Large-Scale Synthesis of Uniform and Extremely Small-Sized Iron Oxide Nanoparticles for High-Resolution T1 Magnetic Resonance Imaging Contrast Agents

Highly monodisperse low-magnetization magnetite nanocubes as simultaneous T(1)-T(2) MRI contrast agents

We report the first study of highly monodisperse and crystalline iron oxide nanocubes with sub-nm controlled size distribution (9.7 ± 0.5 nm in size) that achieve simultaneous contrast enhancement in both T1- and T2-weighted magnetic resonance imaging (MRI). Here, we confirmed the magnetite structure of iron oxide nanocubes by X-ray diffraction (XRD), selected area electron diffraction (SAED) pattern, optical absorption and Fourier transformed infrared (FT-IR) spectra. These magnetite nanocubes exhibit superparamagnetic and paramagnetic behavior simultaneously by virtue of their finely controlled shape and size. The magnetic measurements reveal that the magnetic moment values are favorably much lower because of the small size and cubic shape of the nanoparticles, which results in an enhanced spin canting effect. As a proof-of-concept demonstration, we showed their potential as dual contrast agents for both T1- and T2-weighted MRI via phantom studies, in vivo imaging and relaxivity measurements. Therefore, these low-magnetization magnetite nanocubes, while being non-toxic and bio-compatible, hold great promise as excellent dual-mode T1 and T2 contrast agents for MRI.

Vascular toxicity of ultra-small TiO2 nanoparticles and single walled carbon nanotubes in vitro and in vivo

Ultra-small nanoparticles (USNPs) at 1-3 nm are a subset of nanoparticles (NPs) that exhibit intermediate physicochemical properties between molecular dispersions and larger NPs. Despite interest in their utilization in applications such as theranostics, limited data about their toxicity exist. Here the effect of TiO2-USNPs on endothelial cells in vitro, and zebrafish embryos in vivo, was studied and compared to larger TiO2-NPs (30 nm) and to single walled carbon nanotubes (SWCNTs). In vitro exposure showed that TiO2-USNPs were neither cytotoxic, nor had oxidative ability, nevertheless were genotoxic. In vivo experiment in early developing zebrafish embryos in water at high concentrations of TiO2-USNPs caused mortality possibly by acidifying the water and caused malformations in the form of pericardial edema when injected. Myo1C involved in glomerular development of zebrafish embryos was upregulated in embryos exposed to TiO2-USNPs. They also exhibited anti-angiogenic effects both in vitro and in vivo plus decreased nitric oxide concentration. The larger TiO2-NPs were genotoxic but not cytotoxic. SWCNTs were cytotoxic in vitro and had the highest oxidative ability. Neither of these NPs had significant effects in vivo. To our knowledge this is the first study evaluating the effects of TiO2-USNPs on vascular toxicity in vitro and in vivo and this strategy could unravel USNPs potential applications.

Chemical synthesis and assembly of uniformly sized iron oxide nanoparticles for medical applications

Magnetic iron oxide nanoparticles have been extensively investigated for their various biomedical applications including diagnostic imaging, biological sensing, drug, cell, and gene delivery, and cell tracking. Recent advances in the designed synthesis and assembly of uniformly sized iron oxide nanoparticles have brought innovation in the field of nanomedicine. This Account provides a review on the recent progresses in the controlled synthesis and assembly of uniformly sized iron oxide nanoparticles for medical applications. In particular, it focuses on three topics: stringent control of particle size during synthesis via the "heat-up" process, surface modification for the high stability and biocompatibility of the nanoparticles for diagnostic purposes, and assembly of the nanoparticles within polymers or mesoporous silica matrices for theranostic applications. Using extremely small 3 nm sized iron oxide nanoparticles (ESION), a new nontoxic T1 MRI contrast agent was realized for high-resolution MRI of blood vessels down to 0.2 mm. Ferrimagnetic iron oxide nanoparticles (FION) that are larger than 20 nm exhibit extremely large magnetization and coercivity values. The cells labeled with FIONs showed very high T2 contrast effect so that even a single cell can be readily imaged. Designed assembly of iron oxide nanoparticles with mesoporous silica and polymers was conducted to fabricate multifunctional nanoparticles for theranostic applications. Mesoporous silica nanoparticles are excellent scaffolds for iron oxide nanoparticles, providing magnetic resonance and fluorescence imaging modalities as well as the functionality of the drug delivery vehicle. Polymeric ligands could be designed to respond to various biological stimuli such as pH, temperature, and enzymatic activity. For example, we fabricated tumor pH-sensitive magnetic nanogrenades (termed PMNs) composed of self-assembled iron oxide nanoparticles and pH-responsive ligands. They were utilized to visualize small tumors (<3 mm) via pH-responsive T1 MRI and fluorescence imaging. Also, superior photodynamic therapeutic efficacy in highly drug-resistant heterogeneous tumors was observed. We expect that these multifunctional and bioresponsive nanoplatforms based on uniformly sized iron oxide nanoparticles will provide more unique theranostic approaches in clinical uses.

Europium-engineered iron oxide nanocubes with high T1 and T2 contrast abilities for MRI in living subjects

Magnetic resonance imaging (MRI) contrast agents with both positive (T1) and negative (T2) contrast abilities are needed in clinical diagnosis for fault-free accurate detection of lesions. We report a facile synthesis of europium-engineered iron oxide (EuIO) nanocubes as T1 and T2 contrast agents for MRI in living subjects. The Eu(iii) oxide-embedded iron oxide nanoparticles significantly increase the T1 relaxivity with an enhanced positive contrast effect. EuIO nanocubes with 14 nm in diameter showed a high r1 value of 36.8 mM(-1) s(-1) with respect to total metal ions (Fe + Eu), which is about 3 times higher than that of Fe3O4 nanoparticles with similar size. Moreover, both r1 and r2 values of EuIO nanocubes can be tuned by varying their sizes and Eu doping ratios. After citrate coating, EuIO nanocubes can provide enhanced T1 and T2 contrast effects in small animals, particularly in the cardiac and liver regions. This work may provide an insightful strategy to design MRI contrast agents with both positive and negative contrast abilities for biomedical applications.

Enhanced in vitro and in vivo cellular imaging with green tea coated water-soluble iron oxide nanocrystals

Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) through green tea (GT) polyphenols produced water-soluble Fe3O4 nanocrystals coated with GT extracts namely epigallocatechin gallate (EGCG) and epicatechin (EC). Electron donating polyphenols stoichiometrically reduced Fe(3+) ions into Fe(2+) ions resulting in the formation of magnetite (Fe3O4) nanoparticles and corresponding oxidized products (semiquinones and quinones) that simultaneously served as efficient surface chelators for the Fe3O4 nanoparticles making them dispersible and stable in water, PBS, and cell culture medium for extended time periods. As-formed iron oxide nanoparticles (2.5-6 nm) displayed high crystallinity and saturation magnetization as well as high relaxivity ratios manifested in strong contrast enhancement observed in T2-weighted images. Potential of green tea-coated superparamagnetic iron oxide nanocrystals (SPIONs) as superior negative contrast agents was confirmed by in vitro and in vivo experiments. Primary human macrophages (J774A.1) and colon cancer cells (CT26) were chosen to assess cytotoxicity and cellular uptake of GT-, EGCGq-, and ECq-coated Fe3O4 nanoparticles, which showed high uptake efficiencies by J774A.1 and CT26 cells without any additional transfection agent. Furthermore, the in vivo accumulation characteristics of GT-coated Fe3O4 nanoparticles were similar to those observed in clinical studies of SPIONs with comparable accumulation in epidermoid cancer-xenograft bearing mice. Given their promising transport and uptake characteristics and new surface chemistry, GT-SPIONs conjugates can be applied for multimodal imaging and therapeutic applications by anchoring further functionalities.

Surface and interfacial engineering of iron oxide nanoplates for highly efficient magnetic resonance angiography

Magnetic resonance angiography using gadolinium-based molecular contrast agents suffers from short diagnostic window, relatively low resolution and risk of toxicity. Taking into account the chemical exchange between metal centers and surrounding protons, magnetic nanoparticles with suitable surface and interfacial features may serve as alternative T1 contrast agents. Herein, we report the engineering on surface structure of iron oxide nanoplates to boost T1 contrast ability through synergistic effects between exposed metal-rich Fe3O4(100) facets and embedded Gd2O3 clusters. The nanoplates show prominent T1 contrast in a wide range of magnetic fields with an ultrahigh r1 value up to 61.5 mM(-1) s(-1). Moreover, engineering on nanobio interface through zwitterionic molecules adjusts the in vivo behaviors of nanoplates for highly efficient magnetic resonance angiography with steady-state acquisition window, superhigh resolution in vascular details, and low toxicity. This study provides a powerful tool for sophisticated design of MRI contrast agents for diverse use in bioimaging applications.

Manganese doped iron oxide theranostic nanoparticles for combined T1 magnetic resonance imaging and photothermal therapy

Photothermal therapy (PTT) is a noninvasive and convenient way to ablate tumor tissues. Integrating PTT with imaging technique could precisely identify the location and the size of tumor regions, thereby significantly improving the therapeutic efficacy. Magnetic resonance imaging (MRI) is widely used in clinical diagnosis due to its superb spatial resolution and real-time monitoring feature. In our work, we developed a theranostic nanoplatform based on manganese doped iron oxide (MnIO) nanoparticles modified with denatured bovine serum albumin (MnIO-dBSA). The in vitro experiment revealed that the MnIO nanoparticles exhibited T1-weighted MRI capability (r1 = 8.24 mM(-1) s(-1), r2/r1 = 2.18) and good photothermal effect under near-infrared laser irradiation (808 nm). Using 4T1 tumor-bearing mice as an animal model, we further demonstrated that the MnIO-dBSA composites could significantly increase T1 MRI signal intensity at the tumor site (about two times) and effectively ablate tumor tissues with photoirradiation. Taken together, this work demonstrates the great potential of the MnIO nanoparticles as an ideal theranostic platform for efficient tumor MR imaging and photothermal therapy.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

One-step synthesis of degradable T(1)-FeOOH functionalized hollow mesoporous silica nanocomposites from mesoporous silica spheres

The combination of a hollow mesoporous structure and a magnetic resonance (MR) contrast agent has shown its potential in simultaneous drug delivery and cell tracking applications. However, the preparation of this kind of nanocomposite is complicated and usually takes several days, which is unsuitable for scaled-up production. To overcome these hurdles, we report herein a facile method to synthesize iron oxide hydroxide functionalized hollow mesoporous silica spheres (FeOOH/HMSS) in a one-step manner. By carefully controlling the reaction kinetics of K2FeO4 in water, the gram-scale production of FeOOH/HMSS can be readily achieved at 60 °C for as short as 30 min. Most importantly, this synthetic process is also cost-effective and eco-friendly in both the precursor (K2FeO4 and H2O) and the product (FeOOH). The mechanism for the formation of a hollow structure was carefully investigated, which involves the synergetic effect of the surfactant CTAB and the side product KOH. Having outstanding biocompatibility, these degradable nanocolloids also demonstrate their feasibility in in vitro/vivo MR imaging and in vitro drug delivery.

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.

An "imaging-biopsy" strategy for colorectal tumor reconfirmation by multipurpose paramagnetic quantum dots

Glucose transporter1 (Glut1) plays important roles in treatment of colorectal cancer (CRC) involving early-stage diagnosis, subtype, TNM stage, and therapeutic schedule. Currently, in situ marking and tracking of the tumor biomarkers via clinical imaging remains great challenges in early stage CRC diagnosis. In this study, we have developed a unique cell-targeted, paramagnetic-fluorescent double-signal molecular nanoprobe for CRC in vivo magnetic resonance imaging (MRI) diagnosis and subsequent biopsy. The unique molecular nanoprobe is composed of a fluorescent quantum dot (QD) core; a coating layer of paramagnetic DTPA-Gd coupled BSA ((Gd)DTPA∙BSA), and a surface targeting moiety of anti-Glut1 polyclonal antibody. The engineered (Gd)DTPA∙BSA@QDs-PcAb is 35 nm in diameter and colloidally stable under both basic and acidic conditions. It exhibits strong fluorescent intensities and high relaxivity (r1 and r2: 16.561 and 27.702 s(-1) per mM of Gd(3+)). Distribution and expression of Glut1 of CRC cells are investigated by in vitro cellular confocal fluorescent imaging and MR scanning upon treating with the (Gd)DTPA∙BSA@QDs-PcAb nanoprobes. In vivo MRI shows real-time imaging of CRC tumor on nude mice after intravenously injection of the (Gd)DTPA∙BSA@QDs-PcAb nanoprobes. Ex vivo biopsy is subsequently conducted for expression of Glut1 on tumor tissues. These nanoprobes are found biocompatible in vitro and in vivo. (Gd)DTPA∙BSA@QDs-PcAb targeted nanoprobe is shown to be a promising agent for CRC cancer in vivo MRI diagnosis and ex vivo biopsy analysis. The "imaging-biopsy" is a viable strategy for tumor reconfirmation with improved diagnostic accuracy and biopsy in personalized treatment.

Mesoscale assemblies of iron oxide nanocubes as heat mediators and image contrast agents

Iron oxide nanocubes (IONCs) represent one of the most promising iron-based nanoparticles for both magnetic resonance image (MRI) and magnetically mediated hyperthermia (MMH). Here, we have set a protocol to control the aggregation of magnetically interacting IONCs within a polymeric matrix in a so-called magnetic nanobead (MNB) having mesoscale size (200 nm). By the comparison with individual coated nanocubes, we elucidate the effect of the aggregation on the specific adsorption rates (SAR) and on the T1 and T2 relaxation times. We found that while SAR values decrease as IONCs are aggregated into MNBs but still keeping significant SAR values (200 W/g at 300 kHz), relaxation times show very interesting properties with outstanding values of r2/r1 ratio for the MNBs with respect to single IONCs.

Enhanced encapsulation of superparamagnetic Fe3O4 in acidic core-containing micelles for magnetic resonance imaging

Block copolymer-based magnetic nanoassembled structures with acidic cores exhibiting enhanced loading level of superparamagnetic iron oxide nanoparticles, thus having great potential for theranostics based on MRI.

In vivo pharmacokinetics of T2 contrast agents based on iron oxide nanoparticles: optimization of blood circulation times

PEGylated SPIONs using PEG MWs from 1500 to 8000 were intravenously injected in mice. Parametric MRI allowed us to track the pharmacokinetics and determine the effect of MW on the biodistribution and circulation times of PEG-SPIONs (HD < 50 nm).

Recent advances in magnetic nanoparticle-based multi-modal imaging

This tutorial review discusses the concept and up-to-date applications of magnetic nanoparticle-based multi-modal imaging.

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

A water-soluble hybrid two-dimensional nanostructured dual T₁–T₂ MRI contrast agent with fair T₁ and T₂ nanoparticle separation distance and negligible T₁/T₂ signal quenching was developed.

Controllable synthesis of polydopamine nanoparticles in microemulsions with pH-activatable properties for cancer detection and treatment

A simple reverse microemulsion-based method was used to elaborate pH-activatable PEG–Fe–PDA nanoparticles for cancer diagnosis and therapy.

In vitro toxicity evaluation of ultra-small MFe2O4 (M = Fe, Mn, Co) nanoparticles using A549 cells

As ferrite nanoparticles (MFe₂O₄) have been widely used in biomedical field, their safety evaluation has been paid great attention both in vitro and in vivo.

A multiple gadolinium complex decorated fullerene as a highly sensitive T1 contrast agent

A multiple gadolinium complex decorated fullerene (CGD_n) as an enhanced T₁ contrast agent was presented.

A comprehensive review on synthesis methods for transition-metal oxide nanostructures

Recent developments of transition-metal oxide nanostructures with designed shape and dimensionality, including various synthesis methods and applications, are presented.

Gd(iii) complex conjugated ultra-small iron oxide as an enhanced T1-weighted MR imaging contrast agent

In this work, Gd(III) complex conjugated ultra-small iron oxide nanoparticles were simply synthesized and were observed with a novel T₁-weight MR imaging enhancement.

An aqueous method for the controlled manganese (Mn2+) substitution in superparamagnetic iron oxide nanoparticles for contrast enhancement in MRI

Despite the success in the use of superparamagnetic iron oxide nanoparticles (SPION) for various scientific applications, its potential in biomedical fields has not been exploited to its full potential.

Magneto-fluorescent nanoparticles with high-intensity NIR emission, T1- and T2-weighted MR for multimodal specific tumor imaging

Fe₃O₄@NIR semiconducting polymer nanoparticles were used for both T₁-, T₂-weighted MRI and fluorescence imaging of targeted tumors.

Facile synthesis of guanidyl-functionalized magnetic polymer microspheres for tunable and specific capture of global phosphopeptides or only multiphosphopeptides

The highly selective and efficient capture of heterogeneous types of phosphopeptides is critical for comprehensive and in-depth phosphoproteome analysis, but it still remains a challenge since the lack of affinity material with large binding capacity and controllable specificity. Here, a new affinity material was prepared to improve the enrichment capacity and endue the tunable specificity by introducing guanidyl onto poly(glycidyl methacrylate) (PGMA) modified Fe3O4 microsphere (denoted as Fe3O4@PGMA-Guanidyl). The thick polymer shell endows the composite microsphere with large amount of guanidyl and is beneficial to enhancing the affinity interaction between phosphopeptides and the material. Interestingly, the Fe3O4@PGMA-Guanidyl possesses tunable enriching ability for global phosphopeptides or only multiphosphopeptides through simple regulation of buffer composition. The composite has large enrichment capacity (200 mg g(-1)), extremely high detection sensitivity (0.5 fmol), high enrichment recovery (91.30%), great specificity, and rapid magnetic separation. Moreover, the result of the application to capture of phosphopeptides from tryptic digest of nonfat milk has demonstrated the great potential of Fe3O4@PGMA-Guanidyl in detection and identification of low-abundance phosphopeptides of interest in biological sample.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.

Inorganic Janus particles for biomedical applications

Based on recent developments regarding the synthesis and design of Janus nanoparticles, they have attracted increased scientific interest due to their outstanding properties. There are several combinations of multicomponent hetero-nanostructures including either purely organic or inorganic, as well as composite organic-inorganic compounds. Janus particles are interconnected by solid state interfaces and, therefore, are distinguished by two physically or chemically distinct surfaces. They may be, for instance, hydrophilic on one side and hydrophobic on the other, thus, creating giant amphiphiles revealing the endeavor of self-assembly. Novel optical, electronic, magnetic, and superficial properties emerge in inorganic Janus particles from their dimensions and unique morphology at the nanoscale. As a result, inorganic Janus nanoparticles are highly versatile nanomaterials with great potential in different scientific and technological fields. In this paper, we highlight some advances in the synthesis of inorganic Janus nanoparticles, focusing on the heterogeneous nucleation technique and characteristics of the resulting high quality nanoparticles. The properties emphasized in this review range from the monodispersity and size-tunability and, therefore, precise control over size-dependent features, to the biomedical application as theranostic agents. Hence, we show their optical properties based on plasmonic resonance, the two-photon activity, the magnetic properties, as well as their biocompatibility and interaction with human blood serum.

Gadolinium oxide nanoplates with high longitudinal relaxivity for magnetic resonance imaging

Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA-OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)(-1) were measured at 1.41 T for the oleic acid bilayer and PAA-OA coating, respectively. These values moderately reduce as the size of the Gd2O3 nanoplates increases, and are always larger for the PAA-OA coating. Cytotoxicity studies on human dermal fibroblast cells documented no significant toxicity, with 100% cell viability preserved up to 250 μM for the PAA-OA coated Gd2O3 nanoplates. Given the 10 times increase in longitudinal relaxivity over the commercially available Gd-based molecular agents and the favorable toxicity profile, the 2 nm PAA-OA coated Gd2O3 nanoplates could represent a new class of highly effective T1 MRI contrast agents.

Color Tunable Gd-Zn-Cu-In-S/ZnS Quantum Dots for Dual Modality Magnetic Resonance and Fluorescence Imaging

Inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of color tunable Gd-Zn-Cu-In-S/ZnS (GZCIS/ZnS) quantum dots (QDs) with stable crystal structure was successfully synthesized and utilized for magnetic resonance (MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T₁ MR contrast as well as "color-tunable" photoluminescence (PL) in the range of 550-725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield (QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin (BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both HeLa and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imaging.

Hybrid nanotrimers for dual T1 and T2-weighted magnetic resonance imaging

Development of multifunctional nanoparticle-based probes for dual T1- and T2-weighted magnetic resonance imaging (MRI) could allow us to image and diagnose the tumors or other abnormalities in an exceptionally accurate and reliable manner. In this study, by fusing distinct nanocrystals via solid-state interfaces, we built hybrid heteronanostructures to combine both T1 and T2- weighted contrast agents together for MRI with high accuracy and reliability. The resultant hybrid heterotrimers showed high stability in physiological conditions and could induce both simultaneous positive and negative contrast enhancements in MR images. Small animal positron emission tomography imaging study revealed that the hybrid heterostructures displayed favorable biodistribution and were suitable for in vivo imaging. Their potential as dual contrast agents for T1 and T2-weighted MRI was further demonstrated by in vitro and in vivo imaging and relaxivity measurements.

Biocompatible PEGylated Fe₃O₄ nanoparticles as photothermal agents for near-infrared light modulated cancer therapy

In accordance with the World Cancer Report, cancer has become the leading cause of mortality worldwide, and various therapeutic strategies have been developed at the same time. In the present study, biocompatible magnetic nanoparticles were designed and synthesized as high-performance photothermal agents for near-infrared light mediated cancer therapy in vitro. Via a facile one-pot solvothermal method, well-defined PEGylated magnetic nanoparticles (PEG-Fe3O4) were prepared with cheap inhesion as a first step. Due to the successful coating of PEG molecules on the surface of PEG-Fe3O4, these nanoparticles exhibited excellent dispersibility and dissolvability in physiological condition. Cytotoxicity based on MTT assays indicated these nanoparticles revealed high biocompatibility and low toxicity towards both Hela cells and C6 cells. After near-infrared (NIR) laser irradiation, the viabilities of C6 cells were effectively suppressed when incubated with the NIR laser activated PEG-Fe3O4. In addition, detailed photothermal anti-cancer efficacy was evaluated via visual microscope images, demonstrating that our PEG-Fe3O4 were promising for photothermal therapy of cancer cells.

One-step, room-temperature synthesis of glutathione-capped iron-oxide nanoparticles and their application in in vivo T1-weighted magnetic resonance imaging

The room-temperature, aqueous-phase synthesis of iron-oxide nanoparticles (IO NPs) with glutathione (GSH) is reported. The simple, one-step reduction involves GSH as a capping agent and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the reducing agent; GSH is an anti-oxidant that is abundant in the human body while THPC is commonly used in the synthesis of noble-metal clusters. Due to their low magnetization and good water-dispersibility, the resulting GSH-IO NPs, which are 3.72 ± 0.12 nm in diameter, exhibit a low r2 relaxivity (8.28 mm(-1) s(-1)) and r2/r1 ratio (2.28)--both of which are critical for T1 contrast agents. This, together with the excellent biocompatibility, makes these NPs an ideal candidate to be a T1 contrast agent. Its capability in cellular imaging is illustrated by the high signal intensity in the T1-weighted magnetic resonance imaging (MRI) of treated HeLa cells. Surprisingly, the GSH-IO NPs escape ingestion by the hepatic reticuloendothelial system, enabling strong vascular enhancement at the internal carotid artery and superior sagittal sinus, where detection of the thrombus is critical for diagnosing a stroke. Moreover, serial T1- and T2-weighted time-dependent MR images are resolved for a rat's kidneys, unveiling detailed cortical-medullary anatomy and renal physiological functions. The newly developed GSH-IO NPs thus open a new dimension in efforts towards high-performance, long-circulating MRI contrast agents that have biotargeting potential.

Magnetically engineered semiconductor quantum dots as multimodal imaging probes

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.

Tuning the growth pattern in 2D confinement regime of Sm2O3 and the emerging room temperature unusual superparamagnetism

Programming the reaction chemistry for superseding the formation of Sm₂O₃ in a competitive process of formation and dissolution, the crystal growth patterns are varied and two different nanostructures of Sm₂O₃ in 2D confinement regime are designed. Among these, the regular and self-assembled square platelets nanostructures exhibit paramagnetic behavior analogous to the bulk Sm₂O₃. But, the other one, 2D flower like shaped nanostructure, formed by irregular crystal growth, shows superparamagnetism at room temperature which is unusual for bulk paramagnet. It has been noted that the variation in the crystal growth pattern is due to the difference in the binding ability of two organic ligands, oleylamine and oleic acid, used for the synthesis and the magnetic behavior of the nanostructures is related to the defects incorporated during the crystal growth. Herein, we inspect the formation chemistry and plausible origin of contrasting magnetism of these nanostructures of Sm₂O₃.

Multifunctional PEGylated multiwalled carbon nanotubes for enhanced blood pool and tumor MR imaging

Long-circulating multifunctional Gd(III)-loaded multiwalled carbon nanotubes (MWCNTs) modified with polyethylene glycol are designed and synthesized. The formed MWCNTs are water-dispersible, stable, and have good cytocompatibility and antifouling property. With the low r 2 /r 1 relaxivity ratio and relatively long blood circulation time, the multifunctional MWCNTs are able to be used as a platform for enhanced blood pool and tumor MR imaging.

Tunable T1 and T2 contrast abilities of manganese-engineered iron oxide nanoparticles through size control

In this paper, we demonstrate the tunable T1 and T2 contrast abilities of engineered iron oxide nanoparticles with high performance for liver contrast-enhanced magnetic resonance imaging (MRI) in mice. To enhance the diagnostic accuracy of MRI, large numbers of contrast agents with T1 or T2 contrast ability have been widely explored. The comprehensive investigation of high-performance MRI contrast agents with controllable T1 and T2 contrast abilities is of high importance in the field of molecular imaging. In this study, we synthesized uniform manganese-doped iron oxide (MnIO) nanoparticles with controllable size from 5 to 12 nm and comprehensively investigated their MRI contrast abilities. We revealed that the MRI contrast effects of MnIO nanoparticles are highly size-dependent. By controlling the size of MnIO nanoparticles, we can achieve T1-dominated, T2-dominated, and T1-T2 dual-mode MRI contrast agents with much higher contrast enhancement than the corresponding conventional iron oxide nanoparticles.

Screen-based analysis of magnetic nanoparticle libraries formed using peptidic iron oxide ligands

The identification of effective polypeptide ligands for magnetic iron oxide nanoparticles (IONPs) could considerably accelerate the high-throughput analysis of IONP-based reagents for imaging and cell labeling. We developed a procedure for screening IONP ligands and applied it to compare candidate peptides that incorporated carboxylic acid side chains, catechols, and sequences derived from phage display selection. We found that only l-3,4-dihydroxyphenylalanine (DOPA)-containing peptides were sufficient to maintain particles in solution. We used a DOPA-containing sequence motif as the starting point for generation of a further library of over 30 peptides, each of which was complexed with IONPs and evaluated for colloidal stability and magnetic resonance imaging (MRI) contrast properties. Optimal properties were conferred by sequences within a narrow range of biophysical parameters, suggesting that these sequences could serve as generalizable anchors for formation of polypeptide–IONP complexes. Differences in the amino acid sequence affected T₁- and T₂-weighted MRI contrast without substantially altering particle size, indicating that the microstructure of peptide-based IONP coatings exerts a substantial influence and could be manipulated to tune properties of targeted or responsive contrast agents. A representative peptide–IONP complex displayed stability in biological buffer and induced persistent MRI contrast in mice, indicating suitability of these species for in vivo molecular imaging applications.

Interplay between longitudinal and transverse contrasts in Fe3O4 nanoplates with (111) exposed surfaces

Iron oxide has been developed as either T1 or T2 magnetic resonance imaging (MRI) contrast agents by controlling the size and composition; however, the underlying mechanism of T1 and T2 contrasts in one iron oxide entity is still not well understood. Herein, we report that freestanding superparamagnetic magnetite nanoplates with (111) exposed facets have significant but interactional T1 and T2 contrast effects. We demonstrate that the main contribution of the T1 contrast of magnetic nanoplates is the chemical exchange on the iron-rich Fe3O4(111) surfaces, whereas the T2 relaxation is dominated by the intrinsic superparamagnetism of the nanoplates with an enhanced perturbation effect. We are able to regulate the balance of T1 and T2 contrasts by controlling structure and surface features, including morphology, exposed facets, and surface coating. This study provides an insightful understanding on the T1 and T2 contrast mechanisms, which is urgently needed to allow more sophisticated design of high-performance MRI contrast agents.

Radiofrequency heating pathways for gold nanoparticles

This feature article reviews the thermal dissipation of nanoscopic gold under radiofrequency (RF) irradiation. It also presents previously unpublished data addressing obscure aspects of this phenomenon. While applications in biology motivated initial investigation of RF heating of gold nanoparticles, recent controversy concerning whether thermal effects can be attributed to nanoscopic gold highlight the need to understand the involved mechanism or mechanisms of heating. Both the nature of the particle and the nature of the RF field influence heating. Aspects of nanoparticle chemistry which may affect thermal dissipation include the hydrodynamic diameter of the particle, the oxidation state and related magnetism of the core, and the chemical nature of the ligand shell. Aspects of RF which may affect thermal dissipation include power, frequency and antenna designs that emphasize relative strength of magnetic or electric fields. These nanoparticle and RF properties are analysed in the context of three heating mechanisms proposed to explain gold nanoparticle heating in an RF field. This article also makes a critical analysis of the existing literature in the context of the nanoparticle preparations, RF structure, and suggested mechanisms in previously reported experiments.

Fluorescent nanonetworks: a novel bioalley for collagen scaffolds and tissue engineering

Native collagen is arranged in bundles of aligned fibrils to withstand in vivo mechanical loads. Reproducing such a process under in vitro conditions has not met with major success. Our approach has been to induce nanolinks, during the self-assembly process, leading to delayed rather than inhibited fibrillogenesis. For this, a designed synthesis of nanoparticles - using starch as a template and a reflux process, which would provide a highly anisotropic (star shaped) nanoparticle, with large surface area was adopted. Anisotropy associated decrease in Morin temperature and superparamagnetic behavior was observed. Polysaccharide on the nanoparticle surface provided aqueous stability and low cytotoxicity. Starch coated nanoparticles was utilized to build polysaccharide - collagen crosslinks, which supplemented natural crosslinks in collagen, without disturbing the conformation of collagen. The resulting fibrillar lamellae showed a striking resemblance to native lamellae, but had a melting and denaturation temperature higher than native collagen. The biocompatibility and superparamagnetism of the nanoparticles also come handy in the development of stable collagen constructs for various biomedical applications, including that of MRI contrast agents.

PEGylated polyethylenimine as enhanced T₁ contrast agent for efficient magnetic resonance imaging

Currently used small molecular magnetic resonance (MR) imaging contrast agents (CAs) in clinics have relatively short half-lives, which has limited the acquisition of high-resolution organ and angiographic images. Therefore, development of a facile strategy for the synthesis of long-circulating CAs with the transforming potential for MR imaging still remains a great challenge. Here we communicate the design and synthesis of PEGylated polyethylenimine (PEI) and its application as enhanced T1 CA for the long-circulating blood pool as well as efficient organ and tumor imaging. In this study, PEI was covalently grafted with gadolinium (Gd(III)) chelator and mPEG-NHS, followed by acetylation of the remaining amines to improve biocompatibility and prolong circulation time. With the relatively long circulation time (3.8 h), the formed multifunctional PEI (PEI.NHAc-DTPA(Gd(III))-mPEG) can be used as an enhanced T1 CA for blood pool and major organ imaging, and could be cleared from the body 96 h post administration through the urinary system. Importantly, the PEI.NHAc-DTPA(Gd(III))-mPEG complexes displayed a strong T1 contrast effect for tumor imaging through the enhanced permeation and retention effect. These findings suggest that the synthesized PEI.NHAc-DTPA(Gd(III))-mPEG may be used as a promising CA for T1 MR imaging of various biological systems.

Magnetic sensing technology for molecular analyses

Magnetic biosensors, based on nanomaterials and miniature electronics, have emerged as a powerful diagnostic platform. Benefiting from the inherently negligible magnetic background of biological objects, magnetic detection is highly selective even in complex biological media. The sensing thus requires minimal sample purification and yet achieves a high signal-to-background contrast. Moreover, magnetic sensors are also well-suited for miniaturization to match the size of biological targets, which enables sensitive detection of rare cells and small amounts of molecular markers. We herein summarize recent advances in magnetic sensing technologies, with an emphasis on clinical applications in point-of-care settings. Key components of sensors, including magnetic nanomaterials, labeling strategies and magnetometry, are reviewed.