Manipulations of nanocrystal (NC) surfaces have propelled the applications of colloidal NCs across various fields such as bioimaging, catalysis, electronics, and sensing applications.
This study examines the relative binding strength of a series of thiolate ligands to the surfaces of zincblende CdSe/ZnS core/shell quantum dots (QDs) passivated by phosphonate ligands under basic conditions in water by means of isothermal titration calorimetry (ITC). A labile hydrophilic intermediate, 2aminoethylphosphonic acid (AEP), was introduced in place of native hydrophobic carboxylate ligands to produce water-soluble QDs and provide a universal starting point for competitive anionic exchange reactions. We introduce monothiols of different chain lengths, and a dithiol analogue (dihydrolipoic acid), to probe the effects of chain length and denticity on binding strength. The introduction of each of the ligands produces an exothermic response. An increase in chain length among the monothiols led to an increase in the equilibrium exchange constant, K ex , indicating longer chain lengths lead to stronger binding. However, the shorter chain mercaptopropionic acid showed greater total exothermicity, which appears to indicate a greater total number of accessible binding sites. The introduction of a dithiol ligand produces a larger K ex than the monodentate thiols, consistent with greater binding strength and stability inferred from previous observations, and ligand density comparable to the shorter chain mercaptopropionic acid at saturation. This work should aid in the development of stable and versatile water-soluble QD colloids for bioimaging and sensing applications.
Colloidal quantum dots (QDs) are
attractive fluorophores for bioimaging
and biomedical applications because of their favorable and tunable
optoelectronic properties. In this study, the native hydrophobic ligand
environment of oleate-capped sphalerite CdSe/ZnS core/shell QDs was
quantitatively exchanged with a set of imidazole-bearing small-molecule
ligands. Inductively coupled plasma-optical emission spectroscopy
and 1H NMR were used to identify and quantify three different
ligand exchange processes: Z-type dissociation of the Zn(oleate)2, L-type association of the imidazole, and X-type anionic
exchange of oleate with Cl–, all of which contributed
to the overall ligand exchange.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.