Dating of human blood by electron spin resonance spectroscopy

The estimation of the age of a blood stain using reflectance spectroscopy with a microspectrophotometer, spectral pre-processing and linear discriminant analysis

A novel method for the non-destructive age determination of a blood stain is described. It is based on the measurement of the visible reflectance spectrum of the haemoglobin component using a microspectrophotometer (MSP), spectral pre-processing and the application of supervised statistical classification techniques. The reflectance spectra of sample equine blood stains deposited on a glazed white tile were recorded between 1 and 37 days, using an MSP at wavelengths between 442 nm and 585 nm, under controlled conditions. The determination of age was based on the progressive change of the spectra with the aging of the blood stain. These spectra were pre-processed to reduce the effects of baseline variations and sample scattering. Two feature selection methods based on calculation of Fisher's weights and Fourier transform (FT) of spectra were used to create inputs into a statistical model based on linear discriminant analysis (LDA). This was used to predict the age of the blood stain and tested by using the leave-one-out cross validation method. When the same blood stain was used to create the training and test datasets an excellent correct classification rate (CCR) of 91.5% was obtained for 20 input frequencies, improving to 99.2% for 66 input frequencies. A more realistic scenario where separate blood stains were used for the training and test datasets led to poorer successful classification due to problems with the choice of substrate but nevertheless up to 19 days a CCR of 54.7% with an average error of 0.71 days was obtained.

EPR Study of Iron Ion Complexes in Human Blood

Electronic states of iron ion complexes in human blood from patients with melanoma have been investigated by electron paramagnetic resonance (EPR). The measurements were performed at liquid nitrogen temperature (77 K) on an X-band EPR spectrometer. Numerous types of iron paramagnetic centers have been identified. In several kinds of protein complexes exemplified by methemoglobin, transferrin or ferritin, various forms of trivalent iron have been found. Three groups of patients with typical EPR spectra have been individualized. These groups differed in types and concentration of paramagnetic centers in peripheral blood. A good correlation has been found between the EPR results, the total iron ion complexes concentration and transferrin saturation.

Multivariate analysis for estimating the age of a bloodstain

Our objective is to provide crime laboratories with a technique for estimating the age of a bloodstain. Toward that goal, we have used multiplexed, real-time RT-PCR (or qPCR) to determine the relative stability of different-sized segments of the same RNA species as well as differences in stability between two different RNAs' change over time in bloodstains. Our results indicate that a multivariate analysis of the changing ratio of the different RNA segments can be used to differentiate between samples of different ages in the defined population. Bloodstains from 29 of 30 donors could be partitioned into different ages using this technique. Although further improvements will be required before this approach can be implemented in crime laboratories, the multivariate analysis holds promise of providing a reliable approach for temporally linking a bloodstain to the commission of a crime or excluding a bloodstain as being irrelevant to the case in question.

Estimation of the age of human bloodstains by electron paramagnetic resonance spectroscopy: long-term controlled experiment on the effects of environmental factors

In this study, we examined the efficacy and limitations of electron paramagnetic resonance (EPR) for estimating the age of human bloodstains. At 77K, human bloodstains give four striking EPR signals in the g=6.2 (g6), 4.3 (g4), 2.27 (H) and 2.005 (R) regions due to ferric high-spin, ferric non-heme, ferric low-spin and free radical species, respectively. We found that plotting double logarithms of the EPR intensity ratio of H/g4 versus days past bleeding gave a linear correlation up to 432 days with an error range within 25% of the actual number of days under controlled conditions. However, environmental factors such as differences of absorbent, light exposure and fluctuations of storage temperature affected the changes of these EPR-active compounds, which result in misestimation of the time since bleeding occurred. Therefore, one should take such factors into account in estimating the period since bleeding by this method.