How do different surface modification strategies Affect the properties of MnO nanoparticles for biomedical applications?
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How do different surface modification strategies affect the properties of MnO nanoparticles for biomedical applications? Comparison of PEGylated and SiO2-coated MnO nanoparticles Thomas D. Schladt1,2,4, Kerstin Koll2,4, Heiko Bauer2, Stefan Weber3, Laura M. Schreiber3, Wolfgang Tremel2 1 IBM Almaden Research Center, San Jose, CA 95120-6099, U.S.A. 2 Institut für Anorganische und Analytische Chemie, Johannes-Gutenberg Universität, Duesbergweg 10-14, D-55099 Mainz, Germany 3 Institut für medizinische Physik, Klinik und Poliklinik für diagnostische und interventionelle Radiologie, Universitätsklinikum Langenbeckstrasse 1, D-55131 Mainz, Germany 4 Graduate School Materials Science in Mainz, Staudinger Weg 9, D-55128 Mainz, Germay ABSTRACT MnO nanoparticles (NPs) were surface functionalized by two different approaches, (1) using a dopamine-poly(ethylene glycol) (PEG) (DA-PEG) ligand and (2) by encapsulation within a thin silica shell applying a novel approach. Both MnO@DA-PEG and MnO@SiO2 NPs exhibited excellent long-term stability in physiological solutions. In addition, the cytotoxic potential of both materials was comparatively low. Furthermore, owing to the magnetic properties of MnO NPs, both MnO@DA-PEG and MnO@SiO2 lead to a shortening of the longitudinal relaxation time T1 in MRI. In comparison to the PEGylated MnO NPs, the presence of a thin silica shell led to a greater stability of the MnO core itself by preventing excessive Mn ion leaching into aqueous solution. INTRODUCTION The use of inorganic nanoparticles (NPs) for medical purposes has become an exciting and fast growing research field in recent years. The reason is that many inorganic materials exhibit novel physical and chemical properties which are beneficial for biomedical purposes once the crystallite size is reduced to a few nanometers. For instance, MnO a Mott-insulating antiferromagnet in bulk, becomes superparamagnetic in the nanoparticulate state.[1] Owing to this behavior, MnO NPs are able to shorten the longitudinal relaxation time (T1) of water protons in magnetic resonance imaging (MRI) and therefore allow the application of MnO NPs as T1 contrast agents.[2,3] However, due to the synthetic procedure, as-prepared MnO NPs are covered by a shell of hydrophobic capping ligands. A direct transfer into aqueous solution would therefore inevitably lead to particle aggregation and therefore pose an immediate health threat to the patient. To overcome this drawback, numerous surface modification strategies were developed in the past to enhance the hydrophilicity of inorganic NPs.[4,5] Most approaches use hydrophilic polymers, such as Food and Drug Administration (FDA) approved poly(ethylene glycol) (PEG) for this purpose.[6] In fact, PEGylation of magnetic NPs has also evolved as a popular method to increase both, water solubility and stability in bodily fluids.[7-9] A different strategy to reach the same goal is silica encapsulation. Typically, a SiO2 coating is achieved by polymerizing silane monomers, such as tetraethoxysilane (TEOS), inside a water-
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