Imaging electrostatic fingerprints with implications for a forensic timeline

The electrical charge deposited by contact electrification due to a finger touching a thin insulating surface is imaged using an electric field microscopy system. It is based on an ultrahigh impedance electric potential sensor used as a non-contact raster scanning probe to measure surface charge density with a spatial resolution of up to 5 μm. Preliminary results are presented which yield two principle findings. First, they indicate that the spatial resolution of the fingerprint image is sufficient for identification purposes. Secondly, that the decay of the surface charge may be considered as a candidate method for the dating or sequencing of these electrical charge fingerprints. The decay of surface charge with time is well defined, largely material dependent, and may take many days. This intrinsic decay rate for the material may be quantified using the charge imaging system described in this paper and a known test charge. The measurement technique described is non-destructive, may be repeated without degradation of the sample, and does not preclude the subsequent use of other techniques such as DNA analysis or conventional latent fingerprint development.