Photodynamic therapy (PDT) is a promising cancer treatment that involves optical excitation of photosensitizers that promote oxygen molecules to the metastable O2(a1) state (singlet oxygen). This species is believed to be responsible for the destruction of cancerous cells during PDT. We describe a fiber optic-coupled, pulsed diode laser-based diagnostic for singlet oxygen. We use both temporal and spectral filtering to enhance the detection of the weak O2(aX) emission near 1.27 µm. We present data that demonstrate real-time singlet oxygen production in tumor-laden rats with chlorin e6 and 5-aminolevulinic acid-induced protoporphyrin photosensitizers. We also observe a positive correlation between post-PDT treatment regression of the tumors and the relative amount of singlet oxygen measured. These results are promising for the development of the sensor as a real-time dosimeter for PDT.
Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling.
Scaling of EOIL systems to higher powers requires extension of electric discharge powers into the kW range and
beyond with high efficiency and singlet oxygen yield. We have previously demonstrated a high-power microwave
discharge approach capable of generating singlet oxygen yields of ~25% at ~50 torr pressure and 1 kW power. This
paper describes the implementation of this method in a supersonic flow reactor designed for systematic investigations of
the scaling of gain and lasing with power and flow conditions. The 2450 MHz microwave discharge, 1 to 5 kW, is
confined near the flow axis by a swirl flow. The discharge effluent, containing active species including O<sub>2</sub>(a<sup>1</sup>Δ<sub>g</sub>, b<sup>1</sup>Σ<sub>g</sub><sup>+</sup>),
O(<sup>3</sup>P), and O<sub>3</sub>, passes through a 2-D flow duct equipped with a supersonic nozzle and cavity. I2 is injected upstream of
the supersonic nozzle. The apparatus is water-cooled, and is modular to permit a variety of inlet, nozzle, and optical
configurations. A comprehensive suite of optical emission and absorption diagnostics is used to monitor the absolute
concentrations of O<sub>2</sub>(a), O<sub>2</sub>(b), O(<sup>3</sup>P), O<sub>3</sub>, I<sub>2</sub>, I(<sup>2</sup>P<sub>3/2</sub>), I(<sup>2</sup>P<sub>1/2</sub>), small-signal gain, and temperature in both the subsonic and
supersonic flow streams. We discuss initial measurements of singlet oxygen and I* excitation kinetics at 1 kW power.
We discuss experimental results from spectroscopic and kinetic investigations of the reaction sequence starting with
NCI<sub>3</sub> + H. Through a series of abstraction reactions, NCI (a<sup>1</sup>Δ) is produced. We have used sensitive optical emission
diagnostics and have observed both [NCI(a<sup>1</sup>Δ)]and [NCI(b<sup>1</sup>Σ)] produced by this reaction. Upon addition of HI to
the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(<sup>2</sup>P<sub>1/2</sub>) state, and we
observed strong emission from the I atom <sup>2</sup>P <sub>1/2</sub> -> <sup>2</sup>P<sub>3/2</sub> transition at 1.315 μm. With a tunable diode laser we probed
the I atom transition and observed significant transfer of population from ground state (<sup>2</sup>P<sub>3/2</sub>) to the excited state
(<sup>2</sup>P<sub>1/2</sub>) and have observed optical transparency within the iodine atom energy level manifold.