Responsable : Christophe Champod
During the investigation of crime, various elements of forensic nature may help to reconstruct the events and/or potentially associate designated person(s) with the investigated acts. Among these elements, latent fingerprints (or fingermarks) constitute one of the most useful and researched evidence, due to their uniqueness, inalterability and the today's availability of automatic fingerprint recognition systems. A fingermark of sufficient quality possesses all the qualities for personal identification in forensic context. When an object or a surface is touched with the inner surfaces of unprotected hands (or feet), a small amount of secretions (mainly composed of lipids, amino acids, organic molecules, ...) is left on the surface of this object and leave, as a rubber stamp, a latent residual image made of ridges and furrows.
There are three different types of fingerprints that can be discovered: visible, plastic, and latent. The last category is of particular interest here as they are not visible at first examination and require or their visualisation the deployment of dedicated detection techniques. Currently, several different methods exist and are described in Margot & Lennard (1994). The principle in common to all these techniques is the differentiation of search for an optimal detection of the secretion drawings as opposed to the background (= substrate). The existing methods take advantage from optical behaviours, physical or chemical reactions. The visualisation of the end product can take advantage of fluorescence techniques, e.g., ninhydrin analogs (Alaoui & Menzel, 1996), DFO, rare-earth complexes (Allred & Menzel, 1997), or colour-based contrast, e.g., physical developer, cyanoacrylate fuming (Burns et al., 1998), metallic multi-deposition (Schnetz & Margot, 2001). The suitable techniques to apply in a given case is selected as a function of the surface to be treated (porous, semi-porous or non-porous), the environmental constrains, the molecules or elements of interest, e.g., amino acids or lipids (Wilkinson, 1999) and the ability to put the reagents in sequence (Margot & Lennard, 1994).. However, today, there is not a single procedure that would reveal fingermarks in every situation. The large number of different surfaces to be studied (paper, metal, cardboard, wood, clothing, ...), as well as the age and the conditions of conservation of the prints, imply a specific approach dedicated to each situation.
Most of the existing chemical and physical techniques are not free from difficulties and have their own limitations. It is still difficult or even impossible to reveal the latent fingermarks in some cases (such as the human skin). Among the different drawbacks, the background fluorescence constitutes one of the main difficulties encountered with conventional methods, as it decreases the contrast between the print and the support. Furthermore, some techniques, which are successfully developed for laboratory use, are not operational in the field: the toxicity of some reactants or the destruction of the substrates are strong limiting factors here. The aim of our project is to develop a new efficient method for the detection of prints on porous and non-porous surfaces that can take advantage of detection in a luminescence mode (favoured for its increased sensitivity) in a non-toxic environment. We are particularly keen at developing an efficient, portative, non-toxic, and non-destructive detection technique that can challenge the existing processes. Our strategy is based on the use of fluorescent probes combined with molecular recognition as main detecting method, due to its high sensitivity and selectivity. The challenge being to be able to tag the fingerprint with these molecules, e.g., with reactants that specifically interacts with the secretion components or with a metallic layer previously deposited on the print that allows covalent binding of organosulfur molecules. At this purpose, we will firstly explore a way that has not yet been considered, i.e., the use of cyclodextrins as chelating agents, in regard to their successful application in many different domains (food, textiles, chemistry, ...). Secondly, we will focus our work on the improvement of existing biochemical methods, i.e., by introducing a spacer molecule between an antibody/antigen complex and the support of interest in order to higher the resulting fluorescence. These two approaches are described hereafter.