Noncovalent Functionalization of Carbon Nanotubes with Amphiphilic Gd³⁺ Chelates:  Toward Powerful T₁ and T₂ MRI Contrast Agents

Abstract

An amphiphilic gadolinium (III) chelate (GdL) was synthesized from commercially available stearic acid. Aqueous solutions of the complex at different concentrations (from 1 mM to 1 microM) were prepared and adsorbed on multiwalled carbon nanotubes. The resulting suspensions were stable for several days and have been characterized with regard to magnetic resonance imaging (MRI) contrast agent applications. Longitudinal water proton relaxivities, r1, have been measured at 20, 300, and 500 MHz. The r1 values show a strong dependence on the GdL concentration, particularly at low field. The relaxivities decrease with increasing field as it is predicted by the Solomon-Bloembergen-Morgan theory. Transverse water proton relaxation times, T2, have also been measured and are practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been performed at 300 MHz in mice. A negative contrast could be well observed after injection of a suspension of functionalized nanotubes into the muscle of the leg of the mouse.

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

“…9 Gd 3þ ion carbon nanotube (CNT) complexes show promise as high-performance T 1 MRI CAs. [12][13][14][15][16] Wilson and colleagues developed a synthesis method, wherein pristine commercial single-walled carbon nanotubes (SWCNTs, length >1 lm) are chemically cut into ultra-short (US) SWCNTs (US-tubes; length, 20-80 nm); Gd 3þ ions are then loaded into these US-tubes through defects along the side-walls. 2 Richard and coworkers coordinated Gd 3þ ions to multiple ligands, which were non-covalently adsorbed onto multi-walled carbon nanotubes (MWCNTs).…”

“…2 Richard and coworkers coordinated Gd 3þ ions to multiple ligands, which were non-covalently adsorbed onto multi-walled carbon nanotubes (MWCNTs). 16 Both of these methods are "top down" synthesis strategies involving the addition of Gd 3þ ions to bulk commercial CNTs, and result in 3-90 times (depending on magnetic field and Gd 3þ concentration) increase in r 1 relaxivity compared to the clinical MRI CA Magnevist (Gd-DTPA). To date, these MRI CAs have not been demonstrated to be concomitantly suitable as optical CAs.…”

“…18 The lanthanoid nanoparticles are embedded into, and located at one end of the SWCNTs (SWCNT average diameter 2.05 nm, length 500 nm-1.5 lm). 19 Thus, the synthetic strategy in the development of Gd-SWCNTs is distinctly different compared to previous approaches to develop SWCNT Gd 3þ complexes as MRI CAs, [12][13][14][15][16] or multimodal MRI-optical imaging CAs. Here, we report the magnetic behavior, T 1 and T 2 nuclear magnetic resonance dispersion (NMRD) profiles, MRI phantom imaging, and near-infrared (NIR) photoluminescence spectroscopy of water solubilized Gd-SWCNTs toward development as novel multimodal MRIoptical CAs.…”

Hyaluronic acid-functionalized single-walled carbon nanotubes as tumor-targeting MRI contrast agent

“…16 Additionally, the multi-sites of SWCNTs could bind with drugs or molecular targets effectively. 17 All these results suggested a new way of tumor-targeting CA delivery system for MRI.…”

Amalgamation of complex iron(III) ions and iron nanoclusters with MWCNTs as a route to potential T2 MRI contrast agents

“…[23][24][25][26] However, approaches and targets both differed: 1) SPIONs were immobilized via ionic interactions between poly(diallyldimethylammonium)-pretreated oxidized CNTs and lactose-glycine covered Fe 3 O 4 nanoparticles ("indirect" approach), 27,28 or 2) ironbased nanoparticles were produced in situ as "corks" for HiPCO CNTs ("direct" approach); 21,24 the nanotubes were additionally functionalized mainly with polymers. On the basis of our recent experience with Fe 3+ -nanotube complexes as relaxation accelerators, we decided to explore this field further.…”