Photobleaching of phthalocyanines in the complex with colloidal quantum dots

Abstract

Currently, fluorescent nanoparticles are considered as promising enhancers of photodynamic activity of traditional photosensitizers in the procedures of photodynamic therapy of cancer and inactivation of pathogens. On the one hand, such nanoparticles act as a nanoplatform for target delivery of dye molecules to cells, on the other – as light-harvesting antennas that increase the effective absorption cross-section of the dye. In this paper the influence of semiconductor CdSe/ZnS quantum dots coated with a polymer shell on the photostability of zinc or aluminum polycationic phthalocyanines was studied. It was shown that in presence of the quantum dots the rate of photobleaching of phthalocyanines increases significantly both with direct illumination of phthalocyanine by red light and with the quantum dot-mediated illumination by blue light. This effect can be explained by the fact that phthalocyanine is the primary target for the attack of reactive oxygen species inside the polymer shell of the quantum dot. The rate of bleaching of chemical trap of the reactive oxygen species 4-nitroso-N,N-dimethylaniline in phthalocyanine solution increases in the presence of the quantum dot under red light illumination. We believe that the chemical trap is concentrated in the polymer shell of the quantum dot, which increases the probability of its damage by active oxygen species generated by the phthalocyanine. Since the diffusion of reactive oxygen species from the polymer shell of a nanoparticle into the surrounding solution is slow, the use of quantum dots as an enhancer of the photodynamic action of phthalocyanines can be effective only in the absence of significant steric obstacles to the diffusion of reactive oxygen species to the target molecules of photodynamic inactivation.