Generation of Singlet Oxygen via the Composites of Water-Soluble Thiol-Capped CdTe Quantum DotsSulfonated Aluminum Phthalocyanines

Singlet oxygen (1O2), one of the reactive oxygen species, plays an important role in many biomedical applications. The various compounds including the phthalocyanines, quantum dots (QDs) and QD complex, which may have potential to produce 1O2, thus received more and more attentions in recent years. By means of the direct detection of near-infrared 1270 nm, we found that the water-soluble thiol-capped CdTe QDs can photoproduce 1O2 in deuterated water with a low quantum yield (QY) of 1%. When sulfonated aluminum phthalocyanines (AlSPc's) were connected to these QDs, forming water-soluble QD-Pc composites, the 1O2 QY of the composites increased to 15% under the excitation of 532 nm, while little 1O2 production can be found for AlSPc alone at the same excitation because of the poor absorption of AlSPc in this region. The results of indirect measurements of 1O2, obtained from the photodegradation of the 1O2 chemical trap anthracene-9,10-diyl-bis-methylmalonate (ADMA), confirmed 1O2 yields in both QD and QD-Pc composite solutions. The QD-Pc composites have the advantage of extending the excitation region to 400-600 nm with remarkably enhanced extinction coefficients as compared with that of AlSPc. Therefore QD-Pc composites can fully utilize visible region light excitation to effectively produce 1O2, which may facilitate the applications of QD-Pc composites in broad areas.