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Fingerprint Enhancement on Metal Surfaces

This research has demonstrated the ease with which it is possible for eccrine rich fingerprints to corrode a wide range of metal surfaces (both elements and alloys). The corrosion process has been shown to be dependent on the concentration of chemically aggressive chloride ions present in eccrine sweat. The water content of the fingerprint residue (over 99% of a fingerprint is made up of water) acts as an electrolyte to permit galvanic corrosion to take place over the surface of the conducting metal. This corrosion of the metal surface has been exploited by the development of a new technique to enhance fingerprints that requires the metal surface to be electrically charged to ~ 2,500kv followed by the application of a granular conducting powder. This technique (currently the subject of a patent application) has been used to demonstrate a solution to the extremely difficult problem of enhancing a fingerprint placed on a small calibre metal cartridge case prior to firing.

Value of DNA and Fingerprint Evidence

 Both DNA and fingerprints have the ability to identify an offender and detect the crime without the police identifying potential offenders beforehand (what is known as a cold identification). By analysing DNA and fingerprint data we have shown which factors contribute to the successful conversion of forensic material recovered from a crime scene (such as blood, a cigarette end or a fingerprint) into a detection. These factors are many and varied but we have found that they are highly dependent on the skill and accreditation of those engaged in the different parts of the forensic process.

Fingerprint Enhancement by X-Rays

This research utilises the characteristic x-ray emission from elements such as sodium or potassium (Moseley’s Law) and which are both present as inorganic salts in eccrine sweat. It has been shown that an eccrine rich fingerprint deposited on a non-porous surface (and subject to x-ray irradiation or electron bombardment) might be visualized by counting x-ray emission at the characteristic x-ray frequency of both sodium and potassium over an xy scan of the surface of the substrate.

Fingerprint Enhancement by Nanoparticles

We are investigating the enhancement of fingerprints using luminescent semi-conductor nanoparticles. The mechanism for this is the targeting of either amino or carboxyl groups present in fingerprint residue with functionalised nanoparticles that will preferentially adhere to these groups. The frequency of fluorescence may be varied by varying the size of the nanoparticle thus eliminating a problem encountered with existing chemical enhancement techniques, namely background fluorescence at the same frequency as the enhanced fingerprint.

 If you have any questions about any of this research please contact Dr John Bond.