Arnold J. Kell

Clusters of Superparamagnetic Iron Oxide Nanoparticles Encapsulated in a Hydrogel: A Particle Architecture Generating a Synergistic Enhancement of the T2 Relaxation

Clusters of iron oxide nanoparticles encapsulated in a pH-responsive hydrogel are synthesized and studied for their ability to alter the T(2)-relaxivity of protons. Encapsulation of the clusters with the hydrophilic coating is shown to enhance the transverse relaxation rate by up to 85% compared to clusters with no coating. With the use of pH-sensitive hydrogel, difficulties inherent in comparing particle samples are eliminated and a clear increase in relaxivity as the coating swells is demonstrated. Agreement with Monte Carlo simulations indicates that the lower diffusivity of water inside the coating and near the particle surface leads to the enhancement. This demonstration of a surface-active particle structure opens new possibilities in using similar structures for nanoparticle-based diagnostics using magnetic resonance imaging.

The cell labeling efficacy, cytotoxicity and relaxivity of copper-activated MRI/PET imaging contrast agents.

A new class of nanoparticle-based dual-modality positron emission tomography/magnetic resonance imaging (PET/MRI) contrast agents has been developed. The probe consists of a superparamagnetic iron oxide (SPIO) or manganese oxide core coated with 3,4-dihydroxy-D,L-phenylalanine (DL-DOPA). The chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was conjugated to DOPA termini. The DOTA modified nanoparticles allow chelation of copper for PET imaging. These surface functionalized nanoparticle-based probes have been characterized by various analytical techniques. The cell-labeling efficacy, cytotoxicity and relaxivity of these nanoparticles have been evaluated and compared with the same properties of one of the most commonly utilized MRI contrast agents, Feridex(®). Evidently, this new nanoparticle has a great potential for use in cell tracking with MRI and PET in the absence of transfecting agent. It is noteworthy that there is a sharp increase in r(2) relaxivity of these nanoparticles on coordination with Cu(2+) ions. Thus these iron oxide nanoparticles can also be explored as the smart magnetic resonance (MR) sensor for the detection of micromolar changes in copper concentration for neurodegenerative diseases such as Alzheimers disease, Menkes and Wilsons diseases, amyotrophic lateral sclerosis and prion diseases.

Cu2+-labeled, SPION loaded porous silica nanoparticles for cell labeling and multifunctional imaging probes.

We have developed an ion-sensing nanoparticle that is comprised of a superparamagnetic iron oxide (SPIO) core encapsulated with a porous silica shell. The latter can be readily anchored with ligands capable of coordinating with positron-emitting metal. Evidently, this nanoparticle has a great potential for use in cell tracking with magnetic resonance (MR) imaging and positron emission tomography (PET). Herein we report the synthesis, surface functionalization and characterization of the magnetic nanoparticle-based probes and evaluate their cell-labeling efficacy, cytotoxicity and relaxivity in comparison to one of the most commonly utilized MRI contrast agents, Feridex.

Nanobeads Highly Loaded with Superparamagnetic Nanoparticles Prepared by Emulsification and Seeded-Emulsion Polymerization

Functional superparamagnetic colloids possessing high saturation magnetization are prepared by emulsification of superparamagnetic nanoparticles (SPM NPs) and heterogeneous polymerization. The colloids consist of a core of densely packed NPs encapsulated within a thin polymer shell. The cores are made by emulsifying SPM NPs and toluene into an aqueous surfactant solution, and subsequently condensing the emulsion droplets by removal of the solvent generating clusters of SPM NPs. By tuning the emulsification condition, this approach allows for control over the size of the clusters from approximately 40 to 200 nm. The polymer shells encapsulating the clusters are made by using seeded-emulsion polymerization concepts. Control over the thickness of the shell and the incorporation of functional groups to the colloid is achieved. Characterization by thermogravimetric analysis (TGA) and magnetometry shows that these colloids have 66 wt % of magnetic material and saturation magnetization of 47 emu/g, confirming that this route generates colloids with a high loading of SPM NPs and high saturation magnetizations.

Single-Domain Antibody-Nanoparticles: Promising Architectures for Increased Staphylococcus aureus Detection Specificity and Sensitivity

Because antibodies are highly target-specific and nanoparticles possess diverse, material-dependent properties that can be exploited in order to label and potentially identify biomolecules, the development of antibody-nanoparticle conjugates (nanoconjugates) has huge potential in biodiagnostics. Here, we describe a novel superparamagnetic nanoconjugate, one whose recognition component is a single-domain antibody. It is highly active toward its target Staphylococcus aureus, displays long shelf life, lacks cross-reactivity inherent to traditional homologue whole antibodies, and captures a few dozen S. aureus cells in a mixed cell population with ~100% efficiency and specificity. We ascribe the excellent performance of our nanoconjugate to its single-domain antibody component and recommend it as a general purpose recognition element.

Immunomagnetic capture of Bacillus anthracis spores from food.

Food is a vulnerable target for potential bioterrorist attacks; therefore, a critical mitigation strategy is needed for the rapid concentration and detection of biothreat agents from food matrices. Magnetic beads offer a unique advantage in that they have a large surface area for efficient capture of bacteria. We have demonstrated the efficient capture and concentration of Bacillus anthracis (Sterne) spores using immunomagnetic beads for a potential food application. Magnetic beads from three different sources, with varying sizes and surface chemistries, were functionalized with monoclonal antibodies and polyclonal antibodies from commercial sources and used to capture and concentrate anthrax spores from spiked food matrices, including milk, apple juice, bagged salad, processed meat, and bottled water. The results indicated that the Pathatrix beads were more effective in the binding and capture of anthrax spores than the other two bead types investigated. Furthermore, it was observed that the use of polyclonal antibodies resulted in a more efficient recovery of anthrax spores than the use of monoclonal antibodies. Three different magnetic capture methods, inversion, the Pathatrix Auto system, and the new i CropTheBug system, were investigated. The i CropTheBug system yielded a much higher recovery of spores than the Pathatrix Auto system. Spore recoveries ranged from 80 to 100% for the i CropTheBug system when using pure spore preparations, whereas the Pathatrix Auto system had recoveries from 20 to 30%. Spore capture from food samples inoculated at a level of 1 CFU/ml resulted in 80 to 100% capture for milk, bottled water, and juice samples and 60 to 80% for processed meat and bagged salad when using the i CropTheBug system. This efficient capture of anthrax spores at very low concentrations without enrichment has the potential to enhance the sensitivity of downstream detection technologies and will be a useful method in a foodborne bioterrorism response.

Superparamagnetic Nanoparticle-Polystyrene Bead Conjugates as Pathogen Capture Mimics : A Parametric Study of Factors Affecting Capture Efficiency and Specificity

There is currently significant interest in the miniaturization of disease detection platforms. As detection platforms decrease in size there is a need for the development of sample preparation protocols by which cells or biomarkers of interest can be concentrated from large volumes down to volumes more amenable to analysis within microfluidic devices. To address this issue, we present a series of magnetic confinement assays for polystyrene (PS) beads mediated through their covalent modification with a series of superparamagnetic nanoparticles, where the PS beads have many properties similar to bacteria, but are not pathogenic. The magnetic confinement of the PS beads is investigated as a function of (1) the overall nanoparticle size, (2) the loading of superparamagnetic content within the nanoparticle matrix, and (3) the viscosity and volume of the dispersion medium. We demonstrate that the time required for the magnetic capture of the PS beads by the superparamagnetic nanoparticles (1) decreases as the loading of superparamagnetic material into the nanoparticles increases and (2) increases as the viscosity and volume of the dispersion medium are increased. However, limitations in the magnetic confinement efficiency for the PS beads labeled with nanoparticles comprised of low loadings of superparamagnetic material can be overcome through the use of magnetic columns. These magnetic columns provide a practical and fast mode of sample preparation that should facilitate the magnetic concentration of cells and biomarkers from large volumes to volumes more amenable to incorporation into a microfluidic-based analysis system, where they can be analyzed/detected.

Versatile Molecular Silver Ink Platform for Printed Flexible Electronics

A silver molecular ink platform formulated for screen, inkjet, and aerosol jet printing is presented. A simple formulation comprising silver neodecanoate, ethyl cellulose, and solvent provides improved performance versus that of established inks, yet with improved economics. Thin, screen-printed traces with exceptional electrical (<10 mΩ/□/mil or 12 μΩ·cm) and mechanical properties are achieved following thermal or photonic sintering, the latter having never been demonstrated for silver-salt-based inks. Low surface roughness, submicron thicknesses, and line widths as narrow as 41 μm outperform commercial ink benchmarks based on flakes or nanoparticles. These traces are mechanically robust to flexing and creasing (less than 10% change in resistance) and bind strongly to epoxy-based adhesives. Thin traces are remarkably conformal, enabling fully printed metal-insulator-metal band-pass filters. The versatility of the molecular ink platform enables an aerosol jet-compatible ink that yields conductive features on glass with 2× bulk resistivity and strong adhesion to various plastic substrates. An inkjet formulation is also used to print top source/drain contacts and demonstrate printed high-mobility thin film transistors (TFTs) based on semiconducting single-walled carbon nanotubes. TFTs with mobility values of ∼25 cm2 V-1 s-1 and current on/off ratios >104 were obtained, performance similar to that of evaporated metal contacts in analogous devices.

Influence of lipoplex surface charge on siRNA delivery: application to the in vitro downregulation of CXCR4 HIV-1 co-receptor

Objective: Cationic lipidic formulations have been successfully used to deliver small interfering RNA (siRNA) into cells but they show limitations for in vivo application due to their cytotoxicity and instability in the presence of serum. To overcome these limitations, the authors developed an anionic lipid-based carrier named Neutraplex (Nx). Here, they wanted to investigate the influence of the lipoplex (Lx) surface charge on cytotoxicity, delivery and silencing activity of siRNAs. Methods: The efficiency of three Nx formulations (cationic, close to neutrality and anionic) to deliver anti-CXCR4 siRNAs in MAGI cells was investigated and compared with the cationic commercial transfection reagent Lipofectamine RNAiMAX. Cellular uptake and intracellular localization of a fluorescent siRNA was monitored in live cells using fluorescence microscopy and silencing activity was measured by flow cytometry and RT-PCR analysis. Results: The authors found that the Lx surface charge influenced cellular uptake and silencing activity of siRNA in cell cultures. Although cationic Lx formulations were the most efficient carriers to deliver active silencing siRNAs, negatively charged lipoplexes were taken up by cells, delivered active siRNAs and presented low cytotoxicity. Conclusions: Altogether, the findings support further investigation for in vivo delivery of therapeutic siRNAs using Nx. Furthermore, this study indicates that anionic delivery systems may have potential for in vivo RNAi therapeutics.

Rapid Detection and Identification of Yersinia pestis from Food Using Immunomagnetic Separation and Pyrosequencing

Interest has recently been renewed in the possible use of Y. pestis, the causative agent of plague, as a biological weapon by terrorists. The vulnerability of food to intentional contamination coupled with reports of humans having acquired plague through eating infected animals that were not adequately cooked or handling of meat from infected animals makes the possible use of Y. pestis in a foodborne bioterrorism attack a reality. Rapid, efficient food sample preparation and detection systems that will help overcome the problem associated with the complexity of the different matrices and also remove any ambiguity in results will enable rapid informed decisions to be made regarding contamination of food with biothreat agents. We have developed a rapid detection assay that combines the use of immunomagnetic separation and pyrosequencing in generating results for the unambiguous identification of Y. pestis from milk (0.9 CFU/mL), bagged salad (1.6 CFU/g), and processed meat (10 CFU/g). The low detection limits demonstrated in this assay provide a novel tool for the rapid detection and confirmation of Y. pestis in food without the need for enrichment. The combined use of the iCropTheBug system and pyrosequencing for efficient capture and detection of Y. pestis is novel and has potential applications in food biodefence.