Lipoic acid as anchoring groups and reactive sites on nanoparticles coated with multi-coordinating polymers

Coating inorganic nanocrystals (e.g., quantum dots and gold nanoparticles) with polymer ligands presenting many lipoic acid (LA) anchoring groups provides them with excellent colloidal stability in aqueous media. Here we exploit the natural swelling of polymer macromolecules, which imposes a configuration that leaves a fraction of the anchors on the polymerstabilized nanocolloids free or uncoordinated and target them for conjugation using thiol-to-maleimide chemistry. This allows easy surface functionalization of the nanocrystals, without the need to introduce additional reactive groups. We apply a photoligation strategy to coat QDs and AuNPs, followed by coupling with maleimide-modified dyes. We then use optical absorption and resonance energy transfer measurements, to extract estimates for the fraction of accessible LAs per nanocrystal. To further prove the effectiveness of this approach, we construct a ratiometric pH sensing probe made of QDSNARF conjugates. The combination of the multi-coordinating ligand design and in-situ photoligation yields colloidally stable nanocrystals, presenting several thiol reactive sites. Our results are promising and could advance the integration of nanomaterials in biological sensing and imaging applications.