Complex of water-soluble CdSe/ZnS quantum dots and chlorin e 6 : interaction and FRET

Abstract

In this work we present the spectral study on complex formation between CdSe/ZnS-amino (620 nm) quantum dots (QDs) and second-generation photosensitizer chlorin _e6 (Ce₆). In the presence of QDs, significant changes in the absorption and fluorescence properties of Ce6 were observed. The fluorescence spectrum of bound Ce₆ molecules displayed the new intensive fluorescence band at 670 nm, similar to that observed in organic solvent chloroform. With an increase in QDs:Ce₆ molar ratio up to 1:20, the spectrum of QDs-Ce₆ showed the decrease in intensity of QDs fluorescence band at 620 nm, while the intensity of fluorescence band at 670 nm was increasing simultaneously. The fluorescence excitation spectrum of bound Ce₆ molecules exposed a contribution of QDs spectrum. The fluorescence decay measurements of QDs-Ce₆ solution displayed the shortening of QDs fluorescence lifetime at increasing Ce₆concentration. We conclude, that Ce₆ molecules interact with the hydrophobic groups of QDs coating, which results in the changes of spectral properties of Ce₆. Upon binding, Ce₆ molecules are located close enough to the shell/core of QDs for Förster resonance energy transfer (FRET) from QDs to Ce₆ to occur.