The role of wetting effects on the development of latent fingermarks

Fingermarks are believed to be unique to each individual and hence play a pivotal role as a form of evidence. However, despite significant ongoing research into fingermark recovery techniques, there are still many areas that need to be explored. Due to the immense potential of fingermarks as an effective method of identifications an attempt has been made in the present work to analyse one particular area that has been overlooked - the impact of wetting properties of different surfaces. The aim of the study is to investigate the physical and chemical changes in fingermark constituents deposited on polymer substrates of different water contact angles when recovered using the cyanoacrylate fuming technique with the use of camera and FTIR spectroscopy. The effect of aging and the environmental conditions on latent fingermarks was also studied. Meanwhile, visualisation of latent fingermark on metal substrates developed using the conventional technique (cyanoacrylate fuming and staining) was compared with the chemical images obtained from ToF-SIMS. Images from optical microscope showed the influence of substrate wetting properties in the distribution of both types of sweat material (sebaceous and eccrine) which in turn affected the cyanoacrylate polymerisation. On hydrophilic substrates, the fingermark was deposited as a continuous film that allowed higher cyanoacrylate polymerisation whereas on hydrophobic surfaces an irregularly shaped fingermark deposit led to lower amount of cyanoacrylate polymerisation. Aging of fingermarks was shown to be influenced by the underlying substrate wetting properties as fingermark constituents decreased more rapidly on hydrophobic surfaces. The eccrine fingermark aged significantly faster than sebaceous fingermark due to the more volatile nature of the fingermark constituents. Experimental evidence showed that both types of marks developed well by producing a clear fingermark pattern with cyanoacrylate fuming after aged for a week when the marks were not exposed to environmental conditions in comparison to the marks that were aged for the same period of time but exposed to airflow and light. The chemical images from ToF-SIMS demonstrated an exceptional quality of fingermarks (clear ridge definitions and sweat pore position) on the metal surfaces for periods of up to 26 days after deposition when the samples were stored at ambient conditions whereas conventional techniques showed little to no evidence of fingermarks being present on the metal surfaces after a few days

Exposing latent fingermarks on problematic metal surfaces using time of flight secondary ion mass spectroscopy

Fingermarks are a key form of physical evidence for identifying persons of interest and linking them to the scene of a crime. Visualising latent (hidden) fingermarks can be difficult and the correct choice of techniques is essential to develop and preserve any fingermarks or other (e.g. DNA) evidence that might be present. Metal surfaces (stainless steel in particular) have proven to be challenging substrates from which to reliably obtain fingermarks. This is a great cause for concern among police forces around the globe as many of the firearms, knives and other metal weapons used in violent crime are potentially valuable sources of fingermark evidence. In this study, a highly sensitive and non-destructive surface science technique called time of flight secondary ion mass spectroscopy (ToF-SIMS) was used to image fingermarks on metal surfaces. This technique was compared to a conventional superglue based fuming technique that was accompanied by a series of contrast enhancing dyes (basic yellow 40 (BY40), crystal violet (CV) and sudan black (SB)) on three different metal surfaces. The conventional techniques showed little to no evidence of fingermarks being present on the metal surfaces after a few days. However, ToF-SIMS revealed fingermarks on the same and similar substrates with an exceptional level of detail. The ToF-SIMS images demonstrated clear ridge definition as well as detail about sweat pore position and shape. All structures were found to persist for over 26 days after deposition when the samples were stored under ambient conditions

The role of wetting effects on the development of latent fingermarks

Fingermarks are believed to be unique to each individual and hence play a pivotal role as a form of evidence. However, despite significant ongoing research into fingermark recovery techniques, there are still many areas that need to be explored. Due to the immense potential of fingermarks as an effective method of identifications an attempt has been made in the present work to analyse one particular area that has been overlooked - the impact of wetting properties of different surfaces. The aim of the study is to investigate the physical and chemical changes in fingermark constituents deposited on polymer substrates of different water contact angles when recovered using the cyanoacrylate fuming technique with the use of camera and FTIR spectroscopy. The effect of aging and the environmental conditions on latent fingermarks was also studied. Meanwhile, visualisation of latent fingermark on metal substrates developed using the conventional technique (cyanoacrylate fuming and staining) was compared with the chemical images obtained from ToF-SIMS. Images from optical microscope showed the influence of substrate wetting properties in the distribution of both types of sweat material (sebaceous and eccrine) which in turn affected the cyanoacrylate polymerisation. On hydrophilic substrates, the fingermark was deposited as a continuous film that allowed higher cyanoacrylate polymerisation whereas on hydrophobic surfaces an irregularly shaped fingermark deposit led to lower amount of cyanoacrylate polymerisation. Aging of fingermarks was shown to be influenced by the underlying substrate wetting properties as fingermark constituents decreased more rapidly on hydrophobic surfaces. The eccrine fingermark aged significantly faster than sebaceous fingermark due to the more volatile nature of the fingermark constituents. Experimental evidence showed that both types of marks developed well by producing a clear fingermark pattern with cyanoacrylate fuming after aged for a week when the marks were not exposed to environmental conditions in comparison to the marks that were aged for the same period of time but exposed to airflow and light. The chemical images from ToF-SIMS demonstrated an exceptional quality of fingermarks (clear ridge definitions and sweat pore position) on the metal surfaces for periods of up to 26 days after deposition when the samples were stored at ambient conditions whereas conventional techniques showed little to no evidence of fingermarks being present on the metal surfaces after a few days