Use of atomic force microscopy in the forensic application of chronological order of toners and stamping inks in questioned documents

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.

Evaluation of photometric stereo and elastomeric sensor imaging for the non-destructive 3D analysis of questioned documents - A pilot study

Photometric Stereo and Elastomeric Sensor Imaging were assessed for measuring the 3-dimensional (3D) morphology of questioned document samples. Photometric stereo is shown to be a powerful non-contact technique for revealing micron level detail of the samples examined. Elastomeric Sensor Imaging is shown to complement photometric stereo by yielding equivalent results. Additionally, this technique allows quantification of the morphological depth information. The techniques were applied to 2 different types of questioned document sample. Firstly, written signatures were examined. Both techniques were able to reveal characteristic features that could be used to infer stroke direction and ink line application sequence. Secondly toner/ink intersections were examined. Both techniques allowed visualisation of 3D features which were used to infer the sequence of application.

Atomic force microscopy as a biophysical tool for nanoscale forensic investigations

The atomic force microscope (AFM) has found its way to the arsenal of tools available to the forensic practitioner for the analysis of samples at the nano and microscales. As a non-destructive probing tool that requires minimal sample preparation, the AFM is very attractive, particularly in the case of minimal or precious sample. To date, the use of the AFM has primarily been in the arena of imaging where it has been complementary to other microscopic examination tools. Forensic applications in the visual examination of evidence such as blood stains, questioned documents, and hair samples have been reported. While a number of reviews have focused on the use of AFM as an imaging tool for forensic analyses, here we not only discuss these works, but also point to a versatile enhancement in the capabilities of this nanoscale tool - namely its use for force spectroscopy. In this mode, the AFM can determine elastic moduli, adhesion forces, energy dissipation, and the interaction forces between cognate ligands, that can be spatially mapped to provide a unique spatial visualization of properties. Our goals in this review are to provide a context for this capability of the AFM, explain its workings, cover some exemplary works pertaining to forensic sciences, and present a critical analysis on the advantages and disadvantages of this modality. Equipped with this high-resolution tool, imaging and biophysical analysis by the AFM can provide a unique complement to other tools available to the researcher for the analysis and characterization of forensic evidence.