title: Controlled clustering of superparamagnetic nanoparticles using block copolymers: design of new contrast agents for magnetic resonance imaging.
abstract: When polyelectrolyte-neutral block copolymers are mixed in aqueous solutions with oppositely charged species, stable complexes are found to form spontaneously. The mechanism is based on electrostatics and on the compensation between the opposite charges. Electrostatic complexes exhibit a core-shell microstructure. In the core, the polyelectrolyte blocks and the oppositely charged species are tightly bound and form a dense coacervate microphase. The shell is made of the neutral chains and surrounds the core. In this paper, we report on the structural and magnetic properties of such complexes made from 6.3 nm diameter superparamagnetic nanoparticles (maghemite gamma-Fe(2)O(3)) and cationic-neutral copolymers. The copolymers investigated are poly(trimethylammonium ethylacrylate methyl sulfate)-b-poly(acrylamide), with molecular weights 5000-b-30000 g mol(-)(1) and 110000-b-30000 g mol(-)(1). The mixed copolymer-nanoparticle aggregates were characterized by a combination of light scattering and cryo-transmission electron microscopy. Their hydrodynamic diameters were found in the range 70-150 nm, and their aggregation numbers (number of nanoparticles per aggregate) from tens to hundreds. In addition, Magnetic Resonance Spin-Echo measurements show that the complexes have a better contrast in Magnetic Resonance Imaging than single nanoparticles and that these complexes could be used for biomedical applications.
authors.affiliation: Matière et Systèmes Complexes, UMR 7057 CNRS Université Denis Diderot Paris-VII,140 rue de Lourmel, F-75015 Paris, France. jean-francois.berret@ccr.jussieu.fr
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Berret
authors.forename: Nicolas
authors.initials: N
authors.lastname: Schonbeck
authors.forename: Florence
authors.initials: F
authors.lastname: Gazeau
authors.forename: Delphine
authors.initials: D
authors.lastname: El Kharrat
authors.forename: Olivier
authors.initials: O
authors.lastname: Sandre
authors.forename: Annie
authors.initials: A
authors.lastname: Vacher
authors.forename: Marc
authors.initials: M
authors.lastname: Airiau
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D003287:Contrast Media / Q000737:chemistry*; D008027:Light; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D049329:Nanostructures / Q000737:chemistry*; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D012542:Scattering, Radiation; D055672:Static Electricity; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D003287:Contrast Media; D019904:Polymethyl Methacrylate; D000099166:Polyacrylamides; C464425:poly((N-trimethylammonium)ethyl methacrylate)