Detection of latent fingerprint using optical technique

• Main Authors: Seah, Leong Keey., Ong, Lin Seng., Murukeshan, Vadakke Matham.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Research Report
• Language: English
• Published: 2008
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Electronic systems::Biometrics
• Online Access: http://hdl.handle.net/10356/14241
• Institution: Nanyang Technological University

Fluorescence spectroscopy and imaging has lot of applications in forensic science and biomedical areas. Sensitive detection techniques are needed when dealing with very weak fluorescence signals from the test samples. Moreover, in fluorescence based imaging, separation of fluorescence often raises challenging problems when it is overshadowed by the strong background fluorescence or when the background fluorescence lies in close wavelength range as that of sample fluorescence. In this context a sensitive Phase-Resolved (PR) imaging technique is proposed to overcome the above-mentioned major limitations. A theoretical formulation of PR imaging was carried out by incorporating the homodyne and heterodyne concept of signal processing. Theoretical analysis shown that separation and imaging of sample fluorescence can be achieved by suppressing the background fluorescence, which might be in close wavelength ranges. Also, imaging of sample fluorescence can be achieved even if the fluorescence lifetime is longer or shorter than the lifetime of background fluorescence emission. Sensitivity improvement for the homodyne assisted PR imaging was carried out by incorporating the ‘pi’ shift method along with ‘even-step-phase shift’ method. An experiment was set up to validate the formulated theory. The imagings of latent fingerprints on various types of surfaces were carried out using the proposed technique. Often, when fingerprints deposited on strongly fluorescing backgrounds, their separation offer a challenging problem to fingerprint experts.Experiments were carried out for imaging the latent fingerprints, which are deposited on strongly fluorescing backgrounds, even when background fluorescence lifetime is longer than that of fingerprint fluorescence. Imaging of two years old fingerprints were also carried out with improved contrast. The advantage of homodyne assisted PR imaging over heterodyne assisted PR imaging was both theoretically and experimentally demonstrated in the context of latent fingerprint imaging. An Image quality evaluation method for the fingerprint image obtained using PR technique was proposed and carried out. It quantitatively proves the better quality of fingerprint image obtained by PR technique. In order to further demonstrate the high sensitivity and ability of proposed PR technique, experiments were carried out for the imaging of fluorescein chemicals having same emission wavelength but differing in their lifetime values. Suppression of either of the emissions by selective imaging of the other validates the superiority of the proposed technique. Imaging of the sample fluorescence was carried out with sub nanosecond resolution. This imaging principle can find potential applications in fluorescence lifetime imaging along with fluorescence microscopic research in biochemistry, biophysics, and cell physiology. The proposed PR technique can detect weak fluorescence from the sample and also enables to separate sample fluorescence such as fingerprint fluorescence when it is overshadowed by the strong background fluorescence. The ability of PR technique to resolve and separate fluorescence emissions, which are close in wavelength andlifetime value, can be applied for the detection of cell abnormalities such as early detection cancer growth in living cells.