New Ligand Design to Promote Water Compatibility of Luminescent Quantum Dots and Gold Nanoparticles

摘要

We report the design and synthesis of new bidentate ligands to promote biocompatibility of luminescent quantum dots (QDs) and gold nanoparticle (Au-NPs) alike. The ligands use commercially available methoxy-terminated hydroxy-poly(ethylene glycol) (HO-PEG-OCH_3) and thioctic acid (TA) coupled via a stable amide bond to make TA-PEG-OCH3 ligands. Following a simple transformation of the hydroxyl group into an amine group on the methoxy-PEG, the ligand was attached to thioctic acid via DCC coupling. The use of mono-hydroxy-terminated PEG simplifies the reaction and purification steps. Following ring opening of the TA to form DHLA-PEG-OCH_3, cap exchange on CdSe-ZnS core-shell QDs provided homogeneous stable dispersions in buffer solutions. Furthermore, using either the newly designed ligand pure, or mixed with amine-functionalized ligands (DHLA-PEG-NH_2) allowed tuning of the surface functionalities of the nanoparticles. Gel electrophoresis, absorption and fluorescence experiments confirmed cap exchange, while microinjection in live cells provided additional verification of the potential utility of these hydrophilic QDs in biology. These ligands were also applied to functionalize Au-NPs, with a substantial improvement of their stability under high salt conditions compared to citrate-functionalized dispersions.