title: Nanoparticle-based PARACEST agents: the quenching effect of silica nanoparticles on the CEST signal from surface-conjugated chelates.
abstract: Silica nanoparticles of average diameter 53 ± 3 nm were prepared using standard water-in-oil microemulsion methods. After conversion of the surface Si-OH groups to amino groups for further conjugation, the PARACEST agent, EuDOTA-(gly)₄ (-) was coupled to the amines via one or more side-chain carboxyl groups in an attempt to trap water molecules in the inner-sphere of the complex. Fluorescence and ICP analyses showed that approximately 1200 Eu(3+) complexes were attached to each silica nanoparticle, leaving behind excess protonated amino groups. CEST spectra of the modified silica nanoparticles showed that attachment of the EuDOTA-(gly)₄ (-) to the surface of the nanoparticles did not result in a decrease in water exchange kinetics as anticipated, but rather resulted in a complete elimination of the normal Eu(3+) -bound water exchange peak and broadening of the bulk water signal. This observation was traced to catalysis of proton exchange from the Eu(3+) -bound water molecule by excess positively charged amino groups on the surface of the nanoparticles.
authors.affiliation: Department of Chemistry, University of Texas at Dallas, Richardson, TX 75083, USA.
authors.forename: Osasere M
authors.initials: OM
authors.lastname: Evbuomwan
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Merritt
authors.forename: Garry E
authors.initials: GE
authors.lastname: Kiefer
authors.forename: A
authors.initials: A
authors.lastname: Dean Sherry
mesh_terms: D002614:Chelating Agents / Q000737:chemistry* / Q000378:metabolism; D003198:Computer Simulation; D003287:Contrast Media / Q000737:chemistry* / Q000378:metabolism; D056831:Coordination Complexes / Q000737:chemistry* / Q000378:metabolism; D004655:Emulsions; D005063:Europium / Q000737:chemistry / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D015394:Molecular Structure; D008970:Molecular Weight; D058726:Nanoconjugates / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D011522:Protons; D012822:Silicon Dioxide / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D002614:Chelating Agents; D003287:Contrast Media; D056831:Coordination Complexes; D004655:Emulsions; D058726:Nanoconjugates; D011522:Protons; D014867:Water; D005063:Europium; D012822:Silicon Dioxide