Daniel M. Lyons

Preparation of ordered mesoporous ceria with enhanced thermal stability

The use of neutral surfactants to form a thermally stable ordered mesoporous ceria phase is reported. The judicious choice of cerium acetate as the inorganic framework precursor and the inorganic to surfactant ratio in the preparation mixture allowed the condensation of acetate derived inorganic polymer chains about the surfactant phase to form a regular mesoscopically ordered inorganic–organic matrix. Even at the low temperature processing conditions used to prepare the hybrid matrix the cerium precursor was seen to form the fluorite type structure of CeO2. Careful thermal processing of the matrix allowed the subsequent densification (of the pore walls) of the inorganic component and removal of the organic component so that a high quality ordered and truly crystalline mesoporous ceria was formed. The calcination procedure used resulted in a reduction of the long-range order of the pore channels (as evidenced by powder X-ray diffraction) whilst maintaining directionally aligned mesoporous channels as observed by transmission electron microscopy. These ordered pore structures remained even after high temperature ageing. The templating route adopted was found to allow the facile low temperature removal of surfactant due to the hydrogen bonding nature of the surfactant–ceria interaction. Differential scanning calorimetery (DSC) data are consistent with some amount of rapid ceria lattice reduction (Ce4+ to Ce3+) at the surface related to the presence of intimate organic–inorganic interactions most likely the result of hydrogen bonds that exist between the surfactant and the ceria lattice. Any reduction of the ceria pore wall surface during the initial thermal processing is rapidly re-oxidised by rapid mass transport of gas phase oxygen molecules through the open pore system during the process of template removal. The material maintained high surface areas after calcination up to temperatures of 873 K. The preparation of high surface area ceria with a stable uniform array of pores is significant and may allow the development of novel catalytic applications for ceria.

Bistable nanoelectromechanical devices

A combined transmission electron microscopy-scanning tunneling microscopy (TEM-STM) technique has been used to investigate the force interactions of silicon and germanium nanowires with gold electrodes. The I(V) data obtained typically show linear behavior between the gold electrode and silicon nanowires at all contact points, whereas the linearity of I(V) curves obtained for germanium nanowires were dependent on the point of contact. Bistable silicon and germanium nanowire-based nanoelectromechanical programmable read-only memory (NEMPROM) devices were demonstrated by TEM-STM. These nonvolatile NEMPROM devices have switching potentials as low as 1 V and are highly stable making them ideal candidates for low-leakage electronic devices.

Preparation of a series of mesoporous lanthanide oxides by a neutral supramolecular templating routeElectronic supplementary information (ESI) available: DSC results. See http://www.rsc.org/suppdata/jm/b3/b313982d/

In this study, data are provided that detail the first preparation of high surface area and structurally ordered mesoporous lanthanide oxides by a neutral surfactant supramolecular templating route. For the first time, retention of mesoporosity in lanthanide oxides (other than those of cerium) after surfactant removal by simple air calcination at temperatures to 450 °C is demonstrated. The as-prepared lanthanide–surfactant composites displayed long range ordering of the mesoporous phase and although significant amounts of order can be lost, the materials exhibit a large degree of porosity, high surface area and some ordering of the pore array after high temperature calcination. In the case of lanthanum oxide, a mesoporous material displaying a cubic structured array of pores was obtained. The heavier lanthanide analogues readily formed lamellar phases. Removal of water and surfactant from between lamellae was found to result in some collapse of the as-prepared porous structures although in all cases mesoporosity was still evident. Ytterbium was found to exhibit more complex behaviour with a cubic phase being generated. This material was also found to display reduced periodicity of the pore structure on calcination and all materials retained highly textured surfaces after the thermal treatment to remove surfactant.

Effect of Protein Corona on Silver Nanoparticle Stabilization and Ion Release Kinetics in Artificial Seawater

In parallel with the growing use of nanoparticle-containing products, their release into the environment over the coming years is expected to increase significantly. With many large population centers located in near-coastal areas, and increasing evidence that various nanoparticles may be toxic to a range of organisms, biota in estuarine and coastal waters may be particularly vulnerable. While size effects may be important in cases, silver nanoparticles have been found to be toxic in large part due to their release of silver ions. However, there is relatively little data available on how nanoparticle coatings can affect silver ion release in estuarine or marine waters. We have found that albumin, as a model for biocorona-forming macromolecules which nanoparticles may encounter in wastewater streams, stabilizes silver colloids from agglomeration in high salinity marine waters by electrosteric repulsion for long time periods. A minimum mass ratio of about 130 for albumin:silver nanoparticles (40 nm) was required for stable dispersion in seawater. Increasing albumin concentration was also found to reduce dissolution of nanoparticles in seawater with up to 3.3 times lower concentrations of silver ions noted. Persistent colloids and slow sustained ion release may have important consequences for biota in these environmental compartments.

Antibody-based donor-acceptor spatial reconfiguration in decorated lanthanide-doped nanoparticle colloids for the quantification of okadaic acid biotoxin.

With the increasing movement away from the mouse bioassay for the detection of toxins in commercially harvested shellfish, there is a growing demand for the development of new and potentially field-deployable tests in its place. In this direction we report the development of a simple and sensitive nanoparticle-based luminescence technique for the detection of the marine biotoxin okadaic acid. Photoluminescent lanthanide nanoparticles were conjugated with fluorophore-labelled anti-okadaic acid antibodies which, upon binding to okadaic acid, gave rise to luminescence resonance energy transfer from the nanoparticle to the organic fluorophore dye deriving from a reduction in distance between the two. The intensity ratio of the fluorophore: nanoparticle emission peaks was found to correlate with okadaic acid concentration, and the sensor showed a linear response in the 0.37-3.97 μM okadaic acid range with a limit of detection of 0.25 μM. This work may have important implications for the development of new, cheap, and versatile biosensors for a range of biomolecules and that are sufficiently simple to be applied in the field or at point-of-care.

Application of functionalized lanthanide-based nanoparticles for the detection of okadaic acid-specific immunoglobulin G.

Marine biotoxins are widespread in the environment and impact human health via contaminated shellfish, causing diarrhetic, amnesic, paralytic, or neurotoxic poisoning. In spite of this, methods for determining if poisoning has occurred are limited. We show the development of a simple and sensitive luminescence resonance energy transfer (LRET)-based concept which allows the detection of anti-okadaic acid rabbit polyclonal IgG (mouse monoclonal IgG1) using functionalized lanthanide-based nanoparticles. Upon UV excitation, the functionalized nanoparticles were shown to undergo LRET with fluorophore-labeled anti-okadaic acid antibodies which had been captured and bound by okadaic acid-decorated nanoparticles. The linear dependence of fluorescence emission intensity with antigen-antibody binding events was recorded in the nanomolar to micromolar range, while essentially no LRET signal was detected in the absence of antibody. These results may find applications in new, cheap, and robust sensors for detecting not only immune responses to biotoxins but also a wide range of biomolecules based on antigen-antibody recognition systems. Further, as the system is based on solution chemistry it may be sufficiently simple and versatile to be applied at point-of-care.

How similar are amorphous calcium carbonate and calcium phosphate? A comparative study of amorphous phase formation conditions

Amorphous calcium carbonate (ACC) and calcium phosphate (ACP) increasingly attract attention as initial solid phases in vertebrate and invertebrate hard tissue formation, as well as in materials science as a possible new synthetic route for advanced materials preparation. Although much is known about these two amorphous phases and similarities in the mechanisms of their formation are recognized, no attempt has been made to investigate their formation under defined and comparable initial experimental conditions viz supersaturation, constituent ions ratio, ionic strength and presence of relevant inorganic additives. In this paper, the formation of ACC and ACP in three model precipitation systems of increased chemical complexity were investigated: (a) systems containing constituent ions, (b) systems containing additional co-ions, and (c) systems with higher ionic strength and addition of Mg2+. The results have shown that ACP is more stable and was formed at lower relative supersaturations in comparison to ACC. The precipitation domain of both phases expanded with increasing complexity of precipitation systems, with the ACP precipitation domains always being larger than that of ACC. In addition to stability, the presence of inorganic ions, especially Mg2+, influences the composition of both amorphous phases. The obtained results indicate that general similarity between ACC and ACP exists, but it could also be concluded that similar chemical environment in which they form not necessary lead to similar structural properties.

Calcium phosphate and calcium carbonate mineralization of bioinspired hydrogels based on β-chitin isolated from biomineral of the common cuttlefish (Sepia officinalis, L.)

Chitin, a bioactive, antibacterial and biodegradable polymer is commonly utilized by diverse marine organisms as the main scaffold material during biomineralization. Due to its properties, chitin is also of interest as a component of organo-inorganic composites for diverse biomedical applications. In this study, chitinous fibers isolated from the cuttlebone of the common cuttlefish (Sepia officinalis, L.) are characterized and evaluated for use as an integral part of mineralized hydrogels for biomedical applications. Since marine organisms use calcium carbonates (CaCO3), while vertebrates use calcium phosphates (CaP) as the main inorganic hard tissue components, and both minerals are used in hard tissue engineering, they were compared to determine which composite is potentially a better biomaterial. Hydrogel mineralization was conducted by subsequent dipping into cationic and anionic reactant solutions, resulting in the formation of a CaCO3 or CaP coating that penetrated into the hydrogel. Obtained composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), rheology, swelling tests and simple compression. The results indicate that β-chitin can be used for the preparation of moldable hydrogels that are easily mineralized. Mineralized hydrogels have higher elasticity than non-mineralized ones while swelling is better if the extent of mineralization is lower. Further optimization of the hydrogels composition could improve their stress response and Young’s modulus, where the current hydrogel with a higher extent of CaP mineralization excels in comparison to all other investigated composites.

Controlling morphological, orientational and material properties of mesoporous aluminosilicate films: enabling supercritical fluid deposition of perpendicularly ordered nanowire arrays

Highly ordered mesoporous aluminosilicate thin-films were prepared with unidirectional pore alignment. The films were templated from neutral polyethyelene oxide triblock copolymer surfactants. The mesoporous thin-films were characterised by a combination of low angle X-ray diffraction, nitrogen adsorption BET and transmission electron microscopy analysis. These films were successfully used as hosts for the supercritical fluid deposition of perpendicularly oriented nanowire arrays.