Development of manganese-based nanoparticles as contrast probes for magnetic resonance imaging

MRI contrast agents: Classification and application (Review)

Magnetic resonance imaging (MRI) contrast agents are categorised according to the following specific features: chemical composition including the presence or absence of metal atoms, route of administration, magnetic properties, effect on the magnetic resonance image, biodistribution and imaging applications. The majority of these agents are either paramagnetic ion complexes or superparamagnetic magnetite particles and contain lanthanide elements such as gadolinium (Gd3+) or transition metal manganese (Mn2+). These elements shorten the T1 or T2 relaxation time, thereby causing increased signal intensity on T1-weighted images or reduced signal intensity on T2-weighted images. Most paramagnetic contrast agents are positive agents. These agents shorten the T1, so the enhanced parts appear bright on T1-weighted images. Dysprosium, superparamagnetic agents and ferromagnetic agents are negative contrast agents. The enhanced parts appear darker on T2-weighted images. MRI contrast agents incorporating chelating agents reduces storage in the human body, enhances excretion and reduces toxicity. MRI contrast agents may be administered orally or intravenously. According to biodistribution and applications, MRI contrast agents may be categorised into three types: extracellular fluid, blood pool and target/organ-specific agents. A number of contrast agents have been developed to selectively distinguish liver pathologies. Some agents are also capable of targeting other organs, inflammation as well as specific tumors.

Relaxivity and toxicological properties of manganese oxide nanoparticles for MRI applications

Manganese oxide nanoparticles (MONs) have received growing attention as alternative T ₁ MRI contrast agents due to the association of commercial gadolinium-based contrast agents with nephrogenic systemic fibrosis. Since the seminal publication first describing the use of MONs as positive T ₁ contrast agents, there is an ongoing impetus to develop MONs of higher T ₁ signal intensity for better diagnostic efficacy. Indeed, various MON-based nanoprobe designs have been proposed, such as the employment of a mesoporous nanomaterial with MONs evenly dispersed within, or the traditional coating of a biocompatible layer onto the surface of MONs to form a core-shell configuration. Recent advances in this field also propose stimuli-responsive MONs that capitalize on an acidic dissolution or in situ reduction to release Mn²⁺ ions for a multi-fold increase in MRI contrast. However, the potential nanotoxicity of MONs remains a key obstacle to the clinical translation of MON-based T ₁ contrast agents. Due to the wide variety of functionalities and physicochemical properties of MONs, there is also a lack of consensus on the toxicological properties of MONs. In addition, the r ₁ relaxivity of MRI contrast agents typically decreases at higher field strength. Hence, it highlights the need to develop MON-based contrast agents with higher relaxivities. In this regard, this article aims to present a thorough review of MONs for MRI applications, with particular emphasis on their relaxivity and toxicological properties. In order to systematically review the current state-of-the-art for the development of MONs for MRI applications, the MON-based T ₁ contrast agents are categorized based on the structure of the nanomaterial system. Key parameters that influence the nanotoxicity of MONs are also examined while the absorption, distribution, metabolism and excretion of MON in vivo are evaluated to discern how long the nanoparticles will be present within the body, as well as to predict the organs or tissues in which they distribute.

Size-Dependent Toxicity Differences of Intratracheally Instilled Manganese Oxide Nanoparticles: Conclusions of a Subacute Animal Experiment

Incomplete information on toxicological differences of micro- and nanometer-sized particles raised concerns about the effects of the latter on health and environment. Besides chemical composition, size and surface-to-volume ratio of nanoparticles (NPs) can affect toxicity. To investigate size-dependent toxicity differences, we used particles made of dioxide of the neurotoxic heavy metal manganese (Mn), typically found in inhaled metal fumes, in three size ranges (size A, 9.14 ± 1.98 nm; size B, 42.36 ± 8.06 nm; size C, 118.31 ± 25.37 nm). For modeling the most frequent route of exposure to Mn, NPs were given to rats for 6 weeks by intratracheal instillation. Of each NP size, 3 or 6 mg/kg body weight was given while control animals were vehicle treated. Neurotoxicity was assessed by measuring spontaneous locomotor activity in an open field and by recording spontaneous and evoked electrical activity from the somatosensory cortical area. Mn content of brain, lung, and blood, measured by ICP-MS, were correlated to the observed functional alterations to see the relationship between Mn load and toxic effects. Body weight gain and organ weights were measured as general toxicological indices. The toxicity of size A and size B NPs proved to be stronger compared to size C NPs, seen most clearly in decreased body weight gain and altered spontaneous cortical activity, which were also well correlated to the internal Mn dose. Our results showed strong effect of size on NP toxicity, thus, beyond inappropriateness of toxicity data of micrometer-sized particles in evaluation of NP exposure, differentiation within the nano range may be necessary.

Nanomaterial-based activatable imaging probes: from design to biological applications

Activatable imaging probes as alternatives to "always on" imaging probes have attracted more and more attention due to their improved sensitivity and specificity. They are commonly designed to amplify or boost imaging signals only in response to specific biomolecular recognition or interaction. Thus, the design strategies play a vital role in the fabrication of activatable imaging probes. In this review, we focus on the design mechanisms and biological applications of those nanomaterial-based activatable imaging probes reported in the past five years, benefitting greatly from the good development of nanotechnology. These probes not only include the most studied activatable fluorescence imaging probes, but also cover more activatable MR imaging probes based on nanoparticle contrast agents and activatable photoacoustic imaging probes, providing more bases for clinical translation.

Manganese-Enhanced Magnetic Resonance Imaging as a Diagnostic and Dispositional Tool after Mild-Moderate Blast Traumatic Brain Injury

Traumatic brain injury (TBI) caused by explosive munitions, known as blast TBI, is the signature injury in recent military conflicts in Iraq and Afghanistan. Diagnostic evaluation of TBI, including blast TBI, is based on clinical history, symptoms, and neuropsychological testing, all of which can result in misdiagnosis or underdiagnosis of this condition, particularly in the case of TBI of mild-to-moderate severity. Prognosis is currently determined by TBI severity, recurrence, and type of pathology, and also may be influenced by promptness of clinical intervention when more effective treatments become available. An important task is prevention of repetitive TBI, particularly when the patient is still symptomatic. For these reasons, the establishment of quantitative biological markers can serve to improve diagnosis and preventative or therapeutic management. In this study, we used a shock-tube model of blast TBI to determine whether manganese-enhanced magnetic resonance imaging (MEMRI) can serve as a tool to accurately and quantitatively diagnose mild-to-moderate blast TBI. Mice were subjected to a 30 psig blast and administered a single dose of MnCl2 intraperitoneally. Longitudinal T1-magnetic resonance imaging (MRI) performed at 6, 24, 48, and 72 h and at 14 and 28 days revealed a marked signal enhancement in the brain of mice exposed to blast, compared with sham controls, at nearly all time-points. Interestingly, when mice were protected with a polycarbonate body shield during blast exposure, the marked increase in contrast was prevented. We conclude that manganese uptake can serve as a quantitative biomarker for TBI and that MEMRI is a minimally-invasive quantitative approach that can aid in the accurate diagnosis and management of blast TBI. In addition, the prevention of the increased uptake of manganese by body protection strongly suggests that the exposure of an individual to blast risk could benefit from the design of improved body armor.

Synthesis and Characterization of Mn:ZnSe/ZnS/ZnMnS Sandwiched QDs for Multimodal Imaging and Theranostic Applications

In this work, a facile aqueous synthesis method is optimized to produce Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs). In this core-shell co-doped system, paramagnetic Mn(2+) ions are introduced as core and shell dopants to generate Mn phosphorescence and enhance the magnetic resonance imaging signal, respectively. T1 relaxivity of the nanoparticles can be improved and manipulated by raising the shell doping level. Steady state and time-resolved optical measurements suggest that, after high level shell doping, Mn phosphorescence of the core can be sustained by the sandwiched ZnS shell. Because the SQDs are free of toxic heavy metal compositions, excellent biocompatibility of the prepared nanocrystals is verified by in vitro MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. To explore the theranostic applications of SQDs, liposome-SQD assemblies are prepared and used for ex vivo optical and magnetic resonance imaging. In addition, these engineered SQDs as nanocarrier for gene delivery in therapy of Panc-1 cancer cells are employed. The therapeutic effects of the nanocrystals formulation are confirmed by gene expression analysis and cell viability assay.

L-DOPA-Coated Manganese Oxide Nanoparticles as Dual MRI Contrast Agents and Drug-Delivery Vehicles

Manganese oxide nanoparticles (MONPs) are capable of time-dependent magnetic resonance imaging contrast switching as well as releasing a surface-bound drug. MONPs give T2/T2* contrast, but dissolve and release T1-active Mn(2+) and L-3,4-dihydroxyphenylalanine. Complementary images are acquired with a single contrast agent, and applications toward Parkinson's disease are suggested.

Mesoporous manganese silicate coated silica nanoparticles as multi-stimuli-responsive T1-MRI contrast agents and drug delivery carriers

A novel kind of monodisperse mesoporous manganese silicate coated silica nanoparticle (MMSSN) as a highly efficient T1-weighted MRI contrast agent (CA) and drug carrier for cancer diagnosis and chemotherapy has been constructed by a modified "SiO2 sacrifice and in situ silicate growth" approach under a relatively low hydrothermal temperature and alkali-free condition. The mesoporous manganese silicate shell provides a large specific surface area and abundant exposed Mn paramagnetic centers to water molecules, which endows the MMSSNs with extraordinarily high longitudinal relaxivity. Meanwhile, the MMSSNs presented an efficient pH/redox-responsive T1-MRI feature based on the significant enhancement of relaxation rate (r1) stimulated by mild acidic environment or reducing agent (GSH) both in vitro and in vivo. Furthermore, the mesoporous structure and negatively charged pore surface of the manganese silicate shell enable the MMSSNs to attain anti-cancer drug (DOX) storage and a pH-responsive release, which is suitable for on-demand drug release for the chemotherapy of tumors. Therefore, the mesoporous manganese silicate-based nanomaterial is a promising candidate as T1-MRI CAs and anticancer-drug delivery carriers for the theranostics of tumor in an intelligent and on-demand manner.

STATEMENT OF SIGNIFICANCE

MRI is one of the most frequently used imaging techniques in daily clinics for cancer diagnosis. Using contrast agents (CAs) in MRI can afford much clearer and enlarged images of detectable organs. Gadolinium (Gd(3+))-based T1-positive CAs are widely used but associated with the risk of nephrogenic systemic fibrosis. To achieve much safer CAs, various Mn(2+)-based T1-positive CAs have been reported, such as MnO or core-shell MnOx-based nanoparticles. However, the efficiency of these CAs is still lower. Herein, we report a novel kind of mesoporous manganese silicate coated silica nanoparticle as CA and anti-cancer drug carrier. Results obtained from this study, especially the pH/redox-responsive T1-MRI feature are helpful for us to further design efficient MnSiO3-based materials for clinical MRI applications.

Phase transfer preparation of ultrasmall MnS nanocrystals with a high performance MRI contrast agent

In this paper, a phase transfer method is reported which was used to prepare ultrasmall manganese(ii) sulfide nanocrystals in which prefabricated MnS aggregations are transferred from cyclohexane into an aqueous solution of sodium citrate.

PAMAM dendrimer based targeted nano-carrier for bio-imaging and therapeutic agents

In the last several decades, researchers have focused on developing suitable drug carriers to deliver pharmaceutical agents to treat cancer diseases.

Facile synthesis of manganese silicate nanoparticles for pH/GSH-responsive T1-weighted magnetic resonance imaging

Manganese silicate nanoparticles were facilely synthesized and showed high potential as T₁-MRI contrast agents for cancer diagnosis.

Magnetic Nanoparticles in Cancer Theranostics

In a report from 2008, The International Agency for Research on Cancer predicted a tripled cancer incidence from 1975, projecting a possible 13-17 million cancer deaths worldwide by 2030. While new treatments are evolving and reaching approval for different cancer types, the main prevention of cancer mortality is through early diagnosis, detection and treatment of malignant cell growth. The last decades have seen a development of new imaging techniques now in widespread clinical use. The development of nano-imaging through fluorescent imaging and magnetic resonance imaging (MRI) has the potential to detect and diagnose cancer at an earlier stage than with current imaging methods. The characteristic properties of nanoparticles result in their theranostic potential allowing for simultaneous detection of and treatment of the disease. This review provides state of the art of the nanotechnological applications for cancer therapy. Furthermore, it advances a novel concept of personalized nanomedical theranostic therapy using iron oxide magnetic nanoparticles in conjunction with MRI imaging. Regulatory and industrial perspectives are also included to outline future perspectives in nanotechnological cancer research.

Superparamagnetic core/shell GoldMag nanoparticles: size-, concentration- and time-dependent cellular nanotoxicity on human umbilical vein endothelial cells and the suitable conditions for magnetic resonance imaging

Background

GoldMag nanoparticles (GMNPs) possess the properties of colloid gold and superparamagnetic iron oxide nanoparticles, which make them useful for delivery, separation and molecular imaging. However, because of the nanometer effect, GMNPs are highly toxic. Thus, the biosafety of GMNPs should be fully studied prior to their use in biomedicine. The main purpose of this study was to evaluate the nanotoxicity of GMNPs on human umbilical vein endothelial cells (HUVECs) and determine a suitable size, concentration and time for magnetic resonance imaging (MRI).

Results

Transmission electron microscopy showed that GMNPs had a typical shell/core structure, and the shell was confirmed to be gold using energy dispersive spectrometer analysis. The average sizes of the 30 and 50 nm GMNPs were 30.65 ± 3.15 and 49.23 ± 5.01 nm, respectively, and the shell thickness were 6.8 ± 0.65 and 8.5 ± 1.36 nm, respectively. Dynamic light scattering showed that the hydrodynamic diameter of the 30 and 50 nm GMNPs were 33.2 ± 2.68 and 53.12 ± 4.56 nm, respectively. The r₂ relaxivity of the 50 nm GMNPs was 98.65 mM⁻¹ s⁻¹, whereas it was 80.18 mM⁻¹ s⁻¹ for the 30 nm GMNPs. The proliferation, cytoskeleton, migration, tube formation, apoptosis and ROS generation of labeled HUVECs depended on the size and concentration of GMNPs and the time of exposure. Because of the higher labeling rate, the 50 nm GMNPs exhibited a significant increase in nanotoxicity compared with the 30 nm GMNPs at the same concentration and time. At no more than 25 μg/mL and 12 hours, the 50 nm GMNPs exhibited no significant nanotoxicity in HUVECs, whereas no toxicity was observed at 50 μg/mL and 24 hours for the 30 nm GMNPs.

Conclusions

These results demonstrated that the nanotoxicity of GMNPs in HUVECs depended on size, concentration and time. Exposure to larger GMNPs with a higher concentration for a longer period of time resulted in a higher labeling rate and ROS level for HUVECs. Coupled with r₂ relaxivity, it was suggested that the 50 nm GMNPs are more suitable for HUVEC labeling and MRI, and the suitable concentration and time were 25 μg/mL and 12 hours.

Long-circulating PEGylated manganese ferrite nanoparticles for MRI-based molecular imaging

Magnetic resonance based molecular imaging has emerged as a very promising technique for early detection and treatment of a wide variety of diseases, including cancer, neurodegenerative disorders, and vascular diseases. The limited sensitivity and specificity of conventional MRI are being overcome by the development of a new generation of contrast agents, using nanotechnology approaches, with improved magnetic and biological properties. In particular, for molecular imaging, high specificity, high sensitivity, and long blood circulation times are required. Furthermore, the lack of toxicity and immunogenicity together with low-cost scalable production are also necessary to get them into the clinics. In this work, we describe a facile, robust and cost-effective ligand-exchange method to synthesize dual T1 and T2 MRI contrast agents with long circulation times. These contrast agents are based on manganese ferrite nanoparticles (MNPs) between 6 and 14 nm in size covered by a 3 kDa polyethylene glycol (PEG) shell that leads to a great stability in aqueous media with high crystallinity and magnetization values, thus retaining the magnetic properties of the uncovered MNPs. Moreover, the PEGylated MNPs have shown different relaxivities depending on their size and the magnetic field applied. Thus, the 6 nm PEGylated MNPs are characterized by a low r2/r1 ratio of 4.9 at 1.5 T, hence resulting in good dual T1 and T2 contrast agents under low magnetic fields, whereas the 14 nm MNPs behave as excellent T2 contrast agents under high magnetic fields (r2 = 335.6 mM(-1) s(-1)). The polymer core shell of the PEGylated MNPs minimizes their cytotoxicity, and allows long blood circulation times. This combination of cellular compatibility and excellent T2 and r2/r1 values under low magnetic fields, together with long circulation times, make these nanomaterials very promising contrast agents for molecular imaging.

Preparation of manganese(II), chromium(III) and ferric(III) oxides nanoparticles in situ metal citraconate complexes frameworks

The new reactions of some divalent and trivalent transition metal ions (Mn(II), Cr(III), and Fe(III)) with citraconic acid has been studied. The obtained results indicate the formation of citraconic acid compounds with molar ratio of metal to citraconic acid of 2:2 or 2:3 with general formulas Mn2(C5H4O4)2 or M2(C5H4O4)3⋅nH2O where n=6 for Cr, and Fe(III). The thermal decomposition of the crystalline solid complexes was investigated. The IR spectra of citraconate suggested that the carboxylic groups are bidentatically bridging and chelating. In the course of decomposition the complexes are dehydrated and then decompose either directly to oxides in only one step or with intermediate formation of oxocarbonates. This proposal dealing the preparation of MnO2, Fe2O3 and Cr2O3 nanoparticles. The crystalline structure of oxide products were checked by X-ray powder diffraction (XRD), and the morphology of particles by scanning electron microscopy (SEM).

Clinical imaging in regenerative medicine

In regenerative medicine, clinical imaging is indispensable for characterizing damaged tissue and for measuring the safety and efficacy of therapy. However, the ability to track the fate and function of transplanted cells with current technologies is limited. Exogenous contrast labels such as nanoparticles give a strong signal in the short term but are unreliable long term. Genetically encoded labels are good both short- and long-term in animals, but in the human setting they raise regulatory issues related to the safety of genomic integration and potential immunogenicity of reporter proteins. Imaging studies in brain, heart and islets share a common set of challenges, including developing novel labeling approaches to improve detection thresholds and early delineation of toxicity and function. Key areas for future research include addressing safety concerns associated with genetic labels and developing methods to follow cell survival, differentiation and integration with host tissue. Imaging may bridge the gap between cell therapies and health outcomes by elucidating mechanisms of action through longitudinal monitoring.

Solid silica nanoparticles: applications in molecular imaging

Silica and silica-based nanoparticles have been widely used for therapeutic and diagnostic applications in cancer mainly through delivery of drugs, genes and contrast agents. Development of synthesis methods has provided the possibility of fabricating silica nanoparticles with different sizes in nanometer ranges as well as silica-based multimodal nanoparticles with many innovative properties and intriguing applications in biomedicine. The surface of silica particles facilitates different methods of surface modifications and allows conjugation of various biomolecules such as proteins and nucleic acids. In this review, different methods of fabrication of silica and silica-based nanoparticles, their surface modification and the application of these nanoparticles in molecular imaging are discussed. Overall, the aim of this review is to address the development of silica and silica-based multifunctional nanoparticles that are introduced mainly for molecular imaging applications using optical, magnetic (MRI), X-ray (computed tomography) and multimodal imaging techniques.

Enhanced blood-brain barrier transmigration using a novel transferrin embedded fluorescent magneto-liposome nanoformulation

The blood-brain barrier (BBB) is considered as the primary impediment barrier for most drugs. Delivering therapeutic agents to the brain is still a big challenge to date. In our study, a dual mechanism, receptor mediation combined with external non-invasive magnetic force, was incorporated into ferrous magnet-based liposomes for BBB transmigration enhancement. The homogenous magnetic nanoparticles (MNPs), with a size of ∼10 nm, were synthesized and confirmed by TEM and XRD respectively. The classical magnetism assay showed the presence of the characteristic superparamagnetic property. These MNPs encapsulated in PEGylated fluorescent liposomes as magneto-liposomes (MLs) showed mono-dispersion, ∼130 ± 10 nm diameter, by dynamic laser scattering (DLS) using the lipid-extrusion technique. Remarkably, a magnetite encapsulation efficiency of nearly 60% was achieved. Moreover, the luminescence and hydrodynamic size of the MLs was stable for over two months at 4 ° C. Additionally, the integrity of the ML structure remained unaffected through 120 rounds of circulation mimicking human blood fluid. After biocompatibility confirmation by cytotoxicity evaluation, these fluorescent MLs were further embedded with transferrin and applied to an in vitro BBB transmigration study in the presence or absence of external magnetic force. Comparing with magnetic force- or transferrin receptor-mediated transportation alone, their synergy resulted in 50-100% increased transmigration without affecting the BBB integrity. Consequently, confocal microscopy and iron concentration in BBB-composed cells further confirmed the higher cellular uptake of ML particles due to the synergic effect. Thus, our multifunctional liposomal magnetic nanocarriers possess great potential in particle transmigration across the BBB and may have a bright future in drug delivery to the brain.

Manganese graft ionomer complexes (MaGICs) for dual imaging and chemotherapy

Novel manganese graft ionomer complexes (MaGICs) that contain Mn ions complexed with a polyaminobisphosphonate-g-poly(ethylene oxide) (PEO) copolymer were developed for use as T₁-weighted contrast agents for MRI. The complexes exhibited good colloidal stability without release of free manganese and did not result in any in vitro toxicity against mouse hepatocytes. T₁ relaxivities of the MaGICs at physiological pH were 2-10 times higher than that of a commercial manganese-based positive contrast agent. Anticancer drugs including doxorubicin, cisplatin and carboplatin were successfully encapsulated into the MaGICs with high efficiency. Drug release behavior was sustained and depended on pH (faster in acidic environments), drug structures and drug concentration (faster with high concentration). The anticancer drug-loaded manganese nanocarriers exhibited excellent anticancer activity against MCF-7 breast cancer cells together with high relaxivity. Thus, these drug-loaded MaGICs could potentially be utilized for simultaneous diagnosis and treatment of cancer.

MnII-containing coordination nanoparticles as highly efficient T1 contrast agents for magnetic resonance imaging

Nanoparticles of Mn^II-containing Prussian blue analogues reveal large longitudinal relaxivities exceeding that of clinical contrast agents.

Ultrahigh relaxivity and safe probes of manganese oxide nanoparticles for in vivo imaging

Mn-based nanoparticles (NPs) have emerged as new class of probes for magnetic resonance imaging due to the impressive contrast ability. However, the reported Mn-based NPs possess low relaxivity and there are no immunotoxicity data regarding Mn-based NPs as contrast agents. Here, we demonstrate the ultrahigh relaxivity of water protons of 8.26 mM(-1) s(-1) from the Mn3O4 NPs synthesized by a simple and green technique, which is twice higher than that of commercial gadolinium (Gd)-based contrast agents (4.11 mM(-1) s(-1)) and the highest value reported to date for Mn-based NPs. We for the first time demonstrate these Mn3O4 NPs biocompatibilities both in vitro and in vivo are satisfactory based on systematical studies of the intrinsic toxicity including cell viability of human nasopharyngeal carcinoma cells, normal nasopharyngeal epithelium, apoptosis in cells and in vivo immunotoxicity. These findings pave the way for the practical clinical diagnosis of Mn based NPs as safe probes for in vivo imaging.

Image-guided drug delivery to the brain using nanotechnology

Targeting across the blood-brain barrier (BBB) for treatment of central nervous system (CNS) diseases represents the most challenging aspect of, as well as one of the largest growing fields in, neuropharmaceutics. Combining nanotechnology with multiple imaging techniques has a unique role in the diagnosis and treatment (theranostics) of CNS disease. Such imaging techniques include anatomical imaging modalities, such as magnetic resonance imaging (MRI), ultrasound (US), X-ray computed tomography (CT), positron emission tomography (PET), single-photon emission computed tomography (SPECT), electron microscopy, autoradiography and optical imaging as well as thermal images. In this review, we summarize and discuss recent advances in formulations, current challenges and possible hypotheses concerning the use of such theranostics across the BBB.

Real-time infrared thermography detection of magnetic nanoparticle hyperthermia in a murine model under a non-uniform field configuration

PURPOSE

Magnetic nanoparticle hyperthermia consists of an increase of the temperature of magnetic nanoparticles (heat centres) due to the interaction of their magnetic moments with an alternating magnetic field. In vivo experiments using this method usually use a few fibre-optic thermometers inserted in the animal body to monitor the heat deposition. As a consequence, only a few points of the 3D temperature distribution can be monitored by this invasive procedure. It is the purpose of this work to show that non-invasive infrared thermography is able to detect, in real time, magnetic nanoparticle hyperthermia as well as monitor the harmful field-induced eddy currents in a murine model with a subcutaneous tumour. This surface temperature measurement method has the potential to give information about the intratumoral temperature.

MATERIALS AND METHODS

The non-invasive magnetic hyperthermia experiments were performed at 300 kHz in non-uniform field configuration conditions in healthy mice and murine tumour induced by sarcoma S180. A soft ferrite-based biocompatible magnetic colloid consisting of manganese-ferrite nanoparticles surface-coated with citric acid were used in the experiments, which were extensively characterised by several techniques (transmission electron microscopy (TEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM)). The amplitude of the alternating magnetic fields was obtained from measurements using an AC field probe at similar experimental conditions. The temperature measurements were obtained from an infrared thermal camera and a fibre-optic thermometer.

RESULTS

Three-minute magnetic hyperthermia experiments revealed surface temperature increase as high as 11 °K in healthy and (5 °K in S180 tumour) animals when injecting subcutaneously 2 mg of magnetic nanoparticles (86 μL of magnetic fluid), in contrast to around 1.5 °K (for healthy) and 2.5 °K (for cancerous) animals in experiments without the colloid due to field-induced eddy currents at the animal surface. The thermographic temperature measurements were found to agree with the fibre-optic measurements within a 5% error, and were associated with the skin emissivity angle of dependence in the experimental set-up. On the other hand, a 30-min magnetic nanoparticle hyperthermia revealed surface temperature increases as high as 12 °K close to the injection site, while above 2-3 cm no significant temperature increase was observed. Curiously, the intratumoral temperature, monitored by a fibre-optic sensor, was found to be almost the same as the thermal camera surface temperature after achieving an equilibrium temperature regime. From the observed isotherms at the animal surface, using an analytical heat conduction model, taking into account surface conductance, we estimate a magnetic heating power of 0.45 W/cm(3) and a specific loss power (SLP) of 85 W/g for a field of the order of only 10 kA/m at the injection site region.

CONCLUSIONS

The results indicate that infrared thermography may be a promising tool for both early cancer detection and for hyperthermia treatment (at least for subcutaneous tumours), since the method permits access to information about the intratumoral temperature during a real-time magnetic hyperthermia as well as to estimate the in vivo nanoparticles SLP.

Functional magnetic nanoparticles for non-viral gene delivery and MR imaging

Gene therapy is becoming a promising strategy to treat various kinds of genetic and acquired diseases. However, the development of safe, efficient, and targetable gene delivery systems remains a major challenge in gene therapy. The unique material characteristics of magnetic nanoparticles (MNPs), including high surface area, facile surface modification, controllable size, and excellent magnetic properties, make them promising candidates for gene delivery. The engineered MNPs with modifiable functional surfaces and bioactive cores can result in several advantageous diagnostic and therapeutic properties including enhanced magnetic resonance imaging (MRI) signal intensity, long permeation and retention in the circulatory system, specific delivery of therapeutic genes to target sites. In this review, the updated research on the preparation and surface modification of MNPs for gene delivery is summarized.

Nanoparticle-based systems for T(1)-weighted magnetic resonance imaging contrast agents

Because magnetic resonance imaging (MRI) contrast agents play a vital role in diagnosing diseases, demand for new MRI contrast agents, with an enhanced sensitivity and advanced functionalities, is very high. During the past decade, various inorganic nanoparticles have been used as MRI contrast agents due to their unique properties, such as large surface area, easy surface functionalization, excellent contrasting effect, and other size-dependent properties. This review provides an overview of recent progress in the development of nanoparticle-based T1-weighted MRI contrast agents. The chemical synthesis of the nanoparticle-based contrast agents and their potential applications were discussed and summarized. In addition, the recent development in nanoparticle-based multimodal contrast agents including T1-weighted MRI/computed X-ray tomography (CT) and T1-weighted MRI/optical were also described, since nanoparticles may curtail the shortcomings of single mode contrast agents in diagnostic and clinical settings by synergistically incorporating functionality.

Facile synthesis and potential bioimaging applications of hybrid upconverting and plasmonic NaGdF4: Yb3+, Er3+/silica/gold nanoparticles

We present a simple method for preparing water dispersible NaGdF₄: Yb³⁺, Er³⁺/silica/gold nanoparticles. The emission intensity and color of the upconverting cores are modulated by the plasmonic absorbance and field enhancement from the gold nanoparticles. The applicability of hybrid NPs for multi-modal bioimaging probes is illustrated by in vitro confocal microscopy of living cancer cells.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.

Manganese-loaded lipid-micellar theranostics for simultaneous drug and gene delivery to lungs

Gadolinium (Gd) contrast agents are predominantly used for T(1) MR imaging. However, the high toxicity of Gd(3+) and potential side effects including nephrogenic systemic fibrosis have led to the search for alternative T(1) contrast agents. Since manganese (Mn) has paramagnetic properties with five unpaired electrons that permit high spin number, long electronic relaxation times, and labile water exchange, we evaluated Mn as a T(1) magnetic resonance imaging (MRI) contrast agent for lung imaging. Here we report on the design and synthesis of multifunctional lipid-micellar nanoparticles (LMNs) containing Mn oxide (M-LMNs) for MRI that can also be used for DNA and drug delivery. Oleic acid-coated MnO nanoparticles were encapsulated in micelles composed of polyethylene glycol (PEG-2000), phosphatidylethanolamine (PE), DC-cholesterol, and dioleoyl-phosphatidylethanolamine (DOPE). The particles are taken up in vitro by human embryonic kidney (HEK293), Lewis lung carcinoma (LLC1), and A549 cells and are devoid of cytotoxicity. When administered to mice intranasally, they preferentially accumulate in the lungs. In vitro phantom and ex vivo lung MRI results confirmed that M-LMNs are able to enhance T(1) MRI contrast. M-LMNs loaded with plasmid DNA and/or doxorubicin are efficiently taken up by HEK293 cells in vitro and by target cells in vivo. Taken together, these results demonstrate that M-LMNs are capable of simultaneously providing MRI contrast and DNA and/or drug delivery to target cells in the lung and therefore may prove useful as a lung theranostic, especially for lung cancers.

Highly sensitive and rapid detection of Pseudomonas aeruginosa based on magnetic enrichment and magnetic separation

A method for highly sensitive and rapid detection of Pseudomonas aeruginosa, based on magnetic enrichment and magnetic separation, is described in this paper. The magnetic nanoparticles (MNPs) were applied to adsorb genome DNA after the sample was lysed. The DNA binding MNPs were directly subjected to polymerase chain reaction (PCR) to amplify gyrB specific sequence of Pseudomonas aeruginosa. The biotin labeled PCR products were detected by chemiluminescence when they were successively incubated with the probes-modified MNPs and alkaline phosphatase (ALP) labeled streptavidin (SA). Agarose gel electrophoresis analyses approved the method of in situ PCR to be highly reliable. The factors which could affect the chemiluminiscence were studied in detail. The results showed that the MNPs of 400 nm in diameter are beneficial to the detection. The sequence length and the binding site of the probe with a target sequence have obvious effects on the detection. The optimal concentration of the probes, hybridization temperature and hybridization time were 10 μM, 60 ºC and 60 mins, respectively. The method of in situ PCR based on MNPs can greatly improve the utilization rate of the DNA template ultimately enhancing the detection sensitivity. Experiment results proved that the primer and probe had high specificity, and Pseudomonas aeruginosa was successfully detected with detection limits as low as 10 cfu/mL by this method, while the detection of a single Pseudomonas aeruginosa can also be achieved.

Recent advances in benefits and hazards of engineered nanoparticles

Over recent decades, engineered nanoparticles are increasingly produced as the result of the rapid development in nanotechnology. They are currently used in a wide range of industrial and public sectors including healthcare, agriculture, transport, energy, materials, and information and communication technologies. As the result, an increasing concern has been raised over the potential impacts of engineered nanoparticles to human health. In the light of this, it is the purpose of the present review to discuss: (1) novel properties of engineered nanoparticles particularly in biomedical sciences, (2) most recently reported adverse effects of manufactured nanoparticles on human health and (3) different aspects of toxicological risk assessment of these nanoparticles.

A Novel SNPs Detection Method Based on Gold Magnetic Nanoparticles Array and Single Base Extension

To fulfill the increasing need for large-scale genetic research, a high-throughput and automated SNPs genotyping method based on gold magnetic nanoparticles (GMNPs) array and dual-color single base extension has been designed. After amplification of DNA templates, biotinylated extension primers were captured by streptavidin coated gold magnetic nanoparticle (SA-GMNPs). Next a solid-phase, dual-color single base extension (SBE) reaction with the specific biotinylated primer was performed directly on the surface of the GMNPs. Finally, a “bead array” was fabricated by spotting GMNPs with fluorophore on a clean glass slide, and the genotype of each sample was discriminated by scanning the “bead array”. MTHFR gene C677T polymorphism of 320 individual samples were interrogated using this method, the signal/noise ratio for homozygous samples were over 12.33, while the signal/noise ratio for heterozygous samples was near 1. Compared with other dual-color hybridization based genotyping methods, the method described here gives a higher signal/noise ratio and SNP loci can be identified with a high level of confidence. This assay has the advantage of eliminating the need for background subtraction and direct analysis of the fluorescence values of the GMNPs to determine their genotypes without the necessary procedures for purification and complex reduction of PCR products. The application of this strategy to large-scale SNP studies simplifies the process, and reduces the labor required to produce highly sensitive results while improving the potential for automation.

A nanoscale graphene oxide-peptide biosensor for real-time specific biomarker detection on the cell surface

A nanoscale RGD-pyrene-graphene oxide (GO) biosensor was prepared for real-time in situ detection of a cancer cell surface marker, integrin αvβ3. This nanoscale GO-based biosensor is simple, robust, sensitive and of high selectivity. It can also be adapted to other cancer cell surface marker evaluation systems.

Noninvasive monitoring of orthotopic glioblastoma therapy response using RGD-conjugated iron oxide nanoparticles

Noninvasive imaging techniques have been considered important strategies in the clinic to monitor tumor early response to therapy. In the present study, we applied RGD peptides conjugated to iron oxide nanoparticles (IONP-RGD) as contrast agents in magnetic resonance imaging (MRI) to noninvasively monitor the response of a vascular disrupting agent VEGF(121)/rGel in an orthotopic glioblastoma model. RGD peptides were firstly coupled to IONPs coated with a crosslinked PEGylated amphiphilic triblock copolymer. In vitro binding assays confirmed that cellular uptake of particles was mainly dependent on the interaction between RGD and integrin α(v)β(3) of human umbilical vein endothelial cells (HUVEC). The tumor targeting of IONP-RGD was observed in an orthotopic U87 glioblastoma model. Finally, noninvasive monitoring of the tumor response to VEGF(121)/rGel therapy at early stages of treatment was successfully accomplished using IONP-RGD as a contrast agent for MRI, a superior method over common anatomical approaches which are based on tumor size measurements. This preclinical study can accelerate anticancer drug development and promote clinical translation of nanoprobes.

Molecular imaging of stem cells: tracking survival, biodistribution, tumorigenicity, and immunogenicity

Being able to self-renew and differentiate into virtually all cell types, both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have exciting therapeutic implications for myocardial infarction, neurodegenerative disease, diabetes, and other disorders involving irreversible cell loss. However, stem cell biology remains incompletely understood despite significant advances in the field. Inefficient stem cell differentiation, difficulty in verifying successful delivery to the target organ, and problems with engraftment all hamper the transition from laboratory animal studies to human clinical trials. Although traditional histopathological techniques have been the primary approach for ex vivo analysis of stem cell behavior, these postmortem examinations are unable to further elucidate the underlying mechanisms in real time and in vivo. Fortunately, the advent of molecular imaging has led to unprecedented progress in understanding the fundamental behavior of stem cells, including their survival, biodistribution, immunogenicity, and tumorigenicity in the targeted tissues of interest. This review summarizes various molecular imaging technologies and how they have advanced the current understanding of stem cell survival, biodistribution, immunogenicity, and tumorigenicity.

Magnetic nanoparticle-based theranostics

This theme issue provides a timely collection of studies on magnetic nanoparticle-based imaging, bio-sensing, therapy and/or their combinations.