Small Graphene Oxide Sheets Research Articles

Mechanical and Water Absorption Properties of Waterborne Polyurethane/Graphene Oxide Composites.

Nanocomposites based on waterborne polyurethane (WPU) and graphene oxide (GO) have been synthesized and characterized. It was found that after the incorporation of GO, WPU films became mechanically more rigid, and the Young's modulus increased by almost six times. It is shown that the lateral size of GO sheets influences the mechanical properties of WPU/GO composites. In particular, composites with larger lateral size of GO sheets have higher values of Young's modulus. Additionally, if the mechanical properties are improved with the addition of GO additive, then water absorption decreases for WPU modified with small GO sheets whereas it increases for WPU modified with large GO sheets. Possible reasons for this behavior are discussed.

Graphene Oxide Nanoscale Platform Enhances the Anti-Cancer Properties of Bortezomib in Glioblastoma Models.

Graphene-based 2D nanomaterials possess unique physicochemical characteristics which can be utilized in various biomedical applications, including the transport and presentation of chemotherapeutic agents. In glioblastoma multiforme (GBM), intratumorally administered thin graphene oxide (GO) nanosheets demonstrate a widespread distribution throughout the tumor volume without impact on tumor growth, nor spread into normal brain tissue. Such intratumoral localization and distribution can offer multiple opportunities for treatment and modulation of the GBM microenvironment. Here, the kinetics of GO nanosheet distribution in orthotopic GBM mouse models is described and a novel nano-chemotherapeutic approach utilizing thin GO sheets as platforms to non-covalently complex a proteasome inhibitor, bortezomib (BTZ), is rationally designed. Through the characterization of the GO:BTZ complexes, a high loading capacity of the small molecule on the GO surface with sustained BTZ biological activity in vitro is demonstrated. In vivo, a single low-volume intratumoral administration of GO:BTZ complex shows an enhanced cytotoxic effect compared to free drug in two orthotopic GBM mouse models. This study provides evidence of the potential that thin and small GO sheets hold as flat nanoscale platforms for GBM treatment by increasing the bioavailable drug concentration locally, leading to an enhanced therapeutic effect.

Graphene membrane hosted compact lithium metal anode enabled by capillary force-tuned lithium infiltration

Lithium metal anodes, the promising anodes for next-generation batteries, are troubled by the instability and safety issues induced by the dendrite growth. Three-dimensional hosts are widely used to accommodate lithium metal to solve the above problems. However, they are constantly challenged by large thickness and excess space in the host, lowering the volumetric energy density of batteries. Here, we used the reduced graphene oxide membrane (rGOM) assembled with small graphene oxide sheets as the host and obtained a compact, ultrathin (<20 μm) and free-standing lithium metal-rGO composite anode with good flexibility and high volumetric capacity. The overlap sites derived from the stacking of small size of GO act as abundant diffusion channels for the gas release during the spark reduction process, producing narrow interlamellar space in the rGOM and thus enhancing the capillary molten Li infusion to form a compact composite anode. These sites also guide the uniform deposition of Li metal on the surface and interior of the membrane, effectively suppressing the dendrite growth. This compact composite anode delivers a high volumetric capacity (1223 mAh cm−3) and stable cycling performance in the symmetrical cells and the full cells coupled with high mass loading LiFePO4 cathode under a low N/P ratio.

Effect of different lateral dimension graphene oxide sheets on the interface of carbon fiber reinforced polymer composites

The interfacial performance is one of the most important factors that determine the mechanical properties of carbon fiber reinforced polymers (CFRPs). Recently, improving the interfacial properties of CFRPs using graphene oxide (GO) has received intensive attention from researchers. Using GO can effectively improve the interfacial properties of CFRPs, however, the effect of the size of GO on the properties of CFRPs remains unclear. In this study, GO sheets with different lateral dimensions are selected to elucidate the aforementioned issue. Results showed that GO sheets with smaller lateral dimensions are more advantageous to enhance the interfacial properties of CFRPs. The presence of a larger number of functional groups and higher roughness on the surface of CFs that modified by smaller GO sheets is believed to be contributing factor, as evidenced by XPS and AFM. Furthermore, higher surface energy is detected on the surface of smaller GO sheets modified CFs which is likely related to the size effect of nano-scale GO. The above suggests that nano-scale GO can significantly enhance the chemical bonding and mechanical interlocking of matrix-fiber interface. The proposed approach can be easily implemented which does not deteriorate the strength of CFs. This work provides an effective way to improve the interface properties of CFRPs using GO sheets with smaller lateral dimensions.

Tuning of ionic transport through graphene oxide fibers by sheets size ‎

In this study, graphene oxide fibers are introduced as new graphene oxide (GO) membranes with the ‎capability of ion selectivity‏.‏‎ Graphene oxide fibers, like other macro structured membranes, are always ‎associated with cavities and defects. To solve this problem, a 50% combination of graphene oxide ‎suspension including small sheets with an average size of ~ 0.5 µm2 and large sheets with an area of more ‎than 10 µm2 was used. According to the morphological results of scanning electron microscopy, as well as ‎the amount of ionic transport through the fiber, reduction of cavities and its defects were confirmed. ‎Moreover, it was found that ionic current through fibers consist of large and small GO sheets is more ‎controllable. This leads to more ionic selectivity via tunable swelling. Finally, the scalability of graphene ‎oxide fibers investigated and found that increasing number and length of the fibers increases the ionic ‎current as linear trend‎.

Microstructure Dictating Performance: Assembly of Graphene-Based Macroscopic Structures

ConspectusA wide range of groundbreaking advancements in electronics, photonics, nanocomposites, etc., have been achieved in the past decades due to the favorable attributes of single-layer graphene, including its record-breaking thermal conductivity, charge carrier mobility, fracture strength, and Young’s modulus. However, the realization of the potentials of macroscale graphene assemblies has remained challenging. The difficulties mainly lie within manipulating graphene sheets into an orderly intermolecular orientation and controlling the macroscopic ordering of the graphitic domains. Controlling the formation of graphene macroscopic structures and eliminating defects on both the nano- and microscales meanwhile optimizing performance is no easy feat. To address these microstructural issues in macroscopic graphene assemblies, multiple chemical, thermal, and mechanical approaches have been developed with a goal of overall performance enhancement. Therefore, in this Account we provide a brief review of our contributions in the microstructure engineering of macroscale graphene assemblies with the focus on graphene fibers (GFs), graphene papers (GPs), and other graphene-based assemblies with graphene oxide (GO) colloids as precursors.Building upon the developments in wet chemistry on assembling individual GO sheets into macroscopic structures, we successfully intercalated large GO sheets with small GO sheets, which increased compactness for wet-spun GFs without disturbing the sheet orientation and alignment of the large GO sheets. Increasing GO compactness during wet assembly allows for the increase of thermal and electrical conductivities as well as the mechanical strength of GFs at a single stroke. A high degree of alignment of graphene sheets with abundant sp2 carbon atoms is also necessary for achieving high thermal and electrical conductivities in graphene assemblies. Fine control of GO sheet alignment and orientation during the wet-spinning assembly is demonstrated through the shape and size confinement of fluidic flow channels. Utilizing this shear-stress-induced self-alignment strategy, the core–shell nonuniformity problem of GFs is addressed. Also, a correlation between the rheological properties and flow patterns of GO during wet-spinning and the microstructure of the GF assemblies is established.In addition to the orientation of graphene sheets, the crystallite size and macroscopic ordering within graphene assemblies also play important roles in determining their performances. Larger and highly oriented graphitic crystalline domains allow for higher thermal and electrical conductivities. By manipulating crystallite domain size and arrangement through high temperature graphitization, the electrical and thermal conductivities and Young’s modulus of GFs can be significantly enhanced. Fine temperature control can also help retain residual covalent cross-links between neighboring graphene sheets, meeting the need for balancing tensile strength, and thermal and electrical conductivities.The enhancement of GF mechanical, thermal, and electrical properties through optimizing the compactness and alignment of graphene sheets and the orientation of graphene crystallite domains have significantly improved the engineering capability of GFs. Such an improvement has been largely beneficial to flexible electronics research and has shown great potential in multifunctional composite materials. Similar strategies have also been emulated on related graphene-based materials such as graphene papers (GPs) and graphene fiber meshes (GFMs), yielding unique and favorable properties and performances.

Corrosion Protection Coatings from Size-Specified Graphene Oxide

Corrosion performance of graphene oxide (GO) coatings from different sheets sizes in 3.5 wt% NaCl solution was investigated. The GO dispersion was subjected to 5 and 10 hours of ultrasonication before electrophoretically deposited (EPD) onto the copper substrate. It was found that the EPD-GO coating from smaller sheets (10h ultrasonication) possess hydrophobic, thinner film and smooth surfaces. It is suggested that the corrosion performance of the coating from smaller GO sheets is improved due to the surface texture and compactness of the coating as compared to the larger GO sheets.

Microstructure Effects on the Electrochemical Properties of Graphene/Manganese Oxide Porous Electrodes

Manganese oxide (MnO2) nanowires as guest hosts with ultra-large reduced graphene oxide (RGO) sheets form a sandwich structure and may provide electrochemical properties that cannot be achieved with either material alone. Ultra-large graphene oxide (GO) sheets exhibit an order of magnitude larger length to diameter ratio compared to most studies with smaller GO sheets (~70,000 compared to ~2,000) and demonstrate potential for improved electrode design. Understanding the self-assembly properties of the combination of MnO2 nanowires and ultra-large RGO sheets was explored by two methods: a) mixing both dispersions that have been synthesized separately to form a mixture and b) growing the nanowires along the ultra-large GO sheets to form a hybrid material. The pure and multicomponent dispersions were characterized by spectroscopy and microscopy techniques to characterize the materials and gain insight into their dispersion microstructures. The dispersions were then freeze-dried into aerogels with 3D porous architectures. Tuning the initial dispersion parameters, including concentration, MnO2 content, and assembly results in different morphologies and physical and electrochemical properties of the aerogels. Results from this work convey that the hybrid exhibits a more uniform distribution of the nanowires than that of the mixture and the porous electrodes consist of mesopores (diameters between 2 and 50 nm) with interconnected pathways. Furthermore, the electrochemical performance of the hybrid and mixture electrodes suggests that there may be stronger interfacial contact between the RGO sheets and MnO2 nanowires in the hybrid due to the nanowires’ nucleation and growth along the sheets as opposed to the mixture. Comparison of the dispersion and aerogel morphologies as well as electrochemical performance provided insights into the relationships between material type, initial dispersion microstructure, and electrode properties.

Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity

Graphene oxide (GO) is an oxidised form of graphene that has attracted commercial interest in multiple applications, including inks, printed electronics and spray coatings, which all raise health concerns due to potential creation of inhalable aerosols. Although a number of studies have discussed the toxicity of GO sheets, the in vivo impact of their lateral dimensions is still not clear. Here, we compared the effects of large GO sheets (l-GO, 1–20 µm) with those of small GO sheets (s-GO, < 1 µm) in terms of mesothelial damage and peritoneal inflammation, after intraperitoneal (i.p.) injection in mice. To benchmark the outcomes, long and rigid multi-walled carbon nanotubes (MWCNTs) that were shown to be associated with asbestos-like pathogenicity on the mesothelium were also tested. Our aim was to assess whether lateral dimensions can be a predictor of inflammogenicity for GO sheets in a similar fashion as length is for MWCNTs. While long MWCNTs dispersed in 0.5% BSA induced a granulomatous response on the diaphragmatic mesothelium and immune cell recruitment to the peritoneal cavity, GO sheets dispersed under similar conditions did not cause any response, regardless of their lateral dimensions. We further interrogated whether tuning the surface reactivity of GO by testing different dispersions (5% dextrose instead of 0.5% BSA) may change the biological outcome. Although the change of dispersion did not alter the impact of GO on the mesothelium (i.e. no granuloma), we observed that, when dispersed in protein-free 5% dextrose solution, s-GO elicited a greater recruitment of monocytic cells to the peritoneal cavity than l-GO, or when dispersed in protein-containing solution. Such recruitment coincided with the greater ability of s-GO to interact in vivo with peritoneal macrophages and was associated with a greater surface reactivity in comparison to l-GO. In conclusion, large dimension was not a determining factor of the immunological impact of GO sheets after i.p. administration. For an equal dose, GO sheets with lateral dimensions similar to the length of long MWCNTs were less pathogenic than the MWCNTs. On the other hand, surface reactivity and the ability of some smaller GO sheets to interact more readily with immune cells seem to be key parameters that can be tuned to improve the safety profile of GO. In particular, the choice of dispersion modality, which affected these two parameters, was found to be of crucial importance in the assessment of GO impact in this model. Overall, these findings are essential for a better understanding of the parameters governing GO toxicity and inflammation, and the rational design of safe GO-based formulations for various applications, including biomedicine.

GO nanosheets localization by morphological study on PLA-GO electrospun nanocomposite nanofibers

In this study we prepare a nanocomposite substrate from poly lactic acid (PLA) and graphene oxide (GO) using electrospinning. Determining the possible placement of graphene oxide nano-sheets in the electrospun fiber mats is the main goal of this work. The investigative methods employed include scanning electron microscopy (SEM), atomic force microscopy (AFM) micrographs, tensile modulus and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). It is shown that the localization of nanoparticle by different methods controls different final properties. We performed the study of the mechanical properties, surface chemical structure and topology of obtaining nanofiber mats. Studies showed that the location of GO sheets depends on the lateral size of them and based on this claim we estimated three possible locations for them: (1) small GO sheets (less than 200 nm) fully or partially inside the electrospun fibers, (2) some larger ones rolling around and on the fibers surface under the high applied voltage, and (3) parts of large sheets bridging between the fibers.

Self-assembled complexes of graphene oxide and oxidized vapor-grown carbon fibers for simultaneously enhancing the strength and toughness of epoxy and multi-scale carbon fiber/epoxy composites

Reinforcement of polymers with small addition of nanofillers has been intensively investigated. It has been suggested that combination of few-layer graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) is more effective than single nanofillers for polymer reinforcement. Herein, we report that the complexes of single-layer graphene oxide (GO) and oxidized vapor-grown carbon fibers (OVGCFs), with dimensionalities of 2 and 1, respectively, simultaneously improve the strength and toughness of epoxy and multi-scale carbon fiber reinforced composites at an extremely low content (∼0.2 wt%). The GO-OVGCF complexes are formed in water by the π-π stacking-induced self-assembly of OVGCFs and GO, and then rapidly transferred to a tertiary amine type epoxy oligomer for the preparation of epoxy and multi-scale composites. OVGCFs were observed to be wrapped by small GO sheets, which greatly improve the dispersion uniformity of OVGCFs in epoxy matrix and the filler-matrix interfacial interactions. The influences of the complexes with various GO-to-OVGCF ratios on the mechanical properties of epoxy and multi-scale composites were investigated systematically. At the optimized GO-to-OVGCF ratio, the complexes increase the mechanical properties of epoxy and multi-scale composites more significantly than previously reported individual nanofillers and the CNT-GNP hybrids.

Effect of flake size on thermal properties of graphene oxide/poly(methyl methacrylate) composites prepared via in situ polymerization

ABSTRACTThe effect of graphene oxide (GO) flake size on thermal properties of GO/poly(methyl methacrylate) (GO/PMMA) composites prepared via in situ polymerization was investigated. Two styles of GO sheets were synthesized from different sizes of graphite powders by modified Hummers' method and GO/PMMA composites with GO of different sizes were prepared via in situ polymerization. Transmission electron microscopy verified that GO sheets produced from large graphite powders was obviously larger than that from small graphite powders. The similar number of layers and disorder degree of two types of GO sheets were proved by X‐ray diffraction and Raman, respectively. X‐ray diffraction and scanning electron microscopy results of GO/composites proved the homogenous dispersion of both two types of GO sheets in polymer matrix. Dynamic mechanical analysis and thermogravimetric analysis results showed that large GO sheets exhibit better improvement than small GO sheets in thermal properties of the composites. Compared with neat PMMA, the glass transition temperature and decomposition temperature of the composites with large GO sheets (0.20 wt %) were increased by 15.9 and 25.9 °C, respectively. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46290.

Parametric studies of formation and morphology of sub-micron sized GO stabilized PS/GO containers encapsulating 8-HQ

The work identifies parameters and proposes mechanisms that are crucial in making smart containers with encapsulating agents by Pickering emulsion route for anti-corrosion coating and advanced materials applications. We demonstrate the unmodified graphene oxide (GO) particles as potential stabilizers for oil-in-water emulsions not requiring any modification to the properties of the emulsion phases. The model system, GO stabilized styrene in water, was used to explore the mechanistic details of the stable emulsion formation and subsequent formation of polystyrene/graphene oxide (PS/GO) containers after emulsion polymerization. The results indicate a clear size effect during packing of GO at oil-water interface and smaller GO sheets produced homogenous emulsion without any residual water volume. The emulsion droplet size distribution changes from bimodal to monomodal with the increase in GO concentration and it reverses with oil–water phase ratio. For the first time, a correlation was developed between these variables and the size, polydispersity index (PDI), morphology, conversion, and yield of the containers produced by emulsion polymerization. The parametric controls required for preparing PS/GO containers with narrow size distribution (PDI = 0.23), smaller size and various morphologies are discussed, with a probable mechanism. All these studies were carried out in presence of a corrosion inhibitor, 8-Hydroxyquinoline (8-HQ), to be encapsulated in the container. The containers were produced with 75% encapsulation efficiency.

Preparation and Exceptional Mechanical Properties of Bone-Mimicking Size-Tuned Graphene Oxide@Carbon Nanotube Hybrid Paper

The self-assembled nanostructures of carbon nanomaterials possess a damage-tolerable architecture crucial for the inherent mechanical properties at both micro- and macroscopic levels. Bone, or "natural composite," has been known to have superior energy dissipation and fracture resistance abilities due to its unique load-bearing hybrid structure. However, few approaches have emulated the desirable structure using carbon nanomaterials. In this paper, we present an approach in fabricating a hybrid composite paper based on graphene oxide (GO) and carbon nanotube (CNT) that mimicks the natural bone structure. The size-tuning strategy enables smaller GO sheets to have more cross-linking reactions with CNTs and be homogeneously incorporated into CNT-assembled paper, which is advantageous for effective stress transfer. The resultant hybrid composite film has enhanced mechanical strength, modulus, toughness, and even electrical conductivity compared to previously reported CNT-GO based composites. We further demonstrate the usefulness of the size-tuned GOs as the "stress transfer medium" by performing in situ Raman spectroscopy during the tensile test.

Molecular and Genomic Impact of Large and Small Lateral Dimension Graphene Oxide Sheets on Human Immune Cells from Healthy Donors.

Graphene oxide (GO) is attracting great interest in biomedical sciences. The impact of GO on immune cells is one fundamental area of study that is often overlooked, but critical in terms of clinical translation. This work investigates the effects of two types of thoroughly characterized GO sheets, different in their lateral dimension, on human peripheral immune cells provided from healthy donors using a wide range of assays. After evaluation of cell viability, the gene expression was analyzed, following GO exposure on 84 genes related to innate and adaptive immune responses. Exposure to GO small sheets was found to have a more significant impact on immune cells compared to GO large sheets, reflected in the upregulation of critical genes implicated in immune responses and the release of cytokines IL1β and TNFα. These findings were further confirmed by whole-genome microarray analysis of the impact of small GO sheets on T cells and monocytes. Activation in both cell types was underlined by the overexpression of genes such as CXCL10 and receptor CXCR3. Significant energy-dependent pathway modulation was identified. These findings can potentially pave the foundations for further design of graphene that can be used for immune modulation applications, for example in cancer immunotherapy.

More effective use of graphene in photocatalysis by conformal attachment of small sheets to TiO2 spheres

Graphene-pasted TiO2 spheres have been prepared successfully by a two-step method including attaching relatively small graphene oxide sheets onto the surface of the modified TiO2 spheres and in-situ photocatalysis reduction of these graphene oxide sheets. Since coated almost totally on the surface of TiO2 spheres, these added graphene sheets are utilized more fully in these as-obtained graphene-pasted composites, which possess more interfaces between graphene and TiO2 and can make better use of the irradiated light compared with that of traditional graphene-involved TiO2 composites. As a result, these graphene-pasted TiO2 spheres always display higher photocatalysis activity in both methylene orange dye degradation and 4-nitrophenol reduction than that of control graphene-TiO2 spheres in the case of the same usage of these carbon sheets, which indicates more efficient use of graphene sheets in these graphene-pasted samples in photocatalysis systems.

Crucial Role of Lateral Size for Graphene Oxide in Activating Macrophages and Stimulating Pro-inflammatory Responses in Cells and Animals.

Graphene oxide (GO) is increasingly used in biomedical applications because it possesses not only the unique properties of graphene including large surface area and flexibility but also hydrophilicity and dispersibility in aqueous solutions. However, there are conflicting results on its biocompatibility and biosafety partially due to large variations in physicochemical properties of GO, and the role of these properties including lateral size in the biological or toxicological effects of GO is still unclear. In this study, we focused on the role of lateral size by preparing a panel of GO samples with differential lateral sizes using the same starting material. We found that, in comparison to its smaller counterpart, larger GO showed a stronger adsorption onto the plasma membrane with less phagocytosis, which elicited more robust interaction with toll-like receptors and more potent activation of NF-κB pathways. By contrast, smaller GO sheets were more likely taken up by cells. As a result, larger GO promoted greater M1 polarization, associated with enhanced production of inflammatory cytokines and recruitment of immune cells. The in vitro results correlated well with local and systemic inflammatory responses after GO administration into the abdominal cavity, lung, or bloodstream through the tail vein. Together, our study delineated the size-dependent M1 induction of macrophages and pro-inflammatory responses of GO in vitro and in vivo. Our data also unearthed the detailed mechanism underlying these effects: a size-dependent interaction between GO and the plasma membrane.

Antimicrobial Properties of Graphene Oxide Nanosheets: Why Size Matters.

Graphene oxide (GO) is a promising material for the development of antimicrobial surfaces due to its contact-based antimicrobial activity. However, the relationship between GO physicochemical properties and its antimicrobial activity has yet to be elucidated. In this study, we investigated the size-dependency of GO antimicrobial activity using the Gram-negative bacteria Escherichia coli. GO suspensions of average sheet area ranging from 0.01 to 0.65 μm(2) were produced and their antimicrobial activity evaluated in cell suspensions or as a model GO surface coating. The antimicrobial activity of GO surface coatings increased 4-fold when GO sheet area decreased from 0.65 to 0.01 μm(2). The higher antimicrobial effect of smaller GO sheets is attributed to oxidative mechanisms associated with the higher defect density of smaller sheets. In contrast, in suspension assays, GO interacted with bacteria in a cell entrapment mechanism; in this case, the antimicrobial effect of GO increased with increasing sheet area, with apparent complete inactivation observed for the 0.65 μm(2) sheets after a 3 h exposure. However, cell inactivation by GO entrapment was reversible and all initially viable cells could be recovered when separated from GO sheets by sonication. These findings provide useful guidelines for future development of graphene-based antimicrobial surface coatings, where smaller sheet sizes can increase the antimicrobial activity of the material. Our study further emphasizes the importance of an accurate assessment of the antimicrobial effect of nanomaterials when used for antimicrobial surface design.

The Structural Influence of Graphene Oxide on Its Fragmentation during Laser Desorption/Ionization Mass Spectrometry for Efficient Small-Molecule Analysis.

The structural influence of graphene oxide (GO) on laser desorption/ionization mass spectrometry (LDI-MS) analysis of small molecules was systematically investigated by using size-fractionated GO. For fractionation of GO, pH-assisted centrifugation, sequential vacuum filtration, and sonochemical cutting processes were employed and the size-fractionated GO was thoroughly characterized to understand their size-dependent optochemical properties. Then, the fractionated GO was applied to the analysis of various small molecules by LDI-MS to investigate the relationship between their optochemical properties and LDI-MS performance. We found that large GO sheets (>0.5 μm) were more prone to fragmentation under laser irradiation during LDI-MS analysis than small GO sheets (<0.5 μm). In this regard, the LDI-MS analysis efficiency of various small molecules was significantly improved by using nanosized GO (NGO) as a matrix without background interference. In particular, NGO was successfully applied to the sensitive detection of hydrophobic pollutant molecules without requiring any surface-functionalization, enrichment, and separation process. Therefore, the present study could provide important basic information and be a practical tool for the development of simple and efficient LDI-MS platforms by using GO derivatives.

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

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.