John Hulse

Nanoscale aggregation of cellular beta2-adrenergic receptors measured by plasmonic interactions of functionalized nanoparticles.

Adrenergic signaling that controls the contraction of cardiac myocyte cells and the beating of the mammalian heart is initiated by ligand binding to adrenergic receptors contained in nanoscale multiprotein complexes at the cellular membrane. Here we demonstrate that the surface-enhanced Raman scattering (SERS) of functionalized silver nanoparticles can be used to report on the receptor aggregation state of specifically label beta(2)-adrenergic receptors on mouse cardiac myocyte cells. Furthermore, multimodal imaging including Raman, Rayleigh scattering, scanning electron microscopy, and luminescence imaging was combined to fully characterize the beta(2)-adrenergic receptor-mediated aggregation of silver nanoparticles on the membrane of cardiac myocytes. Scanning electron microscopy analysis reveals distinct SERS active clusters of between 10 and 70 nanoparticles per signaling domain from ultra-high-resolution images of beta(2)-adrenergic receptor clusters on the cellular membrane. These techniques can be generally applied to study the aggregation of other cell surface receptors and explore their distribution on cell surfaces.

Detection of acute brain injury by Raman spectral signature

Brain injury can lead to irreversible tissue loss and functional deficit along with significant health care costs. Raman spectroscopy can be used as a non-invasive technique to provide detailed information on the molecular composition of diseased and damaged tissues. This technique was used to examine acute mouse brain injury, focusing on the motor cortex, a region directly involved in controlling execution of movement. The spectral profile obtained from the injured brain tissue revealed a markedly different signature, particularly in the amide I and amide III vibrational region when compared to that of healthy brain tissue. Most noticeably, there was a significant reduction of the amide I vibration at the acute injury site and the appearance of two distinct features at 1586 and 1618 cm(-1). Complementary immunohistochemical analysis of the injured brain tissue showed an abundant expression of Caspase 3 (a cysteine protease marker used for apoptosis), suggesting that the injury-induced specific Raman shifts may be correlated with cell death. Taken together, this study demonstrates that Raman spectroscopy can play an important role in detecting the changes that occur in the injured brain and provide a possible technology for monitoring the recovery process.

Formation of high-quality silicon dioxide films by electron cyclotron resonance plasma oxidation and plasma-enhanced chemical vapour deposition

Abstract High-quality silicon dioxide films have been deposited by plasma-enhanced chemical vapour deposition and plasma oxidation using a single magnet electron cyclotron resonance plasma generator with both oxygen and nitrous oxide as the oxygen source, Langmuir probe measurements were used to characterise both molecular oxygen and nitrous oxide discharges. Low electron temperatures, resulting in low sheath potential drops, coupled with the shape of the field lines results in low sputtering from the chamber walls between the source region and substrate. The resulting buildup of an insulating layer of oxide on the chamber walls results in a very clean process. In situ thermal desorption and ellipsometry measurements coupled with X-ray photoelectron spectroscopy have allowed us to characterise the quality of the silicon surface prior to deposition and just after initiation of the plasma. Plasma oxidation dominates over chemical vapour deposition during the early stages of oxide film growth using either oxygen or nitrous oxide as the oxygen source gas. Extensive ex-situ spectroscopic ellipsometry (SE) indicates that the bulk properties of the films arc comparable to those of high-temperature thermal oxides. There is no interface layer measurable by SE for any of the films produced by plasma oxidation or chemical vapour deposition with silane using either molecular oxygen or nitrous oxide as the oxygen source gas even though the latter results in approximately a monolayer of nitrogen at the Si/SiO2 interface. Chemical analysis by the total reflected X-ray fluorescence technique and by vapour-phase deposition coupled with graphite furnace atomic absorption spectroscopy found no impurities in the films made with silane and molecular oxygen. The high quality of the Si/SiO2 interface made with these two gases was confirmed by capacitance-voltage measurements on Al-gate capacitors. After a 1 min anneal at 950°C interface state densities below 3×1010 eV−1 cm−2 were obtained.

Characterization of very thin Ge epilayers on (100) Si by spectroscopic ellipsometry

A series of very thin Ge epilayers (1–12 monolayers) grown on Si (100) that had previously been characterized by transmission electron microscopy, X-ray reflection, Rutherford back-scattering, secondary-ion mass spectrometry, Raman spectroscopy and extended X-ray absorption fine structure analysis has been examined by spectroscopic ellipsometry (SE). It was found that the SE results significantly enhance the other findings. Analysis of the SE measurements was based on the nominal growth conditions rather than the results of the post mortem findings mentioned above. This analysis was able to provide the thicknesses and compositions of the layers comprising the heterostructures easily and quickly. The findings of the previous characterizations of these samples are compared with the results of the SE measurements. The main result is that not even in the thickest epilayer was there a phase that could be described as pure germanium. Intermingling of the Ge epilayer with the Si cap was substantial in every case. It is concluded that the minimum epilayer thickness that would guarantee at least some pure germanium under these conditions is greater than 12 monolayers.

Characterization of SiGe multiple quantum wells by spectroscopic ellipsometry and photoluminescence

Two SiGe multiple quantum well structures that had been characterized already by double-crystal X-ray diffraction (DCXRD) have been examined by spectroscopic ellipsometry (SE) and photoluminescence (PL). Analysis of the SE measurements was based upon the nominal growth conditions rather than the DCXRD findings. This analysis was able to provide the thicknesses and compositions of the layers comprising the heterostructure easily and quickly. Moreover, the SE analysis also provided estimates of the variation in these thicknesses and compositions, as well as in the heterostructure periodicity. It was found that the SE results confirm and enhance the DCXRD findings. The interpretation of the PL spectra benefits from the SE characterization and illuminates the nature of the small uncertainties in composition and layer thickness found by SE. These results demonstrate that SE provides a quick, extensive and reliable post mortem analysis of such materials.

Analysis of Si/Six Ge1 − x/Si microstructures by spectroscopic ellipsometry

Abstract Spectroscopic ellipsometry is used to examine the microstructure of two buried Six Ge1 − x alloy films grown by molecular beam epitaxy. In each case the optical measurements show these heterostructure materials to differ significantly in composition and thickness from those which were intended. These discrepancies indicate that there is substantial mixing of species across interfaces. Spectroscopic ellipsometry, which in principle could be performed in situ to monitor the growth of such materials, is shown to provide a quick diagnostic of this intermixing.

Surface-enhanced Raman and optical scattering in coupled plasmonic nanoclusters

Optical excitation of small Au nanoparticle (NP) clusters of appropriate wavelength is known to generate intense electromagnetic fields localized uniquely at NP junction sites within the nanoclusters. These intense and localized field hot-sites can induce intense surface-enhanced Raman scattering (SERS) of molecules residing at the junction hot-sites. In this paper, we present a series of electromagnetic simulations, experimental SERS and extinction data obtained from small self-assembled Au NP clusters coated to saturation with a Raman reporter molecule. Our experimental data show that the SERS enhancement factor remains relatively constant despite the heterogeneity of the nanocluster and this is supported by the simulation results. Furthermore, our simulation results show significant variations in the localized electric field intensities of the junction hot-sites in different nanocluster geometries. This explains the observation that increasing the number of hot-sites does not necessarily result in a higher SERS enhancement factor.

Bonding at the CdSe/SiOx (x=0,1,2) interfaces

The chemistry occurring at the CdSe/Si, CdSe/SiO, and CdSe/SiO2 interfaces was investigated by looking at very thin tapered films (0–10 nm) of thermally evaporated CdSe with x-ray photoelectron spectroscopy. The analysis of the attenuation of the x-ray photoelectron signals along the tapered film was used to measure the electron mean free paths in as-deposited CdSe. The electron mean free path was found to increase with the photoelectron energy from 1.5 nm at 720 eV to 2.3 nm at 1200 eV. Our data suggest an island growth mechanism for CdSe on the Si substrate and a more uniform growth on silicon oxide. In the early growth, Se is first adsorbed on the surface creating sites where Cd subsequently adsorbs. Interdiffusion is observed for CdSe on the Si and SiO substrates after a vacuum anneal at 390 °C. The main result of this interdiffusion process is the formation of Si–Se bonds. Similar interdiffusion processes on thermal SiO2 substrates are expected but were too small to be detected.

Multimodal plasmonic nanosensor for the detection of pathogenic bacteria

Multi-modal sensing scheme significantly improves the detection accuracy but can also introduce extra complexity in the overall design of the sensor. We overcome this difficulty by utilizing the plasmonic properties of metallic nanoparticles. In this study, we will present a simple dual optical sensing mechanism which harvests signals of the resonantly excited metallic nanostructure in the form of surface enhanced Raman scattering (SERS) and resonant Rayleigh scattering. Silver and gold nanoparticles labeled with appropriate antibodies act as signal transduction units and upon exposure to the targeted pathogen render the targeted species optically active. We demonstrate that detection of a single pathogen cell is easily attainable with the dual detection scheme. Furthermore, we explore the markedly different SERS intensity observed from the use of two very different antibody recognition units during the pathogen labeling process.

Properties of Gate-Quality SiO 2 Films Prepared by Electron Cyclotron Resonance Chemical Vapour Deposition in an Ultrahigh Vacuum Processing System

We have prepared thin SiO 2 layers on Si(100) wafers by electron cyclotron resonance chemical vapour deposition (ECR-CVD) in a multi-chamber ultra-high vacuum (UHV) processing system. The oxides were characterized in-situ by single wavelength ellipsometry (SWE) and x-ray photoelectron spectroscopy (XPS) and ex-situ by Fourier transform infra-red spectroscopy (FTIR), spectroscopic ellipsometry (SE) and capacitance-voltage (CV) electrical measurements. Films deposited at higher pressures, low powers and low silane flow rates had excellent physical and electrical properties. Films deposited at 400 °C had better physical properties than those of thermal oxides grown in dry oxygen at 700 °C. A 1 minute anneal at 950 °C reduced the fast interface state density from 1.2×10 11 to 7×10 10 eV −1 cm −2