Urazole-Functionalized Carbon Nanotubes as Artificial DNA Strands and Their In Vivo Toxicity

Single-walled carbon nanotubes (SWCNTs) are grafted with multiple phenoxy-triazole-(ethylene glycol) ligands, whose terminals are uniformly functionalized with DNA-binding moieties. Each binder contains one to three binding sites for imidazolidin-2-one, hydantoin, or urazole. Entwinement of these "artificial strands" with ss- and dsDNAs forms pseudoduplex or pseudotriplex DNA structures, respectively. The hybridization preference between the functionalized SWCNTs (i.e., f-SWCNTs 1a-c) and ssDNA is investigated using homo-oligomers ss-dA₂₅, ss-dT₂₅, and ss-dC₂₅. Results show that ss-dA₂₅ bound strongly to f-SWCNT 1c bearing urazoles, ss-dT₂₅ bound exclusively to 1c, and ss-dC₂₅ bound selectively to 1a (imidazolidin-2-one) and 1b (hydantoin). For the formation of pseudotriplets with duplex oligomers dA₂₅•dT₂₅ and dG₂₅•dC₂₅ at pH 7.4, d(A•T) pairs bound strongly to 1c but weakly to 1a and 1b. Conversely, d(G•C) pairs bound strongly to 1a and moderately to 1b and 1c. Under acidic conditions (pH 5.4), 1c exhibits the strongest binding, while 1a and 1b show moderate affinity. These findings highlight the potent binding capability and nucleobase selectivity of f-SWCNT 1c functionalized with urazoles. Biocompatibility is also assessed─touch responses and thrashing assays are performed to evaluate the ecotoxicity of shortened f-SWCNT 1c on the nervous system of C. elegans. No significant toxicity is observed up to concentrations of 250 μg/mL, with f-SWCNT 1c ∼2500-fold less toxic than simple SWCNT-COOH. These results suggest that the newly developed f-SWCNT 1c is not only highly biocompatible but also holds great promise for broad biological applications.