Abstract
The ability to determine the time since deposition of a bloodstain found at a crime scene could prove invaluable to law enforcement investigators, defining the time frame in which the individual depositing the evidence was present. Although various methods of accomplishing this have been proposed, none has gained widespread use due to poor time resolution and weak age correlation. We have developed a method for the estimation of the time since deposition (TSD) of dried bloodstains using UV-VIS spectrophotometric analysis of hemoglobin (Hb) that is based upon its characteristic oxidation chemistry. A detailed study of the Hb Soret band (λmax = 412 nm) in aged bloodstains revealed a blue shift (shift to shorter wavelength) as the age of the stain increases. The extent of this shift permits, for the first time, a distinction to be made between bloodstains that were deposited minutes, hours, days and weeks prior to recovery and analysis. The extent of the blue shift was found to be a function of ambient relative humidity and temperature. The method is extremely sensitive, requiring as little as a 1 µl dried bloodstain for analysis. We demonstrate that it might be possible to perform TSD measurements at the crime scene using a portable low-sample-volume spectrophotometer.
Highlights
Current forensic biochemistry analytical technologies permit a significant amount of individual-specific genetic information to be obtained from a biological stain found at a crime scene [1]
The spectral parameters that appeared to show some degree of age related changes included: 1) changes in the maximum absorbance of the Soret band (DAbsSoret); 2) changes in the wavelength of the lmax for the Soret band (DlmaxSoret); 3) changes in the relative absorbance of the b band at 541 nm, compared to the lmin at 560 nm (DAbsb(541–560)); 4) changes in the relative absorbance of the a band at 576 nm, compared to the lmin at 560 nm (DAbs a(576–560)); 5) the ratio of absorbance changes of the a and b bands (DAbs b(541–560)/ DAbsa(576–560)) (Fig. 1)
Our preliminary studies indicated that neither changes to the absorption values of the a576 and b541 bands nor the Soret band provided a sufficiently high correlation with age to be a useful time since deposition (TSD) diagnostic
Summary
Current forensic biochemistry analytical technologies permit a significant amount of individual-specific genetic information to be obtained from a biological stain found at a crime scene [1]. Many criminal investigations do not include eyewitnesses or bodies for time of commission determinations forensic evidence found at crime scenes is often in the form of dried biological stains or tissues. Many of the methods developed to estimate an approximate age of a bloodstain have focused on deteriorative changes to the visible spectrum of hemoglobin (Hb) over time [17,18,19,21,22,23,24]. One such method used the a-chain to heme ratio determined by HPLC [19]. The previous studies did not consider in detail the effect of important potential variables such as ambient temperature and humidity on TSD estimates
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