Abstract
Singlet oxygen luminescence dosimetry (SOLD) is a highly promising direct monitoring method for photodynamic therapy (PDT) in the treatment of cancer. Early SOLD systems have been hampered by inefficient excitation, poor optical collection and immature infrared single photon detection technology. We report carefully engineered improvements addressing all of these deficiencies. We use a supercontinuum source with a tunable filter to precisely target the peak absorption wavelength of the chosen photosensitizer; we have designed a compact and versatile optical package for precise alignment; we have successfully employed state-of-the-art superconducting photon counting technologies. Through these improvements, we can achieve histogram acquisition from a photosensitizer in solution test sample. This setup opens the pathway to physiological SOLD studies for PDT dosimetry.
Highlights
S INGLET oxygen (1O2), is the electronic excited state (1O2 (a 1Δg )) of molecular oxygen which has by default its electronic ground state in a spin triplet state (3O2 (X 3 −g )) [1]
Singlet oxygen is a main component in many biological processes, and in photodynamic therapy (PDT) cancer treatments, it acts as the cytotoxic agent [1], [2]
For the Singlet oxygen luminescence dosimetry (SOLD) measurements we used three different model photosensitizers in solution: Rose Bengal (RB), an organic dye molecule in the xanthene class, used for efficient excitation of oxygen, with strong absorbance at ∼540 nm, high triplet energy and quantum yield in the order of 75% [2], [24], Methylene Blue (MB), a phenothiazinium dye with strong absorbance at 550–700 nm and a quantum yield of 52% [2], [24], and Eosin Y (EY), a xanthene dye with a high excitation peak at 520 nm and a quantum yield of up to 57% [2], [25]
Summary
S INGLET oxygen (1O2), is the electronic excited state (1O2 (a 1Δg )) of molecular oxygen which has by default its electronic ground state in a spin triplet state (3O2 (X 3 −g )) [1]. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org These three components, being individually harmless for living tissue, have a powerful effect when combined; light activates the photosensitizer compounds which undergo a photochemical process to produce singlet oxygen, causing local cell necrosis [4]. Such a direct dosimetry technique offers the key advantage that it requires only one parameter; the measurement of singlet oxygen luminescence in the near infrared at 1270 nm wavelength. With the SOLD system presented here, we have achieved efficient detection of 1O2 signal on histograms with higher resolution (about 65 ns bin size over the old 1024 ns bin size histograms) using multiple photosensitizers in solution test samples, bringing SOLD a step closer to being incorporated as a valid dosimetry technique into PDT therapies
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