Yaron Cohen

Genipin--a novel fingerprint reagent with colorimetric and fluorogenic activity.

Genipin, the hydrolytic product of geniposide, which is extracted from gardenia fruit, shows good potential as a fingerprint reagent. It develops latent fingerprints on paper as blue impressions with good contrast and resolution. Even very faint impressions that are barely visible in ambient light will fluoresce brightly upon illumination at ca. 590 nm and are best viewed with a barrier filter above 630 nm. Potential advantages of genipin are the combination of colorimetric and fluorogenic activity in one reagent as well as its being a safe and environmentally friendly natural product.

Genipin, a Novel Fingerprint Reagent With Colorimetric and Fluorogenic Activity, Part II: Optimization, Scope and Limitations

Genipin, a hydrolytic product of geniposide extracted from gardenia fruit, was thoroughly studied as a potential fingerprint reagent, and optimal conditions for fingerprint development have been determined. Latent fingerprints on paper items that have been treated with a non-ink running formulation containing 0.17% of the reagent, showed up as both colored and fluorescent images. On brown wrapping paper and on papers with highly luminescent backgrounds, genipin developed more visible and clearer prints than did classical reagents such as ninhydrin or DFO. Another potential advantage of genipin is that it is totally harmless and an environmentally friendly reagent.

Fingerprint Reagents with Dual Action: Color and Fluorescence

ABSTRACT: We define “dual fingerprint reagents” as chemical formulations that produce with latent fingerprints in one stage impressions that are both colored and fluorescent. Solutions containing ninhydrin and group IIb metal salts appear to be true dual reagents. Application of these formulations to latent fingerprints on paper is as efficient as the two‐step process beginning with ninhydrin and followed by treatment with metal salt. In the color mode, fingerprint detectability with the two ninhydrin–metal salt reagents (one with zinc chloride and the other with cadmium chloride) is comparable with that of ninhydrin itself, in spite of the difference in color. The sensitivity is significantly higher in the fluorescence mode. To view the latent impressions the exhibits are treated with ninhydrin–metal salt reagents and observed under white light illumination and under fluorescence conditions. Cooling to liquid nitrogen temperature enhances the fluorescence considerably. In the shorter wavelength domain, ninhydrin–metal salt reagents exhibit higher sensitivity than the recently reported dual reagent, genipin. The latter is advantageous, however, in the longer wavelength domain, on paper items with strong self‐fluorescence, such as brown wrapping paper or paper printed with fluorescent ink. Upon reduction of the ninhydrin concentration 10‐fold, ninhydrin–metal salt formulations become purely fluorogenic reagents; no color is noticed but the fluorescence is as intense as with concentrated solutions. Working at lower concentrations is an advantage from ecological and economical viewpoints.

Dual Fingerprint Reagents with Enhanced Sensitivity: 5‐Methoxy‐ and 5‐Methylthioninhydrin

Abstract:  “Dual fingerprint reagents” are chemical formulations which produce with latent fingerprints in a single step, impressions that are both colored and fluorescent. Pre‐mixed solutions of the two commercially available ninhydrin analogues, 5‐methoxyninhydrin (MN) and 5‐methylthioninhydrin (MTN) with zinc or cadmium salts, are true dual reagents. They are much more sensitive than the parent dual reagent, ninhydrin/ZnCl2. The main advantage of the new formulations is that they can be used at room temperature, with no need to cool the sample to liquid nitrogen temperature. At 0.05% concentration, which is 10‐fold lower than the common ninhydrin working solution, MTN/ZnCl2 is as sensitive as DFO in the fluorescence mode and considerably more sensitive in the color mode. MTN is also slightly cheaper than DFO.

DNA profiling from heroin street dose packages.

ABSTRACT: A large amount of heroin street doses are seized and examined for drug content by the Israel police. These are generally wrapped in heat‐sealed plastic. Occasionally it is possible to visualize latent fingerprints on the plastic wrap itself, but the small size of the plastic item and the sealing process makes the success rate very low. In this study, the possibility of extracting and profiling DNA from the burnt edge of the plastic wrap was investigated. The idea was based on the assumption that epithelial cells might be trapped during the sealing process. The results show that there are sufficient quantities of DNA deposited at the “amorphic” burnt edges of sealed street doses for DNA profiling to be carried out. A controlled experiment using a known donor was performed. This subject carried out sealing of “street drug” packages and consequent DNA extractions were performed to show that known DNA profiles could be recovered from such packages, as a result of handling by the “packer.”“Square‐like” burnt edges did not yield DNA profiles, probably because of differences in the sealing process. It was also shown that DNA could be recovered from the plastic wrap itself and not only from the amorphic burnt edges. As heroin dealers and drug users are often involved in other crimes and run‐ins with the law, the effective extraction and addition of their DNA profiles from such items of evidence to the newly established DNA database in Israel provides new avenues in the continued fight against crime and drug traffickers.

Photoelectrochemistry of colloidal Cu2O nanocrystal layers: the role of interfacial chemistry

Colloidal Cu2O nanocrystal layers on Au substrates are studied as photocathodes in the context of solar electrochemical water-splitting applications. The photoelectrochemical response of the nanocrystal layers in aqueous solutions under simulated solar light conditions depends strongly on the interfacial chemistry and its impact on the transport of the charge carriers across the Au/nanocrystals/liquid interfaces. The Cu2O nanocrystals are originally stabilized with octadecylamine ligands. While octadecylamine is an efficient capping ligand for the colloidal synthesis of highly uniform nanocrystals, its low conductivity impedes the charge transport across the Au/nanocrystals/liquid interfaces. The photoresponse of the nanocrystals can be enhanced by the replacement of the octadecylamine ligands with more conductive and hydrophilic molecules, such as 1,2-ethanedithiol and benzene-1,4-dithiol. The conductivity and hydrophilicity of the ligands were investigated and found to be important for the photo-induced charge separation and transport across the Au/nanocrystals/liquid interfaces and transfer to the liquid. Furthermore, the interfacial energetics of the Au/nanocrystals/liquid junction and the resulting photoresponse of the Cu2O nanocrystal photocathode can be optimized by rational design of the exchanging ligands with desired functionalities and dipoles at the specific interfaces. A comparison of the photoresponse of Cu2O nanocrystal layers to that of electrodeposited Cu2O layers shows that the former is, yet, lower, due to the apparent low conductivity of the ligands. However, the nanocrystal organic ligands impart high hydrophobicity, which prevents the contact of the aqueous solution with the nanocrystals and improves their stability against photocorrosion and reduction to Cu0, as confirmed by X-ray diffraction measurements.

Development of Latent Fingermarks from Rocks and Stones

Since the beginning of recorded history, stones have been used in the commission of crimes due to their widespread availability. Stones can be used as a lethal weapon that sometimes might be the only evidence in a serious case. The common perception, even in professional fingermark circles, is that stones do not yield identifiable latent fingermarks. The authors of this research paper examined the feasibility of developing fingermarks from seven types of stones using three latent fingermark techniques: magnetic powder, cyanoacrylate fuming, and ninhydrin. The paper will demonstrate that by classifying stones and rocks according to their natural properties (porosity, permeability, and the nature of surface area), even application of the simplest development techniques can produce good results. In conclusion, chert and limestone yielded the most qualitative and quantitative results using magnetic powder. The time factor is also important in recovering latent fingermarks on stones and rocks.

Classification Improvements in Automated Gunshot Residue (GSR) Scans

Classification of particles as gunshot residues (GSRs) is conducted using a semiautomatic approach in which the system first classifies particles based on an automatic elemental analysis, and then, examiners manually analyze particles having compositions which are characteristic of or consistent with GSRs. Analyzing all the particles in the second stage is time consuming with many particles classified by the initial automated system as being potentially GSRs excluded as such by the forensic examiner. In this paper, a new algorithm is developed to improve the initial classification step. The algorithm is based on a binary tree that was trained on almost 16,000 particles from 43 stubs used to sample hands of suspects. The classification algorithm was tested on 5,900 particles from 23 independent stubs and performed very well in terms of false positive and false negative rates. A routine use of the new algorithm can reduce significantly the analysis time of GSRs.