Spectroscopic Analysis of Tryptophan as a Potential Optical Biomarker for Estimating the Time of Death

The estimation of the time of death represents a highly complex and challenging task within the field of forensic medicine and science. It is essential to approach this matter with the utmost respect for human rights while acknowledging the inherent limitations of the current methods, which require continuous refinement and expansion. Forensic science recognizes the necessity to improve existing techniques and develop new, more accurate, and non-invasive procedures, such as physicochemical approaches, to enhance the precision and reliability of time of death determinations. This article proposes a novel, non-invasive method for estimating the time of death using a spectroscopic analysis of tryptophan. The initial phase of the study concerns the presentation of the spectroscopic properties of tryptophan at varying pH levels, with consideration given to the pH fluctuations that occur during the decomposition of cadavers. The findings confirm the stability of the spectroscopic properties at different environmental pH levels. Subsequently, preliminary trials were conducted on 15 healthy human volunteers, which demonstrated that tryptophan concentrations in fingerprint samples were within the detection limits using molecular spectroscopy techniques. The final objective was to ascertain whether the composition of the substance present on the skin surface of a deceased individual up to 48 h postmortem is comparable to that of the sweat-fatty substance in living individuals. This was confirmed by the absorption and emission spectral profiles, which showed overlapping patterns with those obtained from living volunteers. The most significant outcome at this stage was the demonstration of a considerable increase in emission intensity in the spectra for samples obtained approximately 48 h after death in comparison to that obtained from a sample taken approximately 24 h after death. This indicates a rise in the concentration of tryptophan on the skin surface as the postmortem interval (PMI) increases, which could serve as a basis for developing a tool to estimate the time of death.