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In the course of experiments for our FET open project Lumiblast, we set off to measure the excitation
of various photoactive drugs (photosensitizers, PS) by the luminescence emission of luminol. Luminol
(5-Amino-2,3-dihydrophthalazine-1,4-dione) is a chemical that interacts with reactive oxygen species
(ROS) in basic conditions, and in the presence of metal catalysts like Fe or Cu, gives out a characteristic
blue luminescence. When dissolved in organic solvents like DMSO, however, luminol only requires
the addition of bases like KOH, NaOH or potassium terbutoxide, to fulfil the conditions for
luminescence emission.
In the present work we employed a detection system based on a spectrograph coupled to a ccd camera
to register fluorescence (Fig 1B) or luminescence (Fig 1 A, C). In the case of characteristic fluorescence
registration (Fig. 1B), the PSs investigated were excited by a 532 nm laser with a variable power output.
We have documented the energy transfer from chemically induced luminol luminescence to a number
of PSs including rose bengal, erythrosin B, hypericin amongst others. In all cases both the luminol
emission and the luminol luminescence-induced PS fluorescence were registered as shown in the
example of luminol and erythrosine b in Fig. 1C.
We further attempted to register the generation of singlet oxygen from luminol-excited PSs. To achieve
this, we employed the near-infrared (NIR) photomultiplier tube (PMT) shown in Fig.1 E, with a cut-off
filter at 900nm and a bandpass filter at 1270±30 nm. This allowed only radiation within this spectral
region to reach the PMT, corresponding to the characteristic phosphorescence of singlet oxygen, spin
forbidden de-excitation to ground state triplet oxygen.
A characteristic steady state singlet oxygen registration can be seen in Fig. 1D, for erythrosine b which
has a high singlet oxygen quantum yield. The luminol luminescence was initiated by addition of
terbutoxide to the DMSO luminol solution, at which point we can see a rise of the signal at 1270 nm.
Upon addition of the singlet oxygen quencher, L-histidine, the signal dropped steeply to background
levels.
NOTE: Figures are not available.
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