Steven J. Oldenburg

Nanoparticle characteristics affecting environmental fate and transport through soil

Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil.

Leveraging Nanoscale Plasmonic Modes to Achieve Reproducible Enhancement of Light

The strongly enhanced and localized optical fields that occur within the gaps between metallic nanostructures can be leveraged for a wide range of functionality in nanophotonic and optical metamaterial applications. Here, we introduce a means of precise control over these nanoscale gaps through the application of a molecular spacer layer that is self-assembled onto a gold film, upon which gold nanoparticles (NPs) are deposited electrostatically. Simulations using a three-dimensional finite element model and measurements from single NPs confirm that the gaps formed by this process, between the NP and the gold film, are highly reproducible transducers of surface-enhanced resonant Raman scattering. With a spacer layer of roughly 1.6 nm, all NPs exhibit a strong Raman signal that decays rapidly as the spacer layer is increased.

Development and Characterization of Healable Carbon Fiber Composites with a Reversibly Cross Linked Polymer

Carbon fiber reinforced polymer (CFRP) laminates with remendable cross-linked polymeric matrices were fabricated using a modified resin transfer mold (RTM) technique. The healable composite resin, bis-maleimide tetrafuran (2MEP4F), was synthesized by mixing two monomers, furan (4F) and maleimide (2MEP), at elevated temperatures. The fast kinetic rate of the reaction of polymer constituents requires a fast injection of the healable resin into the carbon fiber preform. The polymer viscosity as a function of time and temperature was experimentally quantified in order to optimize the fabrication of the composite material and to guarantee a uniform flow of the resin through the reinforcement. The method was validated by characterizing the thermo-mechanical properties of the polymerized 2MEP4F. Additionally, the thermo-mechanical properties of the remendable CFRP material were studied.

Spectroscopic studies of individual plasmon resonant nanoparticles

We present a detailed description of the apparatus and techniques that we have utilized in our experimental study of individual plas on resonant nanoparticles,along with a brief description of some major results. The apparatus consists of a spectroscopic system combined with a modified darkfield microscope, which enables the user to sequentially select individual resonant nanostructures in the microscopic field of view for spectroscopic study. Plasmon resonant nanostructures scatter light elastically,and typically have very large scattering cross-sections at their resonant optical wavelengths. In general, spectra can be obtained with acquisition times between .1 to 30 seconds,and color images can be captured using consumer digital color cameras. Spheres,tetrahedrons,and pentagonal platelets were fabricated using colloidal chemistry techniques. To produce highly anisotropic structures such as nanorods and barbells, templates were used. Many of these nanostructures have been individually spectroscopically characterized,and their spectra correlated with their shape and size as determined by transmission electron icroscope (TEM). The unique shape,size, composition,and dielectric surroundings of the individual plasmon resonant nanostructures determine their plasmon resonant behavior. We will show how the composition of the substrate on which the particles are immobilized and the dielectric of the surrounding medium have a significant effect on the plasmon resonance of the individual particles.

Optimized Nanofluid Coolants for Spacecraft Thermal Control Systems

The addition of metal nanoparticles to coolants used in thermal control systems can dramatically increase the thermal conductivity of the base fluid. Such metal nanoparticle-fluid composite materials are referred to as nanofluids and their use as coolants has the potential to reduce the weight and power requirements of spacecraft thermal control systems. The thermal conductivity of nanofluids is dependent on the concentration, size, shape, surface chemistry, and aggregation state of the constituent nanoparticles. The effects of nanoparticle loading concentration and the aspect ratio of the nanoparticles on the thermal conductivity and viscosity of water and ethylene glycol based coolants were investigated. Silver nanorods with a diameter of 55 ± 12 nm and an average length of 12.8 ± 8.5 μm at a concentration of 0.5% by volume increased the thermal conductivity of water by 68%. The thermal conductivity of an ethylene glycol based coolant was increased by 98% with a silver nanorod loading concentration of 0.5% by volume. Longer nanorods had a greater effect on the thermal conductivity than shorter nanorods at the same loading density. However, longer nanorods also increased the viscosity of the base fluid to a greater extent than shorter nanorods.

Chapter 18:Development of Novel Test Platforms for the Assessment of Brain Injury

The development of successful laboratory testing directed towards the identification of brain biomarkers in biological fluids is presented in this chapter. Highlighted is a roadmap for immunoassays measuring antigens–peptides and antibodies to assess brain injury. The choice of unique reagents, assay design, and platform is described in order to build laboratory and point-of-care tests with high performance characteristics.

Optically Detectable Colloidal Metal Labels: Properties, Methods, and Biomedical Applications

The optical detection of sub-wavelength sized metal particles has its scientific roots nearly a hundred years ago when Zigmondy first reported the observation of individual metal colloids under a microscope However, it was not until the early 1980s that gold colloid (5 nm - 20 nm in diameter) that had antibodies attached to the particle surface were used to specially target immunogenic cellular proteins. The precise location of these electron dense markers labels (immunogold) can be visualized using Transmission Electron Microscopy (TEM) (reviewed by Hayat). Alternatively, the labels can be viewed with a standard optical microscope by increasing their size with an Immuno-Gold Silver Staining (IGSS) procedure that deposits additional silver ions on the colloidal gold nucleation sites to form bulk silver. Another procedure commonly used for RNA in-situ studies is autoradiography, a process where silver ions nucleated as a result of radioactive decay from a 3H or 35S labeled nucleic acid probe form colloids in a silver emulsion film and are detected using optical microscopy techniques.

Metal nanoparticles for biodetection

The large scattering cross section of plasmon resonant gold and silver nanoparticles functionalized with the appropriate ligand allows for sensitive and specific detection of nucleic acids and proteins. By varying the size, shape, and material morphology populations with a specific peak plasmon resonance can be prepared. By varying the order and length of plasmon resonant bar segment in a composite nanowire one can obtain a large number of particle populations. Distinct populations can be used for labels for multiplexing or as a platform for biological assays. An larger number of color populations can be obtained with composite nanowires that are fabricated with various lengths of silver, gold, or nickel segments. The order and length of the different plasmon resonance rod segments can be used to uniquely identify a rod population allowing for a large degree of multiplexing within a single sample.