recently been introduced at ESR for the specific and sensitive identification of body fluids in forensic samples. mRNA was once thought to be unstable and to degrade rapidly. However, it has been shown that mRNA is sufficiently stable to be suitable for use in forensic science. The advantages of mRNA profiling include the potential for automation and increased specificity. Although mRNA has been implemented as part of casework analysis, it was suspected that the success of the technique may be affected by the collection methods used. In this project, aspects of the collection of forensic samples that may impact on successful mRNA profiling were investigated. Overall, results indicate that for the collection of body fluids from porous substrates the stain cut out method should be used. Stains collected with the stain cut out collection method generally resulted in the recovery of more DNA and an increased ability to assist with the identification of the body fluid in the stain using CellTyper mRNA profiling. However, the minitape collection method should be considered for use for stains collected from substrates such as wool, carpet and leather. Results from stains collected from non-porous substrates indicate that the minitape collection method obtains optimum results for DNA recovery and CellTyper mRNA profiling. However, results suggest that where a stain on painted timber is suspected of being either saliva or seminal fluid, it should be collected using the dry swab collection method.
