Harold G. Monbouquette

Nanoparticle-assisted high photoconductive gain in composites of polymer and fullerene

Polymer-inorganic nanocrystal composites offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility and distribution of the nanocrystals in the polymer matrices. Here we show that blending CdTe nanoparticles into a polymer-fullerene matrix followed by solvent annealing can achieve high photoconductive gain under low applied voltages. The surface capping ligand renders the nanoparticles highly soluble in the polymer blend, thereby enabling high CdTe loadings. An external quantum efficiency as high as approximately 8,000% at 350 nm was achieved at -4.5 V. Hole-dominant devices coupled with atomic force microscopy images show a higher concentration of nanoparticles near the cathode-polymer interface. The nanoparticles and trapped electrons assist hole injection into the polymer under reverse bias, contributing to efficiency values in excess of 100%.

Vesicle Size Distributions Measured by Flow Field-Flow Fractionation Coupled with Multiangle Light Scattering

The separation method, flow field-flow fractionation (flow FFF), is coupled on-line with multiangle laser light scattering (MALLS) for simultaneous measurement of the size and concentration of vesicles eluting continuously from the fractionator. These size and concentration data, gathered as a function of elution time, may be used to construct both number- and mass-weighted vesicle size distributions. Unlike most competing, noninvasive methods, this flow FFF/MALLS technique enables measurement of vesicle size distributions without a separate refractive index detector, calibration using particle size standards, or prior assumptions about the shape of the size distribution. Experimentally measured size distributions of vesicles formed by extrusion and detergent removal are non-Gaussian and are fit well by the Weibull distribution. Flow FFF/MALLS reveals that both the extrusion and detergent dialysis vesicle formation methods can yield nearly size monodisperse populations with standard deviations of approximately 8% about the mean diameter. In contrast to the rather low resolution of dynamic light scattering in analyzing bimodal systems, flow FFF/MALLS is shown to resolve vesicle subpopulations that differ by much less than a factor of two in mean size.

Silicon Wafer-Based Platinum Microelectrode Array Biosensor for Near Real-Time Measurement of Glutamate in Vivo

Using Micro-Electro-Mechanical-Systems (MEMS) technologies, we have developed silicon wafer-based platinum microelectrode arrays (MEAs) modified with glutamate oxidase (GluOx) for electroenzymatic detection of glutamate in vivo. These MEAs were designed to have optimal spatial resolution for in vivo recordings. Selective detection of glutamate in the presence of the electroactive interferents, dopamine and ascorbic acid, was attained by deposition of polypyrrole and Nafion. The sensors responded to glutamate with a limit of detection under 1μM and a sub-1-second response time in solution. In addition to extensive in vitro characterization, the utility of these MEA glutamate biosensors was also established in vivo. In the anesthetized rat, these MEA glutamate biosensors were used for detection of cortically-evoked glutamate release in the ventral striatum. The MEA biosensors also were applied to the detection of stress-induced glutamate release in the dorsal striatum of the freely-moving rat.

Patterning and templating for nanoelectronics.

The semiconductor industry will soon be launching 32 nm complementary metal oxide semiconductor (CMOS) technology node using 193 nm lithography patterning technology to fabricate microprocessors with more than 2 billion transistors. To ensure the survival of Moores law, alternative patterning techniques that offer advantages beyond conventional top-down patterning are aggressively being explored. It is evident that most alternative patterning techniques may not offer compelling advantages to succeed conventional top-down lithography for silicon integrated circuits, but alternative approaches may well indeed offer functional advantages in realising next-generation information processing nanoarchitectures such as those based on cellular, bioinsipired, magnetic dot logic, and crossbar schemes. This paper highlights and evaluates some patterning methods from the Center on Functional Engineered Nano Architectonics in Los Angeles and discusses key benchmarking criteria with respect to CMOS scaling.

Transient Extracellular Glutamate Events in the Basolateral Amygdala Track Reward-Seeking Actions

The ability to make rapid, informed decisions about whether or not to engage in a sequence of actions to earn reward is essential for survival. Modeling in rodents has demonstrated a critical role for the basolateral amygdala (BLA) in such reward-seeking actions, but the precise neurochemical underpinnings are not well understood. Taking advantage of recent advancements in biosensor technologies, we made spatially discrete near-real-time extracellular recordings of the major excitatory transmitter, glutamate, in the BLA of rats performing a self-paced lever-pressing sequence task for sucrose reward. This allowed us to detect rapid transient fluctuations in extracellular BLA glutamate time-locked to action performance. These glutamate transients tended to precede lever-pressing actions and were markedly increased in frequency when rats were engaged in such reward-seeking actions. Based on muscimol and tetrodotoxin microinfusions, these glutamate transients appeared to originate from the terminals of neurons with cell bodies in the orbital frontal cortex. Importantly, glutamate transient amplitude and frequency fluctuated with the value of the earned reward and positively predicted lever-pressing rate. Such novel rapid glutamate recordings during instrumental performance identify a role for glutamatergic signaling within the BLA in instrumental reward-seeking actions.

Shear-induced permeability changes in a polymer grafted silica membrane

Abstract The hydrodynamic response of a graft-polymerized membrane was demonstrated for a microporous silica-poly(vinylpyrrolidone) (silica-PVP) membrane. The membrane pores were modified by graft polymerizing vinyl pyrrolidone onto the membrane pore surface, resulting in a polymer surface layer of covalently tethered polymer chains. The hydraulic permeability of the modified membrane increased with increasing transmembrane pressure owing to flow-induced deformation of the grafted polymer chains. The dynamics of the modified pores was investigated by membrane hydraulic permeability studies along with a two-region hydrodynamic pore flow model. The thickness of the grafted polymer layer decreased with increasing pore-wall shear rate by up to about 47%, relative to the thickness at the zero shear limit, depending on the surface density and length of the grafted chains. Although the effective pore size of the polymer-grafted membrane was reduced by 5–36% (at the zero shear rate limit), about 18–59% of the pore size loss was regained at high pore-wall shear rates. Increasing the degree of shear-induced permeability change is feasible by increasing the ratio of the polymer chain length/pore size ratio as well as the surface density of the grafted polymer phase. The present results suggest that hydrodynamic pore size control could provide an additional useful degree of freedom in operating polymer-modified filtration membranes.

Identification and characterization of a novel ferric reductase from the hyperthermophilic Archaeon Archaeoglobus fulgidus.

Archaeoglobus fulgidus, a hyperthermophilic sulfate-reducing Archaeon, contains high Fe3+-EDTA reductase activity in its soluble protein fraction. The corresponding enzyme, which constitutes about 0.75% of the soluble protein, was purified 175-fold to homogeneity. Based on SDS-polyacrylamide gel electrophoresis, the ferric reductase consists of a single subunit with a M r of 18,000. TheM r of the native enzyme was determined by size exclusion chromatography to be 40,000 suggesting that the native ferric reductase is a homodimer. The enzyme uses both NADH and NADPH as electron donors to reduce Fe3+-EDTA. Other Fe3+complexes and dichlorophenolindophenol serve as alternative electron acceptors, but uncomplexed Fe3+ is not utilized. The purified enzyme strictly requires FMN or FAD as a catalytic intermediate for Fe3+ reduction. Ferric reductase also reduces FMN and FAD, but not riboflavin, with NAD(P)H which classifies the enzyme as a NAD(P)H:flavin oxidoreductase. The enzyme exhibits a temperature optimum of 88 °C. When incubated at 85 °C, the enzyme activity half-life was 2 h. N-terminal sequence analysis of the purified ferric reductase resulted in the identification of the hypothetical gene, AF0830, of the A. fulgidusgenomic sequence. The A. fulgidus ferric reductase shares amino acid sequence similarity with a family of NAD(P)H:FMN oxidoreductases but not with any ferric reductases suggesting that theA. fulgidus ferric reductase is a novel enzyme.

The permeability behavior of polyvinylpyrrolidone-modified porous silica membranes

Abstract The surface of 4100 A-pore-size silica membranes was modified with a covalently bonded polyvinyl-pyrrolidone brush layer by a novel graft polymerization process. Hydraulic permeability measurements performed with six different solvents and both unmodified and modified membranes suggest that the permeability of the modified membrane is determined by the configuration of the terminally anchored polymer chains. In the modified ceramic-supported polymeric (CSP) membrane, the swelling of the polymer brush layer increases as the solvent power increases, resulting in a decrease in the pore radius and subsequently, the permeability.

Characterization of vesicles by classical light scattering

Abstract Classical, or static, light scattering techniques can be used to determine the geometric size, shape, apparent molecular weight, and radius of gyration of phosphatidylcholine vesicles in aqueous suspension. A Rayleigh-Gans-Debye (RGD) analysis of multiangle scattered light intensity data yields the size and degree of polydispersity of the vesicles in solution, while the Zimm plot technique provides the radius of gyration and apparent weight-average molecular weight. Together RGD theory and Zimm plots can be used to confirm the geometric shape of vesicles. Vesicles varying from 65 to 90 nm in diameter have been characterized effectively. The static light scattering measurements indicate that, as expected, phosphatidylcholine vesicles in this size range scatter light as isotropic hollow spheres. This dual treatment of the static light scattering data also provides an internal, self-consistent check of the vesicle size determination. The values for geometric radii determined by classical light scattering typically agree with those estimated by dynamic light scattering to within a few percent.

Photocatalytic reduction of aromatic azides to amines using CdS and CdSe nanoparticlesElectronic supplementary information (ESI) available: The preparation of CdS and CdSe nanoparticles, the synthesis of aromatic azides, procedures for the photocatalyzed reduction of aromatic azides, and procedures for the quantum yield measurements. See http://www.rsc.org/suppdata/pp/b4/b404268a/

We have shown that CdS and CdSe nanoparticles can act as very efficient and highly chemoselective photocatalysts for the reduction of aromatic azides to aromatic amines. In several cases, the reaction proceeds with quantum yields near 0.5, which approaches the theoretical maximum for a two-electron process. The wide scope of the reaction was confirmed with compounds containing electron withdrawing (-NO(2), CO(2)R, COR) and electron donating groups (-OMe, -R, -Cl) at the para-, meta-, and ortho-positions. Remarkably, the reaction is relatively insensitive to the electron demands of the substituent. However, azides with meta-substituents give slightly lower yields than those with the same substituent at the ortho- or para-position.