Standard Radio-Iodine Labeling Protocols Impaired the Functional Integrity of Mesenchymal Stem/Stromal Cell Exosomes.

Mesenchymal stem/stromal cells (MSCs) are an extensively studied cell type in clinical trials due to their easy availability, substantial ex vivo proliferative capacity, and therapeutic efficacy in numerous pre-clinical animal models of disease. The prevailing understanding suggests that their therapeutic impact is mediated by the secretion of exosomes. Notably, MSC exosomes present several advantages over MSCs as therapeutic agents, due to their non-living nature and smaller size. However, despite their promising therapeutic potential, the clinical translation of MSC exosomes is hindered by an incomplete understanding of their biodistribution after administration. A primary obstacle to this lies in the lack of robust labels that are highly sensitive, capable of directly and easily tagging exosomes with minimal non-specific labeling artifacts, and sensitive traceability with minimal background noise. One potential candidate to address this issue is radioactive iodine. Protocols for iodinating exosomes and tracking radioactive iodine in live imaging are well-established, and their application in determining the biodistribution of exosomes has been reported. Nevertheless, the effects of iodination on the structural or functional activities of exosomes have never been thoroughly examined. In this study, we investigate these effects and report that these iodination methods abrogate CD73 enzymatic activity on MSC exosomes. Consequently, the biodistribution of iodinated exosomes may reflect the biodistribution of denatured exosomes rather than functionally intact ones.

Radiolabeled Liposomes for Nuclear Imaging Probes.

Quantitative nuclear imaging techniques are in high demand for various disease diagnostics and cancer theranostics. The non-invasive imaging modality requires radiotracing through the radioactive decay emission of the radionuclide. Current preclinical and clinical radiotracers, so-called nuclear imaging probes, are radioisotope-labeled small molecules. Liposomal radiotracers have been rapidly developing as novel nuclear imaging probes. The physicochemical properties and structural characteristics of liposomes have been elucidated to address their long circulation and stability as radiopharmaceuticals. Various radiolabeling methods for synthesizing radionuclides onto liposomes and synthesis strategies have been summarized to render them biocompatible and enable specific targeting. Through a variety of radionuclide labeling methods, radiolabeled liposomes for use as nuclear imaging probes can be obtained for in vivo biodistribution and specific targeting studies. The advantages of radiolabeled liposomes including their use as potential clinical nuclear imaging probes have been highlighted. This review is a comprehensive overview of all recently published liposomal SPECT and PET imaging probes.

Radiochemical Feasibility of Mixing of 99mTc-MAA and 90Y-Microspheres with Omnipaque Contrast.

Yttrium-90 (90Y) microspheres are widely used for the treatment of liver-dominant malignant tumors. They are infused via catheter into the hepatic artery branches supplying the tumor under fluoroscopic guidance based on pre-therapy angiography and Technetium-99m macroaggregated albumin (99mTc-MAA) planning. However, at present, these microspheres are suspended in radiolucent media such as dextrose 5% (D5) solution. In order to monitor the real-time implantation of the microspheres into the tumor, the 90Y microspheres could be suspended in omnipaque contrast for allowing visualization of the correct distribution of the microspheres into the tumor. The radiochemical purity of mixing 90Y-microspheres in various concentrations of omnipaque was investigated. The radiochemical purity and feasibility of mixing 99mTc-MAA with various concentrations of a standard contrast agent were also investigated. Results showed the radiochemical feasibility of mixing 90Y-microspheres with omnipaque is radiochemically acceptable for allowing real-time visualization of radioembolization under fluoroscopy.

Nanomaterial Probes for Nuclear Imaging.

Nuclear imaging is a powerful non-invasive imaging technique that is rapidly developing in medical theranostics. Nuclear imaging requires radiolabeling isotopes for non-invasive imaging through the radioactive decay emission of the radionuclide. Nuclear imaging probes, commonly known as radiotracers, are radioisotope-labeled small molecules. Nanomaterials have shown potential as nuclear imaging probes for theranostic applications. By modifying the surface of nanomaterials, multifunctional radio-labeled nanomaterials can be obtained for in vivo biodistribution and targeting in initial animal imaging studies. Various surface modification strategies have been developed, and targeting moieties have been attached to the nanomaterials to render biocompatibility and enable specific targeting. Through integration of complementary imaging probes to a single nanoparticulate, multimodal molecular imaging can be performed as images with high sensitivity, resolution, and specificity. In this review, nanomaterial nuclear imaging probes including inorganic nanomaterials such as quantum dots (QDs), organic nanomaterials such as liposomes, and exosomes are summarized. These new developments in nanomaterials are expected to introduce a paradigm shift in nuclear imaging, thereby creating new opportunities for theranostic medical imaging tools.

Positron emission tomographic imaging in drug discovery.

Positron emission tomography (PET) is an extensively used nuclear functional imaging technique, especially for central nervous system (CNS) and oncological disorders. Currently, drug development is a lengthy and costly pursuit. Imaging with PET radiotracers could be an effective way to hasten drug discovery and advancement, because it facilitates the monitoring of key facets, such as receptor occupancy quantification, drug biodistribution, pharmacokinetic (PK) analyses, validation of target engagement, treatment monitoring, and measurement of neurotransmitter concentrations. These parameters demand careful analyses for the robust appraisal of newly formulated drugs during preclinical and clinical trials. In this review, we discuss the usage of PET imaging in radiopharmaceutical development; drug development approaches with PET imaging; and PET developments in oncological and cardiac drug discovery.

An In Vivo Study of a Rat Fluid-Percussion-Induced Traumatic Brain Injury Model with [11C]PBR28 and [18F]flumazenil PET Imaging.

Traumatic brain injury (TBI) modelled by lateral fluid percussion-induction (LFPI) in rats is a widely used experimental rodent model to explore and understand the underlying cellular and molecular alterations in the brain caused by TBI in humans. Current improvements in imaging with positron emission tomography (PET) have made it possible to map certain features of TBI-induced cellular and molecular changes equally in humans and animals. The PET imaging technique is an apt supplement to nanotheranostic-based treatment alternatives that are emerging to tackle TBI. The present study aims to investigate whether the two radioligands, [11C]PBR28 and [18F]flumazenil, are able to accurately quantify in vivo molecular-cellular changes in a rodent TBI-model for two different biochemical targets of the processes. In addition, it serves to observe any palpable variations associated with primary and secondary injury sites, and in the affected versus the contralateral hemispheres. As [11C]PBR28 is a radioligand of the 18 kD translocator protein, the up-regulation of which is coupled to the level of neuroinflammation in the brain, and [18F]flumazenil is a radioligand for GABAA-benzodiazepine receptors, whose level mirrors interneuronal activity and eventually cell death, the use of the two radioligands may reveal two critical features of TBI. An up-regulation in the [11C]PBR28 uptake triggered by the LFP in the injured (right) hemisphere was noted on day 14, while the uptake of [18F]flumazenil was down-regulated on day 14. When comparing the left (contralateral) and right (LFPI) hemispheres, the differences between the two in neuroinflammation were obvious. Our results demonstrate a potential way to measure the molecular alterations in a rodent-based TBI model using PET imaging with [11C]PBR28 and [18F]flumazenil. These radioligands are promising options that can be eventually used in exploring the complex in vivo pharmacokinetics and delivery mechanisms of nanoparticles in TBI treatment.

Dealing with PET radiometabolites.

Positron emission tomography (PET) offers the study of biochemical, physiological, and pharmacological functions at a cellular and molecular level. The performance of a PET study mostly depends on the used radiotracer of interest. However, the development of a novel PET tracer is very difficult, as it is required to fulfill a lot of important criteria. PET radiotracers usually encounter different chemical modifications including redox reaction, hydrolysis, decarboxylation, and various conjugation processes within living organisms. Due to this biotransformation, different chemical entities are produced, and the amount of the parent radiotracer is declined. Consequently, the signal measured by the PET scanner indicates the entire amount of radioactivity deposited in the tissue; however, it does not offer any indication about the chemical disposition of the parent radiotracer itself. From a radiopharmaceutical perspective, it is necessary to quantify the parent radiotracer's fraction present in the tissue. Hence, the identification of radiometabolites of the radiotracers is vital for PET imaging. There are mainly two reasons for the chemical identification of PET radiometabolites: firstly, to determine the amount of parent radiotracers in plasma, and secondly, to rule out (if a radiometabolite enters the brain) or correct any radiometabolite accumulation in peripheral tissue. Besides, radiometabolite formations of the tracer might be of concern for the PET study, as the radiometabolic products may display considerably contrasting distribution patterns inside the body when compared with the radiotracer itself. Therefore, necessary information is needed about these biochemical transformations to understand the distribution of radioactivity throughout the body. Various published review articles on PET radiometabolites mainly focus on the sample preparation techniques and recently available technology to improve the radiometabolite analysis process. This article essentially summarizes the chemical and structural identity of the radiometabolites of various radiotracers including [11C]PBB3, [11C]flumazenil, [18F]FEPE2I, [11C]PBR28, [11C]MADAM, and (+)[18F]flubatine. Besides, the importance of radiometabolite analysis in PET imaging is also briefly summarized. Moreover, this review also highlights how a slight chemical modification could reduce the formation of radiometabolites, which could interfere with the results of PET imaging.

Gadolinium-based bimodal probes to enhance T1-Weighted magnetic resonance/optical imaging.

Gd3+-based contrast agents have been extensively used for signal enhancement of T1-weighted magnetic resonance imaging (MRI) due to the large magnetic moment and long electron spin relaxation time of the paramagnetic Gd3+ ion. The key requisites for the development of Gd3+-based contrast agents are their relaxivities and stabilities which can be achieved by chemical modifications. These modifications include coordinating Gd3+ with a chelator such as diethylenetriamine pentaacetic acid (DTPA) or 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), encapsulating Gd3+ in nanoparticles, conjugation to biomacromolecules such as polymer micelles and liposomes, or non-covalent binding to plasma proteins. In order to have a coherent diagnostic and therapeutic approach and to understand diseases better, the combination of MRI and optical imaging (OI) techniques into one technique entity has been developed to overcome the conventional boundaries of either imaging modality used alone through bringing the excellent spatial resolution of MRI and high sensitivity of OI into full play. Novel MRI and OI bimodal probes have been extensively studied in this regard. This review is an attempt to shed some light on the bimodal imaging probes by summarizing all recent noteworthy publications involving Gd3+ containing MR-optical imaging probes. The several key elements such as novel synthetic strategy, high sensitivity, biocompatibility, and targeting of the probes are highlighted in the review. STATEMENT OF SIGNIFICANCE: The present article aims at giving an overview of the existing bimodal MRI and OI imaging probes. The review structured as a series of examples of paramagnetic Gd3+ ions, either as ions in the crystalline structure of inorganic materials or chelates for contrast enhancement in MRI, while they are used as optical imaging probes in different modes. The comprehensive review focusing on the synthetic strategies, characterizations and properties of these bimodal imaging probes will be helpful in a way to prepare related work.

Activatable Cell-Penetrating Peptide Conjugated Polymeric Nanoparticles with Gd-Chelation and Aggregation-Induced Emission for Bimodal MR and Fluorescence Imaging of Tumors.

Activatable cell-penetrating peptide (ACPP) conjugated polymeric nanoparticles containing gadolinium (Gd)-chelates and aggregation-induced emission fluorogens (AIEgens) have been synthesized and applied as a magnetic resonance imaging (MRI) and fluorescence imaging (FI) bimodal imaging probe with active tumor targeting. The polymeric nanoparticles have been generated by dissolving presynthesized linear block copolymers into water directly. With AIEgens, N-BP5-Gd-ACPPs showed tumor cell penetration, which can be characterized by in vitro FI. Preliminary in vivo experiments of Gd-chelated nanoparticles have demonstrated promising characteristics as a tumor-targeting MRI contrast agent with good biocompatibility. This study impacts the synthesis of functional copolymers and polymeric nanoparticles for their applications in bioimaging.

PET-MR and SPECT-MR multimodality probes: Development and challenges.

Positron emission tomography (PET)-magnetic resonance (MR) or single photon emission computed tomography (SPECT)-MR hybrid imaging is being used in daily clinical practice. Due to its advantages over stand-alone PET, SPECT or MR imaging, in many areas such as oncology, the demand for hybrid imaging techniques is increasing dramatically. The use of multimodal imaging probes or biomarkers in a single molecule or particle to characterize the imaging subjects such as disease tissues certainly provides us with more accurate diagnosis and promotes therapeutic accuracy. A limited number of multimodal imaging probes are being used in preclinical and potential clinical investigations. The further development of multimodal PET-MR and SPECT-MR imaging probes includes several key elements: novel synthetic strategies, high sensitivity for accurate quantification and high anatomic resolution, favourable pharmacokinetic profile and target-specific binding of a new probe. This review thoroughly summarizes all recently available and noteworthy PET-MR and SPECT-MR multimodal imaging probes including small molecule bimodal probes, nano-sized bimodal probes, small molecular trimodal probes and nano-sized trimodal probes. To the best of our knowledge, this is the first comprehensive overview of all PET-MR and SPECT-MR multimodal probes. Since the development of multimodal PET-MR and SPECT-MR imaging probes is an emerging research field, a selection of 139 papers were recognized following the literature review. The challenges for designing multimodal probes have also been addressed in order to offer some future research directions for this novel interdisciplinary research field.

Simplified estimation of binding parameters based on image-derived reference tissue models for dopamine transporter bindings in non-human primates using [18F]FE-PE2I and PET.

The aim of this study on dopamine transporter binding by [18F]FE-PE2I and PET was to describe an image-derived approach using reference tissue models: the Logan DVR approach and simplified reference tissue model (SRTM), the features of which were simple to operate and precise in the measurements. Using the approach, the authors sought to obtain binding images and parameters. [18F]FE-PE2I and dynamic PET as well as an MRI was performed on three rhesus monkeys, and metabolite corrected arterial plasma inputs were obtained. After co-registering of PET to MR images, both image sets were resliced. The time-activity curve of the cerebellum was used as indirect input, and binding parametric images were computed voxel-by-voxel. Voxel-wise linear calculations were used for the Logan DVR approach, and nonlinear least squares fittings for the SRTM. To determine the best linear regression in the Logan DVR approach, the distribution volume ratio was obtained using the optimal starting frame analysis. The obtained binding parameters were compared with those obtained by the other independent ROI-based numerical approaches: two-tissue compartment model (2TCM), Logan DVR approach and SRTM using PMOD software. Binding potentials (BP) obtained by the present approach agreed well with those obtained by ROI-based numerical approaches, although reference tissue models tended to underestimate the BP value than 2TCM. Image-derived Logan approach provided a low-noise image, the computation time was short, and the error in the optimal starting frame analysis was small. The present approach provides a high-quality binding parametric image and reliable parameter value easily.

Synthesis and in vivo magnetic resonance imaging evaluation of biocompatible branched copolymer nanocontrast agents.

Branched copolymer nanoparticles (D(h) =20-35 nm) possessing 1,4,7, 10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid macrocycles within their cores have been synthesized and applied as magnetic resonance imaging (MRI) nanosized contrast agents in vivo. These nanoparticles have been generated from novel functional monomers via reversible addition-fragmentation chain transfer polymerization. The process is very robust and synthetically straightforward. Chelation with gadolinium and preliminary in vivo experiments have demonstrated promising characteristics as MRI contrast agents with prolonged blood retention time, good biocompatibility, and an intravascular distribution. The ability of these nanoparticles to perfuse and passively target tumor cells through the enhanced permeability and retention effect is also demonstrated. These novel highly functional nanoparticle platforms have succinimidyl ester-activated benzoate functionalities within their corona, which make them suitable for future peptide conjugation and subsequent active cell-targeted MRI or the conjugation of fluorophores for bimodal imaging. We have also demonstrated that these branched copolymer nanoparticles are able to noncovalently encapsulate hydrophobic guest molecules, which could allow simultaneous bioimaging and drug delivery.

Pharmacokinetics of Gd(DO3A-Lys) and MR imaging studies in an orthotopic U87MG glioma tumor model.

Pharmacokinetics of Gd(DO3A-Lys), a macrocyclic gadolinium-based magnetic resonance imaging (MRI) contrast agent functionalized with a lysine derivative, was studied in Wistar rats. Kinetic data were fitted using a two-compartment model and revealed Gd(DO3A-Lys) to have a distribution half-life, t1/2 (α), of 1.3 min, an elimination half-life, t1/2 (ß), of 24.9 min and a large volume of distribution, VD , of 0.49 L/kg indicative of the agent being able to rapidly distribute into tissues and organs. Contrast-enhanced magnetic resonance angiography (CE-MRA) in an orthotopic U87MG glioma mouse model demonstrated considerable enhancement of both the tumor and surrounding vasculature after intravenous administration of Gd(DO3A-Lys). Applying dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in the glioma of different sizes further showed distinct uptake characteristics and patterns of enhancement, which suggests the potential for differentiating changes at different stages of tumor growth. Our results indicate that Gd(DO3A-Lys) could be a promising candidate for glioma MR imaging.

Negative contrast Cerenkov luminescence imaging of blood vessels in a tumor mouse model using [68Ga]gallium chloride.

BACKGROUND: Cerenkov luminescence imaging (CLI) is an emerging imaging technique where visible light emitted from injected beta-emitting radionuclides is detected with an optical imaging device. CLI research has mostly been focused on positive contrast imaging for ascertaining the distribution of the radiotracer in a way similar to other nuclear medicine techniques. Rather than using the conventional technique of measuring radiotracer distribution, we present a new approach of negative contrast imaging, where blood vessel attenuation of Cerenkov light emitted by [68Ga]GaCl3 is used to image vasculature. METHODS: BALB/c nude mice were injected subcutaneously in the right flank with HT-1080 fibrosarcoma cells 14 to 21 days prior to imaging. On the imaging day, [68Ga]GaCl3 was injected and the mice were imaged from 45 to 90 min after injection using an IVIS Spectrum in vivo imaging system. The mice were imaged one at a time, and manual focus was used to bring the skin into focus. The smallest view with pixel size around 83 µm was used to achieve a sufficiently high image resolution for blood vessel imaging. RESULTS: The blood vessels in the tumor were clearly visible, attenuating 7% to 18% of the light. Non-tumor side blood vessels had significantly reduced attenuation of 2% to 4%. The difference between the attenuation of light of tumor vessels (10% ± 4%) and the non-tumor vessels (3% ± 1%) was significant. Moreover, a necrotic core confirmed by histology was clearly visible in one of the tumors with a 21% reduction in radiance. CONCLUSIONS: The negative contrast CLI technique is capable of imaging vasculature using [68Ga]GaCl3. Since blood vessels smaller than 50 µm in diameter could be imaged, CLI is able to image structures that conventional nuclear medicine techniques cannot. Thus, the negative contrast imaging technique shows the feasibility of using CLI to perform angiography on superficial blood vessels, demonstrating an advantage over conventional nuclear medicine techniques.

Manipulating the surface coating of ultra-small Gd2O3 nanoparticles for improved T1-weighted MR imaging.

In this report, monodispersed ultra-small Gd2O3 nanoparticles capped with hydrophobic oleic acid (OA) were synthesized with average particle size of 2.9 nm. Two methods were introduced to modify the surface coating to hydrophilic for bio-applications. With a hydrophilic coating, the polyvinyl pyrrolidone (PVP) coated Gd2O3 nanoparticles (Gd2O3-PVP) showed a reduced longitudinal T1 relaxation time compared with OA and cetyltrimethylammonium bromide (CTAB) co-coated Gd2O3 (Gd2O3-OA-CTAB) in the relaxation study. The Gd2O3-PVP was thus chosen for its further application study in MRI with an improved longitudinal relaxivity r1 of 12.1 mM(-1) s(-1) at 7 T, which is around 3 times as that of commercial contrast agent Magnevist(®). In vitro cell viability in HK-2 cell indicated negligible cytotoxicity of Gd2O3-PVP within preclinical dosage. In vivo MR imaging study of Gd2O3-PVP nanoparticles demonstrated considerable signal enhancement in the liver and kidney with a long blood circulation time. Notably, the OA capping agent was replaced by PVP through ligand exchange on the Gd2O3 nanoparticle surface. The hydrophilic PVP grants the Gd2O3 nanoparticles with a polar surface for bio-application, and the obtained Gd2O3-PVP could be used as an in vivo indicator of reticuloendothelial activity.

An intravascular MRI contrast agent based on Gd(DO3A-Lys) for tumor angiography.

An intravascular MRI contrast agent Gd(DO3A-Lys), Gadolinium(III) (2,2',2″-(10-(3-(5-benzamido-6-methoxy-6-oxohexylamino)-3-oxopropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetate), has been studied for tumor angiography based on its high relaxivity and long blood half-life. The preparation procedures of the contrast agent have been modified in order to achieve higher yield and improve the synthetic reproducibility. High relaxivity of Gd(DO3A-Lys) has been confirmed by measurements at 3 T, 7 T and 9.4 T magnetic fields. The relaxivity-dependent albumin binding study indicated that Gd(DO3A-Lys) partially bound to albumin protein. In vitro cell viability in HK2 cell indicated low cytotoxicity of Gd(DO3A-Lys) up to 1.2 mM [Gd] concentration. In vivo toxicity studies demonstrated no toxicity of Gd(DO3A-Lys) on kidney tissues up to 0.2 mM [Gd]. While the toxicity on liver tissue was not observed at low dosage (1.0 mM [Gd]), Gd(DO3A-Lys) cause certain damage on hepatic tissue at high dosage (2.0 mM [Gd]). The DO3A-Lys has been labeled with (68)Ga radioisotope for biodistribution studies. (68)Ga(DO3A-Lys) has high uptake in both HT1080 and U87MG xenograft tumors, and has high accumulation in blood. Contrast-enhanced MR angiography (CE-MRA) in mice bearing U87MG xenograft tumor demonstrated that Gd(DO3A-Lys) could enhance vascular microenvironment around the tumor, and displays promising characteristics of an MRI contrast agent for tumor angiography.

Gadolinium-functionalized aggregation-induced emission dots as dual-modality probes for cancer metastasis study.

Understanding the localization and engraftment of tumor cells at postintravasation stage of metastasis is of high importance in cancer diagnosis and treatment. Advanced fluorescent probes and facile methodologies for cell tracing play a key role in metastasis studies. In this work, we design and synthesize a dual-modality imaging dots with both optical and magnetic contrast through integration of a magnetic resonance imaging reagent, gadolinium(III), into a novel long-term cell tracing probe with aggregation-induced emission (AIE) in far-red/near-infrared region. The obtained fluorescent-magnetic AIE dots have both high fluorescence quantum yield (25%) and T1 relaxivity (7.91 mM(-1) s(-1) ) in aqueous suspension. After further conjugation with a cell membrane penetrating peptide, the dual-modality dots can be efficiently internalized into living cells. The gadolinium(III) allows accurate quantification of biodistribution of cancer cells via intraveneous injection, while the high fluorescence provides engraftment information of cells at single cellular level. The dual-modality AIE dots show obvious synergistic advantages over either single imaging modality and hold great promises in advanced biomedical studies.

Gadolinium chelate with DO3A conjugated 2-(diphenylphosphoryl)-ethyldiphenylphosphonium cation as potential tumor-selective MRI contrast agent.

A series of organic cations, such as triphenylphosphonium (TPP), 2-(diphenylphosphoryl)-ethyldiphenylphosphonium (TPEP), represent molecular probes for imaging tumors. These organic cations have been labeled with 64Cu radioisotope for imaging tumors by positron emission tomograghy (PET). Among these organic cation ligands, TPEP was selected for extensive evaluation using magnetic resonance imaging (MRI) based on its higher tumor uptake and better Tumor/Background (T/B) ratios. This report presents the development of a new Gd(III) chelate [Gd(DO3A-xy-TPEP)]⁺ as a cationic MRI contrast agent. The contrast agent was synthesized and characterized in vitro and in vivo. In vitro cell viability showed low cytotoxicity at low [Gd] concentrations. Cell uptake experiment shows that the [Gd(DO3A-xy-TPEP)]⁺ has high affinity for tumor cells. The in vitro T1 relaxivity measured at 9.4 T is about 50% higher than those of contrast agents in clinical use: Gd-DTPA (Magnevist) and Gd-DOTA (Dotarem). In vivo imaging studies in tumor-bearing mice at 7.0 T demonstrated significant signal enhancement at the site of the tumors. [Gd(DO3A-xy-TPEP)]⁺ is a promising tumor-targeting MRI contrast agent for diagnostic imaging.

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.