A rapid and noninvasive method to detect dried saliva stains from human skin using fluorescent spectroscopy

Abstract

Objective:Saliva is one of the vital fluids secreted in human beings. Significant amount of saliva is deposited on the skin during biting, sucking or licking, and can act as an important source in forensic evidence. An enzyme, α amylase, gives a characteristic emission spectrum at 345–355 nm when excited at 282 nm and this can be identified by using fluorescent spectroscopy and can help in forensic identification. This study describes a rapid method to detect dried saliva on the human skin by fluorescent spectroscopy.Materials and Methods:This study included 10 volunteers, who deposited their own saliva on skin of their ventral forearm by licking and water on the contralateral arm as control. This study was carried out at Central Leather Research Institute, Chennai.Study design:Ten volunteers deposited their own saliva on skin of their ventral forearm by licking. A control sample of water was deposited at the contralateral arm. Each sample was excited at 282 nm and emission spectrum was recorded.Results:The emission spectra of 10 swab samples taken from dried saliva were characterized at the primary peak of 345 to 355 nm whereas the emission spectrum of water as a control was recorded at 362 nm.Conclusion:The presence of emission spectrum at 345–355 nm with excitation at 282 nm proves to be a strong indicator of saliva deposited on human skin.

Simultaneous detection and image capture of biological evidence using a combined 360° camera system with single wavelength laser illumination

“…This investigation focused on saliva which had been donated by one participant and further work would seek to utilise more donors as it is known that saliva fluorescence can vary between different donors, as well as within the same individuals, depending on the time of day. This fluctuation is thought to be attributed to different protein contents within the saliva sample [23,24].…”

Saliva in forensic odontology: A comprehensive update

“…Salts like nitrate and thiocyanate have also been used for the detection. [ 4 ] All these methods have limitations and variable sensitivity depending upon the age of the saliva stain and quantity of deposit Lasers and ultraviolet light, quartz arch tube and argon ion laser[ 5 6 ] Fluorescent spectroscopy:- the aromatic amino acid, tryptophan, in α-salivary amylase gives a characteristic emission spectrum on fluorescent spectroscopy, thus possessing a good sensitivity in detecting dried saliva stains on the skin. [ 4 ] …”

“…Salts like nitrate and thiocyanate have also been used for the detection. [ 4 ] All these methods have limitations and variable sensitivity depending upon the age of the saliva stain and quantity of deposit…”

The effect of mark enhancement techniques on the subsequent detection of saliva

“…Furthermore, long exposure times to such fluorescence may be detrimental to subsequent DNA analysis. In addition to colour tests for the detection of saliva, recent advances using analytical techniques such as Raman spectroscopy [2,[13][14][15], fluorescent spectroscopy [16] and in situ analysis with specific antibody-nanoparticle conjugates have been discussed [17].…”