Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Single metal deposition <s> This paper proposes an alternative solution to multimetal deposition (MMD) for the development of latent fingermarks on non-porous and porous surfaces. MMD offers a good sensitivity, however it is very time-consuming and requires many reagents to be carried out. Single-metal deposition (SMD) replaces the silver enhancement of the gold colloids by a gold enhancement procedure. This reduces the number of baths by one as well as the number of reagents and their cost, utilizes reagents with a longer shelf life, and most importantly reduces the labor-intensity of the procedure. It offers quasi-identical results to MMD and thus makes a very attractive alternative. <s> BIB001 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Single metal deposition <s> Following the introduction of single-metal deposition (SMD), a simplified fingermark detection technique based on multimetal deposition, optimization studies were conducted. The different parameters of the original formula were tested and the results were evaluated based on the contrast and overall aspect of the enhanced fingermarks. The new formula for SMD was found based on the most optimized parameters. Interestingly, it was found that important variations from the base parameters did not significantly affect the outcome of the enhancement, thus demonstrating that SMD is a very robust technique. Finally, a comparison of the optimized SMD with multi-metal deposition (MMD) was carried out on different surfaces. It was demonstrated that SMD produces comparable results to MMD, thus validating the technique. <s> BIB002 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Single metal deposition <s> 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. <s> BIB003
In the quest to find a better alternative of MMD, Stauffer et al. (2007) proposed single metal deposition (SMD) that incorporates the use of gold-on-gold method. Basically, the first part of SMD is similar to that of MMD process (initial deposition of metallic colloidal gold nanoparticles). The difference between the two methods lies in the second part of the process where hydroquinone/silver acetate developer in MMD method is replaced with hydroxylamine/gold chloride as the reducing agent. With SMD, the labor intensiveness of the typical metal deposition method is reduced from six (in MMD) to five immersion baths with the use of one less reagent, hence subsequently reducing the cost BIB001 ). In addition, BIB002 reported a condition (20 min of immersion time, intense 70 rpm stirring speed, 1:1 mol/mol gold/hydroxylamine ratio with 3 × 10 −4 M of gold concentration) that had resulted in the best SMD optimized parameters for visualizing groomed fingerprints from two donors on a low-density polyethylene transparent film. The authors also mentioned that the common risk of over-development of fingerprint ridges observed in MMD can be circumvented in the SMD method. Despite reporting satisfactory results, authors BIB001 BIB002 ) did not mention the end-color of the visualized SMD-treated fingerprints, if it is comparable or better than that of the MMD method. Moreover, the authors also did not specify the working pH of SMD used. 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 BIB003 . 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.