Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO2 interactions and the influence of adsorbate polarity upon adsorption isotherms for mesoporous TiO2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Psi and Delta when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data. This approach reveals that mesoporous TiO2 films of similar to 200 nm thickness and similar to 10 nm pore diameter can be loaded with 1.7 nm diameter Pt and 3.9 nm diameter Au nanoparticles up to 26 and 21 wt %, respectively. The BET surface area of a representative mesoporous TiO2 sample using toluene as the adsorbate was found to be 44 m(2)/g with a mean pore diameter of 8.8 nm. EP and XPS depth profiling experiments indicate that 1.7 nm diameter Pt nanoparticles are well dispersed through the mesoporous TiO2 film, while 3.9 nm diameter Au nanoparticles are concentrated at the top of the film, blocking a significant portion of the available TiO2 pore volume. UV irradiation of the TiO2 films indicates that adsorbate-TiO2 interactions and surface wetting effects can play a critical role in the resulting isotherm and in evaluation of PSD.
Ultrasound is a widely used modality with excellent spatial resolution, low cost, portability, reliability and safety. In clinical practice and in the biomedical field, molecular ultrasound-based imaging techniques are desired to visualize tissue pathologies, such as cancer. In this paper, we present an advanced imaging technique - combined photoacoustic and magneto-acoustic imaging - capable of visualizing the anatomical, functional and biomechanical properties of tissues or organs. The experiments to test the combined imaging technique were performed using dual, nanoparticle-based contrast agents that exhibit the desired optical and magnetic properties. The results of our study demonstrate the feasibility of the combined photoacoustic and magneto-acoustic imaging that takes the advantages of each imaging techniques and provides high sensitivity, reliable contrast and good penetrating depth. Therefore, the developed imaging technique can be used in wide range of biomedical and clinical application.
Aqueous suspensions of crystalline naproxen nanoparticles, formed by antisolvent precipitation, were flocculated with sodium sulfate, filtered, and dried to form redispersible powders for oral delivery. The particles were stabilized with polyvinylpyrrolidone (PVP K-15) and/or poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (poloxamer 407). The yield of the drug in the powder was typically 92-99%, and the drug loading was reproducible to within 1-2%. The filtration process increased the drug loading by up to 61% relative to the initial value, as unbound surfactant was removed with the filtrate. Upon redispersion of the dried powder, the average particle size measured by light scattering was comparable to the original value in the aqueous suspension prior to flocculation, and consistent with primary particle sizes observed by scanning electron microscopy (SEM). For 300-nm particles, up to 95% of the drug dissolved in 2 min. The dissolution rate was correlated linearly with the specific surface area calculated from the average particle diameter after redispersion. The redispersion of dried powders was examined as a function of the salt concentration used for flocculation and the surfactant composition and concentration. Flocculation followed by filtration and drying is an efficient and highly reproducible process for the rapid recovery of drug nanoparticles to produce wettable powders with high drug loading and rapid dissolution.
The ability of 20-50 nm nanoparticles to target and modulate the biology of specific types of cells will enable major advancements in cellular imaging and therapy in cancer and atherosclerosis. A key challenge is to load an extremely high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. Herein we report similar to 30 nm stable uniformly sized near-infrared (NIR) active, superparamagnetic nanoclusters formed by kinetically controlled self-assembly of gold-coated iron oxide nanoparticles. The controlled assembly of nanocomposite particles into clusters with small primary particle spacings produces collective responses of the electrons that shift the absorbance into the NIR region. The nanoclusters of similar to 70 iron oxide primary particles with thin gold coatings display intense NIR (700-850 nm) absorbance with a cross section of similar to 10(-14) m(2). Because of the thin gold shells with an average thickness of only 2 nm, the r(2) spin-spin magnetic relaxivity is 219 mM(-1) s(-1), an order of magnitude larger than observed for typical iron oxide particles with thicker gold shells. Despite only 12% by weight polymeric stabilizer, the particle size and NIR absorbance change very little in delonized water over 8 months. High uptake of the nanoclusters by macrophages is facilitated by the dextran coating, producing intense NIR contrast in dark field and hyperspectral microscopy, both in cell culture and an in vivo rabbit model of atherosclerosis. Small nanoclusters with optical, magnetic, and therapeutic functionality, designed by assembly of nanciparticle building blocks, offer broad opportunities for targeted cellular imaging, therapy, and combined imaging and therapy.
The activity of oxygen reduction catalysts for fuel cells often decreases markedly (30-70%) during potential cycling tests designed to accelerate catalyst degradation. Herein we achieved essentially no loss in electrochemical surface area and catalyst activity during potential cycling from 0.5 to 1.2 V for presynthesized Pt-Cu nanoparticles of controlled composition that were infused into highly graphitic disordered mesoporous carbons (DMC). The high stability is favored by the strong metal-support interactions and low tendency for carbon oxidation, which mitigates the mechanisms of degradation. Electrochemical dealloying transforms the composition from Pt20Cu80 to Pt85Cu15 with a strained Pt-rich shell, which exhibits an enhanced ORR activity of 0.46 A/mg(Pt), > 4 fold that of pure Pt catalysts. The high uniformity in particle size and composition both before and after dealloying, as a consequence of the presynthesis/infusion technique, is beneficial For elucidating the mechanism of catalyst activity and, ultimately, for designing more active catalysts.
Dry powders from aqueous dispersions, formed by antisolvent precipitation, dissolved to form solutions with supersaturation values up to 12 in 10 min at pH 6.8 with sodium dodecyl sulfate micelles. Itraconazole/hydroxypropylmethylcellulose (HPMC) aqueous particle dispersions were salt flocculated and filtered to produce medium surface area (2-5 m(2)/g) particles or lyophilized to produce high surface area (13-36 m(2)/g). Over 4 h, the decay in supersaturation was much slower for the medium surface area versus high surface area particles, since the smaller excess surface area of undissolved particles led to slower nucleation and growth from solution. A slow decay in supersaturation was also achieved by initially dissolving part of the drug at pH 1.2, and then shifting the pH to 6.8 thereby reducing the excess surface area of undissolved particles in the pH 6.8 media. This pH shift mimics the transition from stomach to intestines. The ability to generate and sustain high supersaturation at pH 6.8 by minimizing undissolved excess surface area may be expected to be beneficial for raising bioavailability by gastrointestinal delivery.
Particle engineering may be used to improve the physicochemical properties of many new chemical entities to enhance the bioavailability. In "bottom up" technologies, particles may be formed by precipitation to control physicochemical properties including the particle size, surface characteristics, morphology, and crystallinity. This review, provides an overview of various precipitation technologies used in pharmaceutical development. but highlights rapid freezing technologies, with emphasis on thin film freezing (TFF). In thin film freezing, the particle morphology may be controlled by manipulating the fluid dynamics and heat tran, fer properties upon spreading and freezing of liquid droplets on solid surfaces. Finally, in vitro and in vivo studies utilizing TFF are, reviewed to emphasize the potential benefits of this technology in improving drug performance.
In this work, the history of colloids in supercritical fluids in the last two decades and future directions in several promising areas are discussed. The primary focus of this article is on microemulsions and emulsions, although new developments are described involving protein colloids, electrostatic stabilization of inorganic particles and the use of CO(2) as an antisolvent for separation of metal colloids. The focus on the CO(2)-water interface is related to the fact that, historically, the studies of colloids in supercritical fluids began with microemulsions and emulsions, and then evolved to polymer latexes and inorganic dispersions. Moreover, many of the same types of stabilizers have been used for the various types of colloids. (C) 2008 Published by Elsevier B.V.
We have investigated different methods for removing the HF/CO2 post-etch residues from blanket and patterned wafers of borophosphosilicate glass. The use of co-solvents, rinsing the residues with DI water followed by CO2-based drying process, and the use of water-in-CO2 (W/C) microemulsions were explored as possible methods to remove the etch residues. It was found that the addition of co-solvents were ineffective for quantitative removal of residues, whereas rinsing the etch residues with DI water followed by the surfactant-aided scCO(2) drying was found to be effective. To eliminate the pure water rinsing step, W/C microemulsions formed with different surfactants were directly treated with residues. While ionic surfactants such as ammonium carboxylate perfluoropolyether and sodium salt of bis (1H,1H,2H,2H-trideca-fluoro-octyl)-2-sulfosuccinate did not produce stable microemulsions in the presence of HF, due to protonation effect, the reverse micelles formed with an amphiphilic block copolymeric surfactant, poly(ethylene oxide-b-perfluorooctylmethacrylate), was found to be highly efficient as clean and residue-free images were observed by microscopic analysis. (c) 2008 Elsevier B.V. All rights reserved