Chemical Visualization of Sweat Pores in Fingerprints Using GO-Enhanced TOF-SIMS

Application of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) in forensic science - A review

The paper presents the possibilities of using the ToF-SIMS technique in the examination of a range of samples as forensic evidence. These include the analysis of documents, the examination of writing media, the analysis of crossing lines, the analysis of cosmetics, hair analysis, the examination of automobile paints, and the analysis of fingerprints and their contamination with exogenous substances. The advantages and disadvantages of this method were analysed with reference to the information that any forensic investigator would wish to obtain when examining highly significant evidence.

Reactive Gas Cluster Ion Beams for Enhanced Drug Analysis by Secondary Ion Mass Spectrometry

In this study, we investigate the formation and composition of Gas Cluster Ion Beams (GCIBs) and their application in Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis. We focus on altering the carrier gas composition, leading to the formation of (Ar/CO2)n or (H2O)n GCIBs. Our results demonstrate that the addition of a reactive species (CO2) to water GCIBs significantly enhances the secondary ion yield of small pharmaceutical compounds in the positive ion mode. In negative ion mode, the addition of CO2 resulted in either a positive enhancement or no effect, depending on the sample. However, an excess of CO2 in the carrier gas leads to the formation of carbon dioxide clusters, resulting in reduced yields compared to that of water cluster beams. Cluster size also plays a crucial role in overall yields. In a simple two-drug system, CO2-doped water clusters prove effective in mitigating matrix effects in positive ion mode compared to pure water cluster, while in negative ion mode, this effect is limited. These clusters are also applied to the analysis of drugs in a biological matrix, leading to more quantitative measurements as shown by a better fitting calibration curve. Overall, the doping of water clusters with small amounts of a reactive gas demonstrates promising benefits for higher sensitivity, higher resolution molecular analysis, and imaging using ToF-SIMS. The effectiveness of these reactive cluster beams varies depending on the experimental parameters and sample type.

Multi-spectroscopic characterization of organic salt components in medicinal plant

The characterization of structure of organic salts in complex mixtures has been a difficult problem in analytical chemistry. In the analysis of Scutellariae Radix (SR), the pharmacopoeia of many countries stipulates that the quality control component is baicalin (≥9% by high performance liquid chromatography (HPLC)). The component with highest response in SR was also baicalin detected by liquid chromatography-mass spectrometry (LC-MS). However, in the attenuated total reflection Fourier transform infrared spectroscopy, the carbonyl peak of glucuronic acid of baicalin did not appear in SR. The results of element analysis, time of flight secondary ion mass spectrometry, matrix assisted laser desorption ionization mass spectrometry and solid-state nuclear magnetic resonance all supported the existence of baicalin magnesium salt. Based on this, this study proposes an analysis strategy guided by infrared spectroscopy and combined with multi-spectroscopy techniques to analyze the structure of organic salt components in medicinal plant. It is meaningful for the research of mechanisms, development of new drugs, and quality control.

Electrochromic visualization of latent fingermarks deposited on nonconductive surfaces

Electrochromic visualization of latent fingermarks has already been achieved on conducting surfaces such as stainless steel. However, their enhancement on non-conducting surfaces such as glass via electrochromism has not been reported. Considering the non-conductive nature of substrates, a layer of gold was introduced to the fingermark-bearing surfaces, in which gold was used as the cathodes to assemble electrochromic devices for visualization. The contact between gold nanoparticles of the as-obtained conducting layer in the fingermark region should be affected by the height difference within the fingermark, leading to conductivity differences, which give rise to coloration differences in electrochromic devices. It is demonstrated that 1,1'-dibenzyl-4,4'-bipyridinium dichloride can be used as the electrochromic chromophore for the visualization of latent fingermarks deposited on nonconducting surfaces, and the primary and secondary characteristic information can be obtained. The electrochromic visualization herein solves the problem of electrochromically enhancing latent fingermarks on non-conducting surfaces.

Desorption Electrospray Ionization Mass Spectrometry Imaging of Powder-Treated Fingermarks on Forensic Gelatin Lifters and its Application for Separating Overlapping Fingermarks

Fingermarks are frequently collected at crime scenes by using gelatin lifters for preservation and transport of the marks to a forensic laboratory for inspection. The gelatin lifters preserve both the imprint of the fingermark pattern necessary for identification purposes and the chemical residue of the mark potentially useful for profiling the person who left the fingermark. The fingermark patterns are traditionally recorded using photography/optical imaging, but methods for chemical analysis of fingermark residues on gelatin lifters are scarce. Here we report the first method for the chemical analysis of fingermarks on gelatin lifters using desorption electrospray ionization mass spectrometry (DESI-MS) imaging. The imaging can be done directly on the gelatin support without any sample preparation, supporting immediate operational use of the method for fingermarks collected at crime scenes. Operational use of the method is further supported by successful chemical imaging of fingermarks enhanced by traditional dusting with forensic powders and lifted off different surfaces (glass, stainless steel, painted aluminum, polystyrene, cardboard, and plastic) as well as fingermarks lifted multiple times. We also demonstrate that the present method can be used to visually separate natural overlapping powder-treated fingermarks, and the chemical composition of the fingermarks can be analyzed on the gelatin support by DESI-MS/MS. The presented method has potential for integration into the traditional workflow for fingermark analysis, and will allow more fingermarks collected at crime scenes to be evaluated both visually and chemically.

Hydrochromic and piezochromic dual-responsive optical film derived from poloxamer and ethyl cellulose for visual fingerprints identification

Developing new materials that could identify fingerprint using the naked eye and observe the level 3 microscopic details is challenging. Here, we designed a novel hydrochromic and piezochromic dual-responsive optical film, which achieved the visual transparency transition. The performances of hydrochromic and piezochromic responses from high transparency to opaque whiteness were attributed to the introduction of poloxamer. The hygroscopic swelling of the disordered micelles led to light scattering, causing the hydrochromic response. The piezochromic response may be ascribed to the microcracks in the fragments of poloxamer crystals, which changed the refractive index of light. The fascinating combination of hydrochromic and piezochromic response was effectively applied in fingerprint identification. Hydrochromic response accurately recognized sweat pores, and piezochromic response could gradually reveal the ridges and valleys according to the different color of imprinted fingerprints. The film could identify fake fingerprints based on the differences in sweat pores between fake fingerprints and living fingers. More importantly, the film could easily detected not only the clear ridges but also the detailed sweat pores using the naked eye, indicating that the film has profound research significance in fingerprint analysis and liveness fingerprint detection.

TOF-SIMS study of latent fingerprints on challenging substrates with the aid of transfer films

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been applied in forensic science for fingerprint detection. However, due to limitations of the instrument, it is not always possible to directly sample fingerprints on certain substrates. In this report, we indirectly sampled fingerprints using transfer films. First, we optimized the experimental conditions and identified transfer films with better results. We then explored the feasibility of revealing fingerprints after transfer and successfully transferred and revealed the detailed features of fingerprints on several common objects that could not be directly sampled. Fingerprints transferred from smooth surfaces yield clearer feature details in ion images. Additionally, we analyzed the substances in the transferred fingerprints and detected components of morphine and MDMA(3,4-methylenedioxy-n-methylamphetamine). By combining feature details with identified chemical components, the identity of a person can be determined, linking suspects to the crime scene. This work provides a new approach for sample introduction in instrumental analysis, enabling TOF-SIMS to be applied in more scenarios.

Molecular detection of per- and polyfluoroalkyl substances in water using time-of-flight secondary ion mass spectrometry

Detection of per- and polyfluoroalkyl substances (PFASs) is crucial in environmental mitigation and remediation of these persistent pollutants. We demonstrate that time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a viable technique to analyze and identify these substances at parts per trillion (ppt) level in real field samples without complicated sample preparation due to its superior surface sensitivity. Several representative PFAS compounds, such as perfluorooctanesulfonic acid (PFOS), perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluoheptanoic acid (PFHpA), and perfluorononanoic acid (PFNA), and real-world groundwater samples collected from monitoring wells installed around at a municipal wastewater treatment plant located in Southern California were analyzed in this work. ToF-SIMS spectral comparison depicts sensitive identification of pseudo-molecular ions, characteristic of reference PFASs. Additionally, principal component analysis (PCA) shows clear discrimination among real samples and reference compounds. Our results show that characteristic molecular ion and fragments peaks can be used to identify PFASs. Furthermore, SIMS two-dimensional (2D) images directly exhibit the distribution of perfluorocarboxylic acid (PFCA) and PFOS in simulated mixtures and real wastewater samples. Such findings indicate that ToF-SIMS is useable to determine PFAS compounds in complex environmental water samples. In conclusion, ToF-SIMS provides simple sample preparation and high sensitivity in mass spectral imaging, offering an alternative solution for environmental forensic analysis of PFASs in wastewater in the future.

Useless or used less? Poroscopy: The evidence of sweat pores

Poroscopy is the study of sweat pores present on the papillary ridges of the skin. This review paper aims to examine existing literature on poroscopy so that its relevance as a tool in personal identification can be established. Moreover, this paper aims to expound the various aspects of sweat pores as well as, highlight the contribution of poroscopy in latent, partial, and automated fingerprint matching. The relationship between sexual dimorphism, age, and sweat pores, effect of development technique and nature of surface on pore details, and use of sweat pores for liveness detection in biometric systems has also been explored. A review of all potentially relevant articles was conducted wherein, the non-relevant papers were excluded by screening their titles and abstracts following which, full-text review of all articles that met the inclusion criteria was carried out. The authors concluded that sweat pores present additional distinctive information for facilitating personal identification when used along with level 2 details. Furthermore, out of the various pore parameters namely, number, shape, size, inter-distance, position, and type, pore inter-distance was found to be most reliable.

Wet nitrocellulose membrane for the level 3 feature visualization of various latent fingerprints and gender determination

A facile and high-resolution enhancement of latent fingerprints (LFPs) has been developed by using a wet nitrocellulose (NC) membrane as a matrix under natural light. A clear fingerprint pattern was presented on the membrane after a fingertip touch owing to the difference in light transmittance between the ridge residues and the wet-NC-membrane background. Compared with conventional methods, this protocol can provide a higher resolution fingerprint image to extract level 3 details accurately. It is also compatible with commonly used fingerprint visualization techniques (magnetic ferric oxide powder and AgNO₃. The modified membrane could be more general to realize the high-resolution visualization of LFP transferred from various substrates, even independent of light projection. Due to the excellent feasibility and reproducibility of level 3 details extracted by the wet NC membrane, the frequency distribution of the distance between adjacent sweat pores (FDDasp) could be used to effectively distinguish the fragmentary fingerprints. Finally, the level 3 features of LFPs from females and males were conveniently extracted by the wet-NC-membrane method for gender identification. The statistical results indicated that females had a higher average sweat pore density (115/9 mm²) than males (84/9 mm²). Taken together, this approach provided a high-resolution, reproducible, and accurate imaging of LFPs, which shows great promise for forensic information analysis.

A sweat-responsive covalent organic framework film for material-based liveness detection and sweat pore analysis

Covalent organic frameworks have shown considerable application potential and exceptional properties in the construction of stimulus-responsive materials. Here, we designed a sweat-responsive covalent organic framework film for material-based fingerprint liveness detection. When exposed to human sweat, the COF_TPDA-TFPy film can transform from yellow to red. The COF_TPDA-TFPy film, when touched by living fingers, can produce the naked-eye-identified fingerprint pattern through the sweat-induced color change, while artificial fake fingerprints cannot. This technique, which we named material-based liveness detection, can thus intuitively discern living fingers from fake fingerprints with a 100% accuracy rate. Additionally, the distribution of sweat pores on human skin can also be collected and analyzed by shortening the contact time. By merely washing them with ethanol, all the samples can be utilized again. This work inventively accomplished material-based liveness detection and naked-eye-identified sweat pore analysis and highlighted their potential for use in clinical research and personal identification.

New Horizons for Estimating the Time Since Deposition of Fingermarks: Combining Label-Free Physical Visualization and Electrochemical Characterization

The time since deposition (TSD) of latent fingermarks (LFMs) serves as "witnesses" for crime scene reconstructions. Nevertheless, existing TSD prediction approaches focused on either physical or chemical aging parameters leading to inaccurate estimation. A novel label-free protocol has been developed, where both physical ridge patterns and lipid oxide (LipOx) degradation kinetics are realized using optical microscopy and scanning electrochemical microscopy (SECM) and combined for TSD prediction. Specifically, the surface interrogation (SI)-SECM titration was utilized to monitor the LipOx degradation in LFM arrays aligned by hole array masks, through which we derived the LipOx degradation function. After establishing the relationship between several titration parameters and titrated area by experimental and numerical simulation methods, the titrated area could be reasonably estimated and subsequently used to calculate the surface coverage of LipOx. Results demonstrated that the tip transient revealed the LipOx coverage of deposited LFMs. Notably, LipOx coverage was found to increase during the first day and then decrease over time, whose degradation rate was susceptible to light. Thus, TSD candidates of an LFM could be limited to two values through the established function. Due to the nonmonotonic trend of LipOx aging, a physical parameter "the gray value ratio (GVR) of furrows to ridges" was proposed to exclude irrelevant TSD through support vector machine (SVM) classification. Ultimately, we predicted TSDs of seven LFMs with estimation errors of 2.2-26.8%. Overall, our strategy, with the outperformed capability of gleaning physical and electrochemical information on LFMs, can provide a truly label-free way of studying LFMs and hold great promise for multidimensional fingerprint information analysis.

Recent Progress in Visualization and Analysis of Fingerprint Level 3 Features

Fingerprints provide sufficient and reliable discriminative characteristics which have been considered one of the most robust evidence for individualization. The limitation of current minutiae-based fingerprint technology seems to be solved with the development of level 3 features since they can offer additional information for problematic fingerprint recognition and even donor profiling. So far, tremendous efforts have been devoted to detecting and analysing the third-level details. This review summarizes the advances in level 3 details with an emphasis on their reliability assessment, visualization methods based on physical interaction, residue-response, mass spectrometry and electrochemical techniques, as well as the potentiality for individualization, donor profiling and even other application scenarios. In the end, we also give a personal perspective on the future direction and the remaining challenges in the third-level-detail-related field. We believe that the new exciting progress is expected in the development of level 3 detail detection and analysis with continued interest and attention to this field.

Reproducibility and reliability of fingerprint microfeatures: Effect of immersing hand in water at different temperatures

Poroscopy is the specialized study of sweat pores found on the papillary ridges of the skin. However, the science of poroscopy is not being used to its full potential. The present study was conducted with the goal to assess the effect of immersing hand in water at various temperatures i.e., room temperature (20-30 °C), hot temperature (40-50 °C), and cold temperature (0-10 °C), for 1, 5 and 10 min, on the reproducibility of pore microfeatures namely, area, inter-distance, and angle, in an attempt to demonstrate their reliability in fingerprint matching. As far as the authors are aware, no prior research has attempted to evaluate the impact of immersing hand in water, at different temperatures, on the reproducibility of third level details. Statistical analysis of data revealed that pore inter-distance and angle were reproducible in nature thereby, highlighting their significance in fingerprint matching.

Simultaneous determination of 36 hypotensive drugs in fingerprints by ultra performance liquid chromatography-triple quadrupole composite linear ion trap mass spectrometry

指印中蕴含着供体摄入成分等相关信息,通过对其分析可对供体进行特征刻画,从而为案件侦查提供线索,指印分析也可用于药物摄入的定性检测,因此检验指印中的降压药具有重要的实际应用价值。建立了超高效液相色谱-三重四极杆复合线性离子阱质谱(UPLC-Q-TRAP/MS)同时检测指印中36种降压药的方法。前处理方法采用沉淀蛋白法,使用3×3 cm滤纸采集指印,将滤纸剪碎置于2 mL塑料离心管中,加入0.50 mL甲醇,涡旋混合1 min,超声振荡3 min,取出后以12000 r/min离心5 min,取上清液进样分析。采用ACQUITY UPLC^® BEH C18柱(100 mm×3.0 mm, 1.7 μm)分离,以0.01%甲酸水溶液和甲醇作为流动相进行梯度洗脱。质谱分析采用可编程多反应监测-信息关联采集-增强子离子(SMRM-IDA-EPI)扫描方式,在高灵敏度分析的同时进行二级谱库检索,增加定性结果的准确性。36种药物在0.05~50.00 ng/fingerprint范围内线性关系良好,相关系数(r)大于0.99,检出限和定量限分别为0.001~0.045 ng/fingerprint和0.002~0.050 ng/fingerprint,在0.25、2.50、25.00 ng/fingerprint 3个加标水平下的基质效应为79.0%~119.2%,回收率为79.3%~116.2%,日内精密度为0.2%~18.3%,日间精密度为1.6%~19.1%。使用该方法检测了87名高血压患者指印中的降压药,大部分样本中可检出其所服用的药物。该方法操作简单,灵敏度高,选择性好,适用于指印中降压药的筛查检验。

Reproducibility of fingerprint microfeatures

Background

Poroscopy, as a means of personal identification, is largely unexplored. The present study aims at assessing the reproducibility of fingerprint microfeatures namely, pore area, inter-distance, and angle, in fingerprints obtained on two surfaces namely, glass and sticky side of adhesive tape, for a period of ten consecutive days. As far as the authors are aware, no prior research has attempted to evaluate pore parameters on sticky side of adhesive tape.

Methods

Plain-inked fingerprints of the left thumb, right thumb, and right index finger were collected on two surfaces namely, glass and sticky side of adhesive tape (using two methods) for ten consecutive days. Photomicrographs were captured and four pores, lying on the same ridge and having clear well-defined margins, were selected from the central region of each print. These specific sweat pores were used to measure the pore area, inter-distance, and angle using Image Pro® Software. Data were analyzed using Statistical Product and Service Solutions (SPSS) software version 16. One way analysis of variance (ANOVA) was carried out using “area,” “length,” and “angle” as the dependent variables.

Results

Results obtained depict pore area, inter-distance, and angle to be significant (p<0.001), on all 10 days for both the surfaces. In terms of quality, better pore details were depicted by fingerprints obtained on the sticky side of adhesive tape (using procedure (iii), wherein the sticky side of adhesive tape was pressed against the inked thumb of the participant). Furthermore, the pore area was found to be non-reproducible while the pore inter-distance and angle were found to be reliable and reproducible in nature.

Conclusions

Crime scene fingerprints should be first matched with specimen fingerprints on the basis of ridge characteristics. However, on occasions when sufficient number of ridge characteristics are not available for comparison, sweat pores should be employed. This study highlights the reproducibility and reliability of pore inter-distance and angle and encourages their use in fingerprint matching.

Quantitative analysis of 17 hypoglycemic drugs in fingerprints using ultra-high-performance liquid chromatography/tandem hybrid triple quadrupole linear ion trap mass spectrometry

RATIONALE

The objective of this study was to develop, optimize, and validate a method for the determination and quantification of 17 hypoglycemic drugs in fingerprints using ultra-high-performance liquid chromatography/tandem hybrid triple quadrupole linear ion trap mass spectrometry (UHPLC/QTRAP-MS/MS). We also aimed to apply the present method to the fingerprints collected from patients with hyperglycemia.

METHODS

The scheduled multiple reaction monitoring information-dependent acquisition-enhanced product ion (SMRM-IDA-EPI) scanning mode was utilized. The chromatographic system consisted of an Acquity UHPLC® BEH C18 column (3.0 × 100 mm, 1.7 μm) and a mobile phase of 0.01% (v/v) formic acid in water and methanol. Analytes were extracted via a precipitation protein procedure. The method was validated in accordance with the US Food and Drug Administration (FDA) guidance and applied to the analysis of fingerprint deposits from subjects who had taken the drugs.

RESULTS

The limits of detection (LODs) and the lower limits of quantification (LLOQs) of 17 hypoglycemic drugs were 0.001 to 0.020 and 0.002 to 0.050 ng/fingerprint, respectively. The correlation coefficients (r) for the calibration curves were > 0.99 in the range of 0.050-50.000 ng/fingerprint. The matrix effect and recovery of 17 hypoglycemic drugs at three concentrations ranged from 81.1 to 117.3% and 80.0 to 109.6%, respectively. The validation data (intra- and inter-day combined) for accuracy ranged from 85.5 to 117.2%, the CV (%) data were ≤19.7%. All analytes were found to be stable stored in the autosampler (4°C) for 24 h. This validated method was successfully applied to detect hypoglycemic drugs in fingerprints from patients with hyperglycemia.

CONCLUSIONS

A quantification method for hypoglycemic drugs in fingerprints was developed, optimized, and validated. This sensitive method could be used for drug monitoring and providing reference information in forensic investigations.

Nanoscale Three-Dimensional Imaging of Drug Distributions in Single Cells via Laser Desorption Post-Ionization Mass Spectrometry

Exploring the three-dimensional (3D) drug distribution within a single cell at nanoscale resolution with mass spectrometry imaging (MSI) techniques is crucial in cellular biology, yet it remains a great challenge due to limited lateral resolution, detection sensitivities, and reconstruction problems. Herein, a microlensed fiber laser desorption post-ionization time-of-flight mass spectrometer (MLF-LDPI-TOFMS) was developed for the 3D imaging of two anticancer drugs within single cells at a 500 × 500 × 500 nm³ voxel resolution. Nanoscale desorption was obtained with a microlensed fiber (MLF), and a 157 nm post-ionization laser was introduced to enhance the ionization yield. Furthermore, a new type of alignment method for 3D reconstruction was developed on the basis of our embedded uniform circular polystyrene microspheres (PMs). Our findings demonstrate that this 3D imaging technique has the potential to provide information about the 3D distributions of specific molecules at the nanoscale level.

Fast and quantitative analysis of level 3 details for latent fingerprints

Level 3 details play essential roles in practical latent fingerprint (LFP) identification. To reliably extract reproducible and identifiable level 3 features, high-resolution images of fingerprints with adequate quality are required. Conventional methods for acquiring level 3 details often involve specific pretreatment, intricate peripheral, leading to time-consuming analysis. Herein, we simply used water to develop the sebaceous LFPs deposited on nitrocellulose (NC) membranes with only one step, and then the high-resolution (2048 pixels per inch) optical micrographs were captured to reflect the live fingertip with high fidelity. From the pictures, level 3 features, including all dimensional attributes of the ridges and pores such as number, size, location, shape, and edge contour can be extracted accurately and reproducibly. Among them, qualitative features (the structures of ridge edges) and several quantitative characteristics (the number and the relative location of sweat pores) exhibit good reproducibility. Remarkably, we proposed a new parameter termed "frequency distribution of the distance between adjacent sweat pores", short form "FDDasp", which was further proved highly identifiable in different individuals, enabling the successful distinguishment between two fragmentary fingerprints with similar level 2 structures. We believe that this methodology provides a fast and quantitative analytical paradigm for latent fingerprint identification at level 3 details.

Simultaneous determination and quantitation of hypolipidemic drugs in fingerprints by UPLC-Q-TRAP/MS

An ultra-performance liquid chromatography tandem triple quadrupole compound linear ion trap mass spectrometry (UPLC-Q-TRAP/MS) method was developed and validated for the detection of hypolipidemic drugs in fingerprints. 13 hypolipidemic drugs were well separated by the gradient elution of 0.01% formic acid in water and methanol at a flow rate of 0.4 mL/min within 11 min. The analytes were detected in positive (ESI⁺) and negative (ESI^-) modes and scanned using scheduled multiple reaction monitoring-information dependent acquisition-enhanced product ion (SMRM-IDA-EPI) for best selectivity and sensitivity. The calibration curves showed good linearity in the range of 0.050-50.000 ng/patch with coefficients (r²) higher than 0.9904 for all analytes. Meantime, the LODs and LLOQs were in ranges of 0.001-0.034 and 0.003-0.050 ng/patch. The accuracies, intra-day and inter-day precision ranged from -13.3 to 0.3%, 1.1-10.4% and 3.7-14.5%, respectively. The recoveries ranged from 79.9 to 114.8%, while the absolute and relative matrix effects were in the range of 83.0-107.2% and 2.2-9.7%. By comparing the non-spiked fingerprints from healthy volunteers with the fingerprints obtained from patients, demonstrated that the method was competent for determination and quantitation of hypolipidemic drugs in fingerprints.

Fluorescence imaging of surface-versatile latent fingerprints at the second and third level using double ESIPT-based AIE fluorophore

The nano-aggregates of HPBI on both porous and non-porous surfaces provide fluorescent latent fingerprints with resolution up to the third level, which could be relocated on the tape.

Application of MALDI MS imaging after sequential processing of latent fingermarks

Latent fingermarks are routinely visualised by subjecting them to one or more CSI/crime lab processes to maximise the recovery of ridge flow and minutiae permitting an identification. In the last decade mass spectrometric imaging (MSI) techniques have been applied to fingermarks to provide information about a suspect and/or on the circumstances of the crime as well as yielding additional images of the ridge pattern. In some cases, these techniques have shown the ability to provide further ridge detail, "filling in the gaps" of the developed mark. Matrix Assisted Laser Desorption Ionisation Mass Spectrometry Imaging (MALDI MSI) is presently the most advanced of the so-called 'surface analysis' techniques, in terms of compatibility with a number of fingermark enhancement processes and implementation in operational casework. However, for the use of this technique in major crimes to become widespread, compatibility with sequential processing must be demonstrated. This short study has assessed compatibility with a number fingermark processing sequences applied to natural marks on the adhesive side of brown (parcel) and clear tapes. Within the study undertaken, the results confirm the possibility to use MALDI MSI in sequence with multiple processes offering in some instances, complementary ridge detail with respect to that recovered from marks developed by conventional sequence processing.

Cryogenic OrbiSIMS Localizes Semi-Volatile Molecules in Biological Tissues

OrbiSIMS is a recently developed instrument for label-free imaging of chemicals with micron spatial resolution and high mass resolution. We report a cryogenic workflow for OrbiSIMS (Cryo-OrbiSIMS) that improves chemical detection of lipids and other biomolecules in tissues. Cryo-OrbiSIMS boosts ionization yield and decreases ion-beam induced fragmentation, greatly improving the detection of biomolecules such as triacylglycerides. It also increases chemical coverage to include molecules with intermediate or high vapor pressures, such as free fatty acids and semi-volatile organic compounds (SVOCs). We find that Cryo-OrbiSIMS reveals the hitherto unknown localization patterns of SVOCs with high spatial and chemical resolution in diverse plant, animal, and human tissues. We also show that Cryo-OrbiSIMS can be combined with genetic analysis to identify enzymes regulating SVOC metabolism. Cryo-OrbiSIMS is applicable to high resolution imaging of a wide variety of non-volatile and semi-volatile molecules across many areas of biomedicine.

Methodologies Applied to Fingerprint Analysis

This systematic review deals with the last 10 years of research in analytical methodologies for the analysis of fingerprints, regarding their chemical and biological constituents. A total of 123 manuscripts, which fit the search criteria defined using the descriptor "latent fingermarks analysis," were selected. Its main instrumental areas (mass spectrometry, spectroscopy, and innovative methods) were analyzed and summarized in a specific table, highlighting its main analytical parameters. The results show that most studies in this field use mass spectrometry to identify the constituents of fingerprints, both to determine the chemical profile and for aging. There is also a marked use of mass spectrometry coupled with chromatographic methods, and it provides accurate results for a fatty acid profile. Additional significant results are achieved by spectroscopic methods, mainly Raman and infrared. It is noteworthy that spectroscopic methods using microscopy assist in the accuracy of the analyzed region of the fingerprint, contributing to more robust results. There was also a significant increase in studies using methods focused on finding new developers or identifying components present in fingerprints by rapid tests. This systematic review of analytical techniques applied to the detection of fingerprints explores different approaches to contribute to future studies in forensic identification, verifying new demands in the forensic sciences and assisting in the selection of studies for the progress of research.

Latent Fingermark Imaging by Single-Metal Deposition of Gold Nanoparticles and Surface Enhanced Raman Spectroscopy

In forensic science, there is a high demand for a technique that allows the revelation of fingermarks invisible to the naked eye as well as the chemical information they contain. Here, we present a feasibility study consisting of using both the luminescence enhanced by surface plasmon of gold nanoparticles, and the surface enhanced Raman spectroscopy signal of fingermark chemical components to image latent fingermarks. A latent fingermark deposited on a transparent glass substrate was visually revealed using single-metal deposition employing gold nanoparticles. The resulting enhanced luminescence was monitored over a developed area of the latent fingermark, displaying light regions of 200-400 μm, corresponding to the fingermark ridges. The Raman signal of the fingermark's chemical components was enhanced into a measurable signal. Imaging those Raman peaks revealed the ridges pattern, attesting to the potential of our method. Since SMD is an end-of-sequence revelation technique for which further enhancement techniques do not exist, this work aims at demonstrating the feasibility of the technique in order to apply it on different systems, able to illuminate a complete surface of a few cm, and thus capable of both detecting contaminants in LFM and imaging features of the size of a complete LFM.

Elemental analysis and imaging of sunscreen fingermarks by X-ray fluorescence

Chemical composition in fingermarks could provide useful information for forensic studies and applications. Here, we evaluate the feasibility of analysis and imaging of fingermarks via elements by synchrotron radiation X-ray fluorescence (SRXRF) and commercial X-ray fluorescence (XRF). As a proof of concept, we chose four brands of sunscreens to make fingermarks on different substrates, including plastic film, glass, paper, and silicon wafer. We obtained an evident image of fingermarks via zinc and titanium by XRF methods. In addition, the ratios of element concentrations in sunscreen fingermarks were obtained, which were in accordance with the results obtained by acid digestion and ICP-OES analysis. In comparison, commercial XRF offers the most advantages in terms of non-destructive detection, easy accessibility, fast element images, and broad applicability. The possibility to acquire fingermark images simultaneously with element information opens up new avenues for forensic science. Graphical abstract.

Graphene quantum dots enhanced ToF-SIMS for single-cell imaging

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has shown promising applications in single-cell analysis owing to its high spatial resolution molecular imaging capability. One of the main drawbacks hindering progress in this field is the relatively low ionization efficiency for biological systems. The complex chemical micro-environment in single cells typically causes severe matrix effects, leading to significant signal suppression of biomolecules. In this work, we investigated the signal enhancement effect of graphene quantum dots (GE QDs) in ToF-SIMS analysis. A × 160 magnification of ToF-SIMS signal for amiodarone casted on glass slide was observed by adding amino-functionalized GE QDs (amino-GE QDs), which was significantly higher than adding previously reported signal enhancement materials and hydroxyl group-functionalized GE QDs (hydroxyl-GE QDs). A possible mechanism for GE QD-induced signal enhancement was proposed. Further, effects of amino-GE QDs and hydroxyl-GE QDs on amiodarone-treated breast cancer cells were compared. A significant signal improvement for lipids and amiodarone was achieved using both types of GE QDs, especially for amino-GE QDs. In addition, ToF-SIMS chemical mapping of single cells with better quality was obtained after signal enhancement. Our strategy for effective ToF-SIMS signal enhancement holds great potential for further investigation of drug metabolism pathways and the interactions between the cell and micro-environment.