Materials Science and Technology of Polymers

Synthesis of functionalized amphiphilic polymers for coating quantum dots

Published online 15 September 2011; doi:10.1038/nprot.2011.381

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. We present a complete protocol for the synthesis and water solubilization of hydrophobic CdSe/ZnSQDs using designer amphiphilic polymeric coatings. 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. We 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.

In this report, we present a simple protocol for the synthesis of hydrophobically capped CdSe/ZnS nanocrystals and their transfer to water using designer amphiphilic polymers. The major advan­tages of the presented method include the wide availability of the robust, commercially available and cheap polymeric precursors, as well as the simple functionalization of the polymer backbone based on anhydride ring opening with any nucleophilic agent. We also show that the desired functionality can be integrated into the poly­meric shell at the time of the coating synthesis. Therefore, there is no need for functionalization reactions after solubilization in water. In addition, no cross-linking is needed to achieve highly stable QD dis­persions. The robustness of the amphiphilic coating is demonstrated by hydrophilization of the QDs with amphiphilic polymers bear­ing attached polymeric chains such as PEG, PNIPAM and highly hydrophobic functional ligands. The latter feature is unique to this method, as it allows one to obtain hydrophilic nanoparticles functionalized with inherently hydrophobic molecules that are not soluble in water, therefore preclud­ing their attachment after the solubilization. The presented method can also be applied to other types of hydrophobic nanoparticles.

Right image
Transmission electron microscope image of the QDs transferred into water and encapsulated by the amphiphilic polymeric micelle.

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