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

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 Fe 2 O 3 and superparamagnetic. The Fe 2 O 3 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 (T 1 /T 2 ) of approximately 12. These complexes have a longer spin−spin relaxation time (T 2 ∼ 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.

The magnetic, relaxometric, and optical properties of gadolinium-catalyzed single walled carbon nanotubes

“…These peaks are red-shifted by 5-20 nm, compared to SWCNTs coated with ionic surfactants or DNA. [34][35][36] Fluorescence intensity between 800 and 1100 nm is lower than the intensity beyond 1100 nm. Previous studies show that semiconducting SWCNTs at wavelengths above 1200 nm have higher diameters (>1.4 nm).…”

“…Previous studies show that semiconducting SWCNTs at wavelengths above 1200 nm have higher diameters (>1.4 nm). 36 The higher intensity peaks beyond 1100 nm suggest that the Gd-SWCNT solutions either contain a greater number of large-diameter SWCNTs (>1.4 nm), or that more fluorescence quenching occurs in smaller diameter SWCNTs. In this study, a bath sonicator was used which does not cut the SWCNTs, or reduce their PL intensity.…”

“…9 Additionally, the NIR fluorescence of the Gd-SWCNTs is unaffected by photo-bleaching, tunable, and not significantly hindered by background auto-fluorescence. 36 Thus, the high relaxivities and NIR fluorescence, combined with the possibility that the exterior surface of the Gd-SWCNTs acts as a scaffold for attachment of groups to target biomacromolecules, cells or tissues make them excellent candidates for use in molecular imaging applications. Furthermore, the Gd-SWCNTs due to their large NIR absorption cross-sections can be employed for photothermal therapy.…”

The contributions of metal impurities and tube structure to the toxicity of carbon nanotube materials

“…Several groups reported the use of metal impurities, such as iron oxides, in CNTs for magnetic resonance imaging. Choi et al 17 first demonstrated the use of the SWNT (single-walled nanotube)/ iron oxide NP complexes as multimodal biomedical imaging agents. In another study, the presence of single-walled CNTs (SWCNTs) with associated metal impurities was detected in vivo using noninvasive MR techniques.…”

Micellar Hybrid Nanoparticles for Simultaneous Magnetofluorescent Imaging and Drug Delivery

“…[1][2][3][4][5][6][7][8][9] To date, several types of hybrid nanosystems containing multiple different types of nanoparticles have been developed that allow multimodal imaging. For example, formulations containing quantum dots (QD) and magnetic iron oxide nanoparticles (MN) provide a means to perform simultaneous fluorescent optical imaging and magnetic resonance imaging (MRI).…”