Supramolecular Functionalisation of B/N Co-Doped Carbon Nano-Onions for Novel Nanocarrier Systems

Abstract

Boron/nitrogen co-doped carbon nano-onions (BN-CNOs) are spherical nanoparticles that consist of multiple inter-nestled fullerene layers, giving them an onion-like internal structure. They have potential as nanocarriers due to their small size, aqueous dispersibility, and biocompatibility. The non-covalent attachment of a biocompatible polymer to BN-CNOs is a simple and effective method of creating a scaffold for a novel nanocarrier system as it allows for increased aqueous dispersibility whilst preventing the immune system from recognising the particle as a foreign object. The non-covalent approach also preserves the electronic and structural properties of the BN-CNOs. In this study, we attached a hyaluronic acid-phospholipid (HA-DMPE) conjugate polymer to the BN-CNO's surface to improve its hydrophilicity and provide targetability toward HA-receptor overexpressing cancer cells. To this end, various ratios of HA-DMPE to BN-CNOs were investigated. The resulting supramolecular systems were characterised via UV-Vis absorption and FTIR spectroscopy, dynamic light scattering, and zeta potential techniques. It was found that the HA-DMPE conjugate polymer was permanently wrapped around the BN-CNO nanoparticle surface. Moreover, the resulting BN-CNO/HA-DMPE supramolecular systems displayed enhanced aqueous solubility compared to unfunctionalised BN-CNOs, with excellent long-term stability observed in aqueous dispersions.

Keywords: CD44; aqueous dispersibility; boron/nitrogen doping; carbon nano-onions; carbon nanomaterials; conjugate polymer; hyaluronic acid; nanocarrier; phospholipid; supramolecular system.

Figure 1

(Top) Hyaluronic acid-1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine non-covalently bound to the BN-CNO surface. (Framed) The functional groups present on the BN-CNO surface. The size ratio of HA-DMPE to the BN-CNOs presented is for schematic purposes; in reality, the BN-CNOs are much larger than the HA-DMPE polymer chains. They also exist as clusters in solution, not individual particles. (Bottom) Illustration of a dynamic dispersion and a static dispersion.

Figure 2

UV-Vis absorption spectra of (a) 2:1 BN-CNO/HA-DMPE, (b) 5:1 BN-CNO/HA-DMPE, and (c) 10:1 BN-CNO/HA-DMPE at various times with a 100 µg/mL starting concentration; (d–f) = UV-Vis spectra of 2:1, 5:1, and 10:1 BN-CNO/HA-DMPE, respectively, at various times (50 µg/mL starting concentration); solvent = deionised water.

Figure 3

Photos of (a–c) 2:1, 5:1, and 10:1 BN-CNO/HA-DMPE dispersions straight after sonication; (d–f) 2:1, 5:1, and 10:1 BN-CNO/HA-DMPE dispersions after 21 days; (solvent = deionised water; 50 µg/mL starting concentration).

Figure 4

DLS spectra of BN-CNO/HA-DMPE at 2:1, 5:1, and 10:1 ratios in deionised water, where (a–c) are spectra at various concentrations, and (d–f) are spectra at various timepoints with a 100 µg/mL starting concentration.

Figure 5

FTIR spectra of HA-DMPE, 10:1 BN-CNO/HA-DMPE (Washed), and BN-CNOs.

Figure 6

UV-Vis absorbance (a) and DLS (b) spectra of 10:1 BN-CNO/HA-DMPE washed sample at various times (solvent = deionised water; 100 µg/mL starting concentration).