Nanomechanical mapping of latent fingermarks: A preliminary investigation into the changes in surface interactions and topography over time.

Crime scene investigations often rely on successful development of latent fingermarks for personal identification. In this context, exploring fundamental properties of latent fingermarks is vital for developing robust and more effective detection techniques. Here in a novel approach, PeakForce quantitative nanomechanical mapping (PF QNM) atomic force microscopy (AFM) has been used to study the variations in surface adhesion and topography of latent fingermark droplets over time. It was found that variation in adhesion was exhibited even across the surface of a single fingermark droplet, suggesting that individual droplets are heterogeneous in chemical composition on the nanoscale. The technique was successfully employed in observing the topographical variation of eccrine droplets, which has not been achieved using other optical microscopy techniques. In addition, the adhesion of fingermark droplets changed significantly as they aged. Propagation of a thin film of material from the fingermark ridges across the furrows, starting immediately after deposition, was captured in real-time, demonstrating the dynamic nature of the deposit. These results will aid in providing a more complete fundamental understanding of latent fingermark residue, allowing the more rational development of new detection techniques, especially those involving nanostructured materials.