Multimodal Biomedical Imaging with Asymmetric Single-Walled Carbon Nanotube/Iron Oxide Nanoparticle Complexes

TLDR

Magnetic iron oxide nanoparticles and near‑infrared fluorescent single‑walled carbon nanotubes form heterostructured complexes that can be used as multimodal bioimaging agents. Fe catalyst‑grown SWNT were individually dispersed in aqueous solution via encapsulation by d(GT)15 oligonucleotides and enriched using a 0.5 T magnetic array. The complexes exhibit distinct NIR fluorescence, Raman scattering, and absorbance, contain ~3 nm Fe₂O₃ particles that are superparamagnetic (≈56 emu g⁻¹, 35 wt % content, T1/T2 ≈ 12, T2 ≈ 164 ms), and enable macrophage imaging by MRI and NIR, confirming their multimodal biomedical imaging potential.

Abstract

Magnetic iron oxide nanoparticles and near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWNT) form heterostructured complexes that can be utilized as multimodal bioimaging agents. Fe catalyst-grown SWNT were individually dispersed in aqueous solution via encapsulation by oligonucleotides with the sequence d(GT)15, and enriched using a 0.5 T magnetic array. The resulting nanotube complexes show distinct NIR fluorescence, Raman scattering, and visible/NIR absorbance features, corresponding to the various nanotube species. AFM and cryo-TEM images show DNA-encapsulated complexes composed of a ∼3 nm particle attached to a carbon nanotube on one end. X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) measurements reveal that the nanoparticles are primarily Fe2O3 and superparamagnetic. The Fe2O3 particle-enriched nanotube solution has a magnetic particle content of ∼35 wt %, a magnetization saturation of ∼56 emu/g, and a magnetic relaxation time scale ratio (T1/T2) of approximately 12. These complexes have a longer spin−spin relaxation time (T2 ∼ 164 ms) than typical ferromagnetic particles due to the smaller size of their magnetic component while still retaining SWNT optical signatures. Macrophage cells that engulf the DNA-wrapped complexes were imaged using magnetic resonance imaging (MRI) and NIR mapping, demonstrating that these multifunctional nanostructures could potentially be useful in multimodal biomedical imaging.