Eugene Shi Guang Choo

Optimization of surface coating on Fe3O4 nanoparticles for high performance magnetic hyperthermia agents

Highly monodispersed magnetite nanoparticles with controlled particle size and mPEG surface coating have been successfully synthesized as a model system to investigate the effect of surface coating on the specific absorption rate (SAR) under an alternating magnetic field. Enhanced SAR with decreased surface coating thickness was observed and ascribed to the increased Brownian loss, improved thermal conductivity as well as improved dispersibility. By elaborate optimization of the surface coating and particle size, a significant increase of SAR (up to 74%) could be achieved with a minimal variation of the saturation magnetization (<5%). In particular, the 19nm@2000 sample exhibited the highest SAR of 930 W g−1 among the samples. Furthermore, this high heating capacity can be maintained in various simulated physiological conditions. Our results provide a general strategy for surface coating optimization of magnetic cores for high performance hyperthermia agents.

One-pot synthesis of water-stable ZnO nanoparticles via a polyol hydrolysis route and their cell labeling applications.

ZnO nanoparticles have been identified as a new generation of biofriendly cell labeling agents since they are nontoxic, less expensive, and chemically stable in air. However, ZnO nanoparticles show poor water stability due to high equilibrium concentration of Zn species in water in a wide pH range. In this work, a one-pot polyol hydrolysis method was developed for synthesizing water-stable ZnO nanoparticles with blue emission. The as-synthesized ZnO nanoparticles were hydrophilic and stable in water, even at basic or acidic aqueous conditions. The PL properties of the ZnO nanoparticles stored at various pH values (i.e., 4.5-11) could be preserved for at least 3 days. The good water stability of the ZnO nanoparticles was offered by the surface attachment of an ester compound, which was formed as a result of the reaction between the stearic acid and triethylene glycol (TREG). This method provides a new approach to synthesize water-stable ZnO nanoparticles. The resultant ZnO nanoparticles demonstrated promising applications in cell labeling.

Synthesis of CuInS2–ZnS alloyed nanocubes with high luminescence

CuInS(2)-ZnS alloyed nanocubes with high luminescence were synthesized through a solution-based diffusion method.

Synthesis of Manganese Ferrite/Graphene Oxide Nanocomposites for Biomedical Applications

In this study, MnFe(2)O(4) nanoparticle (MFNP)-decorated graphene oxide nanocomposites (MGONCs) are prepared through a simple mini-emulsion and solvent evaporation process. It is demonstrated that the loading of magnetic nanocrystals can be tuned by varying the ratio of graphene oxide/magnetic nanoparticles. On top of that, the hydrodynamic size range of the obtained nanocomposites can be optimized by varying the sonication time during the emulsion process. By fine-tuning the sonication time, MGONCs as small as 56.8 ± 1.1 nm, 55.0 ± 0.6 nm and 56.2 ± 0.4 nm loaded with 6 nm, 11 nm, and 14 nm MFNPs, respectively, are successfully fabricated. In order to improve the colloidal stability of MGONCs in physiological solutions (e.g., phosphate buffered saline or PBS solution), MGONCs are further conjugated with polyethylene glycol (PEG). Heating by exposing MGONCs samples to an alternating magnetic field (AMF) show that the obtained nanocomposites are efficient hyperthermia agents. At concentrations as low as 0.1 mg Fe mL(-1) and under an 59.99 kA m(-1) field, the highest specific absorption rate (SAR) recorded is 1588.83 W g(-1) for MGONCs loaded with 14 nm MFNPs. It is also demonstrated that MGONCs are promising as magnetic resonance imaging (MRI) T(2) contrast agents. A T(2) relaxivity value (r(2) ) as high as 256.2 (mM Fe)(-1) s(-1) could be achieved with MGONCs loaded with 14 nm MFNPs. The cytotoxicity results show that PEGylated MGONCs exhibit an excellent biocompatibility that is suitable for biomedical applications.

Controlled loading of superparamagnetic nanoparticles in fluorescent nanogels as effective T2-weighted MRI contrast agents

Spherical superparamagnetic iron oxide nanoclusters (IONCs) with well-controlled shape and size were fabricated. The formation of IONCs was induced by a solvent template-assisted organization of nanoparticles in a polymeric nanogel. An amphiphilic brush copolymer was chosen as the nanogel material because it had a high density of alkyl side-chains that interdigitate through hydrophobic interactions in water to form a stable nanogel matrix. Additionally, the hydrophilic backbone of the copolymer mixed into the nanogel matrix conferred both colloidal stability and important water swelling properties. The hydrodynamic size of IONCs was well-controlled to <200 nm using appropriate emulsion process conditions and displayed excellent long-term dispersibility in water and phosphate buffer saline. The IONCs acted as effective centers of magnetism and MRI measurements clearly showed substantial improvement as the packing density of the magnetic cores increased. A method of estimating intra-particle magnetic interaction distance was established based on calculations from SPION/IONC size and SPION loading. Further functionality was readily introduced by modifying the nanogel with fluorescein for optical tagging. This work offers a robust and versatile platform for the development of waterborne nanoprobes with tunable magnetic properties and versatile chemical functionalities for bio-applications.

Synthesis of ZnO-Pt nanoflowers and their photocatalytic applications

The photocatalytic behaviors of ZnO nanoparticles have been intensively studied recently. However, the photocatalytic efficiency of pure ZnO nanoparticles always suffers from the quick recombination of photoexcited electrons and holes. In order to suppress the electron-hole recombination and then raise the photocatalytic efficiency of ZnO, metal nanoparticles have been combined with ZnO to form ZnO-metal heterostructures. In this work, the feasibility of synthesizing ZnO-Pt composite nanoflowers for optimized catalytic properties was studied. Three different Pt nanocrystals, i.e. cubic Pt nanocrystals enclosed by {100} facets, octahedral Pt nanocrystals enclosed by {111} facets, and truncated octahedral Pt nanocrystals enclosed by both {111} and {100} facets, were selected as seeds for epitaxial growth of ZnO. A ZnO-Pt flowerlike nanostructure was formed by selective growth of ZnO nanolobes at {111} facets of the truncated octahedral Pt nanocrystals. The resultant nanoflowers had well defined ZnO-Pt interfaces and exposed Pt {100} facets, as confirmed by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) measurements. The photocatalytic behaviors of the resultant ZnO-Pt nanoflowers were demonstrated in the photodegradation of ethyl violet. In comparison with the commercial TiO(2) photocatalyst P25, the ZnO-Pt flowerlike nanostructures showed improved catalytic efficiency. Notable ferromagnetism of the obtained ZnO-Pt flowerlike nanostructures was also observed. It is believed that the ZnO-Pt interface played an important role in the enlarged magnetic coercivity of the ZnO-Pt nanoflowers.

Magnetic nanoparticle-loaded polymer nanospheres as magnetic hyperthermia agents

Uniform magnetic nanoparticle-loaded polymer nanospheres with different loading contents of manganese ferrite nanoparticles were successfully synthesized using a flexible emulsion process. The MnFe2O4-loaded polymer nanospheres displayed an excellent dispersibility in both water and phosphate buffer saline. The effect of loading ratio and size of MnFe2O4 nanoparticles within the nanospheres on the specific absorption rate (SAR) under an alternating magnetic field was investigated. Our results indicate that a large size (here 18 nm) and a low loading ratio are preferable for a high SAR. For a smaller particle size (6 nm), the low loading ratio did not result in an enhancement of the SAR value, while a very low SAR value is expected for 6 nm. In addition, the SAR of low-content MnFe2O4 (18 nm)-loaded polymer nanospheres in the agarose gel which is simulated for in vivo environment is the highest among the samples and does not change substantially in physiological environments. This differs largely from the behaviour of singly dispersed nanoparticles. Our results have paved the way for the design of MnFe2O4-loaded polymer nanospheres as magnetic hyperthermia agents for in vivo bio-applications.

Monodisperse transfer of superparamagnetic nanoparticles from non-polar solvent to aqueous phase

The use of superparamagnetic nanocrystals (MNPs) for biomedical applications generally requires a synthetic route in which the resultant MNPs are water soluble and biocompatible with good morphology and size distribution control, as well as optimized hydrodynamic size. To achieve this, hydrophobic MNPs are typically synthesized through the thermolysis process and thereafter water solubilized by using amphiphilic brush co-polymers. In this paper, two types of MNPs were synthesized, i.e. magnetite and manganese ferrite nanocrystals. We presented the optimization process of a water solubilization route by employing poly(isobutylene-alt-maleic anhydride) grafted with dodecylamine (PIMA-g-C12) as the coating. Several parameters that would lead to monodisperse phase transfer of the superparamagnetic nanocrystals (i.e. minimization of the overall MNPs hydrodynamic size) were investigated. These included the PIMA-g-C12/MNPs ratio, the amount of hydrolyzing agent and the initial MNPs concentration in non-polar organic solvent. Such PIMA-g-C12 coated MNPs were found to exhibit good colloidal stability (pH, temperature and kinetic stability). Lastly, PIMA-g-C12 coated MNPs also exhibited excellent in vitro biocompatibility when incubated with NIH/3T3 fibroblast and MCF-7 breast cancer cells.