Gadonanotubes as Ultrasensitive pH-Smart Probes for Magnetic Resonance Imaging

• Published in: Nano letters 2008-01, Vol.8 (2), p.415-419
• Main Authors: Hartman, Keith B, Laus, Sabrina, Bolskar, Robert D, Muthupillai, Raja, Helm, Lothar, Toth, Eva, Merbach, Andre E, Wilson, Lon J
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl0720408PII:S1530-6984(07)02040-1

With their nanoscalar, superparamagnetic Gd super(3+)-ion clusters (1 x 5 nm) confined within ultrashort (20-80 nm) single-walled carbon nanotube capsules, gadonanotubes are high-performance T sub(1)-weighted contrast agents for magnetic resonance imaging (MRI). At 1.5 T, 37 degree C, and pH 6.5, the r sub(1) relaxivity (ca. 180 mM super(-1) s super(-1) per Gd super(3+) ion) of gadonanotubes is 40 times greater than any current Gd super(3+) ion-based clinical agent. Herein, we report that gadonanotubes are also ultrasensitive pH-smart probes with their r sub(1)/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.