Biomedical subjects

Jeffrey W Elam

Publications and source records attributed to Jeffrey W Elam.

4 recordsLinked to original sources

PubMed2006

Ultrastable substrates for surface-enhanced Raman spectroscopy: Al2O3 overlayers fabricated by atomic layer deposition yield improved anthrax biomarker detection.

A new method to stabilize and functionalize surfaces for surface-enhanced Raman spectroscopy (SERS) is demonstrated. Atomic layer deposition (ALD) is used to deposit a sub-1-nm alumina layer on silver film-over-nanosphere (AgFON) substrates. The resulting overlayer maintains and stabilizes the SERS activity of the underlying silver while presenting the surface chemistry of the alumina overlayer, a commonly used polar adsorbent in chromatographic separations. The relative affinity of analytes for alumina-modified AgFON substrates can be determined by their polarity. On the basis of SERS measurements, dipicolinic acid displays the strongest binding to the ALD alumina-modified AgFON among a set of pyridine derivatives with varying polarity. This strong affinity for carboxylate groups makes the SERS substrate an ideal candidate for bacillus spores detection using the dipicolinate biomarker. The SERS signal from extracted dipicolinate was measured over the spore concentration range 10(-14)-10(-12) M to determine the saturation binding capacity of the alumina-modified AgFON surface. The adsorption constant was determined to be Kspore = 9.0 x 10(13) M(-1). A 10-s data collection time is capable of achieving a limit of detection of approximately 1.4 x 10(3) spores. The shelf life of prefabricated substrates is at least 9 months prior to use. In comparison to the bare AgFON substrates, the ALD-modified AgFON substrates demonstrate twice the sensitivity with 6 times shorter data acquisition time and 7 times longer temporal stability. ALD expands the palette of available chemical methods to functionalize SERS substrates, which will enable improved and diverse chemical control over the nature of analyte-surface binding for biomedical, homeland security, and environmental applications.

Aluminum Oxide↗

PubMed2006

Imaging of atomic layer deposited (ALD) tungsten monolayers on alpha-TiO2(110) by X-ray standing wave Fourier inversion.

A single atomic layer of tungsten grown by atomic layer deposition (ALD) on a single-crystal rutile TiO2(110) support is studied by the X-ray standing wave (XSW) technique. The surface structural and chemical properties were also examined using atomic force microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. The XSW measured set of hkl Fourier components for the W atomic distribution function are summed together to produce a model-independent 3D map of the W atoms relative to the rutile lattice. The 3D atomic image shows surface tungsten atoms equally occupying the two nonequivalent Ti sites with a slight outward displacement. This corresponds to the atop and bridge sites with respect to the underlying lattice oxygen atoms. These XSW measurements clearly show that ALD conformal layers can be highly coherent with respect to the substrate lattice.

Journal Article↗

PubMed2005

Localized surface plasmon resonance nanosensor: a high-resolution distance-dependence study using atomic layer deposition.

Atomic layer deposition (ALD) is used to deposit 1-600 monolayers of Al(2)O(3) on Ag nanotriangles fabricated by nanosphere lithography (NSL). Each monolayer of Al(2)O(3) has a thickness of 1.1 A. It is demonstrated that the localized surface plasmon resonance (LSPR) nanosensor can detect Al(2)O(3) film growth with atomic spatial resolution normal to the nanoparticle surface. This is approximately 10 times greater spatial resolution than that in our previous long-range distance-dependence study using multilayer self-assembled monolayer shells. The use of ALD enables the study of both the long- and short-range distance dependence of the LSPR nanosensor in a single unified experiment. Ag nanoparticles with fixed in-plane widths and decreasing heights yield larger sensing distances. X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, and quartz crystal microbalance measurements are used to study the growth mechanism. It is proposed that the growth of Al(2)O(3) is initiated by the decomposition of trimethylaluminum on Ag. Semiquantitative theoretical calculations were compared with the experimental results and yield excellent agreement.

Aluminum Oxide↗

PubMed2005

Effect of atomic layer deposition coatings on the surface structure of anodic aluminum oxide membranes.

Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with Al2O3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature >900 degrees C. ALD was used to cover the surface of AAO with either Al2O3 or TiO2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al2O3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO2 show a more complicated behavior. UV Raman results show that very thin TiO2 coatings (1 nm) are not stable upon annealing to 500 degrees C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 degrees C.

Journal Article↗