Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> The silver physical developer is currently the most successful reagent used for visualizing the water-insoluble components (e.g., lipids) of latent prints on porous surfaces. It is normally used after the amino acid visualizing reagents (e.g., ninhydrin and DFO) are used. This work found that the performance of the current formulation of silver physical developer is strongly reduced when the water used is changed from the usual distilled water to the more purified reverse osmosis/deionized (RO/DI) water. Based on numerous experiments involving the systematic variation of the component concentrations, the performance was restored and even improved by reducing the concentration of all the components (except that of the ferric salt) and by including malic acid in the formulation. These modifications resulted in a new silver physical developer formulation that performs as well as or better than the current formulation and is less expensive to make. <s> BIB001 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> This is a systematic study that examines several acid prewashes and water rinses on paper bearing latent prints before its treatment with a silver physical developer. Specimens or items processed with this method are usually pretreated with an acid wash to neutralize calcium carbonate from the paper before the treatment with a physical developer. Two different acids at varying concentrations were tested on fingerprints. Many different types of paper were examined in order to determine which acid prewash was the most beneficial. Various wash times as well as the addition of a water rinse step before the development were also examined. A pH study was included that monitored the acidity of the solution during the wash step. Scanning electron microscopy was used to verify surface calcium levels for the paper samples throughout the experiment. Malic acid at a concentration of 2.5% proved to be an ideal acid for most papers, providing good fingerprint development with minimal background development. Water rinses were deemed unnecessary before physical development. <s> BIB002 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Latent fingerprints deposited on commercial photocopy paper were treated using various preparations of silver-based physical developer and the results from each were compared to those obtained with the standard formulation used by the Australian Federal Police. Five redox stock solutions were prepared with altered orders of reagent addition, and a further solution prepared with exchanged iron concen- trations, to test the robustness of the method. Three redox solutions were prepared with specific reagents omitted to determine the signifi- cance of the role played by each in development. One redox solution was prepared using Tween 20 as the non-ionic surfactant to assess its suitability as a replacement for Synperonic N. An acid prewash was also prepared using malic acid as an alternative to maleic acid. Results showed the method to be robust to alterations in reagent addition, but not to significant concentration changes. The presence of all compo- nents was found to be desirable for distinguishable development of fingerprint detail. It was additionally found that Tween 20 gave at least equal performance to Synperonic N on recently deposited fingerprints. Finally, the use of malic acid gave equivalent fingerprint development but higher background in comparison to maleic acid. <s> BIB003 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> This paper describes the application of a luminescent lipid stain, nile red, for the development of latent fingermarks on porous surfaces. An optimised formulation is presented that provides rapid development of latent fingermarks on porous surfaces that are or have been wet. A comparison with physical developer (PD), the method of choice to enhance such fingermarks, indicated that nile red was a simpler and more stable technique for the development of fingermarks. The nile red formulation showed similar performance to PD across a range of substrates and ageing conditions, although PD still showed greater sensitivity on five-year-old examination booklets used in a pseudo-operational study. The pseudo-operational trial also indicated that nile red consistently developed different fingermarks to those enhanced by PD, suggesting that it preferentially targets a different fraction of the latent fingermark deposit. Significantly, the compatibility of nile red in a detection sequence with indanedione-zinc, ninhydrin and PD is reported. <s> BIB004 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Fingerprints are the world’s oldest means of individual identification, and most of the work completed by CSIs hinges on latent fingerprinting and impression evidence. Many processes are available to reveal hidden physical evidence, and this chapter provides a look at those procedures that have been scientifically proven and accepted in court. <s> BIB005 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Physical developer (PD) is a fingermark development technique that deposits silver onto fingermark ridges. It is the only technique currently in routine operational use that gives results on porous substrates that have been wet. There is a reasonable understanding of the working solution chemistry, but the chemical constituent(s) contained in fingermark residue that are specifically targeted by PD are largely unknown. A better understanding of the PD technique will permit a more informed selection of alternative or complementary detection methods, and greater usage in operational laboratories. Recent research by our group has shown that PD does not selectively target the lipids present in the residue. This research investigated the hypothesis that PD targets the eccrine constituents in fingermark residue. This was tested by comparison of PD and indanedione-zinc (Ind-Zn) treated natural fingermarks that had been deposited successively, and marks that had been deposited with a ten second interval in between depositions. Such an interval allows for the regeneration of secretions from the pores located on the ridges of the fingers. On fingermark depletions with no time interval between depositions, PD and Ind-Zn treated depletions successively (and comparatively) decreased in development intensity as the amount of residue diminished. Short time intervals in between successive depletions resulted in additional secretions from the pores intermittently occurring, the increased development of which was visualised by treatment with both PD and Ind-Zn. The changes in development intensity were seen with both techniques on the same split depletions in a series, comparably and proportionately. These results indicate that the components targeted by PD are contained in the material excreted by the friction ridge pores through its mirrored development with Ind-Zn. Repetition of the experiments on marks that only contained eccrine material showed good Ind-Zn development but poor results with PD. This indicates that there are other constituents contained in "natural" fingermarks that are required to be present for PD to be able to target constituents in the eccrine sweat. It may be that the required constituents in the natural residues are non-water soluble, and that these protect the eccrine constituents from solubilisation in the aqueous washes employed in the PD method. Further research is being undertaken to determine whether PD is targeting specific compounds in the pore secretions, or a mixture of compounds consisting of the eccrine material, epidermal lipids and sebaceous lipids typically present in latent fingermark residues. <s> BIB006 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Friction ridge examination is one of the bedrock disciplines in forensic science and has been employed for over 100 years. It is considered the pre-eminent method of individualization in forensic science. That status, however, has recently been upset by court challenges and high-profile misidentifications. Friction ridge examination will no doubt continue as a mainstay of forensic science, but changes in methodology and interpretation may be on the horizon. How the discipline weathers these changes depends on the willingness of the profession to critically examine their foundations, procedures, and methods. <s> BIB007 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Fingerprints have been used for human identification in criminal investigation for over 100 years. The detection of invisible or latent marks at crime scenes has been one of the great scientific challenges in forensic science and there have been considerable advances in this capability. The technological age and increasing power of computing has had a major influence on fingerprint identification providing the capacity to search large databases and provide rapid identification of persons of interest. This chapter discusses the important contribution of fingerprints to criminal investigation. <s> BIB008 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Physical developer <s> Abstract: The physical developer technique is a means to detect fingerprints on dry and wet, porous items, including paper articles, clay-based products and adhesive tapes. The process involves an oxidation–reduction couple whereby a solution of an iron salt reduces aqueous silver nitrate to finely divided metallic silver. The technique derives its name from the photographic physical developer which, during processing of film rolls, undergoes a similar redox reaction. The physical developer reveals the fingerprints as dark gray or black images due to the adsorption of metallic silver particles on the fatty acid and lipid components of sweat residue. <s> BIB009
The use of physical developer (PD) reagent in visualizing latent fingerprints was dated far back in the early of 1970s  ). The development of PD for visualizing latent fingerprints on wet-porous surfaces, by targeting the water-insoluble (e.g., lipids) constituents, is undoubtedly useful BIB002   BIB006 BIB007 BIB008 ). However, de la Hunty et al. (2015b) recently challenged such classic assumption on the basis that PD still revealed positive results upon the artificial removal of lipid constituents of fingerprints using various organic solvents. In another study by the same authors (de la Hunty et al. 2015a), PD was found to be positively reactive toward the eccrine secretions, thereby postulating that PD may not be exclusively targeting lipids, but may be selective toward eccrine constituents too, or a mixture of both. Nevertheless, the real target constituents of PD remain baffling, and hence, necessitating the need to further explore the chemistry behind PD. In addition,  and BIB003 stated that PD is especially effective in providing identifiable and good quality of visualized fingerprints on porous objects where other visualization methods might have failed, along with developing aged fingerprints  BIB004 BIB005 BIB006 . It has been reported that PD is also useful on dry, porous surfaces   ). However, if PD is to be used along with other visualization methods (e.g., ninhydrin), it must be in the last of sequential processing, a concept which is agreed upon by many researchers   BIB006 BIB008 . The formulation of PD reagent mainly includes Ag + (from silver nitrate) and Fe 2+ (from ferrous ammonium sulphate) (reducing agent). Additionally, citric acid and Fe 3+ (from ferric nitrate) are added into the formulation to suppress the reduction of Ag + to Ag, unless it is prompted by the presence of triggering/nucleating sites (i.e., water-insoluble constituents of fingerprints). However, due to this instability, spontaneous reduction of Ag + to Ag may still occur to form colloidal-sized Ag particles in the solution; the formed silver triggers more chain reduction of silver, thereby increasing background staining. To overcome this and to maintain the stability of the working solution, the addition of cationic and non-ionic surfactants appeared advantageous BIB002  . It has been reported that spontaneous formation of colloidal-sized Ag particles obtains its negative charge from citrate ions. Thus, the addition of cationic surfactant (n-dodecylamine acetate) stabilizes the PD formulation by suppressing the negative charge of the formed Ag colloids through the formation of micelle that surrounds the Ag colloids. Thereby, causing a shift into positively charged particles to prevent aggregation with other Ag +  . In view of stabilizing the developing colloid Ag particles  and aiding the dissolution of cationic surfactant  , the non-ionic surfactant (e.g., Synperonic N or Tween 20) is introduced. In addition, substitution of Tween 20 in PD formulation offers a longer shelf life, as documented by  . Generally, PD formulation is made up of three separate stock solutions viz. surfactants (cationic and non-ionic), silver nitrate, as well as redox solutions (ferric nitrate, ferrous ammonium sulphate, and citric acid)  BIB006 BIB008 . Although literature  suggested that the three stock solutions are to be added in a manner of ferric nitrate, ferrous ammonium sulphate, citric acid, and lastly the surfactants, BIB003 disputed this suggestion. The authors reported that the order of addition of the stock solutions did not influence (no significant difference) the performance of each working formulation. However, for standard laboratory practical purposes, the authors suggested that the order of addition was to remain as such. While investigating the modifications of PD formulation, BIB001 discovered that with the incorporation of reverse osmosis/deionized (RO/DI) water as a substitution for distilled water in the traditional formulation, the amount of surfactants needed can be subsequently reduced. This is largely because RO/DI water contains relatively less ions than that of distilled water, thus, less amount of surfactant is needed to suppress the negatively charged Ag colloids. Additionally, the authors also revealed that by reducing the concentration of silver nitrate solution from 20 to 16%, relatively comparable and better results were obtained when compared with that of traditional PD formulation. Despite being advantageous in visualizing aged latent fingerprints, PD is tedious since it requires pre-washing with non-chlorinated acids (e.g., maleic, malic, and dilute nitric acids) to remove the calcium carbonate (which may act as nucleation site) on papers BIB001  BIB008 . Apparently, this step is necessary as calcium carbonate is a common filler used in the manufacturing of papers  . While comparable effectiveness in visualizing latent fingerprints on photocopy paper was observed between malic and traditional maleic acids in the acid pre-wash process, the use of malic acid increases background staining that partially obscured the fingerprint ridge BIB003 , thus complicates the identification process. Aside from being costly BIB009 and the need to use extremely clean laboratory glassware, the use of PD is somewhat destructive as the method tends to permanently stain the evidence. Also, pre-washing with malic acid may inevitably weaken the fibers of the paper-based forensic evidence, further increasing the possibility of destroying the evidence BIB006 .