Amino acid residues give away bloodstain's age
10 January 2012
Chemists in the US have developed a quick and simple way to find out how old bloodstains are using natural fluorescence measurements. Knowing when blood has been spilled can help forensic scientists pinpoint when a crime took place, but current techniques - such as optical measurements of haemoglobin degradation - can be unreliable.
Now, Mikhail Berezin and colleagues at Washington University in St Louis, US, have developed a technique that relies on the fluorescence lifetime of the tryptophan in blood proteins.
'We were studying fluorescence lifetimes of blood to try and diagnose diseases,' says Berezin. 'Then I was reading a paper about measuring the age of bloodstains and I thought we could try it with our technique.' He explains that there are many different fluorescent molecules in blood and their fluorescence lifetime - the average time the molecule remains in its excited state before decaying back to its ground state by emitting light - is strongly dependent on the environment they are in. As the environment changes and the proteins age, the fluorescence lifetime decreases.
Tryptophan residues in proteins found in blood could be used to date bloodstains at crime scenes
© Chem. Eur. J.
'First, we tried adding dyes [to blood samples] to probe the environment inside the albumin, but that didn't really work,' says Berezin. But then a new type of laser became available, with a wavelength of 295nm. 'It was specifically designed to excite tryptophan,' points out Berezin, and tryptophan's fluorescence is known to be very sensitive to its environment, 'so that's what we tried and it worked'.
'I think it's a great idea and may prove to be a valuable tool for crime scene investigators,' says Clifton Bishop from West Virginia University, US, who has studied blood aging by monitoring decay of RNA in blood samples. However, he raises concerns about the robustness of the technique. 'It worked well when the sample was deposited on a clean, sterile Petri dish,' he says. 'What happens with a sample on an organic surface, such as cloth, or in the presence of bacteria?'
Berezin agrees that it will take a lot more work to determine precisely how such external environmental factors influence the lifetime of the fluorescence signal and turn this into a reliable method to age bloodstains. One way to overcome some of the problems might be to combine readings from several different fluorescent molecules. If that can be done, the technique would have several advantages. It would be independent of concentration, he says, which means only a tiny sample of blood is needed, and the signal changes most in the first week of aging, which makes it complementary to optical methods, which tend to be better at distinguishing longer timescales.
Interesting? Spread the word using the 'tools' menu on the left.
K Guo, S Ahilefu and M Berezin, Chem. Eur. J., 2012, DOI: 10.1002/chem.201102935)
Also of interest
04 May 2010
Cheap paper test can reveal blood type in a matter of minutes
Forensic analyst Raychelle Burk explains that real-life forensic scientists have rather more paperwork on TV. Bea Perks is relieved to find they don't carry guns, either
Synthetic alternatives to donor blood have been stuck in development for decades. Nina Notman reports on recent promising progress
Comment on this story at the Chemistry World blog
Read other posts and join in the discussion
External links will open in a new browser window