21 oct 2011 - Nature protocols: coating quantum dots

Synthesis of functionalized amphiphilic polymers for coating quantum dots

Quantum dots (QDs) need to be attached to other chemical species if they are to be used as biomarkers, therapeutic agents or sensors. These materials also need to disperse well in water and have well-defined functional groups on their surfaces. QDs are most often synthesized in the presence of ligands such as trioctylphosphine oxide, which render the nanoparticle surfaces hydrophobic. Julius Vancso (MESA+, UTwente) and co-workers at A*STAR, Singapore and Nat. University of Singapore present a complete protocol for the synthesis and water solubilization of hydrophobic CdSe/ZnSQDs using designer amphiphilic polymeric coatings in Nature Protocols. The method is based on functionalization of an anhydride polymer backbone with nucleophilic agents. Small functional groups, bulky cyclic compounds and polymeric chains can be integrated into the coating prior to solubilization. They describe the preparation of acetylene- and azide-functionalized QDs for ‘click’ chemistry. The method is universal and applicable to any type of nanoparticle stabilized with hydrophobic ligands able to interact with the alkyl chains in the coating in water.

The important advantages of the presented protocol are: the ability to introduce hydrophobic functional groups onto the surface of water-soluble QDs; the lack of a cross-linking step at the end of the procedure; easy control over the number of functional units introduced into the polymeric coating; control over the number of hydrophobic n-octyl chains, and hence over the hydrophilic/hydrophobic balance of the polymeric coating; and the lack of a carbodiimide (dicyclohexylcarbodiimide (DCC) or EDC) coupling step.

The polymer-coated QDs display good colloidal stability in water, which is sufficient for many proposed applications, such as in cell imaging. They carried out successful cell imaging for the mammalian cancer cells C-6.

The fixed cells are shown in a and the live cells are shown in b. Cells were incubated with QDs for 1 h and then washed to remove the excess of free nanocrystals. Images revealed that QD-polymer assemblies were internalized by endocytosis.

Synthesis of functionalized amphiphilic polymers for coating quantum dots

Dominik Jańczewski, Nikodem Tomczak, Ming-Yong Han & G Julius Vancso

Nature Protocols 6 (2011) 1546–1553 doi:10.1038/nprot.2011.381