Singlet oxygen detection and photodynamic therapy


Singlet oxygen (1O2), the lowest excited state of molecular oxygen, is a fascinating species in many ways. Its chemistry differs significantly from that of ground state triplet oxygen. Singlet oxygen readily reacts with a wide range of biological and organic materials which leads to their alteration and degradation. Arguably the most important way of singlet oxygen formation is the so-called photosensitizing process: A light excited molecule of an appropriate dye - so called photosensitizer (PS) - transfers energy to molecular oxygen giving rise to singlet oxygen. Nature is figuratively full of such dyes which support the formation of singlet oxygen, e.g. photosynthetic dyes or Protoporphyrin IX (a precursor for heme). Singlet oxygen is involved in a rich variety of diverse biochemical processes, such as photosynthesis, cell signaling, immune responses or polymer degradation [Gilbert]. Research involving singlet oxygen and the photosensitizing process has various perspectives [Ogilby].

Photodynamic therapy (PDT) for cancer and other diseases is an especially interesting research field. PDT is a very important and promising application of photosensitizers in medicine. Singlet oxygen and free radicals produced via the photosensitizing process can be used for fighting cancer, other lesions (e.g. macular degeneration), or even bacteria and viruses [Allison]. The photosensitizer is administrated to the patient and is more or less selectively absorbed by cells of the targeted tissue. The particular spot is then irradiated by visible light and singlet oxygen and other reactive species are produced at the spot. Oxidative stress can induce apoptosis or necrosis of cells of the targeted tissue. The selectivity of photodynamic therapy is reached both by the selective absorption of the photosensitizer and by localized irradiation [Castano].

What we do

Both singlet oxygen and photosensitizers show weak near-infrared phosphorescence emission, which allows for their optical detection. The main research interest of our group is the developement and application of optical tools and methods for detection of singlet oxygen in various systems, e.g. solutions, solid and polymeric samples, cell cultures or even whole laboratory animals. Currently our main research tool is the unique experimental setup for measuring time- and spectral-resolved near-infrared luminiscence, which allows us to observe dynamics of interaction among photosensitizers, singlet oxygen, antioxidants and other biologically relevant molecules, e.g. [ Dedic (2007) J Mol Struct, Korinek (2004) J Fluorescence, Dedic (2003) J Luminescence ]. This tool is combined with methods of fluorescence, absorption and transient absorption spectroscopy. Lately we have been working on developement of setup for microscopic measurement of near-infrared luminiscence in order to investigate interactions of singlet oxygen directly in heterogenous environment of living cells. Such a fundamental research is necessary for successful progress of photodynamic therapy and a variety of other applications involving singlet oxygen.