Researchers at the Optical Spectroscopy Group, Charles University (Prague, Czech Republic) and the Center for Oxygen Microscopy and Imaging, University of Aarhus (Aarhus, Denmark) have developed an experimental setup that microspectroscopically monitors singlet oxygen using what they call a "novel near-infrared sensitive InGaAs 2D-array detector"1—which is actually a camera made by Princeton Instruments (Acton, MA) called the NIRvana 640.
Singlet oxygen, the first excited state of molecular oxygen, is a highly reactive species that plays an important role in a wide range of biological processes, including cell signaling, immune response, macromolecule degradation, and elimination of neoplastic tissue during photodynamic therapy. Often, a photosensitizing process is used to produce singlet oxygen from ground-state oxygen.
VIS and NIR channels
The researchers used two detection channels (VIS and NIR) provided by the indium gallium arsenide (InGaAs)-based camera to perform real-time imaging of the very weak near-IR phosphorescence of singlet oxygen and photosensitizer simultaneously with visible fluorescence of the photosensitizer. Their new experimental setup enables acquisition of spectral images based on singlet oxygen and photosensitizer luminescence from individual cells, where one dimension of the image is spatial and the other is spectral, covering a spectral range from 500 to 1700 nm.
To achieve these results, the NIRvana 2D InGaAs camera was coupled to an imaging spectrograph, also made by Princeton Instruments (Acton SpectraPro 2500i). According to Charles University researcher Marek Scholz, the main advantage of the near-IR–sensitive NIRvana camera over previously used 1D InGaAs detectors is the NIRvana detection array's two-dimensionality, which leads to much shorter acquisition times and avoids some of the problems caused by photobleaching of the sample. Rounding out the Princeton Instruments-supplied devices was a back-illuminated silicon CCD camera (Spec-10:400B) used to detect visible light in the setup.
Scholz et al. indicate that the introduction of spectral images for such studies addresses the issue of a potential spectral overlap of singlet oxygen phosphorescence with NIR-extended luminescence of the photosensitizer and provides a powerful tool for distinguishing and separating them, which can be applied to any photosensitizer manifesting NIR luminescence.
REFERENCE:
1. Marek Scholz et al., Photochemical & Photobiological Sciences (2014); doi: 10.1039/c4pp00121d
