Identification of Foreign Particles in Human Tissues Using Raman Microscopy

The goal of this study was to precisely and unambiguously identify foreign particles in human tissues using a combination of polarized light microscopy and Raman microscopy, which provides chemical composition and microstructural characterization of complex materials with submicrometer spatial resolution. This identification for patient care and research has been traditionally studied using polarized light microscopy, electron microscopy with X-ray analysis, and electron diffraction, all with some limitations. We designed a model system of stained and unstained cells that contained birefringent talc particles and systematically investigated the influence of slide and coverslip materials, laser wavelengths, and mounting media on the Raman spectra obtained. Hematoxylin and eosin stained slides did not produce useful results because of fluorescence interference from the stains. Unstained cell samples prepared with standard slides and coverslips produce high quality Raman spectra when excited at 532 nm; the spectra are uniquely assigned to talc. We also obtain high quality Raman spectra specific for talc in unstained tissue samples (pleural tissue following talc pleurodesis and ovarian tissue following long-term perineal talc exposure). Raman microscopy is sufficiently sensitive and compositionally selective to identify particles as small as one micrometer in diameter. Raman spectra have been catalogued for thousands of substances, which suggests that this approach is likely to be successful in identifying other particles of interest in tissues, potentially making Raman microscopy a powerful new tool in pathology.