Gadonanotubes as Ultrasensitive pH-Smart Probes for Magnetic Resonance Imaging

• Published in: Nano letters 2008-02, 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
• Subjects: Applied sciences; Biological and medical sciences; Chemical Sciences; Contrast Media - chemistry; Cross-disciplinary physics: materials science; rheology; Crystallization - methods; Electronics; Exact sciences and technology; Gadolinium - chemistry; General equipment and techniques; Hydrogen-Ion Concentration; Image Enhancement - methods; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging - methods; Materials science; Materials Testing - methods; Medical sciences; Miscellaneous. Technology; Molecular Conformation; Molecular electronics, nanoelectronics; Molecular Probe Techniques; Nanoscale materials and structures: fabrication and characterization; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology - methods; Nanotubes; Particle Size; Physics; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl0720408

With their nanoscalar, superparamagnetic Gd3+-ion clusters (1 × 5 nm) confined within ultrashort (20−80 nm) single-walled carbon nanotube capsules, gadonanotubes are high-performance T 1-weighted contrast agents for magnetic resonance imaging (MRI). At 1.5 T, 37 °C, and pH 6.5, the r 1 relaxivity (ca. 180 mM-1 s-1 per Gd3+ ion) of gadonanotubes is 40 times greater than any current Gd3+ ion-based clinical agent. Herein, we report that gadonanotubes are also ultrasensitive pH-smart probes with their r 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.