Design of pyridyl-modified amphiphilic polymeric ligands: Towards better passivation of water-soluble colloidal...

An effective surface passivation is crucial to obtain quantum dots (QDs) with good photoluminescence response. Whereas the encapsulation of QDs inside amphiphilic polymers provides colloidal stability, a decrease in the quantum yield (QY) is observed. Pyridyl motifs are known to bind strongly to the ZnS on core/shell QD and increase the structure rigidity. Hence, the incorporation of pyridyl groups into the polymer could make it more compact in order to improve the optical behavior of the QDs.

Pyridyl-modified amphiphilic polymeric ligands were synthesized based on a poly(isobutylene-alt-maleic anhydride) backbone with pyridyl and alkyl end-groups as anchoring groups. The proportion of both ligands was optimized. The resulting QDs were characterized using complementary techniques such as absorption spectroscopy, static and time-resolved photoluminescence spectroscopy, transmission electron microscopy, and dynamic light scattering.

Coating with the designed polymer maintains the high QY of the QDs after being transferred to water and provides them colloidal stability under relevant biological conditions (i.e. wide range of pH and ionic strength, biological buffers and stability over time). The significant improvements of such ligand may be attributed to the synergistic effect of two anchoring groups (pyridyl and alkyl groups) which establish different types of interaction with the QD.