Date Published: January 24, 2017
Publisher: Public Library of Science
Author(s): Ji Zhang, Wei Lin, Hancheng Lin, Zhenyuan Wang, Hongmei Dong, Nikolas K. Haass.
In forensic practice, determination of electrocution as a cause of death usually depends on the conventional histological examination of electrical mark in the body skin, but the limitation of this method includes subjective bias by different forensic pathologists, especially for identifying suspicious electrical mark. The aim of our work is to introduce Fourier transform infrared (FTIR) spectroscopy in combination with chemometrics as a complementary tool for providing an relatively objective diagnosis. The results of principle component analysis (PCA) showed that there were significant differences of protein structural profile between electrical mark and normal skin in terms of α-helix, antiparallel β-sheet and β-sheet content. Then a partial least square (PLS) model was established based on this spectral dataset and used to discriminate electrical mark from normal skin areas in independent tissue sections as revealed by color-coded digital maps, making the visualization of electrical injury more intuitively. Our pilot study demonstrates the potential of FTIR spectroscopy as a complementary tool for diagnosis of electrical mark.
One of the most important aspects in forensic science is electrocution diagnosis. As electrical fatalities are generally caused by cardiac arrhythmia, respiratory arrest and damage to brainstem, autopsy findings are not evident or non-specific in the multiple vital organs [1, 2]. Electrical mark reflects the fact that the skin contacts with electrical conductors. Its pathological examination is crucial for diagnosis of fatal electrocution, especially when the death circumstances are suspicious [3, 4]. Histologically, it is well-known that epidermal nuclear elongation is a typical hallmark of electrical mark and of great diagnostic value for electrocution. However, histological examination is primarily dependent upon the individual subjective judgement, and thus forensic pathologists usually incorporate other methods with routine histopathology for determination of this mark, such as computerized image analysis and detection of metallization by scanning electron microscopy. But few provide more insights into the electrical mark at the molecular level, and make an objective diagnosis.
The skin samples in all cases were first subjected to morphological examination to determine the area of electrical mark for FTIR analysis. As exemplified in Fig 1, macroscopic examination showed hallmarks of the electrical injury characterized by pale, cave-like lesions with a raised margin. Microscopically, electrical mark revealed separation of epidermis and dermis, elongated epidermal cells arranged in a polarized direction and darkly stained cell nuclei in contrast to normal skin.
In our study, FTIR spectroscopy with an infrared microscopy was applied to characterize protein conformations of electrical mark in the human skin. The observed spectral variances between electrical mark and normal skin suggest that some skin proteins rich in α-helix, antiparallel β-sheet and β-sheet may be used as biomarkers for identification of electrical mark. Further, the application of FTIR imaging in combination with PLS model appeared to make a more objective and intuitive diagnosis than routine histological examination.