2008 appeared to be the year for spectroscopists attempting to assist our colleagues in forensic biology. Two papers caught our eye, both published in Forensic Science International.
"In search of blood - Detection of minute particles using spectroscopic methods" described in detail the different morphological appearances of blood particles on tapings. This hadn't been done before and was very interesting. The authors proceeded to show how particles of blood can be identified using a combination of MSP and raman spectroscopies, the advantage being that the analysis is performed in-situ and non-destructively. One question that does arise is whether or not the analysis would have had a detrimental effect on DNA recovery later - which was not explored in this study. Our own experience with raman technologies would suggest that it is unlikely to have any detrimental effect.
The current method for identification of blood in tapings appears to be to use the same presumptive test as is used for the identification of blood on clothing etc. Expose the surface of the blood fragment, rub a piece of pointed filter paper on the surface, apply your chemical treatment to the paper and observer the colour change. It is a very sensitive test, and my colleagues in forensic biology are confident that it would detect very small fragments and it has been used successfully in the past.
On the other hand the chemical test relies on a physical interaction between the blood and the paper so that sufficient material is transferred to the filter paper. The presence of the glue matrix could interfere with this process, although perhaps not for bigger particles where sufficient contact could be made.
"In search of blood - Detection of minute particles using spectroscopic methods" described in detail the different morphological appearances of blood particles on tapings. This hadn't been done before and was very interesting. The authors proceeded to show how particles of blood can be identified using a combination of MSP and raman spectroscopies, the advantage being that the analysis is performed in-situ and non-destructively. One question that does arise is whether or not the analysis would have had a detrimental effect on DNA recovery later - which was not explored in this study. Our own experience with raman technologies would suggest that it is unlikely to have any detrimental effect.
The current method for identification of blood in tapings appears to be to use the same presumptive test as is used for the identification of blood on clothing etc. Expose the surface of the blood fragment, rub a piece of pointed filter paper on the surface, apply your chemical treatment to the paper and observer the colour change. It is a very sensitive test, and my colleagues in forensic biology are confident that it would detect very small fragments and it has been used successfully in the past.
On the other hand the chemical test relies on a physical interaction between the blood and the paper so that sufficient material is transferred to the filter paper. The presence of the glue matrix could interfere with this process, although perhaps not for bigger particles where sufficient contact could be made.
So when would you consider tapings as a source of tiny blood fragments? Perhaps in these situations, where:
- the surface of the item is particularly smooth and the standard blood search is negative
- the item of clothing itself is no longer available but tapings taken from the item are present - such as cold cases
The authors specifically mention cases where items have been washed but where minute particles in low numbers may remain undetected by the standard protocols. This may seem to be unlikely, but studies on sperm have shown that sperm can be transferred from one item of clothing to others whilst being washed in a machine. Enzymatic activity of the particles, on which the presumptive tests would rely, could have been destroyed, leaving particles of blood undetectable by the presumptive tests on the clothing.
The best thing about this study is that it provides forensic scientists with more options when considering complex questions - such as is there blood on this item? After all, if the Damilola Taylor case has taught us anything, it is that we can't take a negative blood screen for granted.
The second paper "Raman Spectroscopy offers great potential for the nondestructive confirmatory identification of body fluids" described the analysis of body fluids to ascertain whether or no they could be uniquely identified. Semen, Vaginal fluid, saliva, sweat and blood were all analysed. This preliminary study shows that each type of body fluid bears its own raman signature, however as the study used only single samples of each body fluid for analysis, the results should be treated with some caution. One very interesting result was the presence of thiocyanate in saliva which did not appear in any other body fluid.
