Amphipol-encapsulated CuInS2/ZnS quantum dots with excellent colloidal stability

Abstract

CuInS₂ quantum dots encapsulated in ZnS shells have emerged as less-toxic alternatives to cadmium-based nanoparticles. A well-established synthesis route for hydrophobic CIS/ZnS core/shell QDs has been developed using dodecanethiol as a ligand, solvent and source of sulfur, although the transfer of these nanoparticles into the aqueous phase still proves to be non-trivial. In this study we demonstrate that coating CIS/ZnS with an amphipol, poly(maleic anhydride-alt-1-tetradecene), 3-(dimethylamino)-1-propylamine derivative is an effective method to disperse CIS/ZnS QDs in the aqueous environment. The polymer-coated QDs display good colloidal stability over a wide pH range and low sensitivity to the presence of various metal salts, except Cu²⁺ for which some sensitivity is observed. Cytotoxic effects were tested in HaCat cells and compared to thioglycolic acid modified CdTe/ZnS QDs. Neither CdTe nor CIS QDs decreased viability until above 10 μg mL⁻¹ in a WST-1 assay. By also assessing the toxicity of the PMAL-d polymer it is clear that remaining toxicity of the CIS/ZnS QDs is predominately due to the polymer coating rather than the QD core. Interestingly, MTT assays seem to artificially exaggerate cytotoxicity of the QDs, which we ascribe to the QDs interfering with the MTT or formazan crystals.