Nitroxide Radicals@US‐Tubes: New Spin Labels for Biomedical Applications

Abstract

The encapsulation of nitroxide radicals within ultrashort (ca. 50 nm) singlewalled carbon nanotubes (US-tubes) is achieved. Tempo-and Iodo-Tempo@ US-tubes are characterized by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Electron paramagnetic resonance (EPR) spectra display characteristic signals due to the detection of the spin probes within the US-tubes. Longitudinal proton relaxivities ( r 1 ) of both nitroxide@US-tubes samples are 7 to 13 times greater than the free nitroxide radicals in solution, giving relaxivities comparable to the clinical contrast agent (CA) Magnevist. In addition, transverse proton relaxivities ( r 2 ) show unprecedented proton relaxation enhancement in comparison to any other reported nitroxide radical-based system or the clinically approved T 2 CA, Resovist, under the same conditions. T 2 -weighted magnetic resonance imaging (MRI) phantom images show that the encapsulation of nitroxide radicals within the US-tubes produces good contrast enhancement due to their high r 2 relaxivities. The nitroxide radicals@US-tube agents are a new promising class of spin probes for MRI and electronic paramagnetic resonance imaging (EPRI) labeling, tracking, and diagnosis.

Bismuth@US-tubes as a potential contrast agent for X-ray imaging applications

“…A similar behavior has been observed for the encapsulation of ions and/or organic molecules in SWNTs. 42, 59, 60 Compared to our previous findings for the encapsulation of nitroxide radicals within the US-tubes (Tempo- and Iodo-Tempo@US-tubes), 42 the G-band shoulder and RBM peaks of the Bi@US-tubes (Figure 5b and 5c) are less intense due to the presence of Bi 3+ ions than for organic molecules within the US-tubes. The peak at 125 cm −1 and the broad tail from 170 to 275 cm −1 in the RBM region are in good agreement with Bi-Cl and Bi-O vibration modes, 46, 61-65 suggesting the presence of Bi 3+ -ion clusters within the US-tube.…”

Applications of Pristine and Functionalized Carbon Nanotubes, Graphene, and Graphene Nanoribbons in Biomedicine

“…All of these techniques have been extensively used for various bioapplications including bioimaging, biosensors, and drug delivery (Figure 3). Magnetic resonance imaging (MRI) requires magnetic atoms in a contrast agent such as gadolinium (III) salts, iron oxide, or nitroxide radicals [106]. Functionalized SWCNTs filled with BiOCl/Bi 2 O 3 [107] and radiocontrast agents such as I 2 [108] and 125 I − [109] have been used for X-ray computed tomography.…”

Applications of Filled Single-Walled Carbon Nanotubes: Progress, Challenges, and Perspectives

“…Contrast agents such as gadolinium (III) salts [135][136][137][138][139], iron oxide [140], and nitroxide radicals [141] are commonly used in magnetic resonance imaging (MRI). Pristine as well as functionalized SWCNTs filled with BiOCl/Bi 2 O 3 [142] or radiocontrast agents such as I 2 [143,144] and 125 I - [145,146] have been used for X-ray computer tomography.…”