Abstract
Indocyanine green (ICG) has a wide optical absorption band extending from 600nm to above 800nm wavelength, and the maximum absorption near 800nm has been used for the fluorescence diagnosis in Ophthalmology, and for dye-enhanced photocoagulation. To clarify the effect of ICG irradiation, we investigated the singlet oxygen (1O2) generation in the ICG irradiation by means of a highly sensitive near infrared (NIR) detection system, and the activity in a HeLa tumor in a mouse by irradiation after an ICG injection.
We obtained the NIR spectrum at around 1270nm from irradiated ICG solutions dissolved in water, heavy water, and ethanol. The spectrum intensity was maximum in ethanol and minimum in water. Sodium azide (NaN3, known as an 1O2 quencher) was added to a water solution of ICG, and the spectrum was diminished dose-dependently by the concentration of NaN3, revealing that the spectrum was the result of 1O2. Laser irradiations (635nm, 670nm) to HeLa tumors in mice after an ICG injection resulted in tumor necrosis due to PDT. However, with irradiation at 823nm, the severe necrosis was caused by the combination of PDT and the thermal effect. When using an ICG injection to diagnose conditions of the choroid and the retina, we recommend the use of limited light power or energy during the irradiation to avoid the occlusion of veins.
