Detection of fingermarks by colloidal gold (MMD/SMD) – beyond the pH 3 limit

Abstract

This work is part of a continuing goal to improve the multimetal deposition technique (MMD), as well as the single-metal deposition (SMD), to make them more robust, more user-friendly, and less labour-intensive. Indeed, two major limitations of the MMD/SMD were identified: (1) the synthesis of colloidal gold, which is quite labour-intensive, and (2) the sharp decrease in efficiency observed when the pH of the working solution is increased above pH 3. About the synthesis protocol, it has been simplified so that there is no more need to monitor the temperature during the synthesis. The efficiency has also been improved by adding aspartic acid, conjointly with sodium citrate, during the synthesis of colloidal gold. This extends the range of pH for which it is possible to detect fingermarks in the frame of the MMD/SMD. The operational range is now extended from 2 to 6.7, compared to 2-3 for the previous formulations. The increased robustness of the working solution may improve the ability of the technique to process substrates that tend to increase the pH of the solution after their immersion.

Nanoparticles used for fingermark detection—A comprehensive review

“…To further simplify the technique, the first SMD I step was revisited in 2012 (Bécue, Scoundrianos, & Moret, 2012). A simpler colloidal gold synthesis protocol was chosen and a small amount of amino acid (L-aspartic acid) was added during the synthesis.…”

Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review

“…Despite its universal ability in visualizing latent fingerprints on a wide range of porosity (Saunders 1989;Zhang et al 2007), this silver-on-gold method is rarely applied in practical caseworks (Becue et al 2012), attributable to major drawbacks which include the use of expensive reagents and scrupulously clean glassware, laborious procedures (at least 1 h of processing due to the requirement of many immersion baths) (Saunders 1989;Ramotowski 2012b), and the possibility of over-development of prints (Becue et al 2012;Ramotowski 2012b). In addition, MMD-I also suffers from limited working pH (~pH 3) (Saunders 1989;Becue et al 2012); at higher pH, significant decrease in the efficiency of the method was observed (Bécue and Cantú 2012;Becue et al 2012). Such outcome is observed due to the loss of electrostatic attraction between the positively charged constituents of fingerprints (water-insoluble proteins that are trapped within the lipids) and negatively charged citrate-capped colloidal gold nanoparticles (Schnetz and Margot 2001;Becue et al 2007;Bécue and Cantú 2012).…”

“…Since pH is an important factor in MMD method, this can be suggestive that the pH working range for this method being narrow. The addition of aspartic acid conjointly with sodium citrate during the synthesis of gold has significantly extended the working pH of SMD (from pH 2 to pH 6.7), hence improving the robustness of the method (Becue et al 2012). Although the increased quality of visualized fingerprints at low pH is characterized by the increased electrostatic interactions (since aspartic acid has a lower pKa value), the active role of aspartic acid in allowing the detection of fingerprints at an extended working range of pH remains baffling.…”

Advances in the development and component recognition of latent fingerprints

“…The multimetal deposition (MMD) introduced by Saunders et al [36] in 1989 is a very sensitive method for visualizing LFPs on a range of surfaces. Since then, a great deal of effort has been devoted to reducing the labor-intensity of this procedure [37][38][39]. Recently, MMD has been performed in a reverse manner by developing a paper substrate rather than fingerprint residue [40,41].…”