Magnetic-Fluorescent Colloidal Nanobeads: Preparation and Exploitation in Cell Separation Experiments

Scaling Up Magnetic Nanobead Synthesis with Improved Stability for Biomedical Applications

The growing interest in multifunctional nano-objects based on polymers and magnetic nanoparticles for biomedical applications motivated us to develop a scale-up protocol to increase the yield of polymeric magnetic nanobeads while aiming at keeping the structural features at optimal conditions. The protocol was applied to two different types of magnetic ferrite nanoparticles: the Mn-ferrite selected for their properties as contrast agents in magnetic resonance imaging and iron oxide nanostar shaped nanoparticles chosen for their heat performance in magnetic hyperthermia. At the same time, some experiments on surface functionalization of nanobeads with amino modified polyethyelene glycol (PEG) molecules have provided further insight into the formation mechanism of magnetic nanobeads and the need to cross-link the polymer shell to improve the stability of the beads, making them more suitable for further manipulation and use. The present work summarizes the most important parameters required to be controlled for the upscaling of nanobead synthesis in a bench protocol and proposes an alternative cross-linking strategy based on prefunctionalization of the polymer prior to the nanobead formation as a key parameter to improve the nanobead structural stability in solutions at different pHs and during surface functionalization.

Decorated magnetic nanoparticles with polyvinyl alcohol brushes modified with metal chelate affinity groups for purification of proteins

Refining is a serious challenge in the production of recombinant proteins, and this study proposes a new and easy strategy for the synthesis of magnetic affinity nanoparticles. First, the nanoparticles attached to polyvinyl alcohol brushes were synthesized, and then the hydroxyl groups of this polymer were converted to chelate groups. The nanoparticles were examined by (SEM) scanning electron microscopy, (TEM) transmission electron microscopy, (DLS) dynamic light scattering, (FT-IR) Fourier transform infrared, (XRD) X-ray powder diffraction, (VSM) vibrating sample magnetometry, and (TGA) thermal gravimetric analysis. The results confirm that uniform and spherical magnetic polymer nanoparticles with high magnetization and superparamagnetic properties were successfully synthesized. The S100A9 protein, a His-tagged recombinant protein, was expressed and purified using the synthesized nanoparticles. According to the (SDS-PAGE) sulfate-polyacrylamide gel electrophoresis results, there is a high degree of resolution in protein separation. The synthesized nanoparticles have a high protein binding capacity of about 208 mg of protein per gram of nanoparticles.

Colorful Luminescent Magnetic Supraparticles: Expanding the Applicability, Information Capacity, and Security of Micrometer-Scaled Identification Taggants by Dual-Spectral Encoding

(Sub)micrometer-scaled identification (ID) taggants enable direct identification of arbitrary goods, thereby opening up application fields based on the possibility of tracking, tracing, and anti-counterfeiting. Due to their small dimensions, these taggants can equip in principle even the smallest subcomponents or raw materials with information. To achieve the demanded applicability, the mostly used optically encoded ID taggants must be further improved. Here, micrometer-scaled supraparticles with spectrally encoded luminescent and magnetically encoded signal characteristics are reported. They are produced in a readily customizable bottom-up fabrication procedure that enables precise adjustment of luminescent and magnetic properties on multiple hierarchy levels. The incorporation of commonly used magnetic nanoparticles and fluorescent dyes, respectively, into polymer nanocomposite particles, establishes a convenient toolbox of magnetic and luminescent building blocks. The subsequent assembly of selected building blocks in the desired ratios into supraparticles grants for all the flexibility to freely adjust both signal characteristics. The obtained spectrally resolved visible luminescent and invisible magnetic ID signatures are complementary in nature, thus expanding applicability and information security compared to recently reported optical- or magnetic-encoded taggants. Additionally, the introduced ID taggant supraparticles can significantly enhance the coding capacity. Therefore, the introduced supraparticles are considered as next-generation ID taggants.

Magneto-plasmonic nanostars for image-guided and NIR-triggered drug delivery

Smart multifunctional nanoparticles with magnetic and plasmonic properties assembled on a single nanoplatform are promising for various biomedical applications. Owing to their expanding imaging and therapeutic capabilities in response to external stimuli, they have been explored for on-demand drug delivery, image-guided drug delivery, and simultaneous diagnostic and therapeutic (i.e. theranostic) applications. In this study, we engineered nanoparticles with unique morphology consisting of a superparamagnetic iron oxide core and star-shaped plasmonic shell with high-aspect-ratio gold branches. Strong magnetic and near-infrared (NIR)-responsive plasmonic properties of the engineered nanostars enabled multimodal quantitative imaging combining advantageous functions of magnetic resonance imaging (MRI), magnetic particle imaging (MPI), photoacoustic imaging (PAI), and image-guided drug delivery with a tunable drug release capacity. The model drug molecules bound to the core-shell nanostars were released upon NIR illumination due to the heat generation from the core-shell nanostars. Moreover, our simulation analysis showed that the specific design of the core-shell nanostars demonstrated a pronounced multipolar plasmon resonance, which has not been observed in previous reports. The multimodal imaging and NIR-triggered drug release capabilities of the proposed nanoplatform verify their potential for precise and controllable drug release with different applications in personalized medicine.

Esterase-Cleavable 2D Assemblies of Magnetic Iron Oxide Nanocubes: Exploiting Enzymatic Polymer Disassembling To Improve Magnetic Hyperthermia Heat Losses

Here, we report a nanoplatform based on iron oxide nanocubes (IONCs) coated with a bioresorbable polymer that, upon exposure to lytic enzymes, can be disassembled increasing the heat performances in comparison with the initial clusters. We have developed two-dimensional (2D) clusters by exploiting benchmark IONCs as heat mediators for magnetic hyperthermia and a polyhydroxyalkanoate (PHA) copolymer, a biodegradable polymer produced by bacteria that can be digested by intracellular esterase enzymes. The comparison of magnetic heat performance of the 2D assemblies with 3D centrosymmetrical assemblies or single IONCs emphasizes the benefit of the 2D assembly. Moreover, the heat losses of 2D assemblies dispersed in water are better than the 3D assemblies but worse than for single nanocubes. On the other hand, when the 2D magnetic beads (2D-MNBs) are incubated with the esterase enzyme at a physiological temperature, their magnetic heat performances began to progressively increase. After 2 h of incubation, specific absorption rate values of the 2D assembly double the ones of individually coated nanocubes. Such an increase can be mainly correlated to the splitting of the 2D-MNBs into smaller size clusters with a chain-like configuration containing few nanocubes. Moreover, 2D-MNBs exhibited nonvariable heat performances even after intentionally inducing their aggregation. Magnetophoresis measurements indicate a comparable response of 3D and 2D clusters to external magnets (0.3 T) that is by far faster than that of single nanocubes. This feature is crucial for a physical accumulation of magnetic materials in the presence of magnetic field gradients. This system is the first example of a nanoplatform that, upon exposure to lytic enzymes, such as those present in a tumor environment, can be disassembled from the initial 2D-MNB organization to chain-like assemblies with clear improvement of the heat magnetic losses resulting in better heat dissipation performances. The potential application of 2D nanoassemblies based on the cleavable PHAs for preserving their magnetic losses inside cells will benefit hyperthermia therapies mediated by magnetic nanoparticles under alternating magnetic fields.

Design and Application of Cisplatin-Loaded Magnetic Nanoparticle Clusters for Smart Chemotherapy

One of the major challenges of drug delivery is the development of suitable carriers for therapeutic molecules. In this work, a novel nanoformulation based on superparamagnetic nanoclusters [magnetic nanocrystal clusters (MNCs)] is presented. In order to control the size of the nanoclusters and the density of magnetic cores, several parameters were evaluated and tuned. Then, MNCs were functionalized with a polydopamine layer (MNC@PDO) to improve their stability in aqueous solution, to increase density of functional groups and to obtain a nanosystem suitable for drug-controlled release. Finally, cisplatin was grafted on the surface of MNC@PDO to exploit the system as a magnetic field-guided anticancer delivery system. The biocompatibility of MNC@PDO and the cytotoxic effects of MNC@PDO-cisplatin complex were determined against human cervical cancer (HeLa) and human breast adenocarcinoma (MCF-7) cells. In vitro studies demonstrated that the MNC@PDO-cisplatin complexes inhibited the cellular proliferation by a dose-dependent effect. Therefore, by applying an external magnetic field, the released drug exerted its effect on a specific target area. In summary, the MNC@PDO nanosystem has a great potential to be used in targeted nanomedicine for the delivery of other drugs or biofunctional molecules.

Design strategies for shape-controlled magnetic iron oxide nanoparticles

Ferrimagnetic iron oxide nanoparticles (magnetite or maghemite) have been the subject of an intense research, not only for fundamental research but also for their potentiality in a widespread number of practical applications. Most of these studies were focused on nanoparticles with spherical morphology but recently there is an emerging interest on anisometric nanoparticles. This review is focused on the synthesis routes for the production of uniform anisometric magnetite/maghemite nanoparticles with different morphologies like cubes, rods, disks, flowers and many others, such as hollow spheres, worms, stars or tetrapods. We critically analyzed those procedures, detected the key parameters governing the production of these nanoparticles with particular emphasis in the role of the ligands in the final nanoparticle morphology. The main structural and magnetic features as well as the nanotoxicity as a function of the nanoparticle morphology are also described. Finally, the impact of each morphology on the different biomedical applications (hyperthermia, magnetic resonance imaging and drug delivery) are analysed in detail. We would like to dedicate this work to Professor Carlos J. Serna, Instituto de Ciencia de Materiales de Madrid, ICMM/CSIC, for his outstanding contribution in the field of monodispersed colloids and iron oxide nanoparticles. We would like to express our gratitude for all these years of support and inspiration on the occasion of his retirement.

Multilayered Magnetic Nanobeads for the Delivery of Peptides Molecules Triggered by Intracellular Proteases

In this work, the versatility of layer-by-layer technology was combined with the magnetic response of iron oxide nanobeads to prepare magnetic mesostructures with a degradable multilayer shell into which a dye quenched ovalbumin conjugate (DQ-OVA) was loaded. The system was specifically designed to prove the protease sensitivity of the hybrid mesoscale system and the easy detection of the ovalbumin released. The uptake of the nanostructures in the breast cancer cells was followed by the effective release of DQ-OVA upon activation via the intracellular proteases degradation of the polymer shells. Monitoring the fluorescence rising due to DQ-OVA digestion and the cellular dye distribution, together with the electron microscopy studying, enabled us to track the shell degradation and the endosomal uptake pathway that resulted in the release of the digested fragments of DQ ovalbumin in the cytosol.

Promoted Iron Nanocrystals Obtained via Ligand Exchange as Active and Selective Catalysts for Synthesis Gas Conversion

Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na₂S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process. The catalyst composition was optimized for the Fischer–Tropsch direct conversion of synthesis gas into lower olefins. At industrially relevant conditions, these nanocrystal-based catalysts with controlled composition were more active, selective, and stable than catalysts with similar composition but synthesized using conventional methods, possibly due to their homogeneity of properties and synergic interaction of iron and promoters.

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

The current state of the art in the use of colloidal methods to form nanoparticle assemblies, or clusters (NPCs) is reviewed. The focus is on the two-step approach, which exploits the advantages of bottom-up wet chemical NP synthesis procedures, with subsequent colloidal destabilization to trigger assembly in a controlled manner. Recent successes in the application of functional NPCs with enhanced emergent collective properties for a wide range of applications, including in biomedical detection, surface enhanced Raman scattering (SERS) enhancement, photocatalysis, and light harvesting, are highlighted. The role of the NP-NP interactions in the formation of monodisperse ordered clusters is described and the different assembly processes from a wide range of literature sources are classified according to the nature of the perturbation from the initial equilibrium state (dispersed NPs). Finally, the future for the field and the anticipated role of computational approaches in developing next-generation functional NPCs are briefly discussed.

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.

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.

Self-assembly of a superparamagnetic raspberry-like silica/iron oxide nanocomposite using epoxy–amine coupling chemistry

We used epoxy–amine coupling chemistry for the straightforward fabrication of a stable superparamagnetic colloidal composite from a simple mixture of its constituent nanoparticles, in the absence of any other reactant.

Colloidal assemblies of oriented maghemite nanocrystals and their NMR relaxometric properties

¹H-NMR relaxometric experiments over an extended frequency range show that ferrimagnetic colloidal nanoclusters exhibit enhanced transverse relaxivity, r₂.

Polymeric nanocarriers for magnetic targeted drug delivery: preparation, characterization, and in vitro and in vivo evaluation

In this paper the preparation of magnetic nanocarriers (MNCs), containing superparamagnetic domains, is reported, useful as potential magnetically targeted drug delivery systems. The preparation of MNCs was performed by using the PHEA-IB-p(BMA) graft copolymer as coating material through the homogenization-solvent evaporation method. Magnetic and nonmagnetic nanocarriers containing flutamide (FLU-MNCs) were prepared. The prepared nanocarriers have been exhaustively characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and magnetic measurements. Biological evaluation was performed by in vitro cytotoxicity and cell uptake tests and in vivo biodistribution studies. Magnetic nanocarriers showed dimensions of about 300 nm with a narrow size distribution, an amount of loaded FLU of 20% (w/w), and a superparamagnetic behavior. Cell culture experiments performed on prostate cancer cell line LNCaP demonstrated the cytotoxic effect of FLU-MNCs. In vivo biodistribution studies carried out by the application of an external magnetic field in rats demonstrated the effect of the external magnet on modifying the biodistribution of FLU-MNCs. FLU-MNCs resulted efficiently internalized by tumor cells and susceptible to magnetic targeting by application of an external magnetic field. The proposed nanocarriers can represent a very promising approach to obtain an efficient magnetically targeted anticancer drug delivery system.

Bio-inspired encapsulation and functionalization of living cells with artificial shells

In nature, most single cells do not have structured shells to provide extensive protection apart from diatoms and radiolarians. Fabrication of biomimetic structures based on living cells encapsulated with artificial shells has a great impact on the area of cell-based sensors and devices as well as fundamental studies in cell biology. The past decade has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of encapsulated cells. In this review, the latest fabrication strategies on how to encapsulate living cells with functional shells based on the diversity of artificial shells are discussed: hydrogel matrix shells, sol-gel shells, polymeric shells, and induced mineral shells. Classical different types of artificial shells are introduced and their advantages and disadvantages are compared and explained. The biomedical applications of encapsulated cells with particular emphasis on cell implant protection, cell separation, biosensors, cell therapy and tissue engineering are also described and a recap of this review and the future perspectives on these active areas is given finally.

Multifunctional PEGylated nanoclusters for biomedical applications

A simple and versatile synthesis method to form water soluble multifunctional nanoclusters using polyethylene glycol (PEG) functionalized poly(maleic anhydride-alt-1-octadecene) amphiphilic brush copolymers (PMAO-g-PEG) was presented. Simply by tuning the core size and the initial nanocrystal concentration, manganese ferrite nanoparticles (MFNPs) were used to demonstrate the versatility of tuning the loading amount of the nanoclusters. The resultant nanoclusters were found to have a well-controlled spherical shape. When Zn-doped AgInS2 quantum dots (AIZS QDs) were loaded together with the MFNP nanocrystals, bi-functional nanoclusters with fluorescent and magnetic behaviors were obtained. Such bi-functional nanoclusters were also successfully demonstrated for cellular bio-imaging. Moreover, the presence of another type of nanocrystals together with MFNPs was found to have a negligible effect on the overall properties of the nanoclusters as demonstrated by the MR relaxivity test. From the time-dependent colloidal stability test, it was found that the presence of the PEG chain grafted onto PMAO was able to reduce protein adsorption onto the nanocluster surface. An in vitro study on NIH/3T3 demonstrated the biocompatibility of the nanoclusters. Such biocompatible and colloidally stable nanoclusters with an approximate size of 80-120 nm were suitable for both MRI and cell labeling applications.

Theranostic magnetic nanoparticles for efficient capture and in situ chemotherapy of circulating tumor cells

Cancer is considered to be the leading factor which threatens human lives nowadays, and 90% of cancer-related deaths are attributed to the metastasis of cancer. Thus an effective and simultaneous separation and therapeutic method for circulating tumor cells is crucial for improving the diagnosis, prognosis, and treatment of cancer. Here, we report the design of theranostic magnetic nanoparticles conjugated with the targeting peptide SP94 and the anticancer drug doxorubicin (DOX) (symbolized as Fe₃O₄-DOX/SP94) for the targeted isolation of the human hepatocellular carcinoma cell line (HepG2), followed by the in situ chemotherapy of cancer cells upon capture. It was found that the capture efficiencies of 400 μg Fe₃O₄-DOX/SP94 for HepG2 cells and human embryonic kidney transformed 293 cells (293T) were around 75% and 5% respectively after 15 min incubation. Furthermore, it is worth mentioning that DOX was covalently conjugated via pH-sensitive hydrazone bonds, and the in vitro release studies demonstrated that DOX was released much faster at pH 5.0 than at pH 7.4. According to the in vitro cytotoxicity assays, significantly reduced cell viability was observed in HepG2 cells when the concentration of Fe₃O₄-DOX/SP94 nanoparticles was 300 μg mL^-1. Such a rapid and facile approach has considerable potential for the targeted capture as well as effective chemotherapy of circulating tumor cells, in an attempt to improve the curative effects against metastatic diseases.

Controlled release of doxorubicin loaded within magnetic thermo-responsive nanocarriers under magnetic and thermal actuation in a microfluidic channel

We report a procedure to grow thermo-responsive polymer shells at the surface of magnetic nanocarriers made of multiple iron oxide superparamagnetic nanoparticles embedded in poly(maleic anhydride-alt-1-ocatadecene) polymer nanobeads. Depending on the comonomers and on their relative composition, tunable phase transition temperatures in the range between 26 and 47 °C under physiological conditions could be achieved. Using a suitable microfluidic platform combining magnetic nanostructures and channels mimicking capillaries of the circulatory system, we demonstrate that thermo-responsive nanobeads are suitable for localized drug delivery with combined thermal and magnetic activation. Below the critical temperature nanobeads are stable in suspension, retain their cargo, and cannot be easily trapped by magnetic fields. Increasing the temperature above the critical temperature causes the aggregation of nanobeads, forming clusters with a magnetic moment high enough to permit their capture by suitable magnetic gradients in close proximity to the targeted zone. At the same time the polymer swelling activates drug release, with characteristic times on the order of one hour for flow rates of the same order as those of blood in capillaries.

Magnetophoresis at the nanoscale: tracking the magnetic targeting efficiency of nanovectors

Aim: Most of the research efforts in magnetic targeting have been focused on the development of magnetic nanovectors, while the investigation of methods for tracking their magnetic targeting efficiency remains inappropriately addressed. We propose herein a miniaturized approach for appraising magnetophoretic mobility at the nanoscale. Materials & methods: A simple and easy-to-use chamber including a microtip as a magnetic attractor was developed to perform magnetophoretic measurement at the size scale of nano-objects, and under bright field or fluorescence microscopy. Different sets of magnetic nanocontainers were produced and their magnetophoretic mobility was investigated. Real-time observations of the Brownian motion of the nanocontainers were also carried out for simultaneous size determination. Results: Attraction of the nanocontainers at the microtip is demonstrated as a qualitative method that immediately distinguishes magnetically responsive nano-objects. The combination of the analysis of Brownian motion, together with the magnetophoretic mobility, inferred both the size, the magnetophoretic velocity and the magnetic content of the nanocontainers. Additionally, nanomagnetophoresis experiments under fluorescence microscopy provided information on the constitutive core/shell integrity of the nanocontainers and the co-internalization of a fluorescent cargo. Conclusion: This nanomagnetophoresis method represents a promising tool to estimate the feasibility of magnetic targeting in laboratory routine.

Original submitted 28 November 2011; Revised submitted 28 February 2012; Published online 18 June 2012

Magnetic nanobeads decorated with silver nanoparticles as cytotoxic agents and photothermal probes

A versatile method for decorating magnetic nanobeads (being composite materials from polymers and superparamagnetic nanoparticles) with silver nanoparticles of 3-6 nm size is presented. Control over the silver nanoparticle coverage at the nanobead surface is achieved by changing the reaction parameters. Moreover, the silver-decorated magnetic nanobeads (Ag-MNBs) are studied with respect to their in vitro cytotoxicity on two distinct tumour cell lineages under different parameters, i.e., dose, incubation time, magnetic field applied during the culturing, silver ion leakage, and colloidal stability. It is found that enhanced magnetically mediated cellular uptake and silver ion leakage from the Ag-MNBs surface are the main factors which affect the toxicity of the Ag-MNBs and allow the half-maximal inhibitory dose of silver to be reduced to only 32 μg mL(-1) . Furthermore, a synergic cytotoxicity induced by photo-activation of silver nanoparticles was also found.

Ultra magnetic liposomes for MR imaging, targeting, and hyperthermia

Magnetic liposomes offer opportunities as theranostic systems. The prerequisite for efficient imaging, tissue targeting or hyperthermia is high magnetic load of these vesicles. Here we describe the preparation of Ultra Magnetic Liposomes (UMLs), which may encapsulate iron oxide nanoparticles in a volume fraction of up to 30%. This remarkable magnetic charge provides UMLs with high magnetic mobilities, MRI relaxivities, and heating capacities for magnetic hyperthermia. Moreover, these UMLs are rapidly and efficiently internalized by cultured tumor cells and, when they are administered to mice, they can be vectorized to tumors by an external magnet.

Ultrasmall biocompatible nanocomposites: a new approach using seeded emulsion polymerization for the encapsulation of nanocrystals

We report a novel approach of seeded emulsion polymerization in which nanocrystals are used as seeds. Ultrasmall biocompatible polymer-coated nanocrystal with sizes between 15 and 110 nm could be prepared in a process that avoids any treatment with high shear forces or ultrasonication. The number of nanocrystals per seed, the size of the seeds, and the shell thickness can be independently adjusted. Single encapsulated nanocrystals in ultrasmall nanobeads as well as clusters of nanocrystals can be obtained. Polysorbat-80 was used as surfactant. It consists of poly(ethylene glycol) (PEG) chains, giving the particles outstanding biofunctional characteristics such as a minimization of unspecific interactions.

Magnetic nanocarriers with tunable pH dependence for controlled loading and release of cationic and anionic payloads

Superparamagnetic nanocarriers with tunable pH dependence of the surface charge are designed by a simple co-precipitation method. By exploiting electrostatic interactions, cationic or anionic payloads can be adsorbed and desorbed depending on the pH. On three different resulting nanocarrier systems, experiments of loading and release of gold nanoparticles as well as effective siRNA loading and in vitro delivery on human cells are performed.

Synthesis and Characterization of Dual-Magnetic Thermosensitive Microspheres

Fe3O4nanoparticles and poly(N-isopropylacrylamide-co-methacrylic acid) were combined to form dual-magnetic thermosensitive microspheres. The results of fourier-transform infrared (FTIR) spectroscopy, transmission electron microscope (TEM) and thermogravimetric analyzer (TGA) confirm that the microspheres are characterized with a magnetic Fe3O4core, a poly(N-isopropylacrylamide-co-methacrylic acid) shell, and an average diameter of about 150-300nm. Spectra of wide angle X-ray diffraction (WAXD) indicate that the copolymer on the surface of Fe3O4nanoparticles shows no influence on the inverse cubic spinel phase of Fe3O4. The lower critical solution temperature (LCST) of the thermosensitive copolymer-shell is about 39°Cas determined by a turbidimeter. Besides, the microspheres exhibit an obvious advantage using magnetic separation, and can be heated through an external alternating magnetic field to generate thermal effects, thus possess dual-magnetic responses (including magnetic delivery and magnetic-thermal effects). The synthesized microspheres with dual-magnetic and thermosensitive responses have potential applications in a magnetic drug-targeting delivery system for controlled drug release.

A nanobeads amplified QCM immunosensor for the detection of avian influenza virus H5N1

As a potential pandemic threat to human health, there has been an urgent need for rapid detection of the highly pathogenic avian influenza (AI) H5N1 virus. In this study, magnetic nanobeads amplification based quartz crystal microbalance (QCM) immunosensor was developed as a new method and application for AI H5N1 virus detection. Polyclonal antibodies against AI H5N1 virus surface antigen HA (Hemagglutinin) were immobilized on the gold surface of the QCM crystal through self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA). Target H5N1 viruses were then captured by the immobilized antibodies, resulting in a change in the frequency. Magnetic nanobeads (diameter, 30nm) coated with anti-H5 antibodies were used for further amplification of the binding reaction between antibody and antigen (virus). Both bindings of target H5N1 viruses and magnetic nanobeads onto the crystal surface were further confirmed by environmental scanning electron microscopy (ESEM). The QCM immunosensor could detect the H5N1 virus at a titer higher than 0.0128 HA unit within 2h. The nanobeads amplification resulted in much better detection signal for target virus with lower titers. The response of the antibody-antigen (virus) interaction was shown to be virus titer-dependent, and a linear correlation between the logarithmic number of H5N1 virus titers and frequency shift was found from 0.128 to 12.8 HA unit. No significant interference was observed from non-target subtypes such as AI subtypes H3N2, H2N2, and H4N8. The immunosensor was evaluated using chicken tracheal swab samples. This research demonstrated that the magnetic nanobeads amplification based QCM immunosensor has a great potential to be an alternative method for rapid, sensitive, and specific detection of AI virus H5N1 in agricultural, food, environmental and clinical samples.

Polymer brush-modified magnetic nanoparticles for His-tagged protein purification

Growth of poly(2-hydroxyethyl methacrylate) brushes on magnetic nanoparticles and subsequent brush functionalization with nitrilotriacetate-Ni(2+) yield magnetic beads that selectively capture polyhistidine-tagged (His-tagged) protein directly from cell extracts. Transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis, and magnetization measurements confirm and quantify the formation of the brushes on magnetic particles, and multilayer protein adsorption to these brushes results in binding capacities (220 mg BSA/g of beads and 245 mg His-tagged ubiquitin/g of beads) that are an order of magnitude greater than those of commercial magnetic beads. Moreover, the functionalized beads selectively capture His-tagged protein within 5 min. The high binding capacity and protein purity along with efficient protein capture in a short incubation time make brush-modified particles attractive for purification of recombinant proteins.

Multifunctional nanobeads based on quantum dots and magnetic nanoparticles: synthesis and cancer cell targeting and sorting

Trifunctional polymer nanobeads are prepared by destabilization of a mixture of magnetic nanoparticles, quantum dots, and an amphiphilic polymer, followed by functionalization of the bead surface with folic acid molecules. The distribution of the nanoparticles within the nanobeads can be tuned using either acetonitrile or water as destabilizing solvent. The luminescence of the resulting beads can be tuned by varying the ratio of quantum dots per magnetic nanoparticles. The application of an external magnetic field (such as a small static magnet of 0.3 T) to the magnetic-fluorescent nanobeads allows the quantitative accumulation of the beads within a few hours depending on the total size of the beads. Furthermore, specific targeting of cancer cells overexpressing folate receptors is achieved thanks to the folic acid decorating the surface of the as-synthesized nanobeads. Folate receptor mediated cellular uptake of the folic acid-functionalized nanobeads is proven via both confocal imaging and transmission electron microscopy characterization. Cell sorting experiments performed with trifunctional nanobeads show quantitative recovering of targeted cells even when they are present at low percentage (up to 1%).

Fluorescent-magnetic-biotargeting multifunctional nanobioprobes for detecting and isolating multiple types of tumor cells

Fluorescent-magnetic-biotargeting multifunctional nanobioprobes (FMBMNs) have attracted great attention in recent years due to their increasing, important applications in biomedical research, clinical diagnosis, and biomedicine. We have previously developed such nanobioprobes for the detection and isolation of a single kind of tumor cells. Detection and isolation of multiple tumor markers or tumor cells from complex samples sensitively and with high efficiency is critical for the early diagnosis of tumors, especially malignant tumors or cancers, which will improve clinical diagnosis outcomes and help to select effective treatment approaches. Here, we expanded the application of the monoclonal antibody (mAb)-coupled FMBMNs for multiplexed assays. Multiple types of cancer cells, such as leukemia cells and prostate cancer cells, were detected and collected from mixed samples within 25 min by using a magnet and an ordinary fluorescence microscope. The capture efficiencies of mAb-coupled FMBMNs for the above-mentioned two types of cells were 96% and 97%, respectively. Furthermore, by using the mAb-coupled FMBMNs, specific and sensitive detection and rapid separation of a small number of spiked leukemia cells and prostate cancer cells in a large population of cultured normal cells (about 0.01% were tumor cells) were achieved simply and inexpensively without any sample pretreatment before cell analysis. Therefore, mAb-coupled multicolor FMBMNs may be used for very sensitive detection and rapid isolation of multiple cancer cells in biomedical research and medical diagnostics.

Magnetic nanobeads decorated by thermo-responsive PNIPAM shell as medical platforms for the efficient delivery of doxorubicin to tumour cells

Medical nanoplatforms based on clusters of superparamagnetic nanoparticles decorated with a PNIPAM thermo-responsive shell have been synthesized and used as drug carriers for doxorubicin (DOXO), a common chemotherapeutic agent. The nanosystem here developed has a total diameter below 200 nm and exploits the temperature responsive behaviour of the PNIPAM polymeric shell for the controlled loading and release of DOXO. The system has been tested in vitro on tumour cells and it clearly demonstrates the effectiveness of drug polymer encapsulation and time-dependent cell death induced by the doxorubicin release. Comparative cellular studies of the DOXO loaded nanoplatform in the presence or absence of an external magnet (0.3 T) showed the synergic effect of accumulation and enhanced toxicity of the system, when magnetically guided, resulting in the enhanced efficacy of the system.

Bifunctional nanocomposites with magnetic and luminescence properties

Many applications require nanoparticles that exhibit high magnetic moment and luminescence. Compounds exhibiting this combination of properties do not exist. However, this combination of properties may be obtained by nanocomposites. There are two possible configurations for these composites: the core-shell design, leading to the smallest composite particles, and agglomerates containing separated particles with the properties in question. The magnetic core is, in most cases, maghemite or magnetite, whereas the luminescence carrier is either an organic molecule or an inorganic quantum dot. One of the basic problems in designing such composites, to be overcome by the appropriate layout choice, is the potential incompatibility between the magnetic core and the lumophore. Experimentally realized solutions of these problems are presented.