RESEARCH ARTICLE Stability of core/shell quantum dots—role of pH and small organic ligands

Abstract The improvement of knowledge about the toxic-ity and even processability, and stability of quantum dots (QD) requires the understanding of the relationship between the QD binding head group, surface structure, and interli-gand interaction. The scanned stripping chronopotentiome-try and absence of gradients and Nernstian equilibrium stripping techniques were used to determine the concentra-tion of Cd dissolved from a polyacrylate-stabilized CdTe/ CdS QD. The effects of various concentrations of small organic ligands such as citric acid, glycine, and histidine and the roles of pH (4.5–8.5) and exposure time (0–48 h) were evaluated. The highest QD dissolution was obtained at the more acidic pH in absence of the ligands (52 %) a result of the CdS shell solubility. At pH 8.5 the largest PAA ability to complex the dissolved Cd leads to a further QD solubility until the equilibrium is reached (24 % of dissolved Cd vs. 4 % at pH 6.0). The citric acid presence resulted in greater QD dissolution, whereas glycine, an amino acid, acts against QD dissolution. Surprisingly, the presence of histidine, an amino acid with an imidazole functional group, leads to the formation of much strong Cd complexes over time, which may be non-labile, inducing variations in the local environ-ment of the QD surface