Novel Quantitative Microscopy of Wet-Powdered Latent Fingermarks of Different Ages

As submitted by the proposer:
Fingerprints (i.e., fingermarks) have been used for more a century to uniquely identify individuals, and latent fingermarks are probably the most common type of evidence collected and analyzed in forensic science. The usual picture of a latent fingermark is a binary image consisting of bright ridges and dark grooves which shows a fingerprint, coated with a layer of fingerprint powder to make the ridges opaque, illuminated and viewed from above. Although various features of such an image can be matched to fingerprints in a database to identify individuals, such an image gives almost no quantitative information about the characteristics (e.g. morphology, chemical composition) of the fingermark itself.
We propose instead to image latent fingermarks from below, and hence through, the fingermark using evanescent-wave illumination, also known as total internal reflection microscopy. By using evanescent waves, which will be strongly attenuated as they pass through the fingermark, it should be possible to obtain quantitative information about the fingermarks from the local intensity variations across the fingermark. The goal of this research is therefore to determine whether evanescent-wave imaging can be used to quantify the characteristics of latent fingermarks, focusing on two specific aspects:

• how well do the powders used to enhance these fingermarks actually adhere to fingermarks of different ages, and how can the wet-powdering methods used to apply these powders be optimized to maximize enhancement?
• can intensity variations of a well-enhanced fingermark be correlated to the thickness profile of the fingermark secretions?
A systematic program of experimental studies, grounded in colloid and surface science, is proposed to address these questions. The researchers performing this work will communicate with local experts in friction-ridge analysis to ensure that their results will be useful to the forensic science community. Given the currently underdeveloped state of optical microscopy of latent fingermarks (cf. Ref. [28]), applying this type of quantitative optical microscopy to friction-ridge analysis could lead to major advances, especially when used with “next generation” fingerprint powders that both enhance and chemically analyze the fingermark.

Note: This project contains a research and/or development component, as defined in applicable law.

ca/ncf