Quantitative Scanning Probe Microscopy for Nanomechanical Forensics

Abstract

Atomic force microscopy (AFM) was used to assess the indentation modulus Ms and pull-off force Fpo in four case studies of distinct evidence types, namely hair, questioned documents, fingerprints, and explosive particle-surface interactions. In the hair study, Ms decreased and Fpo increased after adding conditioner and bleach to the hair. For the questioned documents, Ms and Fpo 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 Fpo decreased over a three-day period. Finally, the study on explosive particle-surface interactions illustrated that two fabrics exhibited similar Ms, but different Fpo. 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.

Interpol review of fingermarks and other body impressions 2016–2019

“… Donor profiling – The following studies aim at providing additional information from a fingermark, other than the ridge pattern: a new biometric identification tool built on an amino acid-based chemical assay [ 184 ]; donor-related information (i.e., gender, ethnicity, and donor age) obtained from secretion residue lipid profiling (technique: DESI-MSI) [ 185 ]; impact of gender and ethnicity on the lipid composition of residues present on an individual’s fingertips (technique: HPLC-ACPI-MS) [ 186 ]; donor gender determination using an amino acid-based chemical assay [ 187 ] or by specifically targeting the chromosomes X and Y contained in nucleated cells (technique: fluorescent in situ hybridization) [ 188 ]; donor characteristics and behavioural information (e.g., gender, ethnicity, diet, occupational activities, use of hand sanitizers) gained from bacterial profiling [ 189 ]; impact of donors and secretion types (i.e., eccrine, sebum-rich, and natural) on secretion residue composition (technique: MALDI-MSI-based metabolomics approach combined with chemometrics tools) [ 190 ]. Evolution of secretion residue with time – Surface adhesion monitoring and topography variation (technique: PeakForce QNM AFM) [ 191 ]; molecular composition variation (e.g., carotenoids, squalene, unsaturated fatty acids and proteins – technique: Raman spectroscopy) [ 192 ]; migration imaging of endogenous fatty acids contained in sebum-rich fingermarks (technique: hyperspectral SRS) [ 193 ]; topological modifications (e.g., decrease of ridge height from 200 nm to 100 nm over three days – technique: AFM) [ 194 ]; thermal degradation of sebum-rich fingermarks (technique: FTIR microspectroscopy) [ 195 ]; intermolecular interactions between lipids (technique: FTIR microspectroscopy) [ 196 ], physical modifications of fingermarks left on metallic substrates (technique: EIS) [ 197 ], secretion residue composition variation (technique: SALDI-MS combined with MCF) [ 198 ] – caution: the last approach requires the dusting of nano-sized MCF (See section 3.2.6 for details). Age determination – Flatbed scanner combined with feature extraction was proposed to distinguish eccrine-rich and sebum-rich secretion residues as well as to estimate their age (i.e., 2-h-old, half-a-day-old and one-day-old) [ 199 ].…”

Forensic Potential of Atomic Force Microscopy with Special Focus on Age Determination of Bloodstains

“…Particularly, the interfacial regions between crystalline zones of complex composite materials such as explosive residues were indicated as important areas where impurities, unreacted molecules, additives and binders form a heterogeneous structure. The study of DelRio and Cook also investigated adhesion forces of explosive particles on different fabric types using a colloidal probe [18]. The results showed for two fabrics similar modulus of indentation (29.0 AE 8.0 MPa for cotton and 30.7 AE 7.0 MPa for rayon) that differed from the values given in the literature (3 and 11 GPa for respectively cotton and rayon fibers) [70].…”

“…Electrical signals based on the conductivity through sample and tip may be monitored as well while the tip is moving over the sample [9]. It may be noticed that for mechanical studies with lateral resolution a sharp silicon or silicon nitride tip can be used but a spherical, colloidal probe may render more specific data on material-material mechanical interactions like forensically relevant adhesion interactions between gunshot and explosive residues and textile fibers [18].…”

“…As demonstrated in several studies, little research has been carried out into the forensic possibilities of AFM imaging [7,18]. Subjects that have been investigated concern human hair analysis [19][20][21][22][23][24], document forgery [25][26][27][28], textile fibers [29,30], fingermarks [31], gunshot and explosive residues [32,33].…”

“…Force-distance and friction measurements between individual hair strands have been documented by Max et al for direct quantification of hair-hair (other types of fiber) interactions in the range of 10-100 mm diameter (AFM Atomic Force F&E, MFP-3D; spring constant 1.2-8.5 N/m) [62]. DelRio and Cook have also provided interesting data of hair samples (untreated virgin hairs and conditioned and bleached hairs) [18]. They reported an indentation modulus of 2.4 AE 1.1 GPa and 1.8 AE 0.9 GPa for respectively the virgin and the bleached hairs.…”