Controlled Clustering of Superparamagnetic Nanoparticles Using Block Copolymers: Design of New Contrast Agents for Magnetic Resonance Imaging

• Published in: Journal of the American Chemical Society 2006-02, Vol.128 (5), p.1755-1761
• Main Authors: Berret, Jean-François, Schonbeck, Nicolas, Gazeau, Florence, El Kharrat, Delphine, Sandre, Olivier, Vacher, Annie, Airiau, Marc
• Format: Article
• Language: English
• Subjects: Acrylic Resins - chemistry; Biological and medical sciences; Chemical Sciences; Chemistry; Colloidal state and disperse state; Condensed Matter; Contrast Media - chemistry; Contrast media. Radiopharmaceuticals; Exact sciences and technology; General and physical chemistry; Light; Magnetic Resonance Imaging - methods; Magnetics; Material chemistry; Medical sciences; Nanostructures - chemistry; Pharmacology. Drug treatments; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physics; Polymethyl Methacrylate - chemistry; Scattering, Radiation; Soft Condensed Matter; Static Electricity
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0562999

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 γ-Fe2O3) 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.