Erwin Peng

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.

Graphene oxide based fluorescent nanocomposites for cellular imaging

Carbon based 2-D material graphene oxide (GO) is a promising platform for preparing composites for biomedical applications because of its superior water solubility and low toxicity. Herein, we reported a convenient route to prepare fluorescent nanocomposites incorporating water-soluble GO sheets and Zn doped AgInS2 nanoparticles. According to the study, the photoluminescence of the Zn doped AgInS2 nanoparticles was well maintained after the hybridization using GO. No obvious emission shift was observed and the PL intensity was stable for over three months with negligible quenching. The PEGylated AIZS-GO nanocomposites could be readily up-taken by NIH/3T3 cells (mouse embryonic fibroblast cell line) while no distinct cytotoxicity was observed. The subsequent in vitro cellular imaging of NIH/3T3 cells proved that the as-prepared AIZS-GO-PEG nanocomposites were potential fluorescent probes for biomedical targeting and imaging.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

Size dependent magnetic hyperthermia of octahedral Fe3O4 nanoparticles

Magnetic nanoparticle hyperthermia is promising as a cancer therapeutic treatment. Shape and size are two crucial factors for the magnetic hyperthermia performance of nanoparticles. In this work, octahedral Fe3O4 nanoparticles with different sizes are successfully synthesized and their magnetic hyperthermia performances are investigated systematically in a gel suspension. The results suggest a wide size range (43–98 nm) for high SAR values (up to 2629 W g−1). The SAR values are verified by hysteresis loss measured in the gel suspension. This study demonstrates that octahedral Fe3O4 nanoparticles can serve as an excellent thermal seed for high performance magnetic hyperthermia cancer treatment.

Concentration-dependent magnetic hyperthermic response of manganese ferrite-loaded ultrasmall graphene oxide nanocomposites

Water soluble and biocompatible ∼18 nm manganese-doped ferrite (MnxFe1−x)Fe2O4 decorated ultrasmall graphene oxide (GO) nanocomposites were synthesized. Ultrasmall nanocomposites were fabricated with a hydrodynamic size of 50.6 ± 0.3 nm, approximately ∼80 nm lateral dimension and ∼20 nm thickness (from AFM analysis), indicating a sheet-like structure with only a few nanoparticles attached. The concentration-dependent magnetic hyperthermic response of such nanocomposites under an alternating magnetic field (AMF) and very dilute conditions (<0.3 mg mL−1) was also investigated. The field-dependent specific absorption rate (SAR) values of the nanocomposites were found to have increased by approximately two-fold when their concentration was reduced by a factor of 3. Such nanocomposites also exhibited excellent colloidal stability as well as suitable biocompatibility (up to 2 mM iron concentration) with NIH/3T3 fibroblast cells.

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.

Succinic anhydride functionalized alkenoic ligands: a facile route to synthesize water dispersible nanocrystals

In this work, a simple and versatile strategy to synthesize water dispersible high quality nanocrystals was reported. To demonstrate this strategy, thermolysis synthesis of magnetite nanocrystals was coupled with a classical maleinization reaction. The resulting nanocrystals were protected with hydrophobic oleic acid ligands bearing the succinic anhydride functional group. Through a simple anhydride ring opening process, the ligand could be readily converted into its hydrophilic analogue and therefore the nanocrystals were dispersible in aqueous phase. The TEM, XRD and VSM results revealed that the size, shape monodispersity and the physical properties of the obtained hydrophilic nanocrystals did not differ considerably from the hydrophobic nanocrystals obtained from a typical thermolysis process. The cell cytotoxicity tests with NIH/3T3 revealed the biocompatibility of such hydrophilic functional capping agents of magnetite nanocrystals even at a high concentration (15.84 mM Fe). Lastly, our preliminary results with up-converting nanocrystals showed that this strategy was readily extendable to other nanocrystalline systems.

Ferrite-based soft and hard magnetic structures by extrusion free-forming

Functional ceramic materials, especially those with unique magnetic properties, with complex geometries have become increasingly important for various key technologies in industry. Herein, ferrite-based soft (NiFe2O4) and hard (BaFe12O19) bulk magnetic structures with three-dimensional morphologies are successfully fabricated from inexpensive metal oxide powder (NiO/Fe2O3 and BaCO3/Fe2O3) precursors through a simple extrusion free-forming (EFF) technique coupled with a high temperature solid-state reaction process. Dense polycrystalline microstructures with negligible porosity are observed for samples sintered above 1200 °C and highly crystalline NiFe2O4 and BaFe12O19 phases are successfully formed. The printed structures also exhibit either soft or hard magnetic material behavior with (i) saturation magnetization values up to approximately 86% and 95% of the NiFe2O4 and BaFe12O19 theoretical bulk magnetization values, respectively, and (ii) high densities up to ∼93% of their respective theoretical bulk density. Bulk magnetic structures with unique geometries (e.g. mesh, gear, ring and cylinder) are successfully fabricated. The EFF technique demonstrated in this work can be readily extended to other functional ferrite or titanate ceramic materials simply by changing the metal oxide powder precursors.

Mechanically robust glucose strutted graphene aerogel paper as a flexible electrode

With the advent of next generation wearable technologies, energy storage devices at present not only have to achieve high energy densities they also need to possess reasonable mechanical robustness. Traditional graphene paper is mechanically robust which is ideal for a flexible electrode. However, the restacking issue and the degradation in performance with increasing thickness, limit the usage of graphene paper as a functional electrode. In this paper, porous, flexible, and free-standing graphene aerogel paper was prepared from an acid-treated glucose-strutted graphene aerogel via mechanical compression. The sulphur groups on the glucose struts served as a strengthening function due to thiol-carboxylic acid esterification and the increase in hydrogen bonding. The resulting nanostructured composite was able to exhibit a high ultimate tensile strength of 0.6 MPa which is 3 times that of the graphene aerogel paper without the glucose struts (0.2 MPa). It was also able to withstand 100 cyclic loadings of 0.13 MPa without failure. When electrochemically tested, it was able to discharge with a specific capacitance of 311 F g−1 at a current density of 1 A g−1, and a modest specific capacitance of 262 F g−1 at a high current density of 20 A g−1. Therefore, such results validate its promising application as a flexible electrode in energy storage devices.

Synthesis of Ferromagnetic Fe0.6Mn0.4O Nanoflowers as a New Class of Magnetic Theranostic Platform for In Vivo T1-T2 Dual-Mode Magnetic Resonance Imaging and Magnetic Hyperthermia Therapy

Uniform wüstite Fe0.6 Mn0.4 O nanoflowers have been successfully developed as an innovative theranostic agent with T1 -T2 dual-mode magnetic resonance imaging (MRI), for diagnostic applications and therapeutic interventions via magnetic hyperthermia. Unlike their antiferromagnetic bulk counterpart, the obtained Fe0.6 Mn0.4 O nanoflowers show unique room-temperature ferromagnetic behavior, probably due to the presence of an exchange coupling effect. Combined with the flower-like morphology, ferromagnetic Fe0.6 Mn0.4 O nanoflowers are demonstrated to possess dual-modal MRI sensitivity, with longitudinal relaxivity r1 and transverse relaxivity r2 as high as 4.9 and 61.2 mm(-1) s(-1) [Fe]+[Mn], respectively. Further in vivo MRI carried out on the mouse orthotopic glioma model revealed gliomas are clearly delineated in both T1 - and T2 -weighted MR images, after administration of the Fe0.6 Mn0.4 O nanoflowers. In addition, the Fe0.6 Mn0.4 O nanoflowers also exhibit excellent magnetic induction heating effects. Both in vitro and in vivo magnetic hyperthermia experimentation has demonstrated that magnetic hyperthermia by using the innovative Fe0.6 Mn0.4 O nanoflowers can induce MCF-7 breast cancer cell apoptosis and a complete tumor regression without appreciable side effects. The results have demonstrated that the innovative Fe0.6 Mn0.4 O nanoflowers can be a new magnetic theranostic platform for in vivo T1 -T2 dual-mode MRI and magnetic thermotherapy, thereby achieving a one-stop diagnosis cum effective therapeutic modality in cancer management.