Multiwavelength excitation of photosensitizers interacting with gold nanoparticles and its impact on optical properties of their hybrid mixtures

Abstract

In a hybrid mixture of organic (dye) and inorganic (metallic nanoparticles) components, the optical properties of a dye can be easily controlled by tailoring the shape or the concentration of the noble metal nanoparticles (NPs). The influences of multiexcitation (multiwavelength excitation) of photosensitizers (pheophorbide a and hematoporphyrin) on the interactions with pegylated Au-NPs and on the photophysical parameters of the dyes are studied. Detailed, systematic fluorescence quenching studies were performed in the mixtures of different contents of Au-NPs, and interpreted together with the results of quantum singlet oxygen yield examinations. According to the results, the fluorescence of the two dyes studied was effectively quenched in the presence of Au-NPs, mainly because of the resonance energy transfer between the donor (dye) and the acceptor (Au-NPs). Stern–Volmer quenching constants were determined by a few orders of magnitude higher than those describing the photochemical quenching process. In hybrid mixtures analyzed, the mechanism of energy transfer between the donor and the acceptor was nanometal surface energy transfer. Furthermore, different behavior of the mixtures on excitation with the wavelengths from the Soret and Q bands of the dyes and with those corresponding to the surface plasmon resonance band of Au-NPs was analyzed. Moreover, for certain concentrations of Au-NPs and for certain excitation wavelengths, an increase in singlet oxygen generation was observed. The results obtained indicate the significance of further studies of photosensitizers in hybrid mixtures with NPs.