Matt Carroll

Anti-fouling magnetic nanoparticles for siRNA delivery

Iron oxide nanoparticles (IONPs), with a diameter of 8 nm, have been coated with two different polymers, i.e. poly(oligoethylene glycol) methyl ether acrylate (P(OEG-A)) and poly(dimethylaminoethyl acrylate) (P(DMAEA)). The polymers were attached to the nanoparticle surface using two different strategies, with the aim of creating an internal layer of P(DMAEA) and an outer shell of P(OEG-A). The subsequent polymer-stabilized IONPs were characterized using ATR, XPS and TGA, proving the presence of polymers on the IONP surfaces with a grafting density ranging from 0.05 to 0.22 chain per nm2. High grafting densities were demonstrated when the two homopolymers were assembled on the surfaces of the IONPs simultaneously. The polymer composition at the surfaces of the IONPs could be controlled by manipulating the feed ratio P(OEG-A)–P(DMAEA) present in solution. These hybrid organic–inorganic particles (70–150 nm) proved to be stable in both water and 50 vol% fetal bovine serum (FBS). In addition, zeta-potential measurements confirmed that P(OEG-A) chains effectively mask the positive charge originating from P(DMAEA) thereby limiting protein adsorption on these particles. Hybrid nanoparticles were exploited for the complexation of siRNA, thereby generating IONP siRNA nano-carriers with anti-fouling P(OEG-A) shells. The transfection efficiency was measured using human neuroblastoma SHEP cells both in the presence and in the absence of a magnetic field in FBS. The transfection efficiency was determined by both fluorescence microscopy and flow cytometry. Cytotoxicity studies revealed that the IONP carriers were non-toxic to SHEP cells. In addition, studies on the proton transverse relaxation enhancement properties of these stabilized IONPs indicated high relaxivities (∼160 s−1 per mM of Fe).

Experimental validation of proton transverse relaxivity models for superparamagnetic nanoparticle MRI contrast agents

Analytical models of proton transverse relaxation rate enhancement by magnetic nanoparticles were tested by making measurements on model experimental systems in a field of 1.4 T. Proton relaxivities were measured for five aqueous suspensions of iron oxide (maghemite) nanoparticles with nominal mean particle sizes of 6, 8, 10, 11, and 13 nm. Proton relaxivity increased with mean particle size ranging from 13 s(-1) mM Fe(-1) for the 6 nm sample, up to 254 s(-1) mM Fe(-1) for the 13 nm sample. A strong correlation between the measured and predicted values of the relaxivity was observed, with the predicted values being consistently higher than the measured values. The results indicate that the models give a reasonable agreement with experimental results and hence can be used as the basis for the design of new magnetic resonance imaging contrast and labelling agents.

Stability of Polydimethylsiloxane-Magnetite Nanoparticle Dispersions Against Flocculation: Interparticle Interactions of Polydisperse Materials

The colloidal stability of dispersions comprised of magnetite nanoparticles coated with polydimethylsiloxane (PDMS) oligomers was investigated theoretically and experimentally. Particle-particle interaction potentials in a theta solvent and in a good solvent for the PDMS were predicted by calculating van der Waals, electrostatic, steric, and magnetic forces as functions of interparticle separation distances. A variety of nanoparticle sizes and size distributions were considered. Calculations of the interparticle potential in dilute suspensions indicated that flocculation was likely for the largest 1% of the population of particles. Finally, the rheology of these complexes over time in the absence of a solvent was measured to probe their stabilities against flocculation as neat fluids. An increase in viscosity was observed upon aging, suggesting that some agglomeration occurs with time. However, the effects of aging could be removed by exposing the sample to high shear, indicating that the magnetic fluids were not irreversibly flocculated.

The effect of polymer coatings on proton transverse relaxivities of aqueous suspensions of magnetic nanoparticles

Iron oxide magnetic nanoparticles are good candidates for magnetic resonance imaging (MRI) contrast agents due to their high magnetic susceptibilities. Here we investigate 19 polyether-coated magnetite nanoparticle systems comprising three series. All systems were synthesized from the same batch of magnetite nanoparticles. A different polyether was used for each series. Each series comprised systems with systematically varied polyether loadings per particle. A highly significant (p < 0.0001) linear correlation (r = 0.956) was found between the proton relaxivity and the intensity-weighted average diameter measured by dynamic light scattering in the 19 particle systems studied. The intensity-weighted average diameter measured by dynamic light scattering is sensitive to small number fractions of larger particles/aggregates. We conclude that the primary effect leading to differences in proton relaxivity between systems arises from the small degree of aggregation within the samples, which appears to be determined by the nature of the polymer and, for one system, the degree of polymer loading of the particles. For the polyether coatings used in this study, any changes in relaxivity from differences in water exclusion or diffusion rates caused by the polymer are minor in comparison with the changes in relaxivity resulting from variations in the degree of aggregation.

Labeling of cancer cells with magnetic nanoparticles for magnetic resonance imaging

The process of invasion and metastasis formation of tumor cells can be studied by following the migration of labeled cells over prolonged time periods. This report investigates the applicability of iron oxide nanoparticles as a magnetic resonance imaging (MRI) contrast agent for cell labeling.

Nanostructure of PEO-polyurethane-PEO triblock copolymer micelles in water

Novel hydrophilic triblock copolymers which form micelles in aqueous solution were studied by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS) and densitometry. The polymers were symmetric A-B-A block copolymers having two poly(ethylene oxide) (PEO) tail blocks and a polyurethane (PU) center segment that contained pendant carboxylic acids. The aggregation number of the micelles decreased with increasing PEO mass content. When attempting to fit the SANS data it was found that no single model was suitable over the entire range of block lengths and PEO mass concentrations investigated here. For the polymer with the highest aggregation number, the data were fitted with a triblock model consisting of a homogeneous core with a corona of non-interacting Gaussian chains for which only two free parameters were required: the radius of the core and the radius of gyration of the corona. In this case, the core was found to be effectively dry. At lower aggregation numbers, a star polymer model generated significantly better fits, suggesting the absence of any identifiable central core structure. Good agreement was found between the sizes measured by DLS, SANS and theoretical predictions of micelle size from a density distribution theory. These results show that when significant changes in aggregation number occur, the nanostructure of the micelle can change substantially even for polymers that are remarkably similar.

Quantitative produced water analysis using mobile 1H NMR

Measurement of oil contamination of produced water is required in the oil and gas industry to the (ppm) level prior to discharge in order to meet typical environmental legislative requirements. Here we present the use of compact, mobile 1H nuclear magnetic resonance (NMR) spectroscopy, in combination with solid phase extraction (SPE), to meet this metrology need. The NMR hardware employed featured a sufficiently homogeneous magnetic field, such that chemical shift differences could be used to unambiguously differentiate, and hence quantitatively detect, the required oil and solvent NMR signals. A solvent system consisting of 1% v/v chloroform in tetrachloroethylene was deployed, this provided a comparable 1H NMR signal intensity for the oil and the solvent (chloroform) and hence an internal reference 1H signal from the chloroform resulting in the measurement being effectively self-calibrating. The measurement process was applied to water contaminated with hexane or crude oil over the range 1–30 ppm. The results were validated against known solubility limits as well as infrared analysis and gas chromatography.

NMR on iron rich cores and cuttings ? the importance of short Tes

The moisture content of iron ore is a critical factor in determining its subsequent processing, transportation, quality and general handling. In particular, high moisture content can lead to extremely dangerous liquefaction of the ore during sea-transportation, with major financial and safety implications. NMR has long been used to measure moisture content in rocks but the presence of magnetic materials such as iron affects the NMR signal leading to data that cannot be interpreted by known methods. There has recently been interest in determining how the properties of the rock affect the NMR signal, particularly where there are different concentrations of magnetic materials or rocks with different mineralogical properties. There has, however, been less work in determining how the measurement techniques should be changed to accommodate these systems. In this work we measure iron rich rock cores and show the importance of selecting an appropriate echo time in the CPMG sequence. We show that longer echo times can lead to estimations of a T2 distribution that is not representative of the system. This in turn would lead to inaccurate measurements of the water content. We demonstrate the importance of short echo times and show that for the systems studied in this work, an upper limit of 0.4 ms should be imposed.