Beyond fingerprint morphology: chemical mapping of functional groups

Fingerprints are one the oldest biometrics used in investigations. The fingerprint morphology is considered unique and immutable and it is routinely used to identify an individual from the mark found at the crime scene. The comparison is based solely on the ridges flow and on their discontinuities (i.e. the minutiae), without considering other information possibly embedded in the fingerprint itself. In this work we used a Fourier Transform Infrared microspectroscopy (FT-IRMS) to obtain the morphology and the chemical map of functional groups in fingerprints. The FT-IRMS technique is able to acquire hyperspectral images of the organic compounds present in the samples under examination. However both sophisticated processing and user interaction are required to process the spectra, and no fully automated procedure is currently available. We prepared a set of test fingerprints and collected the data with the FT-IRMS; we then developed an automated procedure to process the data without user interaction and were able to produce maps related to fingerprint deposits. More in details, the developed system is able to produce both integral maps, providing a summary of the contribution in a specific wavelength range, and peak maps, which show the contribution of a selected functional group. The automatic processing steps, although born with the fingerprint in mind, are fairly general, and can be applied to all fields where there is the need to process a large amount of spectra without user interaction.