Urazole-Functionalized Carbon Nanotubes as Artificial DNA Strands and Their <i>In Vivo</i> Toxicity.

Abstract

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., <i>f</i>-SWCNTs <b>1a</b>-<b>c</b>) and ssDNA is investigated using homo-oligomers ss-dA₂₅, ss-dT₂₅, and ss-dC₂₅. Results show that ss-dA₂₅ bound strongly to <i>f</i>-SWCNT <b>1c</b> bearing urazoles, ss-dT₂₅ bound exclusively to <b>1c</b>, and ss-dC₂₅ bound selectively to <b>1a</b> (imidazolidin-2-one) and <b>1b</b> (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 <b>1c</b> but weakly to <b>1a</b> and <b>1b</b>. Conversely, d(G•C) pairs bound strongly to <b>1a</b> and moderately to <b>1b</b> and <b>1c</b>. Under acidic conditions (pH 5.4), <b>1c</b> exhibits the strongest binding, while <b>1a</b> and <b>1b</b> show moderate affinity. These findings highlight the potent binding capability and nucleobase selectivity of <i>f</i>-SWCNT <b>1c</b> functionalized with urazoles. Biocompatibility is also assessed─touch responses and thrashing assays are performed to evaluate the ecotoxicity of shortened <i>f</i>-SWCNT <b>1c</b> on the nervous system of <i>C. elegans</i>. No significant toxicity is observed up to concentrations of 250 μg/mL, with <i>f</i>-SWCNT <b>1c</b> ∼2500-fold less toxic than simple SWCNT-COOH. These results suggest that the newly developed <i>f</i>-SWCNT <b>1c</b> is not only highly biocompatible but also holds great promise for broad biological applications.