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Biocompatible and stable ZnOquantum dots generated by functionalization with siloxane-core PAMAM dendrons

2009; Royal Society of Chemistry; Volume: 20; Issue: 6 Linguagem: Inglês

10.1039/b917629b

1364-5501

Ralph‐Olivier Moussodia, Lavinia Balan, Christophe Merlin, Christian Mustin, Raphaël Schneider,

Advanced biosensing and bioanalysis techniques

Despite the growing interest of quantum dots (QDs) in biological applications, there are many concerns regarding the potential accumulation and toxic effects of Cd-containing QDs in animals and humans. Zinc oxide QDs are promising alternatives for diagnosis and imaging but their aqueous instability has markedly limited their use. Generations 1, 2 and 3 (noted G1, G2, and G3, respectively) of new poly(amidoamine) (PAMAM) dendrons bearing a siloxane group at the focal point were prepared from 3-aminopropyltrimethoxysilane. Using tetramethylammonium hydroxide as cross-linking agent, hydrophobic oleate-capped ZnO QDs were functionalized with G1 or G2 dendrons, as evidenced by FT-IR, UV-visible and XPS analyses, and were successfully transferred in aqueous solution. AFM and TEM images show that ZnO@G1 and ZnO@G2 QDs have a spherical shape with average crystalline sizes of 5.3 and 5.1 nm, respectively. Immediately after dispersion in water, ZnO@G1 and ZnO@G2 QDs exhibit a broad and strong visible emission peak centered at 550 nm with a quantum yield of ca. 18%. A strong increase of photoluminescence quantum yields was observed over time and values up to 59% could be reached after ca. 20 days of storage in water at room temperature. The good quantum yields and the stabilities of PAMAM-dendron capped ZnO QDs ensured their potential applications in cell imaging. ZnO@G2 was successfully used for the labelling of the Gram+ bacterium Staphylococcus aureus. The biocompatibility of these QDs is markedly improved compared to Cd-based ones as growth inhibition tests showed that ZnO@G2 QDs could be used with concentrations up to 1 mM without altering the cell growth of the Escherichia coli bacterium while most Cd-containing QDs already exhibit cytotoxicity at the nM level.