Photoligation
of an Amphiphilic Polymer with Mixed
Coordination Provides Compact and Reactive Quantum Dots
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Abstract
We introduce a new
set of multicoordinating polymers as ligands
that combine two distinct metal-chelating groups, lipoic acid and
imidazole, for the surface functionalization of QDs. These ligands
combine the benefits of thiol and imidazole coordination to reduce
issues of thiol oxidation and weak binding affinity of imidazole.
The ligand design relies on the introduction of controllable numbers
of lipoic acid and histamine anchors, along with hydrophilic moieties
and reactive functionalities, onto a poly(isobutylene-<i>alt</i>-maleic anhydride) chain via a one-step nucleophilic addition reaction.
We further demonstrate that this design is fully compatible with a
novel and mild photoligation strategy to promote the in situ ligand
exchange and phase transfer of hydrophobic QDs to aqueous media under
borohydride-free conditions. Ligation with these polymers provides
highly fluorescent QDs that exhibit great long-term colloidal stability
over a wide range of conditions, including a broad pH range (3–13),
storage at nanomolar concentration, under ambient conditions, in 100%
growth media, and in the presence of competing agents with strong
reducing property. We further show that incorporating reactive groups
in the ligands permits covalent conjugation of fluorescent dye and
redox-active dopamine to the QDs, producing fluorescent platforms
where emission is controlled/tuned by Förster Resonance Energy
Transfer (FRET) or pH-dependent charge transfer (CT) interactions.
Finally, the polymer-coated QDs have been coupled to cell-penetrating
peptides to facilitate intracellular uptake, while subsequent cytotoxicity
tests show no apparent decrease in cell viability