Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Oil Red O <s> A modified detection sequence is presented for the recov- ery of latent fingermarks on porous substrates. 1,2-Indanedione, Oil Red O (ORO) in propylene glycol, and physical developer (PD) were successfully used to develop recently deposited latent fingermarks when applied in the order given. The incorporation of ORO into the detection sequence increased the number of latent fingermarks that were detected compared to using the standard sequence of 1,2-indane- dione followed by PD only. <s> BIB001 </s> Relevant visualization technologies for latent fingerprints on wet objects and its challenges: a review <s> Oil Red O <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> BIB002
Having considered the limitations of PD, the development of Oil Red O (ORO) (a pinkish lipophilic stain used in histology) as an alternative was first popularized by  . The author revealed that ORO works best in visualizing latent fingerprints, particularly on porous and semi-porous surfaces, although no direct comparisons with PD were made. In another study by  , the authors revealed the superiority of ORO reagent over PD in visualizing latent fingerprints, particularly on thermal and standard white papers. In addition, the authors reported that the mean quality of visualized fingerprints on wet papers following the use of both methods (ORO and PD reagents) was statistically insignificant.  while investigating the sequential processing of ORO with 1,8-diazafluoren-9-one, ninhydrin and PD suggested that ORO is to be used after the application of amino acid sensitive reagents, but before PD since it permanently stains the surface BIB002 . BIB001 also concurred that PD should be used as the last method in the sequential processing. In an attempt to produce a relatively non-toxic, economical, and simpler ORO reagent,  proposed the use of ORO in propylene glycol. The authors found out that while the development time using the modified ORO reagent was reduced to only 15 min, the contrast and ridge detail of modified ORO-treated fingerprints were comparable to that of traditional ORO formulation with 60 min of development time. While researchers have consistently agreed on the relatively comparable performance of traditional/modified ORO with that of PD in visualizing fresh latent fingerprints, the latter remains as the best-known reagent to visualize aged latent fingerprints on porous surfaces   BIB001 . Despite a number of advantages ORO reagent has to offer, the real chemical interactions/mechanisms between those of ORO chemicals with that of constituents of latent fingerprints which has enabled the successful visualization of latent fingerprints are yet to be fully understood.