Ninhydrin Thiohemiketals: Basic Research Towards Improved Fingermark Detection Techniques Employing Nano‐Technology*

Abstract: In the first part of a comprehensive research project towards more efficient application of nano‐technology to fingerprint visualization, we investigated the possibility of more selective binding of gold nanoparticles (NP) to fingerprint material. We synthesized derivatives of ninhydrin and 1,2‐indanedione containing loosely bound thiol groups. In particular: thiohemiketals (THK) of ninhydrin, and thioketals of 1,2‐indanedione were prepared and tested as potential fingerprint reagents. By reacting ninhydrin with various thiols we were able to produce a series of novel THK, bearing the SR group always at C2. Ninhydrin THK reacted with amino acids to produce the expected Ruhemann’s purple, and they also developed latent fingermarks on paper in a similar manner to ninhydrin. Ketals and thioketals derived from 1,2‐indanedione reacted neither with amino acids nor with latent fingermarks. In the second part of the research, the thiols which are formed on the ridges as byproducts of the reaction with amino acids will be tested for their potential as stabilizers for gold NP that will become covalently bound to the fingerprint ridges.     

The Influence of Selected Fingerprint Enhancement Techniques on Forensic DNA Typing of Epithelial Cells Deposited on Porous Surfaces

Fingerprints deposited at crime scene can be a source of DNA. Previous reports on the effects of fingerprint enhancement methods have focused mainly on fingermarks deposited in blood or saliva. Here, we evaluate the effects of fingerprint enhancement methods on fingerprints deposited on porous surfaces. We performed real‐time quantification and STR typing, the results of which indicated that two methods (iodine fuming and 1,2‐indanedione in ethyl acetate enhancement) had no effect on the quantity of DNA isolated and resultant STR alleles when compared to control samples. DNA quantities and allele numbers were lower for samples enhanced with silver nitrate and 1,2‐indanedione in acetic acid when compared to control samples. Based on DNA quantity, quality, and observable stochastic effects, our data indicated that iodine fuming and 1,2‐indanedione in ethyl acetate were the preferred options for the enhancement of fingerprints on porous surfaces.     

Chemical development of latent fingerprints: 1,2-indanedione has come of age

The performance of 1,2-indanedione as a latent fingerprint reagent on some types of paper was found to exceed that of DFO, the leading fluorogenic fingerprint reagent. It even exceeds the performance of the sequence, DFO, followed by ninhydrin. No new prints could be observed when ninhydrin was applied after indanedione. On a large number of actual exhibits (used checks) indanedione developed 46% more identifiable prints than the sequence DFO-ninhydrin. A standard procedure for fingerprint development by indanedione is proposed. Best results are obtained with a 0.2% indanedione solution in HFE7100 solvent containing 7% ethyl acetate, but no acetic acid. It can be recommended to start using 1,2-indanedione, which is already commercially available, in actual fingerprint casework.     

Latent Fingerprint Development on Thermal Paper Using Traditional Ninhydrin and 1,2‐indanedione

Thermal paper poses a significant challenge to latent print development as it tends to change color when traditional fingerprint development formulations are applied to it. In this study, the optimal components of ninhydrin, 1,2‐indanedione, 1,8‐diazafluoren‐9‐one (DFO), and 5‐methylthioninhydrin (5‐MTN) for yielding clear fingerprints on thermal paper were determined by systematically adjusting the relative amounts of the reagents, polar solvents, and the nonpolar diluent petroleum ether, followed by validation on text‐printed thermal paper. Specifically, 3.0% ethyl acetate as the polar solvent in petroleum ether was found to be the optimal combination; the optimal dilution ratios of ninhydrin, DFO, and 5‐MTN original solutions with petroleum ether were 1 to 2, 11, and 7, respectively. The optimal concentration of 1,2‐indanedione in petroleum ether was 0.125 g/L, with a string of 0.5% ethyl acetate in petroleum ether.     

纸张上潜在手印三种前处理方法对DNA检验的影响

目的通过比较常见纸张上潜在手印盲提法与显现后精准提取法的接触DNA检出率,探讨常见纸张上接触DNA前处理的优选方案。方法比较五种常见纸张上使用盲提法和显现潜在手印(茚二酮显现法、茚三酮熏显法)后精准提取法采集的接触DNA样本检出率。结果粗糙日历纸盲提的接触DNA检出率为17.8%,通过茚二酮法和茚三酮法显现的潜在手印所提取的DNA检出率分别为75.6%、77.8%;光滑日历纸三种方法所提取的接触DNA检出率为4.4%、11.1%、11.1%;A4复印纸三种方法接触DNA检出率为20%、37.8%、66.7%;牛皮纸三种方法接触DNA检出率为20%、68.9%、64.4%;快递纸袋的三种方法接触DNA检出率为2.2%、6.7%、46.7%。结论不同纸张上潜在手印经显现后接触DNA检出率不同,通过茚二酮或茚三酮显示潜在手印后精准提取DNA的前处理方法相较于盲提法的接触DNA检出率高。实战中可应用此类方法同时获得手印与DNA分型,以有效提高证据力。     

Development of a GC-MS method for the simultaneous analysis of latent fingerprint components

Latent fingerprint residue is a complex mixture of organic and inorganic compounds. A full understanding of the composition of this mixture and how it changes after deposition is lacking. Three solvent systems were compared for the simultaneous extraction and derivatization with ethyl chloroformate of selected amino and fatty acids from a nonporous substrate (Mylar for subsequent analysis by gas chromatography-mass spectrometry. A solvent system comprised of sodium hydroxide, ethanol, and pyridine was found to be the most effective. This method was applied to the analysis of latent fingerprint residue deposited on Mylar and preliminary data are presented. Twelve amino acids (e.g., serine, glycine, and aspartic acid) and 10 fatty acids (e.g., tetradecanoic, hexadecanoic, and octadecanoic acids) were identified. The potential application of this method to further the understanding of latent fingerprint chemistry has been demonstrated.     

Latent Fingermark Development on Thermal Paper using 1,2‐Indanedione/Zinc and Polyvinylpyrrolidone,

Polyvinylpyrrolidone (PVP) has been used in combination with 1,2‐indanedione (1,2‐IND) and ZnCl₂ (Zn) to develop latent fingermarks. The results show that the optimal ratio of 1,2‐IND/Zn:PVP is 1.0:0.4 (the concentration of PVP is 8%) for developing fingermark. The developed formulation was tested on the surfaces of 12 kinds of thermal papers. The variation in the fingermark development efficiency was observed within the same and among different kinds of thermal papers. The fingermark development efficiency was mostly better on the thermally sensitive surface compared to the thermally nonsensitive surface. However, similar or even better development was observed from a few thermally nonsensitive surfaces. The present method has shown better efficiency compared to the three other proposed methods on the thermally sensitive surface. In contrast, the present method was proven not the best for the thermally nonsensitive surface.     

Thermal degradation analysis of amino acids in fingerprint residue by pyrolysis GC-MS to develop new latent fingerprint developing reagents

Conventional development of latent fingerprints is compromised when the prints are decomposed by extreme temperatures, such as those encountered when a weapon cartridge is fired, an improvised explosive device is detonated, and/or in arson cases. Understanding how these extreme temperatures alter the chemical and physical properties of latent fingerprint residue could aid in the discovery of a reagent that could effectively develop these decomposed fingerprints. To mimic scenarios where fingerprints may be exposed to high heat conditions, standards of the five most abundant amino acids in fingerprint residue as well as extracted fingerprint residue were pyrolized under controlled conditions. Compounds identified as pyrolytic decomposition products were 3,6-dimethylpiperazine-2,5-dione (from alanine), maleimide, and 2,5-furandione (from aspartic acid). The pyrograms and selected ion traces show these products to hold promise as indicators of decomposed fingerprint residues and, therefore, may serve as good candidate substrates for a developing reagent.     

Aging studies on fingerprint residues using thin-layer and high performance liquid chromatography

The chemical substances of perspiration found in latent fingerprint residue may hold the key for dating latent fingerprints. To study the chemical transformations of these components as a function of time and environment, fingerprint residues from four males and four females were analysed by thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC). Three major and two or three minor components were detected by both methods and the variation in the quantity of the major components with time was observed.     

Fingerprints' third dimension: the depth and shape of fingerprints penetration into paper--cross section examination by fluorescence microscopy

In an attempt to maximize the yield of latent fingerprints from paper items, we conducted a study of a fundamental process between fingerprint deposits and paper. Fingerprint ridges have been observed in the cross section of paper by fluorescence microscopy. It was possible to see, for the first time, how residue from fingerprint ridges is embedded in paper. Undeveloped, latent fingerprints, as well as latent prints developed by the two fluorogenic reagents, DFO and 1,2-indanedione, have been examined. The shape and depth of penetration of fingerprints vary with different types of paper. An inverse relationship between the smoothness of the paper and the penetration depth was observed: higher smoothness values result in lower depths of penetration. High quality prints appear to correlate with an optimal penetration depth-between 40 and 60 microns.     

胺端基型CdS／PAMAM潜在显现指印的应用

目的探索一种新型纳米荧光材料的制备方法及其在潜在指印显现方面的应用前景。方法以聚酰胺-胺（PAMAM）树形分子为模板，原位合成CdS纳米簇。并使用荧光光谱法对产物进行表征：应用这种新型荧光材料对多种客体表面、不同陈旧程度的潜在指印进行显现．并将显现结果与传统荧光染料进行比对。结果该荧光材料在365nm紫外光激发下可以发出很强的可见荧光：与传统的荧光染料相比。-NH2端基型CdS／PA—MAM可以同指印残留物进行靶向结合．其荧光强度高、背景干扰小，指印纹线与客体反差大。结论-NH2端基型CdS／PAMAM可以有效地显出非渗透性客体表面的潜在指EP。     

The effect of zinc chloride, humidity and the substrate on the reaction of 1,2-indanedione-zinc with amino acids in latent fingermark secretions

Anecdotal evidence from forensic practitioners and studies conducted under controlled conditions have indicated that the reaction between 1,2-indanedione and the amino acids present in latent fingermark deposits is highly susceptible to ambient humidity. The addition of catalytic amounts of zinc chloride to the 1,2-indanedione working solution--usually in the order of 1:25 to 1:4 molar ratio (indanedione:zinc)--significantly improves the colour and luminescence of fingermarks treated under dry conditions but appears to have a negligible effect on fingermarks treated in humid environments. The results presented in this paper confirmed that zinc(II) ions added to the 1,2-indanedione working solution act as a Lewis acid catalyst, stabilising a key intermediate during a rate-limiting hydrolysis step. Furthermore, studying the reaction using a chromatography-grade cellulose substrate method previously reported confirmed that cellulose substrates play a major role in facilitating the indanedione-amino acid reaction by acting as a surface catalyst in the early stages of the reaction and by directing the formation of the desired luminescent product (Joullié's Pink).     

Photo‐ and Thermal‐Degradation Studies of Select Eccrine Fingerprint Constituents

Abstract: Photo‐ and thermal‐degradation studies on eccrine fingerprint components are presented herein. Dilute distinct solutions of urea, lactic acid, and seven amino acids were deposited on steel coupons and Teflon^® disks, exposed to artificial sunlight or heat, extracted, and analyzed. This aim of this study was to determine whether the investigated eccrine components, previously determined to be Raman active for a parallel study, experienced photo‐ or thermally induced degradation, and if so, to determine the rate and identify any detectable products. Neither the amino acids nor urea exhibited photo‐degradation; however, when heated for a period of three minutes, the onset of thermal‐degradation was initiated at 100°C for the amino acids and 100°C for urea. Lactic acid, the major polymerization initiator of superglue fuming, showed photochemical and thermal‐degradation. These results could be used for future development of new latent fingerprint visualization methods, especially when lactic acid is degraded.     

The effect of 1,2-indanedione,a latent fingerprint reagent on subsequent DNA profiling

The compound 1,2-indanedione was recently introduced in our laboratory as an operational reagent for developing latent fingerprints on porous surfaces. As part of the reagent implementation, a study was carried out in order to determine whether either of the two operational 1,2-indanediones formulations interferes with further DNA profiling. Both formulations are based on HFE7100 solvent. One is acidic and the other neutral. In a controlled experiment, known donors attached stamps to envelopes by licking them. The stamped envelopes were initially treated with either one indanedione formulation or the other, and DNA was then extracted for STR typing. No differences were observed between the STR profiles obtained from treated and untreated stamps and envelopes, indicating that 1,2-indanedione does not adversely affect the extraction and subsequent amplification of the STRs examined. However, preliminary results indicate that potential DNA analysis depends on the time interval between the indanedione treatment and DNA extraction as no DNA can be recovered six days following treatment. For this reason, it is strongly recommended to extract DNA from treated items of evidence as soon as possible after indanedione treatment.     

Toward multidimensional information: A derivatization-free UHPLC-QqQ MS/MS method for amino acid components of fingerprint

The analysis of fingerprint chemical composition is a meaningful way to excavate the multidimensional information of fingerprint, including the donor profiling information and the age of a fingerprint, which broadens the evidential values of fingerprint, especially for the partial and distorted fingerprint. But the research remains still in the pilot phases or is ongoing. Amino acids are the dominant organic substances in latent sweat fingerprint and influenced by many donor factors. Hence, their content reflects personal information of donors. Forensic science will be revolutionized if suspects can be individualized by their amino acid content. The diverse nature, distinct physicochemical properties, and ultra-micro levels of amino acids present in fingerprints make it hard to detect. A high sensitivity method for detecting and quantifying multiple amino acid components is required. UHPLC-QqQ MS/MS offers high sensitivity, high separation, simultaneous multicomponents detection, and no derivatization, making it an ideal method for detecting and analyzing amino acids in fingerprints. Therefore, in this study, we propose and validate an efficient UHPLC-QqQ MS/MS method for the extraction and analysis of 13 amino acids from fingerprint. We compared the results of amino acids of 10 different substrates and found that the inherent amino acids in most porous substrates would have been extracted along with the fingerprint amino acids, making them unsuitable for quantitative amino acid analysis. Instead, plastic sheets are ideal substrates for laboratory studies. Then, extensive experiments were conducted among 30 donors for multidimensional information analysis. The type of samples analyzed were eccrine-rich fingerprints. A Binary Logistic Regression (BLR) model was developed, and the female and male donors were successfully differentiated by amino acids in fingerprints. Two other mathematical models were also developed to verify the accuracy, and all three different mathematical models were able to identify donors of different genders with over 90% accuracy. This demonstrates that amino acids have the potential to provide more information for donors as metabolic markers. In the future, we will conduct a series of experiments to analyze more multidimensional information for individual identification by amino acid content in the fingerprint.     

Diimide-enhanced fingerprint detection with photoluminescent CdS/dendrimer nanocomposites

The chemical development of latent fingerprints by nanocomposites that involve photoluminescent cadmium sulfide nanoparticle aggregates with Starburst dendrimer is demonstrated. The dendrimer bonds to fingerprint residue via its terminal functional groups. When these are amino groups (generation 4 dendrimer), the binding is enhanced by fingerprint pre-treatment with diimide. The diimide converts carboxylic acid moieties of the fingerprint residue to esters that then react with the dendrimer amino groups to form amide linkages. The cadmium sulfide/generation 4 dendrimer development of fingerprints is enhanced by elevated temperature also. Finally, fingerprint development with carboxylate-functionalized cadmium sulfide/generation 3.5 dendrimer nanocomposites is examined. Here, diimide treatment of the dendrimer itself aids the subsequent fingerprint labeling, which involves amino acid of the figerprint residue. Nanocomposite fingerprint detection is compatible with time-resolved imaging for background fluorescence elimination.     

Visualization of latent fingerprints using fluorescence lifetime imaging on paper emitting strong fluorescence

Latent fingerprints were successfully visualized using fluorescence lifetime imaging (FLIM) on paper which emits strong fluorescence with a lifetime close to that of fingerprints and thus from which it is difficult for time-resolved spectroscopy to visualize fingerprints. Latent fingerprint samples on paper were excited using a 450 nm or 532 nm nanosecond pulsed-laser, and time-resolved fluorescence images were obtained at a delay time of 6–16 ns in intervals of 1 ns, to the excitation pulse. The excitation beam was expanded using a lens, and the fluorescence from the fingerprints was captured using an intensified CCD camera. Because of the large fluorescence intensity of the background paper of approximately two to four orders of magnitude larger than that of the fingerprint, the fingerprint was not visualized on each fluorescence image by time-resolved spectroscopy. However, the fingerprint was visualized in a FLIM image constructed using a series of the fluorescence images for the case with the fluorescence intensity of the background paper being four orders of magnitude larger than that of the fingerprint. The difference in fluorescence lifetime in the FLIM image of the visualized fingerprint and background paper was in the order of 0.1 ns, which was an order of magnitude smaller than the inherent fluorescence lifetime of a few nanoseconds for the fingerprints and paper. It was demonstrated that, at a background fluorescence intensity with a certain order of magnitude larger than that of fingerprints, FLIM has the potential to visualize latent fingerprints which cannot be visualized by time-resolved spectroscopy.     

Optimization and initial evaluation of 1,2-indandione as a reagent for fingerprint detection

1,2-Indandione has been used to develop fluorescent fingerprints on porous materials such as paper. The compound reacts with amino acid residues to produce highly fluorescent fingerprint ridges. An optimized formulation and treatment protocol for using the reagent is presented here. The reagent is applied as a solution in HFE7100 containing acetic acid and ethyl acetate. Treated articles are heated at 100 degrees C for 10 min at ambient humidity and stored in the dark before recording the fingerprints using fluorescence photography or digital imaging. Photodecomposition of the fluorescent fingerprints has been observed. Storage in the dark reduces degradation, extending the lifetime of the fingerprints. Other chemical methods to stabilize the fingerprints proved unsuccessful. Comparisons of the performance of 1,2-indandione with DFO in CFC113 performed on a limited range of substrates indicated that the reagent might be an effective method for the development of latent fingerprints despite the new reagent producing less intense fluorescence.     

卫生纸上汗潜手印显现方法比较研究

目的通过比较实验来探寻卫生纸上汗潜手印的最佳显现方法,为实际工作提供指导性建议。方法选择市面上常见的四种卫生纸,在每种卫生纸上制作汗潜指印实验样本,分别将茚三酮溶液浸泡法与茚二酮溶液浸泡法、茚二酮溶液浸泡法与茚二酮溶液超声雾化法、茚二酮溶液超声雾化法与(对)-二甲(替)氨基肉桂醛(DMAC)显现纸冷熏法、茚二酮溶液浸泡法与红外加热显现法、茚二酮溶液超声雾化后加热显现法与室温显现法进行两两比较,分析显现效果。结果茚二酮显现的灵敏度和质量均优于其他几种方法,特别是超声雾化后室温显现,既能很好地显现手印又不影响后期的DNA检验。结论采取茚二酮超声雾化室温条件显现方法显现卫生纸上的汗潜手印具有显现效果好、设备条件要求低、操作性强的特点,在实际案件中可以借鉴应用。