Signature Peptide Identification for Body Fluids in Sexual Assault Cases by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Body fluids contain proteins that perform functions specific to different types of body fluids. Therefore, the detection of signature peptides for these proteins can potentially identify a body fluid in a forensic investigation. This project aimed to validate a method to detect signature peptides in body fluids commonly found in sexual assault cases by LC-MS/MS. Signature peptides for semen and saliva fluids were combined with two signature peptides for vaginal fluids. Samples created using two donors each for saliva, semen, and vaginal fluids were extracted using a trypsin digest, with separation of the protein and DNA fractions. The LC-MS/MS was utilized in MRM mode to analyze the protein fractions and DNA fractions were quantified. In a sensitivity study, a minimum volume of 0.005 of semen and 0.01 vaginal fluid could still be detected. A study of stains on different substrates showed variability between protein and DNA recovery. Two and three-component mixtures were created to analyze the interferences between the body fluids. The semen peptides were detected in all but one mixture while saliva peptides were detected as only a major component in a mixture. The DNA fractions for semen stains or swabs contained sufficient male DNA for further analysis. One of the vaginal peptides was detected in all vaginal samples with good sensitivity, but the second vaginal peptide was not detected. This assay needs to be optimized further