Generation of Nitrogen Oxide and Oxygen Radicals by Quantum Dots

So far most of the work on nanoparticles and quantum dots has been focused on methods of production and applications in fluorescence imaging. The possibility to use quantum dots as photo-sensitizers (nanosensitizers) remains unexplored: Can these nanocrystals generate reactive oxygen and nitrogen species (RONS) in biological environments? A potential possibility of using quantum dots simultaneously with red light for photodynamic therapy has been demonstrated in this study in aqueous solutions, cultured cells and skin of mice. Dihydrorhodamine 123 (DHR) had been chosen as a radical probe. High production of Rh123 (oxidation product of DHR) confirms radical generation of nitrogen oxides (NOx). One of them, peroxynitrite (ONOO-), is a product of the reaction of nitric oxide (NO) with superoxide (O-2(-)) being evidence for that the latter anion can also be generated by quantum dots and red light. Lack of photooxidation of 9,10-dimethylanthracene (DMA) and the Singlet Oxygen Sensor Green (SOSG) indicates that singlet oxygen may not be generated by quantum dots under the present conditions. Quantum dots can also be used in photochemical internalization: Exposure of cancer cells incubated with quantum dots in vitro to blue light leads to lysosomal rupture and to increase of the fluorescence of the quantum dots (photoactivation). Quantum dots composed of CdSe with ZnS shell were more effective to oxidize DHR than quantum dots composed of non-heavy metals InGaP with ZnS shell.