New Templated Ostwald Ripening Process of Mesostructured FeOOH for Third‐Harmonic Generation Bioimaging

Emerging advances in iron oxide nanoparticles exploit their high magnetization for various applications, such as bioseparation, hyperthermia, and magnetic resonance imaging. In contrast to their excellent magnetic performance, the harmonic generation and luminescence properties of iron oxide nanoparticles have not been thoroughly explored, thus limiting their development as a tool in photomedicine. In this work, a seed/growth‐inspired synthesis is developed combined with primary mineralization and a ligand‐assisted secondary growth strategy to prepare mesostructured α‐FeOOH nanorods (NRs). The sub‐wavelength heterogeneity of the refractive index leads to enhanced third‐harmonic generation (THG) signals under near‐infrared excited wavelengths at 1230 nm. The as‐prepared NRs exhibit an 11‐fold stronger THG intensity compared to bare α‐FeOOH NRs. Using these unique nonlinear optical properties, it is demonstrated that mesostructured α‐FeOOH NRs can serve as biocompatible and nonbleaching contrast agents in THG microscopy for long‐term labeling of cells as well as in angiography in vivo by modifying lectin to enhance the binding efficiency to the glycocalyx layers on the wall of blood vessels. These results provide a new insight into Fe‐based nanoplatforms capable of emitting coherent light as molecular probes in optical microscopy, thus establishing a complementary microscopic imaging method for macroscopic magnetic imaging systems.     

Benchtop MRI for pharmacokinetic evaluation of two aqueous-based nano-scaled formulations of oleic acid stabilized magnetite nanocrystals

Background: The interplay between numerous factors, including the size, shape, coating, surface charge and composition of particles is known to affect the pharmacokinetics and biodistribution of superparamagnetic iron oxides (SPIOs). This makes understanding the role of each factor independently quite challenging.

Methods: In the present study, the in vivo magnetic resonance imaging (MRI), biodistribution and hepatic clearance evaluations of two SPIOs Formulations A and B developed from ～13.5?nm hydrophobic oleic acid stabilized monodisperse magnetite nanocrystals core and lipid-based amphiphilic stabilizers were performed using a prototype benchtop MR imager (22?MHz) and pulsed nuclear magnetic resonance (NMR) system (20?MHz), respectively. Formulation A was composed of mPEG-2000-DSPE and Formulation B was composed of Phospholipon-100H, sucrose ester M-1695 and Cremophor RH-40.

Results: The in vivo MRI investigations showed that both formulations were safe and effective as potential liver MR contrast agents with sustained liver contrast for at least seven days. In addition, ex vivo relaxometric investigations revealed that the formulations predominantly distribute to the liver and spleen following I.V. injection. The hepatic clearance kinetics determined based on the relaxometric quantification method indicated that both formulations exhibited a biphasic clearance process with a slow terminal clearance half-life of 11.5 and 12.7 days, respectively, for Formulations A and B.

Conclusions: The results of this study showed the potential biomedical applications of the investigated magnetopharmaceutical formulations as MRI contrast agents.     

Amphiphilic polymer-coated hybrid nanoparticles as CT/MRI dual contrast agents

We describe hybrid nanoparticles, composed of iron oxide and gold nanoparticles, as potential dual contrast agents for both computed tomography (CT) and magnetic resonance imaging (MRI). The hybrid nanoparticles are synthesized by thermal decomposition of mixtures of Fe-oleate and Au-oleylamine complexes. Using a nano-emulsion method, the nanoparticles are coated with amphiphilic poly(DMA-r-mPEGMA-r-MA) to impart water-dispersity and antibiofouling properties. An in?vitro phantom study shows that the hybrid nanoparticles have high CT attenuation, because of the constituent gold nanoparticles, and afford a good MR signal, attributable to the contained iron oxide nanoparticles. Intravenous injection of the hybrid nanoparticles into hepatoma-bearing mice results in high contrast between the hepatoma and normal hepatic parenchyma in both CT and MRI. These results suggest that the hybrid nanoparticles may be useful as CT/MRI dual contrast agents for in?vivo hepatoma imaging.     

Magnetic Targeting of Human Mesenchymal Stem Cells with Internalized Superparamagnetic Iron Oxide Nanoparticles

Cell therapies offer exciting new opportunities for effectively treating many human diseases. However, delivery of therapeutic cells by intravenous injection, while convenient, relies on the relatively inefficient process of homing of cells to sites of injury. To address this limitation, a novel strategy has been developed to load cells with superparamagnetic iron oxide nanoparticles (SPIOs), and to attract them to specific sites within the body by applying an external magnetic field. The feasibility of this approach is demonstrated using human mesenchymal stem cells (hMSCs), which may have a significant potential for regenerative cell therapies due to their ease of isolation from autologous tissues, and their ability to differentiate into various lineages and modulate their paracrine activity in response to the microenvironment. The efficient loading of hMSCs with polyethylene glycol‐coated SPIOs is achieved, and it is found that SPIOs are localized primarily in secondary lysosomes of hMSCs and are not toxic to the cells. Further, the key stem cell characteristics, including the immunophenotype of hMSCs and their ability to differentiate, are not altered by SPIO loading. Through both experimentation and mathematical modeling, it is shown that, under applied magnetic field gradients, SPIO‐containing cells can be localized both in vitro and in vivo. The results suggest that, by loading SPIOs into hMSCs and applying appropriate magnetic field gradients, it is possible to target hMSCs to particular vascular networks.     

Coating optimization of superparamagnetic iron oxide nanoparticles for high T2 relaxivity

We describe a new method for coating superparamagnetic iron oxide nanoparticles (SPIOs) and demonstrate that, by fine-tuning the core size and PEG coating of SPIOs, the T2 relaxivity per particle can be increased by >200-fold. With 14 nm core and PEG1000 coating, SPIOs can have T2 relaxivity of 385 s-1 mM-1, which is among the highest per-Fe atom relaxivities. In vivo tumor imaging results demonstrated the potential of the SPIOs for clinical applications.     

Enhanced pulsed magneto-motive ultrasound imaging using superparamagnetic nanoclusters

Recently, pulsed magneto-motive ultrasound (pMMUS) imaging augmented with ultra-small magnetic nanoparticles has been introduced as a tool capable of imaging events at molecular and cellular levels. The sensitivity of a pMMUS system depends on several parameters, including the size, geometry and magnetic properties of the nanoparticles. Under the same magnetic field, larger magnetic nanostructures experience a stronger magnetic force and produce larger displacement, thus improving the sensitivity and signal-to-noise ratio (SNR) of pMMUS imaging. Unfortunately, large magnetic iron-oxide nanoparticles are typically ferromagnetic and thus are very difficult to stabilize against colloidal aggregation. In the current study we demonstrate improvement of pMMUS image quality by using large size superparamagnetic nanoclusters characterized by strong magnetization per particle. Water-soluble magnetic nanoclusters of two sizes (15 and 55 nm average size) were synthesized from 3 nm iron precursors in the presence of citrate capping ligand. The size distribution of synthesized nanoclusters and individual nanoparticles was characterized using dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM). Tissue mimicking phantoms containing single nanoparticles and two sizes of nanoclusters were imaged using a custom-built pMMUS imaging system. While the magnetic properties of citrate-coated nanoclusters are identical to those of superparamagnetic nanoparticles, the magneto-motive signal detected from nanoclusters is larger, i.e. the same magnetic field produced larger magnetically induced displacement. Therefore, our study demonstrates that clusters of superparamagnetic nanoparticles result in pMMUS images with higher contrast and SNR.     

Impact of agglomeration on the relaxometric properties of paramagnetic ultra-small gadolinium oxide nanoparticles

Ultra-small gadolinium oxide nanoparticles (US-Gd(2)O(3)) are used to provide 'positive' contrast effects in magnetic resonance imaging (MRI), and are being considered for molecular and cellular imaging applications. However, these nanoparticles can aggregate over time in aqueous medium, as well as when internalized into cells. This study is aimed at measuring in vitro, in aqueous medium, the impact of aggregation on the relaxometric properties of paramagnetic US-Gd(2)O(3) particles. First, the nanoparticle core size as well as aggregation behaviour was assessed by HRTEM. DLS (hydrodynamic diameter) was used to measure the hydrodynamic diameter of nanoparticles and nanoaggregates. The relaxometric properties were measured by NMRD profiling, as well as with (1)H NMR relaxometers. Then, the positive contrast enhancement effect was assessed by using magnetic resonance scanners (at 1.5 and 7 T). At every magnetic field, the longitudinal relaxivity (r(1)) decreased upon agglomeration, while remaining high enough to provide positive contrast. On the other hand, the transverse relaxivity (r(2)) slightly decreased at 0.47 and 1.41 T, but it was enhanced at higher fields (7 and 11.7 T) upon agglomeration. All NMRD profiles revealed a characteristic relaxivity peak in the range 60-100 MHz, suggesting the possibility to use US-Gd(2)O(3) as an efficient 'positive-T(1)' contrast agent at clinical magnetic fields (1-3 T), in spite of aggregation.     

Pulsed magneto-motive ultrasound imaging to detect intracellular trafficking of magnetic nanoparticles

As applications of nanoparticles in medical imaging and biomedicine rapidly expand, the interactions of nanoparticles with living cells have become an area of active interest. For example, intracellular accumulation of nanoparticles-an important part of cell-nanoparticle interaction-has been well studied using plasmonic nanoparticles and optical or optics-based techniques due to the change in optical properties of the nanoparticle aggregates. However, magnetic nanoparticles, despite their wide range of clinical applications, do not exhibit plasmonic-resonant properties and therefore their intracellular aggregation cannot be detected by optics-based imaging techniques. In this study, we investigated the feasibility of a novel imaging technique-pulsed magneto-motive ultrasound (pMMUS)-to identify intracellular accumulation of endocytosed magnetic nanoparticles. In pMMUS imaging a focused, high intensity, pulsed magnetic field is used to excite the cells labeled with magnetic nanoparticles, and ultrasound imaging is then used to monitor the mechanical response of the tissue. We demonstrated previously that clusters of magnetic nanoparticles amplify the pMMUS signal in comparison to the signal from individual nanoparticles. Here we further demonstrate that pMMUS imaging can identify interaction between magnetic nanoparticles and living cells, i.e.?intracellular accumulation of nanoparticles within the cells. The results of our study suggest that pMMUS imaging can not only detect the presence of magnetic nanoparticles but also provides information about their intracellular accumulation non-invasively and in real-time.     

Multi-functional chitosan nanoparticles encapsulating quantum dots and Gd-DTPA as imaging probes for bio-applications

Chitosan was used to encapsulate both CdSe/ZnS quantum dots (QDs) and the magnetic resonance imaging (MRI) contrast agent gadolinium-diethylenetriaminepentaacetate (Gd-DTPA), forming multi-functional nanoparticles that can be used in a wide range of in vitro or in vivo studies as fluorescent biological labels as well as MRI contrast agents, respectively. Multi-color QDs at pre-determined molar ratios were encapsulated into chitosan nanoparticles to produce bar-coding fluorescent labels. The encapsulated QDs and Gd-DTPA still maintained their desirable optical properties and relatively high relaxivity, respectively. The chitosan nanoparticles also showed good aqueous stability and enhanced biocompatibility on myoblast cells.     

Contrast agents for MRI

Contrast agents are divided into two categories. The first one is paramagnetic compounds, including lanthanides like gadolinium, which mainly reduce the longitudinal (T₁) relaxation property and result in a brighter signal. The second class consists of super-paramagnetic magnetic nanoparticles (SPMNPs) such as iron oxides, which have a strong effect on the transversal (T₂) relaxation properties. SPMNPs have the potential to be utilized as excellent probes for magnetic resonance imaging (MRI). For instance, clinically benign iron oxide and engineered ferrite nanoparticles provide a good MRI probing capability for clinical applications. Furthermore, the limited magnetic property and inability to escape from the reticuloendothelial system (RES) of the used nanoparticles impede their further advancement. Therefore, it is necessary to develop the engineered magnetic nanoparticle probes for the next-generation molecular MRI. Considering the importance of MRI in diagnosing diseases, this paper presents an overview of recent scientific achievements in the development of new synthetic SPMNP probes whereby the sensitive and target-specific observation of biological events at the molecular and cellular levels is feasible.     

Iron-based magnetic nanoparticles for magnetic resonance imaging

Magnetic resonance imaging (MRI) has been an extensive area of research owing to its depth of penetration for clinical diagnosis. Signal intensity under MRI is related to both T₁, spin-lattice relaxation, and T₂, spin-spin relaxation. To increase the contrast variability under MRI, several contrast agents are being used, i.e. T₁ contrast agents (e.g. gadolinium) and T₂ contrast agents (e.g. iron-based magnetic nanoparticles). These contrast agents are administered prior to scanning to increase contrast visibility. They reduce the T₁ and T₂ relaxation times to produce hyperintense and hypointense signals, respectively. Tunable properties of iron-based magnetic nanoparticles and several coating materials provide a platform to get superb MRI contrast in T₂ weighted images. It has been found that contrast enhancement by iron-based magnetic nanoparticles is dependent on the size, shape, composition, surface, and magnetic properties which can be tuned with the synthesis method and coating material. Therefore, understanding the synthesis method and properties of magnetic nanoparticles is vital to contribute to MR signal enhancement which is directing the scientist to design engineered iron-based magnetic nanoparticles. This paper introduces the concept of MRI contrast enhancement. We mainly discuss the synthesis of T₂ contrast agents, i.e. iron-based magnetic nanoparticles and the modification of these T₂ contrast agents by coating followed by their biomedical applications.     

Synthesizing cysteine-coated magnetite nanoparticles as MRI contrast agent: Effect of pH and cysteine addition on particles size distribution

Cysteine capped magnetite nanoparticles (10 to 20 nm) were synthesized via coprecipitation method under ultrasonic irradiation. The influence of pH value of the solution and cysteine addition on the size distribution and hydrodynamic size of nanoparticles were studied via TEM and PCS methods, respectively. The crystal structure and magnetic properties of the nanoparticles were characterized by XRD and VSM techniques, respectively. Coating density was calculated using TGA and TEM results. Cytotoxicity assessment performed by incubation of L929 cells, confirmed that ferrofluids are biocompatible. MRI studies conducted on rats demonstrated suitability of synthesized nanoparticles as contrast agents, especially for imaging of the lymph nodes.     

Anti‐Biofouling Polymer‐Decorated Lutetium‐Based Nanoparticulate Contrast Agents for In Vivo High‐Resolution Trimodal Imaging

Nanomaterials have gained considerable attention and interest in the development of novel and high‐resolution contrast agents for medical diagnosis and prognosis in clinic. A classical urea‐based homogeneous precipitation route that combines the merits of in situ thermal decomposition and surface modification is introduced to construct polyethylene glycol molecule (PEG)‐decorated hybrid lutetium oxide nanoparticles (PEG–UCNPs). By utilizing the admirable optical and magnetic properties of the yielded PEG–UCNPs, in vivo up‐conversion luminescence and T₁‐enhanced magnetic resonance imaging of small animals are conducted, revealing obvious signals after subcutaneous and intravenous injection, respectively. Due to the strong X‐ray absorption and high atomic number of lanthanide elements, X‐ray computed‐tomography imaging based on PEG–UCNPs is then designed and carried out, achieving excellent imaging outcome in animal experiments. This is the first example of the usage of hybrid lutetium oxide nanoparticles as effective nanoprobes. Furthermore, biodistribution, clearance route, as well as long‐term toxicity are investigated in detail after intravenous injection in a murine model, indicating the overall safety of PEG–UCNPs. Compared with previous lanthanide fluorides, our nanoprobes exhibit more advantages, such as facile construction process and nearly total excretion from the animal body within a month. Taken together, these results promise the use of PEG–UCNPs as a safe and efficient nanoparticulate contrast agent for potential application in multimodal imaging.     

Towards a versatile platform based on magnetic nanoparticles for in vivo applications

Magnetic nanoparticles have attracted wide attention because of their usefulness as contrast agents for magnetic resonance imaging (MRI) or colloidal mediators for cancer magnetic hyperthermia. This paper examines these in vivo applications through an understanding of the problems involved and the current and future possibilities for resolving them. A special emphasis is made on magnetic nanoparticle requirements from a physical viewpoint, the factors affecting their biodistribution and the solutions envisaged for enhancing their half-life in the blood compartment and targeting tumour cells. Then, our synthesis strategies are presented and focused on covalent platforms based on maghemite and dextran and capable to be tailorderivatized by surface molecular chemistry. The opportunity of taking advantage of temperature-dependence of magnetic properties of some complex oxides for controlling the in vivo temperature is also discussed.     

Labeling TiO2 Nanoparticles with Dyes for Optical Fluorescence Microscopy and Determination of TiO2–DNA Nanoconjugate Stability

Visualization of nanoparticles without intrinsic optical fluorescence properties is a significant problem when performing intracellular studies. Such is the case with titanium dioxide (TiO₂) nanoparticles. These nanoparticles, when electronically linked to single‐stranded DNA oligonucleotides, have been proposed to be used both as gene knockout devices and as possible tumor imaging agents. By interacting with complementary target sequences in living cells, these photoinducible TiO₂–DNA nanoconjugates have the potential to cleave intracellular genomic DNA in a sequence specific and inducible manner. The nanoconjugates also become detectable by magnetic resonance imaging with the addition of gadolinium Gd(III) contrast agents. Herein two approaches for labeling TiO₂ nanoparticles and TiO₂–DNA nanoconjugates with optically fluorescent agents are described. This permits direct quantification of fluorescently labeled TiO₂ nanoparticle uptake in a large population of living cells (>10⁴ cells). X‐ray fluorescence microscopy (XFM) is combined with fluorescent microscopy to determine the relative intracellular stability of the nanoconjugates and used to quantify intracellular nanoparticles. Imaging the DNA component of the TiO₂–DNA nanoconjugate by fluorescent confocal microscopy within the same cell shows an overlap with the titanium signal as mapped by XFM. This strongly implies the intracellular integrity of the TiO₂–DNA nanoconjugates in malignant cells.     

Preparation and characterization of nanobiocomposites containing iron nanoparticles prepared from blood and coated with chitosan and gelatin

In this study, we report the preparation of magnetic iron nanoparticles (INPs) from goat blood using incineration method. FT-IR and XRD studies have confirmed that the prepared nanoparticles were INPs. These INPs were coated with a mixture of chitosan and gelatin to prepare INP-CG nanobiocomposite and the TEM picture of these composite particles has shown an average particle size of 80-300 nm. MRI scan exhibited magnetic property and VSM studies revealed a magnetic saturation of 18.97 emu/g. This may be used as a MRI contrast agent to enhance cellular imaging and as magnetic nanocarrier for targeted delivery of drugs in the diagnosis and treatment of cancer.     

Polycatechol Nanoparticle MRI Contrast Agents

Amphiphilic triblock copolymers containing Fe^III‐catecholate complexes formulated as spherical‐ or cylindrical‐shaped micellar nanoparticles ( SMN and CMN , respectively) are described as new T ₁‐weighted agents with high relaxivity, low cytotoxicity, and long‐term stability in biological fluids. Relaxivities of both SMN and CMN exceed those of established gadolinium chelates across a wide range of magnetic field strengths. Interestingly, shape‐dependent behavior is observed in terms of the particles' interactions with HeLa cells, with CMN exhibiting enhanced uptake and contrast via magnetic resonance imaging (MRI) compared with SMN . These results suggest that control over soft nanoparticle shape will provide an avenue for optimization of particle‐based contrast agents as biodiagnostics. The polycatechol nanoparticles are proposed as suitable for preclinical investigations into their viability as gadolinium‐free, safe, and effective imaging agents for MRI contrast enhancement.     

Treatment of tumour tissue with radio‐frequency hyperthermia (using antibody‐carrying nanoparticles)

Intelligent inorganic nanoparticles were designed and produced for use in imaging and annihilating tumour cells by radio‐frequency (RF) hyperthermia. Nanoparticles synthesised to provide RF hyperthermia must have magnetite properties. For this purpose, magnetite nanoparticles were first synthesised by the coprecipitation method (10–15 NM). These superparamagnetic nanoparticles were then covered with gold ions without losing their magnetic properties. In this step, gold ions are reduced around the magnetite nanoparticles. Surface modification of the gold‐coated magnetic nanoparticles was performed in the next step. A self‐assembled monolayer was created using cysteamine (2‐aminoethanethiol) molecules, which have two different end groups (SH and NH₂). These molecules react with the gold surface by SH groups. The NH₂ groups give a positive charge to the nanoparticles. After that, a monoclonal antibody (Monoclonal Anti‐N‐CAM Clone NCAM‐OB11) was immobilised by the 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide/N‐hydroxysuccinimide method. Then, the antenna RF system (144.00015 MHz) was created for RF hyperthermia. The antibody‐nanoparticle binding rate and cytotoxicity tests were followed by in vitro and in vivo experiments. As the main result, antibody‐bound gold‐coated magnetic nanoparticles were successfully connected to tumour cells. After RF hyperthermia, the tumour size decreased owing to apoptosis and necrosis of tumour cells.     

AS1411 aptamer-conjugated Gd2O3:Eu nanoparticles for target-specific computed tomography/magnetic resonance/fluorescence molecular imaging

Europium-doped gadolinium oxide （Gd2O3：Eu） nanoparticles have been synthesized, and then their surfaces have been conjugated with nucleolin- targeted AS1411 aptamer to form functionalized target-specific Gd2OB：EU nanoparticles （A-GdO：Eu nanoparticles）. The A-GdO：Eu nanoparticles present strong fluorescence in the visible range, high magnetic susceptibility, X-ray attenuation and good biocompatibility. The A-GdO：Eu nanoparticles have been applied to test molecular expression of nucleolin highly expressed CL1-5 lung cancer cells under a confocal microscope. Fluorescence imaging clearly reveals that the nanoparticles can be applied as fluorescent tags for cancer-targeting molecular imaging. Furthermore, taking together their excellent T1 contrast and strong computed tomography （CT） signal, the A-GdO：Eu nanoparticles demonstrate a great capability for use as a dual modality contrast agent for CT and magnetic resonance （MR） molecular imaging. Animal experiments also show that the A-GdO：Eu nanoparticles are able to contrast the tissues of BALB/c mice using CT modality. Moreover, the obvious red fluorescence of A-GdO：Eu nanoparticles can be visualized in a tumor by the naked eye. Overall, our results demonstrate that the A-GdO：Eu nanoparticles can not only serve as new medical contrast agents but also as intraoperative fluorescence imaging probes for guided surgery in the near future.     

Electrosprayed synthesis of red-blood-cell-like particles with dual modality for magnetic resonance and fluorescence imaging

Red blood cells (RBCs) are able to avoid filtration in the spleen to prolong their half-time in the body because of their flexibility and unique shape, or a concave disk with diameter of some 10 μm. In addition, they can flow through capillary blood vessels, which are smaller than the diameter of RBCs, by morphing into a parachute-like shape. In this study, flexible RBC-like polymer particles are synthesized by electrospraying based on electrospinning. Furthermore, magnetite nanoparticles and fluorescent dye are encapsulated in the particles via in situ hydrolysis of an iron-organic compound in the presence of celluloses. The superparamagnetic behavior of the particles is confirmed by low-temperature magnetic measurements. The particles exhibited not only a dark contrast in magnetic resonance imaging (MRI), but also effective fluorescence. The RBC-like particles with flexibility are demonstrated to have a dual-modality for MRI and fluorescence imaging.