Quantum Dots with a Compact Amphiphilic Zwitterionic Coating

Abstract

Generally speaking, it is difficult to keep nanomaterials encapsulated in amphiphilic polymers like octylamine-grafted poly­(acrylic acid) (OPA) compact in coating-layer, with a small hydrodynamic size. Here, we prepared stable hydrophilic quantum dots (QDs) via encapsulation in ∼3 nm-long amphiphilic and zwitterionic (AZ) molecules. After encapsulation with AZ molecules, the coated QDs are only 2.1 nm thicker in coating, instead of 5.4 nm with OPA. Meanwhile, the hydrodynamic sizes of CdSe/CdS, ZnCdSeS, ZnCdSe/ZnS, and CdSe/ZnS QDs encapsulated in AZ molecules (AZ-QDs) are less than 15 nm, and 6–7 nm smaller than those of QDs in OPA (OPA-QDs). Notably, both extracellular and intracellular nonspecific binding of AZ-QDs is approximately 100-folds lower than that of OPA-QDs.

A guide to small fluorescent probes for single-molecule biophysics

“…CdTe QDs, for instance, are typically capped with mercaptopropionic acid or mercaptosuccinic acid terminated with -COOH for these reasons (188) . Recently, QDs wrapped in functionalized oligonucleotides have shown promise in the context of single particle tracking (189,190) , ligands covalently coupled to polyethylene glycols have helped to minimize nonspecific binding (191,192) , and waterdispersible QDs comprising hydrophobic QDs and zwitterionic moieties have realized liposomal-like structures that preserve optical and colloidal stability (193) . Amphiphilic polymers have also been used to improve bioconjugation (194) , and although challenges still exist, strategies for producing monovalent QDs have been reported (194,195) .…”