Publications

2010
M. N. Patel, Smith, P. G., Kim, J., Milner, T. E., and Johnston, K. P., “Electrophoretic mobility of concentrated carbon black dispersions in a low-permittivity solvent by optical coherence tomography,” Journal of Colloid and Interface Science, vol. 345, pp. 194-199, 2010. Publisher's VersionAbstract
Electrophoretic mobilities of concentrated dispersions of carbon black particles in a low-permittivity solvent were measured using differential-phase optical coherence tomography (DP-OCT). An electrode spacing of only 0.18 mm enables measurement of highly concentrated dispersions up to 1 wt.% of highly absorbing carbon black particles with high electric fields at low potentials. The capabilities of this DP-OCT method, including high sensitivity, high spatial resolution, and strong electric fields, enable enhanced measurement of low electrophoretic mobilities encountered in low-permittivity solvents. The zeta potential of carbon black particles ranged from -24 mV to -12 mV as the concentration of surfactant sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) was increased from 1 mM to 100 mM. A mechanism is presented to explain the electrostatic charging of carbon black particles in terms of the partitioning of the ions between the reverse micelles in the double layer and the surfactant adsorbed on the particle surface, as AOT concentration is varied. (c) 2010 Published by Elsevier Inc.
W. Yang, Chow, K. T., Lang, B., Wiederhold, N. P., Johnston, K. P., and Williams, R. O., “In vitro characterization and pharmacokinetics in mice following pulmonary delivery of itraconazole as cyclodextrin solubilized solution,” European Journal of Pharmaceutical Sciences, vol. 39, pp. 336-347, 2010. Publisher's VersionAbstract
This study aims to make a 2-hydroxypropyl-beta-cyclodextrin (HP beta CD) solubilized itraconazole (ITZ) solution (i.e., HP beta CD-ITZ) suitable for pulmonary delivery by nebulization. and compare pharmacokinetics of inhaled nebulized aerosols of HP beta CD-ITZ versus a colloidal dispersion of ITZ nanoparticulate formulation (i.e., URF-ITZ). Solid state characterizations of lyophilized HP beta CD-ITZ by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the formation of dynamic inclusion complexes between ITZ and HP beta CD. Nebulized aerosols of both HP beta CD-ITZ and colloidal dispersion of URF-ITZ were confirmed suitable for deep lung delivery. Single doses of the nebulized aerosols (equivalent to 5.3 mg ITZ/mL in 5 mL) in mice produced similar ITZ lung depositions and pharmacokinetic profiles, with ITZ lung levels of approximately 4 mu g/g wet lung weight upon completion of nebulization and remained above 0.5 mu g/g at 24 h. HP beta CD-ITZ demonstrated faster systemic absorption of ITZ across lung epithelium than URF-1TZ, with t(max) values of 1.5 and 3.0 h, and AUC(0-infinity) of 2513 and 3717 ng h/mL, respectively. The fast absorption of solubilized ITZ across lung mucosal surface may be due in part to the elimination of the phase-to-phase transition. (C) 2010 Elsevier B.V. All rights reserved.
S. S. Adkins, Chen, X., Nguyen, Q. P., Sanders, A. W., and Johnston, K. P., “Effect of branching on the interfacial properties of nonionic hydrocarbon surfactants at the air-water and carbon dioxide-water interfaces,” Journal of Colloid and Interface Science, vol. 346, pp. 455-463, 2010. Publisher's VersionAbstract
The interfacial tensions, surface pressures, and adsorption of nonionic hydrocarbon surfactants at the air-water (A-W) and carbon dioxide-water (C-W) interfaces were investigated systematically as a function of the ethylene oxide (EO) unit length and tail structure. Major differences in the properties are explained in terms of the driving force for surfactant adsorption, tail solvation, area per surfactant molecule, and surfactant packing. As the surfactant architecture is varied, the changes in tail-tail interactions, steric effects, areas occupied by the surfactant at the interface, and tail hydrophobicity are shown to strongly influence the interfacial properties, including the surfactant efficiency (the concentration to produce 20 mN/m interfacial tension reduction). For linear surfactants at the A-W interface, high efficiencies result from dense monolayers produced by the high interfacial tension driving force for adsorption and strong tail-tail interactions. At the C-W interface, where a low interfacial tension leads to a much lower surfactant adsorption, the contact between the phases is much greater. Branching or increasing the number of tail chains increase the hydrophobicity, tail solvation, and adsorption of the surfactant. Furthermore, the area occupied by the surfactant increases with branching, number of tails, and number of EO monomers in the head group, to reduce contact of the phases. These factors produce greater efficiencies for branched and double tail surfactants at the C-W interface, as well as surfactants with longer EO head groups. (C) 2010 Elsevier Inc. All rights reserved.
G. Gupta, Slanac, D. A., Kumar, P., Wiggins-Camacho, J. D., Kim, J., Ryoo, R., Stevenson, K. J., and Johnston, K. P., “Highly Stable Pt/Ordered Graphitic Mesoporous Carbon Electrocatalysts for Oxygen Reduction,” Journal of Physical Chemistry C, vol. 114, pp. 10796-10805, 2010. Publisher's VersionAbstract
In this manuscript, we have synthesized a stable fuel cell catalyst composed of presynthesized Pt nanocrystals (<4 nm) on graphitic mesoporous carbon. The catalyst shows negligible loss in mass activity and active surface area after an accelerated durability test (1000 cycles, 0.5-1.2 V), whereas the commercial Pt on amorphous carbon loses similar to 70% in activity and area. Strong Pt graphite interactions, resulting from metal/support orbital overlap (pi-backbonding) coupled with partial charge transfer, as shown by XPS, and a low coverage of weakly bound ligands on the Pt surface facilitated high dispersion and loadings up to 20 wt %. The high oxidation resistance of the graphitized carbon, along with the strong Pt-C interactions, helped to maintain electrical contact between the metal and carbon while mitigating Pt dissolution, ripening, and coalescence. The ability to disperse well-defined metal nanoparticles onto graphitic mesoporous carbon offers the potential for creating highly stable and active catalysts.
J. M. Tam, Murthy, A. K., Ingram, D. R., Nguyen, R., Sokolov, K. V., and Johnston, K. P., “Kinetic Assembly of Near-IR-Active Gold Nanoclusters Using Weakly Adsorbing Polymers to Control the Size,” Langmuir, vol. 26, pp. 8988-8999, 2010. Publisher's VersionAbstract
Clusters of metal nanoparticles with an overall size of less than 100 nm and high metal loadings for strong optical functionality are of interest in various fields including microelectronics, sensors, optoelectronics, and biomedical imaging and therapeutics. Herein we assemble similar to 5 nm gold particles into clusters with controlled size, as small as 30 nm and up to 100 nm, that contain only small amounts of polymeric stabilizers. The assembly is kinetically coin rolled with weakly adsorbing polymers, PLA(2K)-b-PEG(10K)-h-PLA(2K) or PEG (MW = 3350), by manipulating electrostatic, van der Waals (VDW), steric, and depletion forces. The cluster size and optical properties are tuned as a function of particle volume fractions and polymer/gold ratios to modulate the interparticle interactions. The close spacing between the constituent gold nanoparticles and high gold loadings (80-85 w/w gold) produce a strong absorbance cross section of similar to 9 x 10(-15) m(2) in the NIR at 700 nm. This morphology results from VDW and depletion attractive interactions that exclude the weakly adsorbed polymeric stabilizer from the cluster interior. The generality of this kinetic assembly platform is demonstrated for gold nanoparticles with a range of surface charges from highly negative to neutral with the two different polymers.
J. M. Tam, Engstrom, J. D., Ferrer, D., Williams, R. O., and Johnston, K. P., “Templated Open Flocs of Anisotropic Particles for Pulmonary Delivery with Pressurized Metered Dose Inhalers,” Journal of Pharmaceutical Sciences, vol. 99, pp. 3150-3165, 2010. Publisher's VersionAbstract
The challenges in forming stable drug suspensions in hydrofluoroalkane (HFA) propellants have limited drug dosages and efficiency of drug delivery with pressurized metered dose inhalers (pMDI). Herein, stable suspensions of weakly flocculated particles, in the shape of thin plates or needles, of a poorly water-soluble drug, itraconazole (Itz), are efficiently delivered by pMDI at high doses, up to 2.4 mg/actuation. These anisotropic particles pack inefficiently and form low-density flocs that stack upon each other to prevent settling. In contrast, spherical particles formed dense aggregates that settled within minutes. Upon actuation of the pMDI, atomized propellant droplets shear apart and thus template the highly friable flocs. Evaporation of the HFA compacts the flocs to yield porous particles with optimal aerodynamic properties. High fine particle fractions (49-64%) were achieved with the stable suspensions for drug loadings up to 50 mg/mL. Furthermore, the micron-sized particles, ideal for pulmonary delivery, are composed of nanoparticles that dissociate and facilitate rapid dissolution of poorly water-soluble drugs. Pulmonary delivery of stable suspensions of templated, open flocs is broadly applicable to a range of anisotropic particle morphologies for poorly water-soluble drugs and proteins for efficient delivery of high doses, up to several milligrams, using minimal amounts of excipients. (C) 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3150-3165, 2010
M. A. Miller, Engstrom, J. D., Ludher, B. S., and Johnston, K. P., “Low Viscosity Highly Concentrated Injectable Nonaqueous Suspensions of Lysozyme Microparticles,” Langmuir, vol. 26, pp. 1067-1074, 2010. Publisher's VersionAbstract
Subcutaneous injection of concentrated protein and peptide solutions, in the range or 100-400 mg/mL, is often not possible with a 25- to 27-gauge needle, as the viscosity can be well above 50 cP. Apparent viscosities below this limit are reported for suspensions of milled lysozyme microparticles up to nearly 400 mg/mL in benzyl benzoate or benzyl benzoate mixtures with safflower oils through a syringe with a 25- to 27-gauge needle at room temperature. These apparent viscosities were confirmed using a cone-and-plate rheometer. The intrinsic viscosity regressed from the Kreiger-Dougherty model was only slightly above the Einstein value of 2.5, indicating the increase in viscosity relative to that of the solvent was caused primarily by the excluded volume. Thus, the increases in viscosity from electrical double layer interactions (electroviscous effects), solvation of the particles, or deviations of the particle shape from a spherical geometry were minimal, and much smaller than typically observed for proteins dissolved in aqueous Solutions. The small electroviscous effects are expected given the negligible zeta potential and thin double layers in the low dielectric constant organic solvent. The Suspensions were resuspendable after a year, with essentially constant particle size after two months as measured by static light scattering. The lower apparent viscosities for highly concentrated protein suspensions relative to protein Solutions, coupled With these favorable characteristics upon resuspension, may offer novel opportunities for Subcutaneous injection of therapeutic proteins.
X. Chen, Adkins, S. S., Nguyen, Q. P., Sanders, A. W., and Johnston, K. P., “Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant,” Journal of Supercritical Fluids, vol. 55, pp. 712-723, 2010. Publisher's VersionAbstract
Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)similar to(4.5)-(ethylene oxide)similar to(8) (2EN-PO(4.5)-EO(8)) at the planar water-CO(2) interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 degrees C and 6.9 to 27.6 MPa. A CO(2) captive bubble technique has been developed to measure the interfacial tension gamma at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO(2) interface. The surface pressure (gamma(o)-gamma) decreases modestly with density at constant temperature as CO(2) solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO(2)-water interface determined from the Gibbs adsorption equation decreases from 250 A(2)/molecule at 24 degrees C and 6.9 MPa. to 200 A(2)/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller gamma(o) driving force for surfactant adsorption. For systems with added NaCl, gamma decreases with salinity at low CO(2) densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO(2) and raises gamma. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO(2)-philic in that it partitions primarily into the CO(2) phase versus the water phase at CO(2) densities above 0.8 g/ml, and produces gamma values below 1 mN/m. With this small gamma, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO(2) densities, whereas macroemulsions were formed at other conditions. (C) 2010 Published by Elsevier B.V.
C. Kotsmar, Yoon, K. Y., Yu, H. Y., Ryoo, S. Y., Barth, J., Shao, S., Prodanovic, M., Milner, T. E., Bryant, S. L., Huh, C., and Johnston, K. P., “Stable Citrate-Coated Iron Oxide Superparamagnetic Nanoclusters at High Salinity,” Industrial & Engineering Chemistry Research, vol. 49, pp. 12435-12443, 2010. Publisher's VersionAbstract
Superparamagnetic nanoclusters may be used in imaging in biomedicine and in mapping of petroleum reservoirs, by generating either ultrasonic or acoustic signals with oscillating magnetic motion For a given magnetization per weight of iron oxide, nanoclusters with diameters from 20 to 100 nm experience a much larger magnetic force than that of the primary sub-10-nm primary particles Aqueous dispersions of 0 1 wt % superparamagnetic iron oxide nanoclusters were stabilized with citric acid on the particle surface, with a high loading of 90% iron oxide The dispersions were stable for months even with high salt concentrations up to 4 wt % at a pH of 6 and 8 based on the hydrodynamic diameter from dynamic light scattering The citrate ligands provide electrostatic repulsion, as characterized by the zeta potential The small size of the clusters, superparamagnetic properties, and high salt tolerance are highly beneficial in various applications including the mapping of petroleum reservoirs with magnetomotive techniques
E. Torino, Reverchon, E., and Johnston, K. P., “Carbon dioxide/water, water/carbon dioxide emulsions and double emulsions stabilized with a nonionic biocompatible surfactant,” Journal of Colloid and Interface Science, vol. 348, pp. 469-478, 2010. Publisher's VersionAbstract
Whereas microemulsions and emulsions of water and carbon dioxide have been reported for various surfactants with fluorocarbon surfactants, relatively few studies have been successful in forming these emulsions with hydrocarbon surfactants. Stable CO(2)/water and water/CO(2) emulsions with droplets smaller than 1 mu m were formed at high shear with the nonionic surfactant polysorbate 80 (Tween 80). In order to understand the emulsion phase behavior at high shear, low shear phase behavior experiments were performed at the same temperature and pressure. For pressures up to 250 bar and temperatures of 25-60 degrees C, C/W emulsions were formed for water concentrations as low as 10%, as the surfactant is highly hydrophilic with limited CO(2)-philicity. However, with added NaCl, the surfactant partitioned away from water toward CO(2), and W/C emulsions were formed with droplet sizes from a few 100 nm to a few mu m in diameter, which were stable for at least 24 h. In addition C/W/C double emulsions are reported for the first time, as well as W/C/W/C triple emulsions. The ability to form emulsions with environmentally benign solvents, CO(2) and water, and biocompatible surfactants is desirable for green reaction and separation processes, as well as production of materials including pharmaceutical particles and composites. Published by Elsevier Inc.
A. S. Paranjape, Kuranov, R., Baranov, S., Ma, L. L., Villard, J. W., Wang, T. Y., Sokolov, K. V., Feldman, M. D., Johnston, K. P., and Milner, T. E., “Depth resolved photothermal OCT detection of macrophages in tissue using nanorose,” Biomedical Optics Express, vol. 1, pp. 2-16, 2010. Publisher's VersionAbstract
Application of photothermal Optical Coherence Tomography (OCT) to detect macrophages in ex vivo rabbit arteries which have engulfed nanoclusters of gold coated iron oxide (nanorose) is reported. Nanorose engulfed by macrophages associated with atherosclerotic lesions in rabbit arteries absorb incident laser (800nm) energy and cause optical pathlength (OP) variation which is measured using photothermal OCT. OP variation in polydimethyl siloxane tissue phantoms containing varying concentrations of nanorose match values predicted from nanoparticle and material properties. Measurement of OP variation in rabbit arteries in response to laser excitation provides an estimate of nanorose concentration in atherosclerotic lesions of 2.5x10(9) particles/ml. OP variation in atherosclerotic lesions containing macrophages taking up nanorose has a different magnitude and profile from that observed in control thoracic aorta without macrophages and is consistent with macrophage presence as identified with RAM-11 histology staining. Our results suggest that tissue regions with macrophages taking up nanorose can be detected using photothermal OCT. (C) 2010 Optical Society of America
J. M. Tam, Tam, J. O., Murthy, A., Ingram, D. R., Ma, L. L., Travis, K., Johnston, K. P., and Sokolov, K. V., “Controlled Assembly of Biodegradable Plasmonic Nanoclusters for Near-Infrared Imaging and Therapeutic Applications,” Acs Nano, vol. 4, pp. 2178-2184, 2010. Publisher's VersionAbstract
Metal nanoparticles with surface plasmon resonance (SPR) in the near-infrared region (NIR) are of great interest for imaging and therapy. Presently, gold nanoparticles with NIR absorbance are typically larger than 50 nm, above the threshold size of similar to 5 nm required for efficient renal clearance. As these nanoparticles are not biodegradable, concerns about long-term toxicity have restricted their translation into the clinic. Here, we address this problem by developing a flexible platform for the kinetically controlled assembly of sub-5 nm ligand-coated gold particles to produce metal/polymer biodegradable nanoclusters smaller than 100 nm with strong NIR absorbance for multimodal application. A key novel feature of the proposed synthesis is the use of weakly adsorbing biodegradable polymers that allows tight control of nanocluster size and, in addition, results in nanoclusters with unprecedented metal loadings and thus optical functionality. Over time, the biodegradable polymer stabilizer degrades under physiological conditions that leads to disassembly of the nanoclusters into sub-5 nm primary gold particles which are favorable for efficient body clearance. This synthesis of polymer/inorganic nanoclusters combines the imaging contrast and therapeutic capabilities afforded by the NIR-active nanoparticle assembly with the biodegradability of a polymer stabilizer.
H. Uchida, Patel, M. N., May, R. A., Gupta, G., Stevenson, K. J., and Johnston, K. P., “Highly-ordered mesoporous titania thin films prepared via surfactant assembly on conductive indium-tin-oxide/glass substrate and its optical properties,” Thin Solid Films, vol. 518, pp. 3169-3176, 2010. Publisher's VersionAbstract
Highly ordered mesoporous titanium dioxide (titania. TiO(2)) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO(2) buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO(2) buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO(2)-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO(2) buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO(2) film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO(2) (similar to 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications. (C) 2009 Elsevier By. All rights reserved.
S. S. Adkins, Chen, X., Chan, I., Torino, E., Nguyen, Q. P., Sanders, A. W., and Johnston, K. P., “Morphology and Stability of CO2-in-Water Foams with Nonionic Hydrocarbon Surfactants,” Langmuir, vol. 26, pp. 5335-5348, 2010. Publisher's VersionAbstract
The morphologies, stabilities, and viscosities of high-pressure carbon dioxide-in-water (C/W) foams (emulsions) formed with branched nonionic hydrocarbons surfactants were investigated by in situ optical microscopy and capillary rheology. Over two dozen hydrocarbon surfactants were shown to stabilize C/W foams with Sauter mean bubble diameters as low as 1 to 2 mu m. Coalescence of the C/W foam bubbles was rare for bubbles larger than about 0.5 mu m over a 60 h time frame, and Oswald ripening became very slow. By better blocking of the CO, and water phases with branched and double-tailed surfactants. the in tension decreases, the surface pressure increases, and the C/W foams become very stable. For branched surfactants with propylene oxide middle groups. the stabilities were markedly lower for foams and decane water emulsions. The greater stability of the C/W foams to coalescence may be attributed to a smaller capillary pressure, lower drainage rates, and a sufficient surface pressure and thus limiting surface elasticity, plus small film sizes, to hinder spatial and surface density fluctuations that lead to coalescence. Unexpectedly, the foams were stable even when the surfactant favored the CO2 phase over the water phase, in violation of Baneroft’s rule. This unusual behavior is influenced by the low drainage rate, which makes Marangoni stabilization of less consequence and the strong tendency of emerging holes in the lamella to close as a result of surfactant tail flocculation in CO2. The high distribution coefficient toward CO2 versus water is of significant practical interest for mobility control in CO2 sequestration and enhanced oil recovery by foam formation.
M. Mehrmohammadi, Ma, L. L., Chen, Y. S., Qu, M., Joshi, P., Chen, R. M., Johnston, K. P., and Emelianov, S., “Combined photothermal therapy and magneto-motive ultrasound imaging using multifunctional nanoparticles,” in Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications Vii, vol. 7574, A. N. Cartwright and Nicolau, D. V., Ed. 2010. Publisher's VersionAbstract
Photothermal therapy is a laser-based non-invasive technique for cancer treatment. Photothermal therapy can be enhanced by employing metal nanoparticles that absorb the radiant energy from the laser leading to localized thermal damages. Targeting of nanoparticles leads to more efficient uptake and localization of photoabsorbers thus increasing the effectiveness of the treatment. Moreover, efficient targeting can reduce the required dosage of photoabsorbers; thereby reducing the side effects associated with general systematic administration of nanoparticles. Magnetic nanoparticles, due to their small size and response to an external magnetic field gradient have been proposed for targeted drug delivery. In this study, we investigate the applicability of multifunctional nanoparticles (e.g., magneto-plasmonic nanoparticles) and magneto-motive ultrasound imaging for image-guided photothermal therapy. Magneto-motive ultrasound imaging is an ultrasound based imaging technique capable of detecting magnetic nanoparticles indirectly by utilizing a high strength magnetic field to induce motion within the magnetically labeled tissue. The ultrasound imaging is used to detect the internal tissue motion. Due to presence of the magnetic component, the proposed multifunctional nanoparticles along with magneto-motive ultrasound imaging can be used to detect the presence of the photo absorbers. Clearly the higher concentration of magnetic carriers leads to a monotonic increase in magneto-motive ultrasound signal. Thus, magneto-motive ultrasound can determine the presence of the hybrid agents and provide information about their location and concentration. Furthermore, the magneto-motive ultrasound signal can indicate the change in tissue elasticity - a parameter that is expected to change significantly during the photothermal therapy. Therefore, a comprehensive guidance and assessment of the photothermal therapy may be feasible through magneto-motive ultrasound imaging and magneto-plasmonic nanoparticles.
M. N. Patel, Wang, X. Q., Wilson, B., Ferrer, D. A., Dai, S., Stevenson, K. J., and Johnston, K. P., “Hybrid MnO2-disordered mesoporous carbon nanocomposites: synthesis and characterization as electrochemical pseudocapacitor electrodes,” Journal of Materials Chemistry, vol. 20, pp. 390-398, 2010. Publisher's VersionAbstract
MnO2-mesoporous carbon hybrid nanocomposites were synthesized to achieve high values of redox pseudocapacitance at scan rates of 100 mV s(-1). High-resolution transmission electron microscopy (HRTEM) along with energy dispersive X-ray spectroscopy (EDX) demonstrated that similar to 1 nm thick MnO2 nanodomains, resembling a conformal coating, were uniformly distributed throughout the mesoporous carbon structure. HRTEM and X-ray diffraction (XRD) showed formation of MnO2 nanocrystals with lattice planes corresponding to birnessite. The electrochemical redox pseudocapacitance of these composite materials in aqueous 1 M Na2SO4 electrolyte containing as little as 2 wt% MnO2 exhibited a high gravimetric MnO2 pseudocapacitance (C-MnO2) of 560 F g(MnO2)(-1). Even for 30 wt% MnO2, a high C-MnO2 of 137 F g(MnO2)(-1) was observed at 100 mV s(- 1). Sodium ion diffusion coefficients on the order of 10(-9) to 10(-10) cm(2) s(-1) were measured using chronoamperometry. The controlled growth and conformal coating of redox-active MnO2-mesoporous carbon composites offer the potential for achieving high power energy storage with low cost materials.
T. Y. Wang, Qiu, J. Z., Ma, L. L., Li, X. K., Sun, J. J., Ryoo, S., Johnston, K. P., Feldman, M. D., and Milner, T. E., “Nanorose and Lipid Detection in Atherosclerotic Plaque Using Dual-wavelength Photothermal Wave Imaging,” in Optical Interactions with Tissues and Cells Xxi, vol. 7562, E. D. Jansen and Thomas, R. J., Ed. 2010. Publisher's VersionAbstract
Atherosclerosis and specifically rupture of vulnerable plaques account for 23% of all deaths worldwide, far surpassing both infectious diseases and cancer. In atherosclerosis, macrophages can infiltrate plaques which are often associated with lipid deposits. Photothermal wave imaging is based on the periodic thermal modulation of a sample using intensity modulated light. Intensity modulated light enters the sample and is absorbed by targeted chromophores and generates a periodic thermal modulation. We report use of photothermal wave imaging to visualize nanoroses (taken up by macrophages via endocytosis) and lipids in atherosclerotic plaques. Two excitation wavelengths were selected to image nanoroses (800 nm) and lipids (1210 nm). Atherosclerotic plaque in a rabbit abdominal artery was irradiated (800 nm and 1210 nm separately) at a frequency of 4 Hz to generate photothermal waves. The radiometric temperature at the tissue surface was recorded by an infrared (IR) camera over a 10 second time period at the frame rate of 25.6 Hz. Extraction of images (256 x 256 pixels) at various frequencies was performed by Fourier transform at each pixel. Frequency amplitude images were obtained corresponding to 800 nm and 1210 nm laser irradiation. Computed images suggest that the distributions of both nanorose and lipid can be identified in amplitude images at a frequency of 4 Hz. Nanoroses taken up by macrophages are distributed at the edges of lipid deposits. Observation of high concentration of nanoroses in atherosclerotic plaque confirms that nanoroses are present at locations associated with lipid deposits.
D. A. Slanac, Li, L., Stevenson, K. J., and Johnston, K. P., “Stable Oxygen Reduction Electrocatalysts from Presynthesized PdPt Nanoparticles on Carbon,” in Polymer Electrolyte Fuel Cells 10, Pts 1 and 2, vol. 33, H. A. Gasteiger, Weber, A., Strasser, P., Edmundson, M., Lamy, C., Darling, R., Uchida, H., Schmidt, T. J., Shirvanian, P., Buchi, F. N., Mantz, R., Zawodzinski, T., Ramani, V., Fuller, T., Inaba, M., Jones, D., and Narayanan, S. R., Ed. 2010, pp. 161-170. Publisher's VersionAbstract
We have synthesized an oxygen reduction catalyst composed of pre-synthesized Pd3Pt2 alloy nanoparticles dispersed on Vulcan carbon. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicate the alloy particles are 4.0nm. The catalyst loses 20% of its activity after potential cycling from 0.5 V to 1.2 V (NHE) in HClO4 compared to 70% for commercial Pt/VC. Even after 20% loss, the final activity of the Pd3Pt2/VC catalyst is 0.095 A/mg(Pt), equal to that of the fresh commercial Pt/VC. After cycling TEM shows only a small increase in particle size to 4.5nm, and X-ray photoelectron spectroscopy reveals no change in the oxidation states of the metals, indicating the stability may result from an increased dissolution resistance of the alloy relative to the base metals. The development of well-defined, stable, and active alloy catalysts facilitates a better understanding of structure-activity relationships and is encouraging for the application of commercially viable fuel cells.
J. O. Tam, Tam, J. M., Murthy, A., Ingram, D., Ma, L. L., Travis, K., Johnston, K. P., and Sokolov, K., “Biodegradable Near-Infrared Plasmonic Nanoclusters for Biomedical Applications,” in Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications Ii, vol. 7576, S. Achilefu and Raghavachari, R., Ed. 2010. Publisher's VersionAbstract
Nanoparticles such as gold and silver with plasmonic resonances in the near-infrared (NIR) optical region, where soft tissue is the most transparent, are of great interest in biomedical applications. A major roadblock in translation of inorganic nanoparticles to clinical practice for systemic targeting of disease is their non-biodegradable nature. In addition, gold nanoparticles that absorb in the NIR are typically greater than 50 nm, which is above the threshold size of 5.5 nm required for effective excretion from the body. Here we describe a new class of biodegradable gold nanoparticles with plasmon resonances in the NIR region. The synthesis is based on controlled assembly of very small (less than 5 nm) primary gold particles into nanoclusters with sub-100 nm overall diameter and an intense NIR absorbance. The assembly is mediated by biodegradable polymers, polyethylene glycol (PEG) and polylactic acid (PLA) copolymer, and small capping ligands on the constituent nanoparticles. Nanoclusters deaggregate into sub-5nm primary gold particles upon biodegradation of the polymer binder in live cells over one week, as shown by dark-field reflectance and hyperspectral imaging.
J. O. Tam, Tam, J. M., Murthy, A., Ingram, D., Ma, L. L., Travis, K., Johnston, K. P., and Sokolov, K., “Biodegradable Near-Infrared Plasmonic Nanoclusters for Biomedical Applications,” in Plasmonics in Biology and Medicine Vii, vol. 7577, T. VoDinh and Lakowicz, J. R., Ed. 2010. Publisher's VersionAbstract
Nanoparticles such as gold and silver with plasmonic resonances in the near-infrared (NIR) optical region, where soft tissue is the most transparent, are of great interest in biomedical applications. A major roadblock in translation of inorganic nanoparticles to clinical practice for systemic targeting of disease is their non-biodegradable nature. In addition, gold nanoparticles that absorb in the NIR are typically greater than 50 nm, which is above the threshold size of 5.5 nm required for effective excretion from the body. Here we describe a new class of biodegradable gold nanoparticles with plasmon resonances in the NIR region. The synthesis is based on controlled assembly of very small (less than 5 nm) primary gold particles into nanoclusters with sub-100 nm overall diameter and an intense NIR absorbance. The assembly is mediated by biodegradable polymers, polyethylene glycol (PEG) and polylactic acid (PLA) copolymer, and small capping ligands on the constituent nanoparticles. Nanoclusters deaggregate into sub-5nm primary gold particles upon biodegradation of the polymer binder in live cells over one week, as shown by dark-field reflectance and hyperspectral imaging.

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