Tuesday, 20 April 2021

Superglue: The surprising (to me) hero of forensics.

 

Superglue is one of the unusual heroes of Forensic Science. In an episode of the BBC’s Death in Paradise, the detective uses it to develop a some fingermarks from inside a pair of surgical gloves.

Did I just say FINGERMARK rather than fingerprint? Well yes, I think the entire cohort I took my course with learned that lesson on the first semester end of term paper – it was  -½ a point for each time we made that mistake.

To be clear:

FINGERPRINTS are the clear, complete images taken at a police station by a dedicated officer.

FINGERMARKS are the dodgy half imprints left behind at a crime scene.

Superglue or rather Cyanoacrylate fuming is primarily used for non-porous surfaces like that surgical glove mentioned about. And of course, the readiest form of cyanoacrylate is superglue. The method was discovered in the late 1970s by the US army stationed in Japan. The cyanoacrylate reacts with moisture to create a hard coating over the lines in the latent fingerprints, and it prevents the mark from accidentally being rubbed away. If you have a big enough ‘fuming cabinet’ it can hold a lot of items that need processing making it a cost effective volume processor for when a number articles are held as evidence. The fuming process produces a faint white mark that requires an extra stain in order to see the print. The vapour also leaves a white residue on surfaces of the cabinet. The fumes from superglue are noxious but not toxic[i].


So who had the brilliant idea about fingerprints in the first place? Sir William Herschel, a British Administrator in India, used fingerprints in1858 to validate civil contracts. The first use in a criminal investigation was in 1891 by an Argentine police official, Juan Vucetich, who used a fingerprint on a door frame to prove a woman had killed her own sons[ii]. In 1901, Scotland Yard adopted the use of fingerprints in identifying criminals, although the fictional detective Sherlock Holmes used fingerprints to solve crimes in stories published before then[iii].

The main issue with fingerprints is they are often ‘latent’, which means hard to see, and require some form of enhancement. The oldest method of fingerprint analysis is the use of silver nitrate. On exposure to sunlight the white silver nitrate, bound to the Chloride in the latent fingerprint, turns black. However, after about a week details in the fingerprint fade and this makes it difficult to make a long-term fingerprint data base. Which is why, nobody uses this method anymore[iv].

The other main method in use at the moment is Ninhydrin dye. Ninhydrin dye is attracted to ammonia and primary and secondary amines – compounds with nitrogen in them – in the sweat residue of fingerprints. The advantage of ninhydrin is that it can be used to enhance a fingerprint on porous paper, as well as the non-porous surfaces that superglue works on. The porous substance is dipped in ninhydrin dye and left to dry – usually for 48 hours but this can be hurried along by warming, as in the case of this experiment. Once dry, the fingerprint is displayed by a deep purple colour called Ruhemann’s Purple, after the man who first noted the effect in 1910. It is also good for enhancing old fingerprints, but the reagents are expensive. As the ninhydrin remains on the treated surface further prints can develop if it is incorrectly handled[v]. Ninhydrin is toxic and an irritant. If gloves are not worn when handling the ninhydrin coated paper then the holder’s fingers will also turn purple.

There are other methods of developing fingerprints but they tend to be more expensive like gold plating the fingerprint, which is long-lasting but not practical for everyday police work. 

For those of you for whom this is not new information, I had never watched an episode of CSI or other serious cop shows. I walked into the Graduate Fair at the University of Strathclyde expecting to sign up for a Pharmaceutical MSc or other Bioscience. Somehow, I ended up getting talked into Forensic Science. I started that course from cold, 30 years after finishing my BSc (hons) Biochemistry, 20 years after I had to give up laboratory work to care for my Autistic son.

And I loved it.

So to me superglue is marvellous, the cheap and cheerful method of storing fingerprints and fingermarks to create a decent database.  


[i] Penven, Don. (2015) ‘Developing latent prints with super glue’, Crime Scene Investigator Network. February 27. [Online] available at https://www.crime-scene-investigator.net/cyanoacrylate-fuming-a-mainstay-of-crime-scene-investigation.html (accessed 28/09/2019)

[ii] ‘History of Fingerprints’ (2018) Crime Scene Forensics, LLC, Concord, NC; www.crimescene-forensics.com [Online] available at http://www.crimescene-forensics.com/History_of_Fingerprints.html (accessed 28/09/2019).

[iii]O’Brien, James. (2014) ‘Sherlock Holmes: Pioneer in Forensic Science’, Encyclopædia  Britannica, Inc, March 31 [Online] available at https://www.britannica.com/topic/Sherlock-Holmes-Pioneer-in-Forensic-Science-1976713 (accessed 28/09/2019).

[iv] ‘Chemical detection Techniques’ (2019) Australian police.com [Online] available at https://www.australianpolice.com.au/dactyloscopy/fingerprint-detection-and-enhancement/chemical-detection-techniques/ (accessed28/09/2019).

[v] ‘Ninhydrin – visualizing of fingerprints’ (2019) Eviscan. German eForensics. [Online] available at https://www.eviscan.com/en/glossary/ninhydrin-visualizing-of-fingerprints/ (accessed 28/09/2019)

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