Examination of line crossings by atomic force microscopy

A comprehensive review on application of atomic force microscopy in Forensic science

The primary objective of forensic investigation of a case is to recognize, identify, locate, and examine the evidence. Microscopy is a technique that provides crucial information for resolving a case or advancing the investigation process by analyzing the evidence obtained from a crime scene. It is often used in conjunction with suitable analytical techniques. Various microscopes are employed; scanning probe microscopes are available in diverse forensic analyses and studies. Among these, the atomic force microscope (AFM) is the most commonly used scanning probe technology, offering a unique morphological and physico-chemical perspective for analyzing multiple pieces of evidence in forensic investigations. Notably, it is a non-destructive technique capable of operating in liquid or air without complex sample preparation. The article delves into a detailed exploration of the applications of AFM in the realms of nanomechanical forensics and nanoscale characterization of forensically significant samples.

Recent Trends of Vibrational Spectroscopy in Examination of Sequence of Strokes: Application in Forensic Documents Examination

Chronological sequencing of ink strokes has been a challenge for the Forensic Document Examiners (FDE). Document forgery is a common practice and the ability to determine the order in which the primary and the subsequent strokes have been made is crucial for establishing the authenticity of a document. Lately, the prime thrust of establishing the sequence of intersection of ink lines has shifted from an optical to an analytical approach. Several studies have been reported to explore the use of spectroscopic techniques in determining the sequence of ink strokes made using gel pen inks, ball pen inks, fountain inks, printed ink, stamp inks, etc. The present study aims to study the existing trends in examining the sequence of ink strokes or crossing of lines using vibrational spectroscopic techniques viz. Infrared and Raman Spectroscopy. Several interesting inferences have been drawn, such as factors like paper type and time gap between the application of two intersecting strokes does not influence the determination of the sequence of inter-crossing strokes. A trend of using two analytical techniques viz. VSC, AFM, HPTLC, TOF-SIMS, and SEM/EDX with vibrational spectroscopic techniques have been found to provide reliable results. The study also suggests future research directions in the field, aiming to address challenges faced by the FDEs and provide accurate and reliable solutions for document examination.

Technical note: A novel 3D scan-based optical method for analyzing lines drawn at different pen pressure

Pen pressure is one of the important elements of handwriting and questioned document analysis which is also crucial to recognize forgery. In this paper, we present a new, non-contact, non-destructive, and relatively inexpensive technique to measure the width of the grooves made by the writing. Results demonstrate a clear difference in measured groove widths for varying pen pressure. The effect of passing a written or signed paper in different types of printers has also been studied. A clear decrease of the groove depth was noted when passing the document through a laser printer. An ink jet printer only resulted in a small decrease of the groove depth, while no effect could be detected from a dot matrix printer.

Initial Study for the Determination of the Sequence of Intersecting Lines between Gel Pens and Seals by Optical Coherence Tomography

Determining the sequence of intersecting lines is a significant issue in the forensic document examination that can reveal the fraud or distinguish between different allegations. Optical coherence tomography (OCT) is a high-resolution cross-sectional imaging technique that has been introduced into forensic science field recently. The potential of OCT as a novel method to determine the sequence of intersecting lines was examined for the first time. In this study, a spectral-domain OCT system with a center wavelength of 900 nm was employed to perform nondestructive examination on determining the sequence of 18 heterogeneous intersecting line samples produced using three types of gel pens and three brands of stamp pad ink seals. Two-dimensional (2D) cross-sectional, and three-dimensional (3D) volumetric images of the intersecting lines were obtained by the OCT system. Several features were noted and analyzed to successfully determine the sequence of all the 18 samples. Blind tests were also conducted to demonstrate the effectiveness of OCT technique. The results illustrate that OCT technology can provide an effective and accurate method for sequencing intersecting lines of gel pen ink and seal ink, which may complement the conventional methods used in the examination of questioned documents.

Separation, characterization and identification of microplastics and nanoplastics in the environment

Microplastics (MPs) have globally been detected in aquatic and marine environments, which has raised scientific interests and public health concerns during the past decade. MPs are those polymeric particles with at least one dimension <5 mm. MPs possess complex physicochemical properties that vary their mobility, bioavailability and toxicity toward organisms and interactions with their surrounding pollutants. Similar to nanomaterials and nanoparticles, accurate and reliable detection and measurement of MPs or nanoplastics and their characteristics are important to warrant a comprehensive understanding of their environmental and ecological impacts. This review elaborates the principles and applications of diverse analytical instruments or techniques for separation, characterization and quantification of MPs in the environment. The strength and weakness of different instrumental methods in separation, morphological, physical classification, chemical characterization and quantification for MPs are critically compared and analyzed. There is a demand for standardized experimental procedures and characterization analysis due to the complex transformation, cross-contamination and heterogeneous properties of MPs in size and chemical compositions. Moreover, this review highlights emerging and promising characterization techniques that may have been overlooked by research communities to study MPs. The future research efforts may need to develop and implement new analytical tools and combinations of hyphenated technologies to complement respective limitations of detection and yield reliable characterization information for MPs. The goal of this critical review is to facilitate the research of plastic particles and pollutants in the environment and understanding of their environmental and human health effects.

Determination of Deposition Order of Toners, Inkjet Inks, and Blue Ballpoint Pen Combining MeV-Secondary Ion Mass Spectrometry and Particle Induced X-ray Emission

Determination of the deposition order of different writing tools is very important for the forensic investigation of questioned documents. Here we present a novel application of two ion beam analysis (IBA) techniques: secondary ion mass spectrometry using MeV ions (MeV-SIMS) and particle induced X-ray emission (PIXE) to determine the deposition order of intersecting lines made of ballpoint pen ink, inkjet printer ink, and laser printer toners. MeV-SIMS is an emerging mass spectrometry technique where incident heavy MeV ions are used to desorb secondary molecular ions from the uppermost layers of an organic sample. In contrast, PIXE provides information about sample elemental composition through characteristic X-ray spectra coming from greater depth. In the case of PIXE, the information depth depends on incident ion energy, sample matrix and self-absorption of X-rays on the way out from the sample to the X-ray detector. The measurements were carried out using a heavy ion microprobe at the Ruđer Bošković Institute. Principal component analysis (PCA) was employed for image processing of the data. We will demonstrate that MeV-SIMS alone was successful to determine the deposition order of all intersections not involving inkjet printer ink. The fact that PIXE yields information from deeper layers was crucial to resolve cases where inkjet printer ink was included due to its adherence and penetration properties. This is the first time the different information depths of PIXE and MeV-SIMS have been exploited for a practical application. The use of both techniques, MeV-SIMS and PIXE, allowed the correct determination of deposition order for four out of six pairs of samples.

Determination of the Sequence of Intersecting Lines Between Toners and Seals by Laser Fluorescence Microscope

Fluorescence microscope is considered to be one of the most effective ways to examine the sequence of intersecting seal and toner lines of questioned documents. In reality, however, the toner (mainly divided into compact and noncompact toners) and seal of a questioned document have such a complex morphology and sequence of crossing lines that current methods cannot meet the requirement of practical document identification. In view of the challenges of document examination, a laser fluorescence microscope and method are developed in this study. The developed microscope provides additional functionality to traditional fluorescence microscopes of transmitted light modality, laser excitation, selectable excitation wavelength, and selectable fluorescence filters. The results obtained from the method of comparisons between transmitted light and fluorescence modalities were positive under most conditions, particularly for noncompact toner examination for which a 100% accuracy rate and 90% detection rate were achieved in blind testing.

Determination of chronological order of crossed lines of ballpoint pens by hyperspectral image in the visible region and multivariate analysis

Determining the chronological order of crossed lines is a recurrent problem in forensic analysis of documents. One of the most important requirement of these analyses is the use of non-destructive techniques to maintain the integrity of the documents for further analysis as judicial evidences. Thus, this work proposes an objective, non-destructive, easy-to-execute analysis protocol for forensic analysis, using the hyperspectral mode of the VSC6000®, which is an equipment found in most laboratories of questioned documents. Seven blue ballpoint pens of different brands were used to make crossings on white paper, a total of 49. The spectra were obtained from 400 to 1000 nm, and analyzed with HYPER-Tools. Initially, univariate analysis was used, selecting discriminating wavelengths to visualize the images and determine the chronological order of the crossings, and then, when necessary, a multivariate approach using Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS) was applied. The interpretation of the order was made visually, taking into account characteristics of the strokes, such as the continuity and amount of ink. In this way, it was possible to determine the chronological order of 31/49 crossings, which corresponds to an overall rate of 63% accuracy. The method was validated by performing a double-blind test with 8 crossings, which indicated only a small influence of the analyst. The method was also applied to the analysis of a police inquiry, which was provided by the Federal Police and compared with the routine analyzes. The results were concordant but the proposed method provided a more objective analysis than the ones currently in practice at the Police.

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics

Atomic force microscopy (AFM) was used to assess the indentation modulus M_s and pull-off force F_po in four case studies of distinct evidence types, namely hair, questioned documents, fingerprints, and explosive particle-surface interactions. In the hair study, M_s decreased and F_po increased after adding conditioner and bleach to the hair. For the questioned documents, M_s and F_po of two inks were markedly different; ballpoint pen ink exhibited smaller variations relative to the mean value than printer ink. The fingerprint case study revealed that both maximum height and F_po decreased over a three-day period. Finally, the study on explosive particle-surface interactions illustrated that two fabrics exhibited similar M_s, but different F_po. Overall, it was found that AFM addresses needs in forensic science as defined by several federal agencies, in particular an improved ability to expand the information extracted from evidence and to quantify its evidentiary value.

Atomic force microscopic investigation of commercial pressure sensitive adhesives for forensic analysis

Pressure sensitive adhesive (PSA), such as those used in packaging and adhesive tapes, are very often encountered in forensic investigations. In criminal activities, packaging tapes may be used for sealing packets containing drugs, explosive devices, or questioned documents, while adhesive and electrical tapes are used occasionally in kidnapping cases. In this work, the potential of using atomic force microscopy (AFM) in both imaging and force mapping (FM) modes to derive additional analytical information from PSAs is demonstrated. AFM has been used to illustrate differences in the ultrastructural and nanomechanical properties of three visually distinguishable commercial PSAs to first test the feasibility of using this technique. Subsequently, AFM was used to detect nanoscopic differences between three visually indistinguishable PSAs.

Time-dependent surface adhesive force and morphology of RBC measured by AFM

Atomic force microscopy (AFM) is a rapidly developing tool recently introduced into the evaluation of the age of bloodstains, potentially providing legal medical experts useful information for forensic investigation. In this study, the time-dependent, morphological changes of red blood cells (RBC) under three different conditions (including controlled, room-temperature condition, uncontrolled, outdoor-environmental condition, and controlled, low-temperature condition) were observed by AFM, as well as the cellular viscoelasticity via force-vs-distance curve measurements. Firstly, the data indicate that substrate types have different effects on cellular morphology of RBC. RBC presented the typical biconcave shape on mica, whereas either the biconcave shape or flattened shape was evident on glass. The mean volume of RBCs on mica was significantly larger than that of cells on glass. Surprisingly, the adhesive property of RBC membrane surfaces was substrate type-independent (the adhesive forces were statistically similar on glass and mica). With time lapse, the changes in cell volume and adhesive force of RBC under the controlled room-temperature condition were similar to those under the uncontrolled outdoor-environmental condition. Under the controlled low-temperature condition, however, the changes in cell volume occurred mainly due to the collapse of RBCs, and the curves of adhesive force showed the dramatic alternations in viscoelasticity of RBC. Taken together, the AFM detections on the time-dependent, substrate type-dependent, environment (temperature/humidity)-dependent changes in morphology and surface viscoelasticity of RBC imply a potential application of AFM in forensic medicine or investigations, e.g., estimating age of bloodstain or death time.

Characterization of MAP1B heavy chain interaction with actin

Microtubule-associated protein 1B is an essential protein during brain development and neurite outgrowth and was studied by several assays to further characterize actin as a major interacting partner. Tubulin and actin co-immunoprecipitated with MAP1B at similar ratios throughout development. Their identity was identified by mass spectrometry and was confirmed by Western blots. In contrast to previous reports, the MAP1B-actin interaction was not dependent on the MAP1B phosphorylation state, since actin was precipitated from brain tissue throughout development at similar ratios and equal amounts were precipitated before and after dephosphorylation with alkaline phosphatase. MAP1B heavy chain was able to bind actin directly and therefore the N-terminal part of MAP1B heavy chain must also contain an actin-binding site. The binding force of this interaction was measured by atomic force microscopy and values were in the same range as those of MAP1B binding to tubulin or that measured in MAP1B self-aggregation. Aggregation was confirmed by negative staining and electron microscopy. Experiments including COS-7 cells, PC12 cells, cytochalasin D and immunocytochemistry with subsequent confocal laser microscopy, suggested that MAP1B may bind to actin but has no obvious microfilament stabilizing effect. We conclude, that the MAP1B heavy chain has a microtubule-stabilization effect, and contains an actin-binding site that may play a role in the crosslinking of actin and microtubules, a function that may be important in neurite elongation.

Potentiality of 3D laser profilometry to determine the sequence of homogenous crossing lines on questioned documents

The determination of the sequence of line crossings is still a current problem in the field of forensic documents examination. Optical examination, lifting technique, ESDA technique, and electron microscopy are the most widely used methods for the determination of the writing order of crossing texts. However, at present many examinations of intersecting lines result in an inconclusive opinion, particularly if the same type and colour of ink is involved. This paper presents the potentiality of the 3D laser profilometry, which has been to determine the chronological sequence of homogenous "crossing lines". The laser profilometry, illustrated in this paper, has been developed on a conoscopic holography based system. It is a non-contact three-dimensional measuring system that allows producing holograms, even with incoherent light, with fringe periods that can be measured precisely to determine the exact distance to the point measured. This technique is suitable to obtain a 3D micro-topography with high resolution also on surfaces with unevenness reflectivity (usual for the paper surface). The proposed technique is able to obtained 3D profile in non-invading way. Therefore, the original draft are not physically or chemically modified, allowing a multi-analysis in different times. The experiments performed with line crossings database show that the proposed method is able of "positive identification" of writing sequence in the majority of the tests. In absence of a positive identification, the result has been "inconclusive" (no false determination did occur in this work).

Age determination of blood spots in forensic medicine by force spectroscopy

We present a new tool for the estimation of the age of bloodstains, which could probably be used during forensic casework. For this, we used atomic force microscopy (AFM) for high-resolution imaging of erythrocytes in a blood sample and the detection of elasticity changes on a nanometer scale. For the analytic procedure we applied a fresh blood spot on a glass slide and started the AFM detection after drying of the blood drop. In a first step, an overview image was generated showing the presence of several red blood cells, which could easily be detected due to their typical "doughnut-like" appearance. The consecutively morphological investigations in a timeframe of 4 weeks could not show any alterations. Secondly, AFM was used to test the elasticity by recording force-distance curves. The measurements were performed immediately after drying, 1.5 h, 30 h and 31 days. The conditions were kept constant at room temperature (20 degrees C) and a humidity of 30%. The obtained elasticity parameters were plotted against a timeline and repeated several times. The elasticity pattern showed a decrease over time, which are most probably influenced by the alteration of the blood spot during the drying and coagulation process. The preliminary data demonstrates the capacity of this method to use it for development of calibration curves, which can be used for estimation of bloodstain ages during forensic investigations.

Membrane deformation of unfixed erythrocytes in air with time lapse investigated by tapping mode atomic force microscopy

Estimation of the time of death is one of the most important problems for forensic medicine and law. Physical and chemical postmortem changes are evaluated together while estimating the time of death. The pattern analysis of antemortem and postmortem bloodstains is one of the important parameters for forensic science, and cellular changes of blood cells can be useful for the quantitative assessment of the time of death. In this study, by successively investigating erythrocytes exposed in air on mica for 5 days using tapping mode atomic force microscopy (TM-AFM), we observed deformation of whole cell and membrane surface of unfixed erythrocytes with time lapse. We found that the time-dependent cellular changes occurred after exposure of erythrocytes in air for several days. At 0.5 days of exposure, fissures and cell shrinkage were observed. At 2.5 days of exposure, the emergence of nanometer-scale protuberances were observed and these protuberances increased in number with increasing time. The changes of cell shape and cell membrane surface ultrastructure can be used to estimate the time of death. Futhermore, smear-induced abnormal erythrocytes and immunostained erythrocytes were observed here. The need for more precise research is indicated, such as the correlation of membrane changes to intervals of less than 0.5 day of air exposure, and use of various substrates in addition to mica, including glass, metals, fabrics, among others, on which the bloodstains appear in crime scenes. The results of this research demonstrate the efficacy of AFM as a potentially powerful analytical tool in forensic science.