title: Strategies for increasing relaxivity of gold nanoparticle based MRI contrast agents.
abstract: The factors limiting the relaxivity (r) of MRI contrast agents based on small (∼2.0 nm) gold nanoparticles functionalised with paramagnetic chelates were explored using EPR spectroscopy. The EPR analysis suggested that nanoparticle-attached chelates exhibit relatively high tumbling rates which restrict their relaxivity. Two different strategies were employed in order to test this hypothesis and hence improve the relaxivity of the nanoparticle-based contrast agents. In the first approach, the particle diameter was increased. This resulted in lower surface curvature and hence tighter ligand packing, which in turn led to increased relaxivity. In the second approach, the nanoparticles were overcoated with multilayers of oppositely charged polyelectrolytes. The restricted motion of Gd(3+) chelates coated by 2-4 polymer layers led to increased relaxivity which was dramatically reduced for thicker layers, presumably due to restricted diffusion of water molecules.
authors.affiliation: Chemistry Department, The University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Muhammad Farooq
authors.initials: MF
authors.lastname: Warsi
authors.forename: Victor
authors.initials: V
authors.lastname: Chechik
mesh_terms: D003287:Contrast Media / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005682:Gadolinium / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D008279:Magnetic Resonance Imaging; D053768:Metal Nanoparticles / Q000737:chemistry*; D004369:Pentetic Acid / Q000737:chemistry; D011108:Polymers / Q000737:chemistry
chemical_list: D003287:Contrast Media; D056831:Coordination Complexes; D004573:Electrolytes; D011108:Polymers; D006046:Gold; D004369:Pentetic Acid; D005682:Gadolinium