Scientists have pioneered a mass spectrometry-based technique for semen detection that can provide more reliable identification for the justice system while placing less stress on the victim.
Current strategies for confirming the presence of semen at a crime scene or on the body of a victim use presumptive tests that typically detect the presence of one or two chemicals strongly associated with semen, such as phosphatase or semenogelin. However, these tests can falsely react with other materials, cannot be performed in situ and are almost always destructive to the sample. Additionally, the tests are slow, exacerbating victims’ anxiety at an already delicate time.
“By allowing investigators to quickly confirm whether or not a substance is semen, the time spent waiting for analysis of potential semen samples can be reduced, ultimately speeding up an investigation,” said lead author Stephanie Rankin-Turner. “Long, drawn-out investigations can obviously be very stressful to victims, so we want to provide technology to make investigations and evidence analysis more efficient.”
The research team from Loughborough University (UK) used an ambient ionization mass spectrometry technique called sheath-flow probe electrospray ionization mass spectrometry (sfPESI-MS). Rankin-Turner explained to Forensic that the technique uses a needle surrounded by a small volume of solvent that, when placed in contact with a surface, extracts chemical traces from the sample surface. It is then placed in front of a mass spectrometer. When a high voltage is applied to the needle, analytes from the sample are ionized and enter the instrument for analysis, providing researchers with a chemical profile of the sample within seconds.
In fact, in their study, the team achieved an analysis time of less than 10 seconds per sample (in situ) with no sample preparation. Additionally, the technique was able to detect fresh semen as well as semen aged 40 days, which the authors note as critical “in criminal investigations [since] biological samples may be encountered weeks, months or even years after deposition.” Forty days seemed to be a turning point—while the chemical profile of semen was largely unchanged at day 40, many of the low-abundance components were reduced or even completely lost beyond that time frame.
But what if there is no semen at the scene of the crime? The use of condoms in sexual assaults has actually increased as offenders become more knowledgeable about DNA evidence and the analysis of biological material. Previous studies have shown DART-MS can be used to analyze and discriminate condoms as well as sexual lubricants. So, Rankin-Turner’s team applied sfPESI-MS to eight condom types to confirm that condom-specific components could be detected and to ascertain the chemical differences between different condom brands.
While a number of components could be detected in multiple samples, each condom did produce a unique mass spectral profile. For example, octylamine, a component frequently encountered in the analysis of condoms, was present in almost all samples. However, researchers recorded the presence of menthone, a component frequently used in mint flavorings, in a condom brand advertised to have a “cooling effect.” The same is true for condoms that were said to contain spermicide—polyethylene glycol (PEG) was detected in those samples.
“Other MS techniques have shown that different types of condom produce distinct chemical profiles that could be used to identify the brand, but so far this has been limited to techniques that aren't really amenable to direct, on-site analysis. The sampling probe used here could be used with both benchtop and portable analyzers, depending on the needs of the user,” Rankin-Turner said. “In the absence of biological evidence like semen, the possibility of detecting traces of condom use can help support a victim's statement.”
For future work, the team is interested in diving deeper into the chemical changes of semen over time to possibly develop a technique for age estimation of semen deposition. Rankin-Turner said they are also working with the firm Foster and Freeman Ltd., which develops technologies for use by police forces, to ensure their lab-based research is applicable to real-world scenarios.