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

An important aspect of any crime scene investigation is to detect, secure and analyze trace evidence. In forensic examinations where topographic characterization is important like in fingermark, textile and document forgery examinations, the atomic force microscopy (AFM) imaging technique can be of value. However, it is the force spectroscopy that could make AFM a versatile tool in crime investigations. Particularly, the ability to measure changes in mechanical properties of forensic trace material over time makes this technology in potential interesting for forensic examinations. The usefulness of force measure- ments to evaluate the elasticity of red blood cells (RBCs) in relation to the age of a bloodstain is an interesting example. With minimally invasive AFM technology, time- dependent alterations in the viscoelasticity of RBCs that occur during the aging of bloodstains can be featured. A discrimination between traces left by the perpetrator and other persons that have been present at the crime scene will thus be enabled. A recently obtained proof-of-concept demonstrating the usefulness of AFM for age estimation of bloodstains will be described. Additionally, the usefulness of AFM imaging and force spectroscopy for human hair, document forgery, textile fiber, fingermark and gunshot and explosive residue examinations will be discussed.