James D. Batteas

Ultrasensitive Copper(II) Detection Using Plasmon-Enhanced and Photo-Brightened Luminescence of CdSe Quantum Dots

Here, we present a simple platform for the use of the enhanced emission of 16-mercaptohexadecanoic acid (16-MHA) capped CdSe quantum dots (QDs) as a probe for ultrasensitive copper(II) detection. In this study, the photoluminescence (PL) of the QDs was first enhanced by Ag nanoprisms which were self-assembled on Si surfaces and then further increased by photobrightening. Using this approach, the control and different analytes could be readily probed all on a single platform using fluorescence microscopy. The enhanced PL intensity of CdSe QDs was selectively quenched in the presence of Cu(2+), accompanied by the emergence of a new red-shifted luminescence band. The quenching mechanism was found to be due to a cation exchange mechanism as confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Herein, we have demonstrated that this simple methodology can offer a rapid and reliable detection of Cu(2+) with a detection limit as low as 5 nM and a dynamic range up to 100 muM in a fixed fast reaction time of 5 min. The potential applications of this technique were tested in two ways, for mixed-ion solutions and in physiological fluids, and both experiments exhibited good selectivity toward Cu(2+).

Porphyrin Tessellation by Design: Metal-Mediated Self-Assembly of Large Arrays and Tapes**

Twenty-one components self-assemble to form the large (ca. 25 nm2 ), planar porphyrin arrays of type 1: four dipyridylporphyrins, four tripyridylporphyrins, one tetrapyridylporphyrin, and twelve PdCl2 units.

Cutin deficiency in the tomato fruit cuticle consistently affects resistance to microbial infection and biomechanical properties, but not transpirational water loss

Plant cuticles are broadly composed of two major components: polymeric cutin and a mixture of waxes, which infiltrate the cutin matrix and also accumulate on the surface, forming an epicuticular layer. Although cuticles are thought to play a number of important physiological roles, with the most important being to restrict water loss from aerial plant organs, the relative contributions of cutin and waxes to cuticle function are still not well understood. Tomato (Solanum lycopersicum) fruits provide an attractive experimental system to address this question as, unlike other model plants such as Arabidopsis, they have a relatively thick astomatous cuticle, providing a poreless uniform material that is easy to isolate and handle. We identified three tomato mutants, cutin deficient 1 (cd1), cd2 and cd3, the fruit cuticles of which have a dramatic (95-98%) reduction in cutin content and substantially altered, but distinctly different, architectures. This cutin deficiency resulted in an increase in cuticle surface stiffness, and in the proportions of both hydrophilic and multiply bonded polymeric constituents. Furthermore, our data suggested that there is no correlation between the amount of cutin and the permeability of the cuticle to water, but that cutin plays an important role in protecting tissues from microbial infection. The three cd mutations were mapped to different loci, and the cloning of CD2 revealed it to encode a homeodomain protein, which we propose acts as a key regulator of cutin biosynthesis in tomato fruit.

Synthesis of CuPt Nanorod Catalysts with Tunable Lengths

Solution chemistry methods have been used to synthesize bimetallic CuPt alloy nanoparticle catalysts with controllable sizes and shapes. By variation of the relative ratios of the oleylamine and oleic acid stabilizers, solvent, and reduction rate, the nanoparticles could be tuned from approximately 2 nm spherical particles to nanorods with diameters of approximately 2.5 nm and aspect ratios tunable from 5:1 to 25:1. These mixed-metal nanoparticles show excellent catalytic properties for CO oxidation, with light-off temperatures that are nearly 200 K below those of conventional supported Pt catalysts.

Evaporation-Induced Assembly of Quantum Dots into Nanorings

Herein, we demonstrate the controlled formation of two-dimensional periodic arrays of ring-shaped nanostructures assembled from CdSe semiconductor quantum dots (QDs). The patterns were fabricated by using an evaporative templating method. This involves the introduction of an aqueous solution containing both quantum dots and polystyrene microspheres onto the surface of a planar hydrophilic glass substrate. The quantum dots became confined to the meniscus of the microspheres during evaporation, which drove ring assembly via capillary forces at the polystyrene sphere/glass substrate interface. The geometric parameters for nanoring formation could be controlled by tuning the size of the microspheres and the concentration of the QDs employed. This allowed hexagonal arrays of nanorings to be formed with thicknesses ranging from single dot necklaces to thick multilayer structures over surface areas of many square millimeters. Moreover, the diameter of the ring structures could be simultaneously controlled. A simple model was employed to explain the forces involved in the formation of nanoparticle nanorings.

The growth and structure of titanium oxide films on Pt(111) investigated by LEED, XPS, ISS, and STM

Titanium oxide films grown on Pt(111) have been investigated using LEED, XPS, ISS, and STM for coverages ranging from 1.0 to 5.0 ML. The oxide overlayers are prepared by vapor phase deposition of titanium metal followed by oxidation in 10−6 Torr O2. Partial dissolution of the overlayer into the Pt substrate occurs upon annealing to temperatures in excess of 500°C. Annealing in 1 × 10−6 Torr O2 at temperatures ranging from 500°C to 700°C leads to a three-fold symmetric structure with a unit cell of 18.2 A × 18.2 A. This structure is observed at coverages ranging from 1.0 to 5.0 ML. XPS measurements of this phase show the stoichiometry of TiO2. Heating in vacuum at 650°C to 850°C leads to a new structure with a unit cell of 18.2 A × 13.9 A which is observed at coverages of 1.0 to 1.5 ML. This oxide overlayer is shown by XPS to have the stoichiometry of Ti4O7. Similarities are observed between the ordered overlayers and reported structures of stoichiometric and reduced rutile TiO2 surfaces. Angle resolved XPS measurements of disordered titanium oxide films, formed by annealing at temperatures below 500°C, indicate that reduced Ti3+ is concentrated at the oxide /Pt(111) interface.

Dynamical LEED analyses of the Pt(111)-p(2× 2)-NO and the Ni(111)-c(4 × 2)-2NO structures: substrate relaxation and unexpected hollow-site adsorption

Abstract Dynamical LEED analyses of ordered structures of NO molecules chemisorbed on Pt(111) and on Ni(111) conclusively yield threefold-coordinated hollow-site adsorption and reasonable bond lengths. Both metal surfaces exhibit molecular induced substrate relaxations; those in Ni(111) are greater than those in Pt(111). The Pt(111)-p(2 × 2)-NO structure has NO adsorbed in a threefold fee site with a small buckling of the first metal layer. NO of the Ni(111)-c(4 × 2)-2NO structure is adsorbed in threefold fee and hep sites with a 0.16 A buckling of the first metal layer. The hollow-site adsorption on both metal surfaces invalidates long-standing bridge and top-site assignments based on vibrational spectroscopy measurements, calling that approach into question. The threefold hollow-site adsorption determined for these systems also contrasts with the lower coordinated bridge and top sites generally found for CO molecules on the same metal surfaces.

Using Patterned Arrays of Metal Nanoparticles to Probe Plasmon Enhanced Luminescence of CdSe Quantum Dots

Here we present a simple platform for probing plasmon enhanced photoluminescence (PL) of quantum dots by confocal microscopy. In this study, self-assembled monolayers of silane-derivative molecules were patterned onto the oxidized GaAs surfaces to direct the attachment of Au or Ag nanoparticles onto the surface. Following the directed binding of metal nanoparticles (MNPs), a layer-by-layer deposition of oppositely charged polymers was used to create films with varying thickness by controlling the numbers of deposited layers. CdSe quantum dots (QDs) of ∼4 and 5.5 nm in diameter with 16-mercaptohexadecanoic acid as a surfactant were then adsorbed onto the outermost polymer layer via electrostatic interactions. Using confocal fluorescence microscopy, the enhanced PL from the CdSe over the Au or Ag nanoparticle patterns could be imaged directly and scaled against the regions with no Au or Ag nanoparticles, and the luminescence of the GaAs (as an internal standard) for different CdSe-metal separations. By using a pattern, PL enhancement as a function of particle-CdSe spacing can be readily probed all on a single platform, where the QDs over MNPs and not over MNPs can be directly compared in the same dielectric environment. The observed luminescence as a function of metal-QD separation can be readily fit to a combined model of metal-fluorophore fluorescence quenching and local electric field enhancement.

Superhydrophobic Surfaces Formed Using Layer-by-Layer Self-Assembly with Aminated Multiwall Carbon Nanotubes

A convenient and simple route to functionalized multiwall carbon nanotubes (MWNTs) using the reaction of the amine (NH) groups of polyethyleneimine (PEI) with MWNTs in N,N-dimethylformamide (DMF) at 50 degrees C is described. The product functionalized MWNTs (MWNT-NH-PEI) contain 6-8% by weight PEI based on elemental analysis, thermal gravimetric analysis, and titration. The products form stable emulsions in water below pH 9 and can be derivatized to form alkylated MWNTs that are dispersible in organic media. Such MWNT-NH-PEI nanoparticles can also be used in covalent or ionic layer-by-layer assembly to form nanocomposite thin films on functionalized polyethylene (PE) films and powders. Such nanocomposite films were analyzed by contact angle analysis, atomic force microscopy (AFM), and confocal Raman microscopy. These analyses show that these superhydrophilic surfaces have micro/nanoroughness with a roughly uniform distribution of MWNT nanoparticles. Superhydrophobic PE films can be formed either from ionic layer-by-layer self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent layer-by-layer self-assembly of MWNT-NH-PEIs and Gantrez if the final graft is acrylated with a mixed anhydride prepared from ethyl chloroformate and octadecanoic acid. The resulting octadecylated surface produced by five covalent layer-by-layer deposition steps has a water contact angle of 165 degrees and a sliding angle of less than 5 degrees. The corresponding surface produced by five ionic layer-by-layer deposition steps has a water contact angle of 155 degrees but exhibits water pinning. The ionically assembled nanocomposite graft is labile under acidic conditions. The covalently assembled graft is more chemically robust.

The Influence of Water on the Nanomechanical Behavior of the Plant Biopolyester Cutin as Studied by AFM and Solid-State NMR

Atomic force microscopy and solid-state nuclear magnetic resonance have been used to investigate the effect of water absorption on the nanoscale elastic properties of the biopolyester, cutin, isolated from tomato fruit cuticle. Changes in the humidity and temperature at which fruits are grown or stored can affect the plant surface (cuticle) and modify its susceptibility to pathogenic attack by altering the cuticles rheological properties. In this work, atomic force microscopy measurements of the surface mechanical properties of isolated plant cutin have been made as a first step to probing the impact of water uptake from the environment on surface flexibility. A dramatic decrease in surface elastic modulus (from approximately 32 to approximately 6 MPa) accompanies increases in water content as small as 2 wt %. Complementary solid-state nuclear magnetic resonance measurements reveal enhanced local mobility of the acyl chain segments with increasing water content, even at molecular sites remote from the covalent cross-links that are likely to play a crucial role in cutins elastic properties.