Scientist Special: Clyde Snow

Scientist Special: Clyde Snow








Unfortunately, Snow passed away in 2014.





Caught Red-Handed: MALDI Mass Spectrometry & Bloodied Fingerprints

Caught Red-Handed: MALDI Mass Spectrometry & Bloodied Fingerprints

Most previous methods of establishing whether a fingermark at a crime scene contain blood are purely presumptive. The suspected fingermark, whether it be a print merely contaminated with traces of blood or an entire mark left in blood, will be subjected to tests which will aim to confirm or refute the presence of blood. However most existing presumptive tests suggest that it is a possibility the fingermark in question contains blood… but that it equally could be another similar substance that happens to produce a positive response with the test used. Thus is the limitation of any presumptive test – they can only give a possibility, not a definitive answer. Obviously not ideal during a forensic investigation.

Suspected bloodstains can be subjected to a wide range of tests to ascertain their composition. Blood may be visualised using alternative light sources, but this is a far cry from confirming its composition and in some cases (such as with the use of short-wave ultraviolet light) can even be destructive to DNA, thus obviously not ideal for the forensic examination of a blood sample. Spectroscopic techniques such as Raman spectroscopy have proved successful in potentially distinguishing blood from other biological fluids, though this has not been widely applied, particularly to blood in fingermarks. Chemical enhancement techniques have also been developed in the past, such as those that react with amino acids or haem-reactive compounds present to produce a colouring or fluorescence to enhance the blood. As successful as these methods may have been in the past, they are still only presumptive and cannot claim with any kind of near-certainty that any positive reaction produced is the result of blood and furthermore whether that blood is of human origin.

As a result of this, more confirmatory tests are needed.

More affirmative procedures do exist and are currently being developed. A particularly interesting method of detecting blood in fingermarks is using a technique known as MALDI MS. That is, Matrix-Assisted Laser Desorption Ionisation Mass Spectrometry. This relatively new analytical technique (relative to the history of mass spectrometry anyway) is most commonly applied to determining the mass of peptides, proteins and polymers, so is ideal for focusing on certain components of blood.

For those unfamiliar with mass spectrometry, in its simplest form it is a technique which is used to determine the identity of sample components based on their mass-to-charge ratio and, in some cases, how the molecule fragments when ionized. MALDI is something of a variation of this technique. In this technique, the sample to be analysed is mixed with a particular matrix material and applied to a plate. A laser irradiates the sample and matrix, causing ablation and desorption, after which the sample is ionized and then accelerated and detected using mass spectrometry.

Researchers have applied MALDI MS to detecting the presence of blood by specifically focusing on the detection of haem and haemoglobin molecules based on their mass-to-charge ratios. These molecules are vital components of blood, with haemoglobin being the protein responsible for oxygen transportation and haem being a compound embedded into haemoglobin which provides the iron essential for oxygen binding. By subjecting known and suspected blood stains and bloodied fingermarks to this technique, haemoglobin chains could be detected even in traces of blood invisible to the naked eye. Initial research into this technique studied human, equine and bovine haemoglobin, establishing that it is possible to determine whether or not haemoglobin was from a human source using mass spectrometry at a high mass range. Both fresh and aged blood samples could be successfully analysed, making the application potentially beneficial to samples from various points in time. Furthermore, the technique has proven to be compatible with other methods often used by investigators when attempting to enhance fingermarks at incident scenes, meaning the new method is not likely to interfere with existing procedures.

A typical haemoglobin molecule.

A typical haemoglobin molecule.

This fascinating application of matrix-assisted laser desorption ionisation mass spectrometry offers a whole new world of possibilities in blood detection in forensic science. Although at present such instrumentation is far from being the norm in the forensic scientist’s arsenal, the applications of advanced mass spectrometry techniques to answering some of the simpler yet vital questions during a criminal investigation make for a captivating read.


Bradshaw, R et al. Direct detection of bloos in fingermarks by MALDI MS profiling and imaging. Science and Justice. 45 (2014), pp. 110-117.

King’s College London. An Introduction to Mass Spectrometry Based Proteomic. [online][Accessed 16 Feb 2015] Available:

Food for Thought: Forensics & Food Fraud

Food for Thought: Forensics & Food Fraud

Recently, organisation Food Forensics became the first laboratory of its kind in the UK to receive UKAS accreditation, which brings me to this post. Some might ask, what does food have to do with forensics? Perhaps a perfectly valid question with the traditional bloodied crime scene on a dark night in mind. However the application of forensic science is growing continuously, including in tackling problems of food fraud.

Many Europeans will remember the food scandal arising in 2013 in which horsemeat was somewhat shockingly detected in a range of food products (obviously in products where horsemeat should not have been popping up). Or perhaps less well-known, the 1858 Bradford sweets poisoning, in which a batch of humbugs was accidentally made using arsenic instead of a sugar substitute, resulting in the poisoning of numerous people. Common mistake to make I’m sure! Concerns over foodstuffs have always been prevalent, but it is only in relatively recent years that advanced analytical techniques have been available to apply to this field of work.


Organisations are now carrying out research and analyses of food and beverages to validate their composition. Of particular note is the use of stable isotope analysis to determine the isotopic composition of a sample. As a brief reminder, isotopes are atoms of the same chemical element (same number of protons but different number of neutrons, thus giving them slightly differing masses). Stable isotopes have a natural abundance which is altered in different locations to a different extent, a process known as fractionation. This will result in samples (whether it be samples of food, plants or anything else) acquiring different ratios of isotopes. Stable isotope analysis examines these non-radioactive isotopes to help establish the isotopic composition of a sample, which can then be compared to others.

With this information available, it is possible to establish the origin of food products. Whereas the origin of a product may seem benign, realistically if you don’t know where your food has come from, you can’t say much about the safety of food. By determining the stable isotopic compositions of food samples and comparing them to known standards, the contents of a sample can be validated or refuted. Some researchers have compiled isotopic data for different regions into a kind of map (sometimes referred to as an “isoscape”) which shows the varying isotopic data throughout different areas. With data such as this at hand, it may be possible to establish the origin of a food sample based on its isotopic composition and how that compares with the isotopic data of particular areas. Using this analytical method, it may be possible to not only investigate the country or even region of origin of a food product, but also further details such as if it is organic.

As an example, the James Hutton Institute based in Scotland has conducted research into the hydrogen and oxygen isotopic composition of Scotch whisky, aiming to prove that fraudulently-produced whisky made outside of Scotland will be detectable if not made with water from within and around Scotland. Whisky made from water sourced elsewhere will have a different isotopic “fingerprint”. It is applications like this that allow for scientists and regulators to crack down on food fraud, ensuring both safety in food supply and preventing food-related criminal activities.


Food Forensics. [online][Accessed 12 Feb 2015] Available:

Earth Magazine. Cold case files: forging forensic isotopes. [online][Accessed 12 Feb 2015] Available:

Cambridge Network. Food forensics achieves UKAS accreditation focussed on combating food fraud. [online][Accessed 12 Feb 2015] Available:

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