Jennifer L. Sample

Carbon nanotube coatings for thermal control

Materials based on carbon nanotubes (CNT) with their high thermal conductivity, the high aspect ratios as well as their mechanical strength, provide innovative materials for thermal control applications such as improved thermal interfaces. We demonstrate the feasibility of carbon nanotube based systems for use in thermal control applications, e.g. as a contact layer between two thermally connected materials. Multi-wall carbon nanotube (MWCNT) arrays of different density and length have been grown on silicon and copper surfaces using chemical vapor deposition. Measurements of the heat flow across different surfaces demonstrates that a CNT array as a contact layer will improve the thermal transport in vacuum, with a significant improvement over thermal grease designed for this purpose. An important application for this technology is in a thermal switch, where the contact between the two surfaces is not static and conducting epoxies or thermal grease cannot be used.

Crystal structure and optical properties of erbium- and neodymium-doped zirconia nanoparticles

We report the synthesis, characterization, and optical properties of high-temperature stable lanthanide-doped luminescent zirconia nanoparticles via a novel method using carbon black as template. Dopant concentrations were varied from 1 to 5% of Er 3+ or Nd 3+ and annealing temperatures were varied from 650 to 1100 °C. The effects of the dopant concentration on crystal structure and emission properties were evaluated using x-ray powder diffraction and fluorescence spectroscopy, respectively. The lanthanide cations were found to stabilize the tetragonal phase of zirconia over the monoclinic phase as dopant concentration was increased to 5%. Increasing the annealing temperature to 1100 °C had the opposite effect and was found to stabilize the monoclinic phase of zirconia. The luminescence intensity of the Nd-doped zirconia was enhanced by two orders of magnitude over the undoped or Er-doped zirconia. In all cases, the luminescence spectra revealed increasing intensity with increasing annealing temperature. Zirconia luminescence at near-infrared wavelengths is likely caused by oxygen vacancies. This work demonstrates that the spectral signatures of fluorescent zirconia nanoparticles can be modified with small lanthanide dopant concentration. These particles will have utility in fluorescent sensors and tags, as well as new in refractory materials.

Microfabricated substrates for spectroscopy and separation

In this paper, we report the preliminary results from a microfabricated substrate system that is amenable to both electromagnetic field-enhanced spectroscopy such as surface enhanced Raman scattering (SERS) and analyte separation and detection. Substrates consisting of arrays of gold post-like and pit-like features of varying pitch on gold substrates were fabricated by electron beam lithography. These substrates were characterized and tested for reproducible SERS activity, as well as evaluated for incorporation into a microfluidic system for separation and identification of components of complex matrices. Identification of analytes relevant to biodetection and biological screening is reported.

Chemiluminescent solid lipid nanoparticles (SLN) and interations with intact skin

We report the synthesis and characterization of a novel nanoparticle formulation designed for skin penetration for the purpose of skin imaging. Solid lipid nanoparticles (SLNs), a drug delivery vehicle, were used as the matrix for targeted delivery of peroxide-sensitive chemiluminescent compounds to the epidermis. Luminol and oxalate were chosen as the chemiluminescent test systems, and a formulation was determined based upon non-toxic components, lotion-like properties, and longevity/visibility of a chemiluminescent signal. The luminescence lifetime was extended in the lipid formulation in comparison to the chemiluminescent system in solution. When applied to porcine skin, our formulation remained detectable relative to negative and positive controls. Initial MTT toxicity testing using HepG2 cells have indicated that this formulation is relatively non-toxic. This formulation could be used to image native peroxides present in tissue that may be indicative of skin disease.

Characterization of SERS substrates for chem/bio processing systems

Surface enhanced Raman spectroscopy (SERS) has promise as an optical sensor for the detection of chemical and biological agents, in particular when combined with front-end processing for sample preparation prior to analysis. In this paper, we report preliminary results from a SERS analysis of Bacillus cereus T strain (BcT), which was prepared for sensor analysis via a microfluidics-based sample processor. In the microfluidics hardware, low and high molecular weight analytes from a sonicated spore sample were separated via mass-dependent diffusion into two independent microchannels. SERS analysis of the sample outputs revealed a significant separation of the low molecular spore biomarker, dipicolinic acid, from the high molecular weight protein and nucleic acid background. In addition to the processing study, measurements were performed on gold core-shell nanospheres, which are considered a potential SERS substrate for the microfluidic system. Finally, field-induced aggregation of silver nanoparticles, an alternative to chemical aggregation, was shown to be an effective approach for the production of highly enhancing SERS substrates.

Non-Covalent Functionalized Nanotubes in Nylon 12

Polyaromatic compounds, with terminal functional groups, can be non-covalently bonded to the sidewall of carbon nanotubes. This architecture preserves the structural, mechanical, electrical, and electromechanical properties of the CNTs and ensures that an unhindered functional group is available to bond with an extended polymer matrix. Spectroscopic measurements and high resolution imaging are used to confirm the functionalization and incorporation of functionalized MWNTs into a nylon 12 matrix.

Doped Zirconia Luminescent Nanoparticles

Nanoparticles that fluoresce or absorb light in the visible and near-IR wavelengths are desirable for a variety of applications including biological tagging for medical imaging purposes and for solar control glazing in the automobile industry. Semiconductor quantum dots are commercially available and dyed polymer nanoparticles as well as organic dye/silica core shell nanoparticles have also been demonstrated. We report the synthesis, characterization, and optical properties of another luminescent nanoparticle: doped zirconia. The zirconia nanoparticles reported in this study are doped with up to 10% of the lanthanide dopants Er, Gd, Nd and Eu. These materials emit in the visible and near-IR wavelengths depending on the dopant and are refractory, making them useful for high temperature applications. These cations were found to stabilize the cubic phase over the monoclinic phase of zirconia, at approximately 10% dopant, as characterized by X-ray diffraction. We report the luminescence spectra of these nanoparticles at various wavelengths which reveal emissions from the matrix as well as from the dopants.