Detection of visible and latent fingerprints by micro-X-ray fluorescence

Numerous methods are available to forensic scientists for detecting fingerprints in which the prints are treated with various agents to enhance the visual contrast between the print and the surface. In the present work, the spatial elemental imaging capabilities of micro-X-ray fluorescence (MXRF) were used to visualize fingerprint patterns based on inorganic elements present in the prints. A major advantage of using MXRF is that the prints are left unaltered for other analyses, such as deoxyribonucleic acid extraction or for archiving. Most of the fingerprints which were examined were imaged from the potassium and chlorine present in the print residue. Among the various prints studied, lower count rates were also observed in the elemental maps of Ca, Al, Na, Mg, Si, P, S, and the X-ray source scatter. A sebaceous oily fingerprint left by one subject was successfully imaged by MXRF, but sebaceous prints left by a different person were undetectable, indicating that print elemental composition may be person and/or diet dependent. Prints containing substances that might be found in real-world cases were also visualized including sweat, lotion, saliva, and sunscreen.