Prevention of Carbon Nanohorn Agglomeration Using a Conjugate Composed of Comb-Shaped Polyethylene Glycol and a Peptide Aptamer

Assured dispersibility is a prerequisite for clinical application of nanomaterials. Carbon nanomaterials have hydrophobic surfaces and thus readily agglomerate under aqueous conditions. Various conjugates composed of a carbon surface-binding moiety and polyethylene glycol (PEG) have been examined as dispersants for carbon nanomaterials. Here we synthesized a conjugate composed of a comb-shaped PEG (cPEG) and carbon nanomaterial-binding peptide (NHBP-1). The resultant cPEG−NHBP3 conjugate displayed multiple units (2.4 on average) of NHBP-1 on a single cPEG molecule whose average molecular weight was 15−20 kDa. cPEG−NHBP3 endowed single-walled carbon nanohorns (SWNHs) with good dispersibility in vitro, which could not be achieved with 20PEG−NHBP, a conjugate composed of linear 20 kDa PEG and a single NHBP-1 peptide. Notably, cPEG−NHBP1, which was similar to 20PEG−NHBP but had a comb-shaped PEG backbone, functioned better as a dispersant than 20PEG−NHBP, suggesting a graft-type PEG formula is better-suited for dispersing nanomaterials. Finally, cPEG−NHBP3 treatment substantially suppressed formation of SWNH agglomerates in mouse lung, suggesting the potential utility of SWNHs as a carrier in drug delivery systems.