Identifying the component responsible for the intrinsic fluorescence of seminal fluid

Author: Thomas Hensel

Hensel, Thomas, 2020 Identifying the component responsible for the intrinsic fluorescence of seminal fluid, Flinders University, School of Chemical and Physical Sciences

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The intrinsic fluorescent property of seminal fluid is routinely used in forensic investigations for the location of seminal fluid stains especially in sexual assault cases. Although used, the compound that is responsible for this intrinsic fluorescent property is not known. There are several compounds in seminal fluid that are known to be fluorescent but none of these have been linked to the more unique fluorescent properties observed with seminal fluid. To potentially improve the current technique used and to gain a better understanding it would be beneficial to know what component is responsible for the fluorescence.

An issue that arises when looking at the fluorescence of seminal fluid is the quenching effect of water. This makes using some traditional methods of analysis difficult as they are wet techniques and the sample must be dry to properly observe the fluorescence. Because of this a reliable method, based on previous ones, for visualising the fluorescence when the sample is dry was developed that included a way of taking photographs to record the fluorescence.

Seminal fluid is also a very complicated sample and since little was known about the compound responsible, simplifying the sample matrix that the fluorescent component is in was not easily achievable. A method using a HPLC system with attached sample collector was used to produce a sample with a simplified matrix. This was further purified using SPE to produce a sample that could be analysed further.

This sample could be analysed using LCMS. The results from this analysis pointed towards the compound responsible being a polypeptide or protein. Following this, the sample was analysed using proteomic techniques, but the final identity of the compound was not determined. Some possible candidates were identified in the sample, but further work is required to confirm what is responsible for the fluorescence in seminal fluid.

A variation in the level of fluorescence was observed between samples from different donors. After removing the variable of the level hydration of the seminal fluid from the samples, the variation of fluorescence between them was reduced but not eliminated. This suggests that the there is a relatively consistent amount of the fluorescent component in seminal fluid, in relation to other compounds excluding water, but there is still some natural variation.

Experiments have led to a much better understanding on using the Far-Infrared beamline at the Australian Synchrotron. Polytetrafluoroethylene was shown to be a suitable alternative to polyethylene, an established disc matrix, and for some compounds it was possible to get a spectrum from a disc of pure compound. The effects of concentration of sample in the disc were studied and it was shown that higher concentrations were better as more information could be obtained. For some compounds, it was shown that a disc that is made up of pure compound could be formed and a clear spectrum obtained. In addition to this, small changes to a molecules structure was shown to have a significant effect on the resultant spectrum.

Keywords: Seminal Fluid, Fluorescence

Subject: Chemistry thesis

Thesis type: Masters
Completed: 2020
School: School of Chemical and Physical Sciences
Supervisor: Stewart Walker