Forensic potential of Atomic Force Microscopy

An important aspect of any crime scene investigation is to detect, secure and analyze trace evidence. Atomic force microscopy (AFM) is a nanotechnology that can be used to generate forensic information. This review aims to briefly explain principles of AFM and review potential forensic applications like age determination of bloodstains, fingermark examination, investigation of textile fibers, document forgery detection, gunshot and explosive residues analysis, and pressure sensitive adhesives investigation. Current techniques are highlighted and the usefulness of AFM is discussed. For the examination of gunshot, explosives and pressure sensitive adhesive residues AFM can determine elastic moduli, adhesion forces, energy dissipation, and dielectric properties of trace material, provide synoptic mapping of these characteristics and identify compositions. Phase imaging and force spectroscopy are important options but cannot unravel chemical identities. Forensic relevance of force spectroscopy for red blood cell age estimation is promising but remains to be fully explored. If not affected by surface roughness AFM height imaging may yield complementary information with respect to fingermark, textile and document examinations. For overlapping, (partially) erased marks or mixtures of biological traces phase imaging could provide composition information. If the chemical identity of trace components is important AFM may be combined with (surface/tip enhanced) Raman spectroscopy. Equipped with high resolution optical microscopy AFM(-Raman) technology may become a valuable forensic tool to characterize and understand trace transfer and persistence and to assess condition and age of evidence material. AFM could thus yield additional options for forensic association and assist in forensic analysis at activity level.