Infrared Spectroscopy

Discovering Donor Characteristics from Bloodstains with Infrared Spectroscopy
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Discovering Donor Characteristics from Bloodstains with Infrared Spectroscopy

From interpreting the incident to pinpointing the perpetrator, the presence of blood at a crime scene can provide clues vital to solving a crime.  Since the advent of DNA profiling in the 1980s, police have been able to use DNA to link suspects to crime scenes, making the detection and collection of biological evidence more important than ever before. However successful DNA profiling relies on a positive match with either a DNA profile from a suspect or one stored in a database. With nothing to compare a profile to, the DNA is of limited use and the trail may quickly run cold.

But what if investigators could gain even more information from a bloodstain at a crime scene? What if it were possible to rapidly figure out whether the donor was male or female, or establish their race? And all of this without shipping samples back to the lab.

New research conducted at the University at Albany in New York has demonstrated that it may be possible to establish some individual donor characteristics in a matter of minutes.

Past research has already demonstrated that the biochemical composition of blood differs between males and females and individuals of different races. But the ability to obtain this information on-site at the crime scene in a matter of minutes could change the way body fluids are processed. In a recent study, Prof. Igor Lednev and his team applied a technique known as attenuated total reflection Fourier transform-infrared (ATR FTIR) spectroscopy to blood analysis, with the aim of establishing whether characteristics such as sex and race can be determined from bloodstains.

FTIR is an analytical technique capable of providing information about a material’s chemical information. In brief, the device directs infrared radiation towards the sample. Some of this radiation is absorbed by the material, and some passes through. The sample’s absorbance of this light at different wavelengths is measured and used to determine the material’s chemical information. After analysis a spectrum is produced, which acts as a kind of molecular ‘fingerprint’ of the sample. The different features in the spectrum relate to the different chemical components in the sample.

Infrared spectra were produced by analysing the blood of 30 donors (a mixture of male and females of Caucasian, African American and Hispanic racial origin). From this, researchers could observe any differences occurring between blood from male and females, and blood from members of different races. Using this data, the researchers built a model capable of classifying samples based on their chemical profile. By taking the chemical profile of an unknown bloodstain and comparing it with a model containing bloodstains from numerous different groups, the model can predict the likely classification (i.e. whether the donor was male or female and which racial group they belong to). In this study, it correctly classified bloodstains around 90% of the time.

Using infrared-based techniques has a number of advantages over other methods of analysis. As the technique simply necessitates the direction of light towards the bloodstain, the technique is non-destructive. Inevitably this is perfect for criminal investigations – destroying the evidence is never ideal. IR spectroscopy is also amenable to portability, lending itself well to on-the-go analysis at crime scenes and so potentially saving a lot of time by avoiding sending unnecessary samples back to the lab for analysis.

Although only a pilot study, this research has demonstrated the possibility of establishing donor characteristics through the rapid and non-destructive analysis of bloodstains. The ability to determine features such as sex and race would enable police to significantly narrow down the search for suspects or victims, ultimately preserving valuable time and money. Furthermore, the ability of FTIR to non-destructively analyse evidence on-site renders it an ideal tool for forensic analysis. Inevitably a great deal more research will be necessary, and if the technique ever becomes operational, it would be years before such technology and methods were suitable for deployment to crime scenes and use as evidence in criminal trials.

 

Mistek et al. Phenotype profiling for forensic purposes: nondestructive potentially on scene attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy of bloodstains. Forensic Chemistry. 2019, In Press.

 

Identifying Insects with Spectroscopy
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Identifying Insects with Spectroscopy

Entomology, that is the study of insects, can provide vital information during a forensic investigation. After an individual dies their body begins to undergo a complex decomposition process almost immediately, attracting a variety of insects along the way who wish to colonise, feed on the temptingly putrefying remains and reproduce.

Specialists have been taking advantage of this fact for hundreds of years, allowing us to discover that the types of insects present on a cadaver and the age of these insects can prove invaluable in estimating how much time has passed since the victim died (known as the post-mortem interval). Simply put, certain species prefer the decomposing corpse at different stages in the decay process, and with the right information, investigators can study the insects and their ages and begin to develop a kind of timeline.

Currently, accurately identifying species and establishing the development stage of an insect can be time-consuming and requires the expertise of an entomologist and potentially DNA analysis. This is obviously not ideal – your average police force does not have an entomologist on hand, nor do they have oodles of times to dedicate to insect identification. Even with the assistance of an entomologist, accurately determining the age of maggots can be problematic. Although larvae may be of a certain age, their length and weight can be affected by a variety of factors that may not be accounted for, such as starvation (Singh and Bala, 2009).

As you might expect, researchers are searching for ways to resolve this issue, and analytical chemistry might just be the answer.

As analytical chemistry progresses and increasingly advanced analytical techniques are developed, we are seeing more and more fascinating applications of these instruments to established areas of study. In a recent study published in Forensic Science International, researchers took a well-established technique and applied it to forensic entomology. In this case, they used a form of infrared spectroscopy.

Infrared spectroscopy is an analytical technique which determines the amount of radiation absorbed by a molecule. Infrared light is directed towards to sample and, depending on the molecule, a certain amount of radiation will pass through the sample and some will be absorbed.  When a molecule absorbs radiation, the bonds within it begin to vibrate. Different bonds will vibrate and be influenced by surrounding atoms to a different extent, thus allowing for a unique ‘spectrum’ to be produced. This spectrum is essentially a graph displaying how much radiation was absorbed by the sample at what wavelength. Scrutinising this spectrum can allow the analyst to determine what kind of molecules are present. Although this is not sufficient to specifically identify compounds, the spectrum produced can at least be used to distinguish between different samples, which will produce different spectra. The spectra essentially act as ‘fingerprints’ for different substances.

FTIRSpectrum

Typical IR spectroscopy spectra.

If you want to know a bit more about this technique, Compound Chemistry has a great little page on IR spectroscopy.

So back to how this analytical technique can be useful in forensic entomology. The proof of principle study to which I’m specifically referring aimed to both identify the species of larvae and the life cycle stage using vibrational spectroscopy, in this case Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy. A slightly long-winded name, but in short this is simply a form of IR spectroscopy that allows in situ analysis of solid or liquid samples without the need for sample preparation. Anyone who has spent many painful hours preparing samples for analysis will appreciate the benefit of this.

Three species commonly encountered at incident scenes were used in the study; C. vomitoria, L. sericata, and M. domestica (that is the bluebottle fly, the green bottle fly and the common housefly respectively). One of these species (the C. vomitoria) was also selected for a study focussing on the life cycle, in which spectra were collected for each time point in the insect’s life cycle. Scans were based on a crushed mixture of epidermis and internal matter (not possible for a ‘no maggots were harmed during the making of’ notice then). The results were promising, indicating FTIR spectroscopy could be a great tool in forensic entomology.

But surely there is a whole range of analytical instruments out there (yes, there sure is), so why would this one be any more suitable for forensic entomology? One of the major benefits of FTIR is the possibility of handheld IR instrumentation, which basically means it can be used in situ at the scene of a crime or other incident. Granted the investigator would need the appropriate equipment, but it beats shipping samples back to the lab and waiting for analysis. IR spectroscopy is a non-destructive technique (okay, the insects were somewhat mutilated in this study, but nevertheless the samples themselves remained after analysis). The ability to perform analyses without destroying the sample has a huge benefit, particularly if the available sample is limited, allowing for alternative tests and future analysis to be conducted if necessary. This of course is an advantage in forensic science. Also of great benefit to a legal investigation, IR instrumentation is fast, with spectra being collected in a matter of minutes.

There is however the glaring problem of the cost of analytical instrumentation. As I previously stated, your average police force may not have a forensic entomologist on hand… they equally may not have the funds to purchase analytical instrumentation such as IR spectrometers.

Bearing in mind this was merely a pilot study, using a very limited sample size, the research shows some promising results – that it is possible to classify species and life cycle stage using IR spectroscopy. Were this to be expanded upon, you could theoretically develop a database of IR spectra collected from different species of insects at different stages of development, allowing future spectra obtained from unknowns to be compared and, hopefully, identified.

References

Pickering, C. L. Hands, J. R. Fullwod, L. M. Smith, J. A. Baker, M. J. Rapid discrimination of maggots utilising ATR-FTIR spectroscopy. Forensic Sci Int. 249 (2015), pp 189-196.

Singh, D. Bala, M. The effect of starvation on the larval behaviour of two forensically important species of blow flies (Diptera: Calliphoridae). Forensic Sci Int. 193 (2009), pp. 118-121.