Abstract
With their nanoscalar, superparamagnetic Gd(3+)-ion clusters (1 x 5 nm) confined within ultrashort (20-80 nm) single-walled carbon nanotube capsules, gadonanotubes are high-performance T1-weighted contrast agents for magnetic resonance imaging (MRI). At 1.5 T, 37 degrees C, and pH 6.5, the r1 relaxivity (ca. 180 mM(-1) s(-1) per Gd(3+) ion) of gadonanotubes is 40 times greater than any current Gd(3+) ion-based clinical agent. Herein, we report that gadonanotubes are also ultrasensitive pH-smart probes with their r1/pH response from pH 7.0-7.4 being an order of magnitude greater than for any other MR contrast agent. This result suggests that gadonanotubes might be excellent candidates for the development of clinical agents for the early detection of cancer where the extracellular pH of tumors can drop to pH=7 or below. In the present study, gadonanotubes have also been shown to maintain their integrity when challenged ex vivo by phosphate-buffered saline solution, serum, heat, and pH cycling.
Highlights
As diagnostic radiology strives for earlier detection of disease, the demand for greater contrast agent performance inevitably grows as well
The rapidly emerging field of molecular imaging seeks to develop contrast agents (CAs) as molecular probes that respond to cellular processes or cellular markers, contrary to the current clinical CAs that are essentially noninteracting bystanders during the imaging process
Some recent prototype magnetic resonance imaging (MRI) CAs have been designed to respond to pH,[1,2,3,4] pO2,5,6 specific enzymes,[7,8] or to metal ion concentration,[9,10] while others have been molecularly targeted to an area of interest.[11,12,13]
Summary
As diagnostic radiology strives for earlier detection of disease, the demand for greater contrast agent performance inevitably grows as well. Superparamagnetic Gd3+-ion clusters (1 × 5 nm) confined within ultrashort (20−80 nm) single-walled carbon nanotube capsules, gadonanotubes are high-performance T1-weighted contrast agents for magnetic resonance imaging (MRI).
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