Production of artificial fingermarks. Part II - The use of a modified inkjet printer for the deposition of synthetic secretions.

This study is the second part of a larger body of research dedicated to the production of synthetic secretions and the use of an inkjet printer to deposit realistic artificial fingermarks. An artificial emulsion combining eccrine and sebaceous compounds, which was described and tested in the first part of this research, was used as it showed a promising compatibility with common detection techniques. An inkjet printer was modified to print the emulsion on two different substrates: paper (porous) and acetate (non-porous). After optimisation of the printing parameters, multiple fingermarks were printed and processed with a range of standalone detection techniques: 1,2-indanedione-zinc, ninhydrin, Oil Red O, and physical developer on paper, and cyanoacrylate fuming, rhodamine 6G, gold/zinc vacuum metal deposition, and silver black powder on acetate. The detection techniques were also applied in sequence, which is considered one of the biggest advantages of the emulsion over simpler amino acid mixtures that are usable with amino acid reagents only. Natural fingermarks deposited by a single donor were processed with the same techniques for comparison. The effect of water immersion was also investigated, where fingermarks printed on paper were immersed in water for 15 min, before being processed with 1,2-indanedione-zinc and Oil Red O. The results showed that realistic-looking fingermarks could be printed on paper and that printing on acetate was also possible albeit of lower quality due to the nature of the substrate. The artificial fingermarks were successfully enhanced by all the detection techniques tested, at the notable exception of physical developer. The results obtained were very similar to what is generally observed with real fingermarks, and it was observed that the impact of water immersion on the artificial fingermarks was comparable as well. These findings open new perspectives for the development of multi-target quality control test strips or for the standardisation of proficiency testing and interlaboratory collaborative exercises where ground truth is crucial to guarantee comparable results and objective assessment.

Production of artificial fingermarks. Part I - Synthetic secretions formulation.

Fingermark variability is a critical parameter. To mitigate the effects of this variability, synthetic secretions in the form of simple mixtures of target compounds found in eccrine sweat have been described in the literature, but they are usually reactive towards only a minimal range of detection techniques. If this approach is acceptable for the production of single-technique test strips, such artificial secretions cannot be considered as reliable fingermark simulants because they do not reproduce the complex matrix that makes up real secretions. Research has shown that sebaceous and eccrine compounds are probably present simultaneously in fingermark residue in the form of an emulsion. This paper is the first part of a research project that aims at producing realistic artificial fingermarks containing an extensive range of eccrine and sebaceous compounds. This first study aimed to reproduce and compare two synthetic fingermark residues formulations and assess their potential to be used as fingermark simulants. Spot tests of the artificial secretions were deposited on paper substrates, and their reactivity with four common detection techniques was tested: 1,2-indanedione-zinc, ninhydrin, oil red O, and physical developer. Both formulations showed very good results when processed with the two amino acid reagents, as well as oil red O, and no obvious differences were observed between the two versions. The results obtained with the physical developer were inconsistent and demonstrated that the fundamental working principle of physical developer needs to be further understood. The results were extremely promising as they showed the potential of such reproducible artificial secretions to be used to assess an extensive range of detection techniques, which would be highly beneficial to guarantee better research and quality control in fingermark detection. The use of spot tests to deposit the simulant was shown to be unreliable and a more controllable and reproducible deposition method using an inkjet printer will be presented in the second part of this research.

Evaluation of the use of chemical pads to mimic latent fingermarks for research purposes.

Fingermark detection is in constant evolution, with new techniques being developed and existing ones being continuously optimised. Recently, researchers have begun to express interest in artificial fingermark secretions to overcome the issues arising from the variability of fingermark composition. Some of these artificial secretions have started to appear on the market in the form of pads that can be used to deposit fingermarks with a known and controlled composition. This study aimed at assessing the reliability of three commercially-available pads by comparing the results to those obtained by real fingermarks, using six detection techniques (1,2-indanedione/zinc, ninhydrin, cyanoacrylate followed by rhodamine 6G staining, gold/zinc vacuum metal deposition, and physical developer) on five substrate types (copy and recycled paper, acetate, glass, and glossy paper). The results showed that the artificial fingermarks deposited with these pads reacted in an unreliable way, notably when treated with complex detection techniques such as Physical Developer. Further, the high concentration of some of the target compounds found in the artificial secretion led to an over performance of some detection techniques, which could mislead the operator to overestimating the efficiency of a given method. The resulting artificial fingermarks are considered too dissimilar to real fingermarks to be used as quality control standards and better simulants need to be found for a more efficient and realistic control of the variability.

Effect of water immersion on multi- and mono-metallic VMD.

The use of vacuum metal deposition (VMD) for fingermark detection has been known for almost 40 years. The technique is applicable on a wide variety of substrates and on wetted items. Several publications compare the relative efficiency of VMD (conventionally based on a successive vaporization of gold followed by zinc) with other detection techniques, or its ability to detect marks on difficult substrates, but few are known about the application of monometallic VMDs and about the impact of immersion on the detection performances. This study aims at partially filling that gap by offering a quantitative and qualitative glance at three VMD processes (i.e., gold/zinc, silver, and sterling silver) applied to dry and wetted substrates. The impact of immersion on the detection process has been studied by using split marks (one half kept dry, the other one wetted). On immersed substrates, a modification of colour shades has been observed with monometallic VMDs (on all substrates considered) and of contrast with conventional VMD (on polyethylene). In terms of ridge details, a relatively good resistance of secretion residue towards immersion has been emphasized (in regards with VMD). This study provides original data, which will hopefully help getting a better understanding of the VMD detection mechanism.