Rapid Stain Biomarker : A Novel Tool for the Forensic Detection of Saliva (Effect of Time and Surface on its Reliability )

Abstract

Saliva is one of the vital fluids secreted by the human body; it can be deposited on the human skin or other materials through biting, sucking, licking and kissing. Saliva stains encountered in forensic casework is an important source of DNA; so, it is considered an important evidence for personnel identification. The rapid Stain Identification of Human Saliva (RSIDTM-Saliva) bioassay is designed to detect specifically the presence of human salivary µ-amylase enzyme. Test development is completed within 10 minutes and can detect as little as 1ml of human saliva. The detection protocol can be completely integrated into the procedures for DNA extraction and analysis. Aim: Assess the efficacy of RSIDTM-Saliva strip test for the detection of human saliva under some different variables (different surfaces & different time intervals).Evaluate the quality of DNA extracted from unpreserved saliva and the possibility of its usage as evidence in forensics. Methodology:Fifty two saliva samples were collected from four volunteers. Forty eight of them were deposited over surfaces of different nature (plastic bottles, glass cup and cigarette butts) at the same time. Four saliva samples were collected directly from the floor of the mouth of each participant by a cotton swab (positive control group). All samples were left to dry for 10 min at room temperature then extracted and analyzed according to the protocol designed for (RSIDTM-Saliva). Collected samples were studied as three tested groups and as control groups. Saliva samples collected from each participant were categorized into four subgroups according to the time interval of saliva extraction [zero (on the spot), 10, 20, and 30 days].Positive samples for saliva identification were subjected to DNA extraction and typing; as three autosomal primers short tandem repeats (STRs) specific to human genomic DNA (D21S11, D18S51 and CSF1PO) were amplified by polymerase chain reaction (PCR); then subjected to separation and analysis of fragments size by agarose gel electrophoresis to determine their allelic size through comparison to the standard allelic 100 bp ladder. Results: Saliva could be identified in 100% of tested samples as well as for the positive control samples, which were subjected to successful DNA extraction followed by PCR amplification of the chosen three STRs. Results of agarose gel revealed that the sizes of these PCR products were in accordance with the 100 bp DNA ladder; validating the good quality and quantity of the extracted DNA Conclusion: the current study demonstrated that non-stored saliva deposited over different surfaces for up to 30 days presents an ideal source for DNA which may be used for forensic identification. The study also evidenced that the new RSID-saliva strip test is a fast, easy, sensitive and reliable method for saliva identification over different surfaces.