Chemical modification of multiwalled carbon nanotube with a bifunctional caged ligand for radioactive labelling

Carboxyl-functionalized multiwalled carbon nanotubes (MWCNTs) have been successfully radiolabelled with cobalt-57 (⁵⁷Co) ('T'¹/² = 270 days) via the attachment of the bifunctional caged ligand MeAMN₃S₃sar. In this study MeAMN₃S₃sar has been synthesized and coupled to MWCNTs to form the conjugate MWCNT–MeAMN₃S₃sar. Synthesis was confirmed with nuclear magnetic resonance. X-ray photoelectron spectroscopy (XPS) confirmed the conjugation. Non-radioactive labelling of this conjugate was completed with Cu(II) ions to confirm the stability of the MeAMN₃S₃sar after coupling with the MWCNTs. The complexation of the Cu(II) was also confirmed with XPS. Transmission electron microscopy was used to demonstrate that the coupling reaction had a negligible effect on the size and shape of the MWCNTs. Radiolabelling of the MWCNT–MeAMN₃S₃sar conjugate and pristine (untreated) MWCNTs (non-specific) with the gamma-emitting radioactive isotope ⁵⁷Co were compared. The radiolabelling efficiency of the MWCNT–MeAMN₃S₃sar conjugate was significantly higher (95% vs. 0.1%) ('P' ≼ 0.001) than for the unconjugated pristine MWCNTs. This will allow for the potential tracking of nanoparticle movement in vitro and in vivo.