Forensic application of fluorescence spectroscopy: An efficient technique to predict the presence of human saliva

Abstract

In this study, we aim to use the fluorescence spectroscopic data as a preliminary forensic evidence for the detection of saliva stains from the surface of drinking glass, to see the potential of utilizing a comparatively simple method to trace the presence of saliva from inanimate objects such as cigars, papers, cloths and envelopes. Since dried stains of saliva are invisible to human eyes, detection of saliva from such sources is a challenge in forensic analysis. The fluorescence emission spectra of dried saliva samples collected from drinking glass were compared to that of undiluted liquid saliva of the same volunteers. The deposition of saliva was predicted based on the emission spectra of the enzyme amylase around 350 nm, which is present in high concentrations in saliva. The dried saliva stains and undiluted liquid saliva showed an emission peak at 350 ± 5 nm and 345 ± 5 nm, respectively. The fluorescence emission spectra obtained from the dried saliva samples confirmed well to those of undiluted liquid saliva and amylase.The fluorescence intensity and area underneath the fluorescence peak of undiluted liquid saliva as well as dried saliva were also studied. The study concludes that by correlating fluorescence emission peak, fluorescence intensity and area under the curve, saliva can be detected from dried stains. The potential of fluorescence spectroscopy is also emphasised to detect the presence of saliva from inanimate objects like that of drinking glass, by identifying the emission peak of amylase, one of the prominent saliva components. Thus by using this simple technique, the best possible samples for a detailed DNA analysis may be screened and selected, which could significantly contribute to forensic identification.