title: Gadonanotubes as ultrasensitive pH-smart probes for magnetic resonance imaging.
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.
authors.affiliation: Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Center for Biological and Environmental Nanotechnology, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Keith B
authors.initials: KB
authors.lastname: Hartman
authors.forename: Sabrina
authors.initials: S
authors.lastname: Laus
authors.forename: Robert D
authors.initials: RD
authors.lastname: Bolskar
authors.forename: Raja
authors.initials: R
authors.lastname: Muthupillai
authors.forename: Lothar
authors.initials: L
authors.lastname: Helm
authors.forename: Eva
authors.initials: E
authors.lastname: Toth
authors.forename: Andre E
authors.initials: AE
authors.lastname: Merbach
authors.forename: Lon J
authors.initials: LJ
authors.lastname: Wilson
mesh_terms: D003287:Contrast Media / Q000737:chemistry*; D003460:Crystallization / Q000379:methods; D005682:Gadolinium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008422:Materials Testing / Q000379:methods; D008968:Molecular Conformation; D015336:Molecular Probe Techniques; D049329:Nanostructures / Q000737:chemistry / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size
chemical_list: D003287:Contrast Media; D005682:Gadolinium