Fenghe Wang

Bio: Fenghe Wang is an academic researcher from National University of Singapore. The author has contributed to research in topics: Magnetic nanoparticles & Aqueous solution. The author has an hindex of 4, co-authored 5 publications receiving 135 citations.

Nanostructured magnetic nanocomposites as MRI contrast agents

Abstract: 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.

Synthesis of Water-Dispersible Gd2O3/GO Nanocomposites with Enhanced MRI T1 Relaxivity

Abstract: Water-dispersible Gd2O3 (GDO) nanoparticles decorated graphene oxide (GO) nanocomposites (or GDO/GO NCs) were successfully synthesized as novel magnetic resonance imaging contrast agents. The nanoc...

Tailoring a two-dimensional graphene oxide surface: dual T1 and T2 MRI contrast agent materials

Abstract: A generalized strategy for developing a hybrid two-dimensional nanostructured dual T1–T2 MRI contrast agent (CA), by co-loading graphene oxide with both Mn-doped Fe3O4 (T2 agent) and MnO (T1 agent) magnetic nanoparticles, is reported. Typical T1/T2 signal quenching, due to magnetic coupling, was not observed because of the fair T1 CA separation distance from the T2 CA on the graphene oxide. The resultant two-dimensional nanostructured MRI CA complements the existing dual T1–T2 MRI CA libraries.

Engineered water-soluble two-dimensional magnetic nanocomposites: towards highly magnetic relaxometric properties.

Abstract: Water dispersible two-dimensional magnetic nanocomposites are formed by phase-transferring hydrophobic manganese-doped ferrite nanoparticles (MFPs) into aqueous solvent using a one-step simple approach involving only graphene oxide (GO) as the phase transfer agent. The resultant hydrophilic magnetic nanocomposites (MFNs) are surprisingly stable in the aqueous phase despite its large hydrodynamic size (dhyd). Because of its unique construct that promotes water accessibility towards the MFP core, large MFNs loaded with an 18 nm MFP core (MFN-18; dhyd = 577.9 nm) exhibits transverse relaxivity (r2) up to ∼6.8 times (r2 = 800.8 mM [Mn + Fe]−1 s−1) higher than the typical individually coated MFP-18 with amphiphilic brush copolymers (r2 = 117.3 mM [Mn + Fe]−1 s−1). Meanwhile, the overall nanocomposites dhyd can be further reduced by employing a smaller pre-sonicated GO sheet phase transfer agent. As a result of using small GO sheets with enhanced hydrophilicity, the r2 of small MFN-18* nanocomposites (dhyd = 224.9 nm) increases by approximately 37% (r2 = 1097.4 mM [Mn + Fe]−1 s−1) as compared to larger MFN-18. From a simple comparative study among various magnetic nanocomposites involving a MFP-18 core, the high MFN-18 r2 relaxivity value can be attributed to enhanced water diffusion and exchange due to the GO sheet, allowing better interaction between magnetic the MFP core and water protons. The proposed method can be readily extended to convert other types of hydrophobic nanoparticles into water-dispersible nanocomposites.

Fluorescence-tagged amphiphilic brush copolymer encapsulated Gd2O3 core-shell nanostructures for enhanced T 1 contrast effect and fluorescent imaging

Abstract: To obtain suitable T 1 contrast agents for magnetic resonance imaging (MRI) application, aqueous Gd2O3 nanoparticles (NPs) with high longitudinal relativity (r 1) are demanded. High quality Gd2O3 NPs are usually synthesized through a non-hydrolytic route which requires post-synthetic modification to render the NPs water soluble. The current challenge is to obtain aqueous Gd2O3 NPs with high colloidal stability and enhanced r 1 relaxivity. To overcome this challenge, fluorescence-tagged amphiphilic brush copolymer (AFCP) encapsulated Gd2O3 NPs were proposed as suitable T 1 contrast agents. Such a coating layer provided (i) superior aqueous stability, (ii) biocompatibility, as well as (iii) multi-modality (conjugation with fluorescence dye). The polymeric coating layer thickness was simply adjusted by varying the phase-transfer parameters. By reducing the coating thickness, i.e. the distance between the paramagnetic centre and surrounding water protons, the r 1 relaxivity could be enhanced. In contrast, a thicker polymeric layer coating prevents Gd3+ ions leakage, thus improving its biocompatibility. Therefore, it is important to strike a balance between the biocompatibility and the r 1 relaxivity behaviour. Lastly, by conjugating fluorescence moiety, an additional imaging modality was enabled, as demonstrated from the cell-labelling experiment.

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Abstract: Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

Structure-Relaxivity Relationships of Magnetic Nanoparticles for Magnetic Resonance Imaging.

Abstract: Magnetic nanoparticles (MNPs) have been extensively explored as magnetic resonance imaging (MRI) contrast agents. With the increasing complexity in the structure of modern MNPs, the classical Solomon-Bloembergen-Morgan and the outer-sphere quantum mechanical theories established on simplistic models have encountered limitations for defining the emergent phenomena of relaxation enhancement in MRI. Recent progress in probing MRI relaxivity of MNPs based on structural features at the molecular and atomic scales is reviewed, namely, the structure-relaxivity relationships, including size, shape, crystal structure, surface modification, and assembled structure. A special emphasis is placed on bridging the gaps between classical simplistic models and modern MNPs with elegant structural complexity. In the pursuit of novel MRI contrast agents, it is hoped that this review will spur the critical thinking for design and engineering of novel MNPs for MRI applications across a broad spectrum of research fields.

Compact Zwitterion-Coated Iron Oxide Nanoparticles for Biological Applications

Abstract: National Institutes of Health (U.S.) (MIT-Harvard Center for Cancer Nanotechnology Excellence Grant 1U54-CA126642)

Colloidal nanocrystal synthesis and the organic-inorganic interface

Abstract: Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.