Generation of singlet oxygen via the composites of water-soluble thiol-capped CdTe quantum dots - Sulfonated aluminum phthalocyanines

Singlet oxygen (O-1(2)), 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 O-1(2), 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 O-1(2) in deuterated water with a low quantum yield (QY) of 1%. When sulfonated aluminum phthalocyanines (AISPc's) were connected to these QDs, forming water-soluble QD-Pc composites, the O-1(2) QY of the composites increased to 15% under the excitation of 532 nm, while little O-1(2) production can be found for AISPc alone at the same excitation because of the poor absorption of AISPc in this region. The results of indirect measurements of O-1(2), obtained from the photodegradation of the O-1(2) chemical trap anthracene-9,10-diyl-bis-methylmalonate (ADMA), confirmed O-1(2) 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 AISPc. Therefore QD-Pc composites can fully utilize visible region light excitation to effectively produce O-1(2), which may facilitate the applications of QD-Pc composites in broad areas.