In Su Lee

Hollow Manganese Oxide Nanoparticles as Multifunctional Agents for Magnetic Resonance Imaging and Drug Delivery

Nanometer-sized colloidal particles with small size and large surface area have many superior properties when used as magnetic resonance imaging (MRI) contrast agents, such as their ability to carry large payloads of active magnetic centers, easy penetration of biological membranes, long blood circulation times, and efficient conjugation to affinity molecules. Thus, they have the potential to allow us to visualize targets at low imaging-agent concentration with high sensitivity and sepcificity. Furthermore, nanoparticles can be used in combination with therapeutic agents as bifunctional medical systems that enable simultaneous MRI diagnosis and drug treatment. For example, superparamagnetic iron oxide nanoparticles have been developed as efficient T2 contrast agents and employed to image tumors, stem cell migration, and cancer metastases. Some colloidal nanoparticles containing gadolinium(III) or manganese(II) have recently been reported as potent T1 MRI contrast agents. [4] Very recently, some of the present authors developed MnO nanoparticles as T1 contrast agents for MRI signal enhancement of the anatomic brain structure. The further development of nanoparticle MRI contrast agents will require materials with higher relaxivity than the current state of the art that can operate at much lower concentrations of potentially toxic metal ions such as Gd and Mn. In this context, hollow nanoparticles with interior void spaces are attractive candidates owing to their large water-accessible surface areas, which are able to carry high payloads of MR-active magnetic centers, and because they can take up a large amount of therapeutic drug within the interior void. While hollow nanoparticles containing magnetic ions have recently been prepared through several synthetic strategies, there are few examples of the investigation of their medical applications. Herein, we report a novel and facile synthesis of hollow manganese oxide nanoparticles (HMONs) and their potential application as multifunctional agents for simultaneous MR imaging and drug delivery. We demonstrate the greatly improved relaxivities of the hollow nanoparticles along with their efficient cellular uptake and drug loading capacities. These properties allow us to develop these particles for the delivery of therapeutic drugs as well as for diagnostic imaging. Manganese oxide nanoparticles with a diameter of 20 nm stabilized by oleic acid (MONs) as well as water-dispersible manganese oxide nanoparticles (WMONs) were prepared using a reported procedure involving the thermal decomposition of a manganese oleate complex and encapsulation with poly(ethylene glycol) phospholipid. The powder X-ray diffraction (XRD) patterns revealed that MnO is the main component of both MONs and WMONs and showed an increase of the Mn3O4 fraction in the WMONs. The analysis of the surface composition with X-ray photoelectron spectroscopy (XPS) indicated the presence of Mn and Mn (see the Supporting Information). On the basis of these observations, it was presumed that the as-synthesized MONs were passivated with Mn3O4 formed by their contact with air, even under an organic solvent, and that further oxidation occurred to form a thicker Mn3O4 shell when they were transferred into water. Very recently, the oxidation of the surface of MnO nanoparticles in air was also reported. The hollow interior of the HMONs was created by selective removal of the core MnO phase from the WMONs in acidic solution (Scheme 1). After being stirred at room

Surfactant‐Free Platinum‐on‐Gold Nanodendrites with Enhanced Catalytic Performance for Oxygen Reduction

Platinum and its alloys play important roles in many industrial applications, such as CO/NOx oxidation in catalytic converters, synthesis of nitric acid, oil cracking, and fuel cells. In particular, platinum has been the most effective catalyst in proton-exchange membrane fuel cells (PEMFCs) owing to its outstanding electrocatalytic characteristics, which facilitate both hydrogen oxidation and oxygen reduction. Although carbon-supported platinum nanoparticles are currently used as cathode catalysts in fuel-cell technology, the commercialization of this technology for automotive applications still requires more economical and effective catalytic materials that can operate with a much smaller amount of expensive platinum. Over the last decade, pioneering researchers reported that the electrocatalytic performance of platinumbased materials can be improved by controlling the morphology of platinum nanocrystals or alloying platinum with other transition metals. In particular, the recently developed platinum nanocrystals with dendritic structures displaying a large number of edges and corner atoms exhibit dramatically enhanced catalytic activity in the oxygen reduction reaction (ORR), the slow kinetics of which is a major problem limiting the efficiency of PEMFCs. Although there has been considerable progress in the preparation of platinum nanodendrites through metal seed or block copolymer mediated processes, the lack of a facile synthetic route has limited the practical applications of nanodendrites. In particular, there is strong demand for a new synthetic method for the mass production of nanodendrites. In this context, the study described herein examines the possibility of large-scale synthesis of platinum nanodendrites in a controllable manner using the recently developed hollow nanoreactor, consisting of a porous silica nanoshell and an entrapped Au nanocrystal, which can confine the growth of metal species inside the silica cavity. The hollow silica nanoreactors provide a consistent and well-isolated environment for the growth of nanocrystals, which enables the morphologycontrolled synthesis of Pt nanodendrites even from a highly concentrated reaction suspension. Moreover, the porous silica shell can be removed readily under basic conditions, leaving a Pt nanodendrite in a surfactant-free form. The surfactant-free Pt dendrites were ready for catalytic applications without additional surfactant-removing processes under harsh conditions, which frequently cause the deformation of the nanocrystals and the decline of catalytic activities. In addition, the surfactant-free nature of the nanocrystals could make it possible to lend the surface various properties and functions through simply coordination of functional ligand molecules. Herein we report the novel synthesis of Pt nanodendrites by Au-seed-mediated growth inside hollow silica nanospheres. The proposed synthetic protocol based on isolated nanoreactors is quite remarkable in terms of the product yield per unit reaction volume compared to traditional cappingagent-based synthesis, which produces only a few milligrams of Pt nanodendrites per milliliter of reaction suspension. The nanoreactor-based synthetic route enabled the synthesis of as much as 1.5 g of uniform Pt nanodendrites from a single reaction in 40 mL aqueous suspension. The prepared ligandfree Pt nanodendrites exhibited greater ORR activity than commercial Pt black catalysts. We also report the extendable utility of the current method to prepare Pt nanodendrite colloid with tunable dispersity and hybrid nanocrystals of various metals. Scheme 1 summarizes the general synthetic routes for various Pt-based nanoparticles based on seed-mediated growth inside porous hollow silica nanospheres. The hollow nanoreactor (Au@h-SiO2), which consists of a porous silica nanoshell with inner and outer diameters of (14 2) and (28 2) nm, respectively, and a (4.0 0.6) nm Au nanocrystal captured inside the cavity, was prepared by selective etching of Fe3O4 from a silica nanosphere encapsulating a Fe3O4/Au hybrid nanocrystal. When an aliquot of Na2PtCl4 was added to an aqueous suspension containing Au@h-SiO2 nanospheres

Electroless Pt deposition on Mn3O4 nanoparticles via the galvanic replacement process: electrocatalytic nanocomposite with enhanced performance for oxygen reduction reaction.

A novel electroless Pt deposition method was exploited by employing the galvanic replacement process occurring between the Mn(3)O(4) surface and PtCl(4)(2-) complexes. The newly discovered process provides a simple protocol to produce the catalytic nanocomposite, in which a high density of ultrafine Pt nanocrystals is stably immobilized in a homogeneously dispersive state on the surface of Mn(3)O(4) nanoparticles. When the eletrocatalytic activity was tested for the oxygen reduction reaction, which limits the rate of the overall process in proton-exchange membrane fuel cells, the resulting Pt/Mn(3)O(4) nanocomposite showed highly enhanced specific activity and durability, compared with those of the commercial Pt/C catalyst.

Highly fluorescent photochromic diarylethene with an excellent fatigue property

A series of diarylethenes and their disulfonyl derivatives such as 1,2-bis(2-heptyl-1-benzothiophene-3-yl)perfluorocyclopentene (HBTF6), 1,2-bis(6-acetyl-2-heptyl-1-benzothiophene-3-yl)perfluorocyclopentene (DAHBTF6), 1,2-bis(2-heptyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (HBTFO4), and 1,2-bis(6-acetyl-2-heptyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (DAHBTFO4), have been prepared for the examination of a substituent and an oxidation effect on photochromic and photophysical properties. Steady state fluorescence studies indicated that the disulfonyl diarylethenes were highly fluorescent only in the closed form. The introduction of acetyl groups at the 6,6′ positions and heptyl groups at the 2,2′ positions in disulfonyl diarylethene gave rise to an increase in the fluorescence quantum yield and fluorescence lifetime. Fatigue properties of oxidized diarylethenes were improved by the introduction of acetyl groups, indicating that the photochromic properties of diarylethene are strongly affected by substituents. We also demonstrated the recording to and erasing of information from the materials by an alternating illumination with UV and visible light, and the accompanying strong fluorescence intensity changes provided a highly efficient information readout system, which may be applicable to erasable optical data-storage elements.

Synthesis of colloidal aqueous suspensions of a layered gadolinium hydroxide: a potential MRI contrast agent

A layered gadolinium hydroxychloride (LGdH), [Gd2(OH)5(H2O)x]Cl, was synthesized from an aqueous solution of GdCl3.6H2O. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) studies showed that this compound crystallizes in the orthorhombic structure (a = 12.88(4) A, b = 7.30(2) A, and c = 8.46(3) A) which is isostructural with [Eu2(OH)5(H2O)x]Cl. Interestingly, this layered material was readily dispersed and led to a stable colloidal nanosheet in aqueous medium. The obtained colloidal solutions were characterized by the evaluation of their stability in acidic solution, their in vitro cytotoxicity, and their magnetic resonance imaging (MRI) relaxation properties. It is reported that the relaxometry analysis of LGdH suspensions exhibits a sufficient contrast effect for T1 weighted magnetic resonance imaging.

Fe3O4/MnO hybrid nanocrystals as a dual contrast agent for both T1- and T2-weighted liver MRI

To investigate whether it is possible to develop a dual magnetic resonance (MR) contrast agent, Fe(3)O(4)/MnO hybrid nanocrystals were modified to integrate the T(1) and T(2) contrast-enhancing abilities of each compound, and their characteristics as MR contrast agents were investigated. In vitro and in vivo investigations revealed that the Fe(3)O(4)/MnO dumbbell-shaped nanocrystal exerted a negative T(2) contrast effect in its intact form and also gave rise to a positive contrast effect in T(1)-weighted MR imaging by releasing Mn(2+) ions in a low pH environment. This induced organ-specific contrast enhancement for both T(1)- and T(2)-weighted in vivo MR imaging. The usefulness of the Fe(3)O(4)/MnO hybrid nanocrystals as dual contrast agents was evaluated by in vivo MR imaging of an orthotopic xenograft model of human hepatocellular carcinoma (HCC). After injection of the Fe(3)O(4)/MnO hybrid nanocrystals, dual contrast-enhanced MR images that synergistically combined the T(2) and T(1) contrast effects from the Fe(3)O(4) grain and released Mn(2+) ions were obtained by a single acquisition of MR imaging. This facilitated the detection of HCC with a high degree of conspicuity that could not be achieved with any single contrast agent.

Fabrication of a silica sphere with fluorescent and MR contrasting GdPO4 nanoparticles from layered gadolinium hydroxide

The delaminated gadolinium hydroxide layers doped with Eu(3+) ions were assembled on the surface of silica spheres and annealed at high temperatures, resulting in the formation of fluorescent and MR active GdPO(4) : Eu nanoparticles at the surface.

Postsynthetic Functionalization of a Hollow Silica Nanoreactor with Manganese Oxide-Immobilized Metal Nanocrystals Inside the Cavity

A postsynthetic protocol of functionalizing the preformed hollow nanoparticles with metal nanocrystals was developed based on galvanic replacement reaction on the Mn3O4 surface inside the cavity. The developed protocol produced hollow nanoreactor systems, in which a high density of ultrafine catalytic nanocrystals of a range of noble metals, such as Pd, Pt, Rh, and Ir and their alloys, are dispersively immobilized on an interior surface enclosed by a selectively permeable silica shell. The fabricated hollow nanoreactor exhibited highly enhanced activity, selectivity, and recyclability in catalyzing the oxidation of hydrosilanes, which are attributable to the synergistic combination of the porous silica nanoshell and the oxide-immobilized catalyst system.

Versatile PEG-derivatized phosphine oxide ligands for water-dispersible metal oxide nanocrystals

We report the simple synthesis of poly(ethylene glycol)(PEG)-derivatized phosphine oxide ligands for water-dispersible metal oxide nanocrystals.

Decoration of superparamagnetic iron oxide nanoparticles with Ni2+: agent to bind and separate histidine-tagged proteins.

The decoration of iron oxide nanoparticles with Ni2+ ions provided the superparamagnetic nanoparticles with a binding site for His-tagged proteins, allowing their selective binding and convenient separation from a multi-component solution with an appropriately applied magnetic field.