Singlet oxygen (1O2) is a powerful oxidizing agent that is generated with visible light on the surface of sensitizer complexes. It has been shown to effectively kill a wide range of bacteria and fungus. Because these excited oxygen molecules rapidly decay to their innocuous, 3O2, ground state within several microseconds, singlet oxygen creates no persistent toxic residues that could affect health and/or promote the growth of resistant micro-organisms. Thus the use of singlet oxygen has been explored for several medical applications. However, for singlet oxygen to gain widespread use, systems for generating high concentrations of 1O2 and assuring the long-term stability of the sensitizer are required. In this presentation, we describe photochemical studies of chlorin and phthalocyanine sensitizer molecules immobilized on silica surfaces as a function of irradiance (W/m2) as well as the ambient in contact with the photosensitizer. Higher irradiance levels should, in theory, increase the rate of singlet oxygen production, however higher irradiance levels have been shown to cause photobleaching of the sensitizer due to self-oxidation by singlet oxygen generated on the surface. The environment has also been shown to affect the activity of singlet oxygen. The lifetime of singlet oxygen is reduced by a factor of ~350 from 3.5 µs to ~1 ms when the excited molecule is in contact with H2O vs air. Thus in this study, we also explore the effect of the local chemical environment about the sensitizer particles by trapping singlet oxygen using aqueous anthracene dipropionate solutions. We use both a 2-phase environment where the trapping solution is in direct contact with the sensitizer, as well as a 3-phase system where the trapping solution is isolated from the sensitizer particles such that 1O2 molecules must be transported across a gas phase boundary.

Effect of irradiance on singlet oxygen generation and photobleaching of photosensitizer molecules immobilized on silica surfaces

254th National Meeting (2017)

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