Master of Science
As DNA analysis has advanced and produced tests with higher sensitivities, attention has turned toward obtaining DNA profiles from cells left with fingermarks. Recent studies have reported that cells deposited within fingermarks can exhibit differences in autofluorescence emission in the ‘red’ region of the visible spectrum (e.g., between 650-670 nm), which can be used to differentiate contributor cell population and separate them before DNA profiles. Interestingly, this emission was not consistent to the individual day-to-day and likely not a genetically-controlled attribute of the contributor. Instead, this emission signature results from extended exposure of the skin to certain materials such as plant material (e.g. kale, collard greens), purple nitrile gloves, and some marker ink (e.g. black or green ink) (Katherine Philpott, 2017). As of yet, the molecule(s) causing this unique signature has not been identified. The purpose of this project is to develop a pathway for elucidating the identity of compounds with specific fluorescent signatures present in fingermarks. This project focuses on the identification of the compound(s) deposited by kale which is responsible for the autofluorescence signature seen between 650 nm and 670 nm.
To accomplish this, the compound(s) of interest was first extracted from kale leaves using isopropyl alcohol. The extracted compound(s) were then analyzed using fluorescence spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Direct Analysis in Real Time Mass Spectrometry (DART-MS), High Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS). Touch samples were collected after handling kale, and the resulting samples were also analyzed using fluorescence spectroscopy, flow cytometry, and DART-MS.
Both the kale extract and kale touch samples exhibited excitation peaks at 435 nm and emission peaks at 665 nm when analyzed with fluorescence spectroscopy, which is consistent with the previous study. When the extract was analyzed using FTIR, the signature seen was similar to that of beeswax indicating that the fluorescent compound may be inherent to the kale. To determine this, extracts and touch samples were obtained from both store-bought kale and home-grown kale and fluorescent signatures from both were consistent, indicating that the compound(s) of interest are inherent to the kale. When the touch samples, extract, and kale leaves were analyzed with DART-MS, a common peak of 423.45 m/z was seen in all three. HPLC was performed on the extract in an attempt to isolate the compound for mass spectrometry analysis but was unsuccessful. GC-MS was also performed on the extract, but the 423 m/z was not seen.
Some glucosinolates were considered as possible identities for the target compound but were eliminated due to differences in both fluorescence and DART-MS with standards of gluconasturtiin and glucoiberin. Currently, LC-MS is being explored to isolate the compound and attempt to gain more fragmentation information about the compound. Ultimately, the scheme used for this compound identification will provide a foundational mechanism that can be used to identify other fluorescent compounds seen with fingermarks.
© Elora Wall
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Available for download on Wednesday, May 11, 2022