A New Family of Pyridine-Appended Multidentate Polymers As Hydrophilic Surface Ligands for Preparing Stable Biocompatible Quantum Dots

Abstract

The growing utility of semiconductor quantum dots (QDs) in biochemical and cellular research necessitates, in turn, continuous development of surface functionalizing ligands to optimize their performance for ever more challenging and diverse biological applications. Here, we describe a new class of multifunctional polymeric ligands as a stable, compact and high affinity alternative to multidentate thiolated molecules. The polymeric ligands are designed with a poly(acrylic acid) backbone where pyridines are used as anchoring groups that are not sensitive to degradation by air and light, along with short poly(ethylene glycol) (PEG) pendant groups which are coincorporated for aqueous solubility, biocompatibility and colloidal stability. The percentages of each of the latter functional groups are controlled during initial synthesis along with incorporation of carboxyl groups which serve as chemical handles for subsequent covalent modification of the QD surface. A detailed physicochemical characterization indicates that the multiple pyridine groups are efficiently bound on the QD surface since they provide for relatively small overall hydrodynamic sizes along with good colloidal stability and strong fluorescence over a wide pH range, under high salt concentration and in extremely dilute conditions at room temperature under room light over extended timeframes. Covalent conjugation of dyes and metal-affinity coordination with functional enzymes to the QD surfaces were also demonstrated. Biocompatibility and long-term stability of the pyridine polymer coated QDs were then confirmed in a battery of relevant assays including cellular delivery by both microinjection and peptide facilitated uptake along with intracellular single QD tracking studies and cytotoxicity testing. Cumulatively, these results suggest this QD functionalization strategy is a viable alternative that provides some desirable properties of both compact, discrete ligands and large amphiphilic polymers.

Understanding How Nanoparticle Attachment Enhances Phosphotriesterase Kinetic Efficiency

“…DHLA-CL4 functionalized QDs demonstrate biocompatibility, high quantum yields, and long-term stability across a broad pH range. 36 Construction of the PTE plasmid and its expression in E. coli is detailed in ref 34. A detailed description of the assembly and characterization of QD-PTE bioconjugates along with performing the enzymatic assays can be found in the Supporting Information.…”

Energy Transfer with Semiconductor Quantum Dot Bioconjugates: A Versatile Platform for Biosensing, Energy Harvesting, and Other Developing Applications

“…177,286 Facilitating this chemistry, laboratory expression and purification of proteins will often have the protein recombinantly modified with a terminal hexahistidine (His 6 ) sequence for IMAC and thus it is prepared in a manner that allows both purification and subsequent coordination to the QD. 120,286,287 Moreover, the small size of these peptidyl tags and its common placement at the protein's termini translates into them having little to no effect on subsequent protein function. Peptides can be easily synthesized to display a terminal His 6 and several ligation chemistries have been developed to modify DNA with such peptidyl motifs.…”

Quantum dots–DNA bioconjugates: synthesis to applications

“…For example, for disulfide containing ligands, prior reduction of the ligands assists in generation of thiol and favours dynamic interactions with the QD surface [38,39]. In the case of some imidazole-or pyridine-based polymers, this reduction step is not required [40,41]. There have been multiple designs of such polymers with various compositions of surface anchoring and water solubilizing monomers.…”