Ryan J. Priore

Growth and Characterization of a Porous Aluminum Oxide Film Formed on an Electrically Insulating Support

Thin films of porous anodic aluminum oxide have been prepared on an electrically insulating support by the anodization of aluminum films sputtered onto glass slides. The resulting transparent aluminum oxide films were characterized by scanning electron microscopy and variable angle ellipsometry. Subsequently, the film was modeled from the ellipsometric data taken. An underlying conductive medium is not necessarily needed to bring about nearly complete anodization of the aluminum layer.

Application of multivariate optical computing to simple near-infrared point measurements

Quantitative multivariate spectroscopic methods seek spectral patterns that correspond to analyte concentrations even in the presence of interferents.By embedding a spectral pattern that corresponds to a target analyte in an interference filter in a beamsplitter arrangement;bulky and complex instrumentation can be eliminated with the goal of producing a field-portable instrument.A candidate filter design for an rganic analyte,of military interest,and an interferent is evaluated.

On-line reoptimization of filter designs for multivariate optical elements

An automated method for producing multivariate optical element (MOE) interference filters that are robust to errors in the reactive magnetron sputtering process is described. Reactive magnetron sputtering produces films of excellent thickness and uniformity. However, small changes in the thickness of individual layers can have severe adverse effects on the predictive ability of the MOE. Adaptive reoptimization of the filter design during the deposition process can maintain the predictive ability of the final filter by changing the thickness of the undeposited layers to compensate for the errors in deposition. The merit function used, the standard error of calibration, is fundamentally different from the standard spectrum matching. This new merit function allows large changes in the transmission spectrum of the filter to maintain performance.

Potential of Raman Spectroscopy and Imaging Methods for Rapid and Routine Screening of the Presence of Melamine in Animal Feed and Foods

The impact of melamine-contaminated animal feed ingredients on food safety has become a major public concern ever since melamine was identified as the organic compound responsible for the deaths of a significant number of cats and dogs in 2007 by way of adulterated pet food. Melamine, a common industrial chemical often added to resins to improve flame resistance and proposed as an alternative form of fertilizer-N for plant growth, was found to be intentionally added to animal feed in amounts ranging from 0.2% to 8% of total mass as a way to boost the products’ apparent protein content. It was also used as a binder in the production of pelleted feed for animals. In addition to melamine, a small amount of cyanuric acid, ammeline, and ammelide were also detected in pet feed and in the tissues and urine of dead pets that had consumed the contaminated food. Even though it is possible that cyanuric acid, ammeline, and ammelide were added, their presence more likely resulted from the degraded derivatives of melamine. There is a great concern that melamine will again enter the food chain and be consumed by humans and animals. As part of the Food Protection Plan, US federal agencies such as the FDA and FSIS and other organizations have established GCMS and LC-MS/MS procedures for the analysis of melamine in food/feed commodities. Although they can detect melamine contaminants in trace amount, these time-consuming laboratory procedures require chemical solvents for the extraction steps and depend on expensive mass spectrometry. Rapid, nondestructive, and routine methods for the specific detection of melamine in raw feed materials are increasingly important, not only for public health concerns but also for melamine screening to prevent protein fraud. Undoubtedly, the well-defined mass spectroscopic technique is preferred due to its low detection limit and capability for structural elucidation; however, since adulteration of raw materials by melamine usually occurs in higher concentrations in order to affect protein content, the high sensitivity of the mass spectroscopic technique may not be necessary. In addition, mass spectrometry might not be sufficiently rapid to screen for the presence of melamine in a large number of food/feed materials from very different sources, because the identification process includes sample-specific extraction procedures, which are labor-intensive and time-consuming. Fast melamine screening requires minimal sample preparation (e.g., no extraction or centrifugation), routine analysis of a number of samples without reagents, minimal procedural steps, and easy operation and interpretation of results. The Raman technique, which has been used to obtain structural information on melamine, is an alternative approach that can be applied to solid materials with no sample pretreatment. In addition, the use of the Fourier transform (FT) methodology and a 1064 nm excitation laser in the near-infrared (NIR) region provides precise wavenumber measurement and good-quality Raman spectra by reducing the interference from fluorescence and photodecomposition of colorants present in food and feed. Raman studies of melamine and melamine-modified resins have been reported in the literature, and the results have revealed the feasibility of the Raman technique for the structural characterization of melamine state in resins. However, there have been few reports on Raman investigation and identification of melamine in complex food and feed systems. The objectives of this study were (1) to identify the characteristic Raman bands in melamine-contaminated wheat flour, corn gluten, and soybean meal mixtures; and (2) to develop simple and universal ratio algorithms for qualitative and quantitative analysis of melamine in mixtures. The ultimate goal is to develop both Raman spectroscopy and Raman chemical imaging methods for rapid, accurate, nondestructive, specific, and routine screening of the presence of melamine in food and feed for public/animal safety and security.

Application of multivariate optical computing to near-infrared imaging

Rapid quantitative imaging of chemical species is an important tool for investigating heterogenous mixtures, such as laminated plastics, biological samples and vapor plumes. Using traditional spectroscopic methods requires difficult computations on very large data sets. By embedding a spectral pattern that corresponds to a target analyte in an interference filter in a beamsplitter arrangement; the chemical information in an image can be obtained rapidly and with a minimal amount of computation. A candidate filter design that is tolerant to the angles present in an imaging arrangement is evaluated in near-infrared spectral region for an organic analyte and an interferent.

Miniature Stereo Spectral Imaging System for Multivariate Optical Computing

Chemical or hyperspectral imaging is a rapidly developing field that has applications ranging from materials characterization to remote environmental sensing.1 Thanks to developments in processing and instrumentation over the past two decades,2–4 it is now possible to use hyperspectral imaging routinely in the laboratory.5–9 However, the technique still suffers from long data collection times and the need for post-collection computer processing.10 Other than satellite remote earth sensing, uses of hyperspectral imaging outside the laboratory have been limited because of the restricted portability of most instruments. Speed, size, maintenance, sensitivity, complexity, and cost remain significant challenges to widespread adoption of hyperspectral measurement platforms outside a laboratory or satellite setting. Interference filter based multivariate optical computing (MOC) attempts to combine the data collection and processing steps of a traditional multivariate chemical analysis in a single step, offering an all-optical computing technology with no moving parts.11 MOC instruments have characteristics that lend themselves well to compact, portable, rapid, and sensitive imaging of multivariate information content in optical spectra. In filter-based MOC, a specialized interference filter called a multivariate optical element (MOE) is used as an optical beamsplitter. The intensity difference between the light rays that are transmitted and reflected by the MOE is designed to equate to the magnitude of a specific multivariate pattern in the light spectrum. Details of the theory and design of these MOEs have been previously reported.12–14 Tradi-

Improved Dispersion of Bacterial Endospores for Quantitative Infrared Sampling on Gold Coated Porous Alumina Membranes

An improved method for qualitative and quantitative sampling of bacterial endospores using Fourier transform infrared (FT-IR) microscopy on gold-coated porous alumina membranes is presented. Bacillus subtilis endospores were filtered onto gold-coated alumina membranes serving as substrates. Studies in the mid-infrared (MIR) region revealed the characteristic bacterial absorption spectrum at low surface concentration, while scanning electron microscopy (SEM) images of the same samples provided precise calculation of the surface concentration of the bacterial endospores. Under the conditions of study, the average concentration of endospores was determined to be 1356 ± 35 spores in a 100 × 100 μm2 area, with a relative standard deviation of 0.0260. Examination of ten random spots on multiple substrates with FT-IR microscopy apertured to the same area gave an average relative standard deviation of 0.0482 in the signal strength of the amide A band at 3278 cm−1. An extinction cross-section in reflection of σext = (7.8 ± 0.6) × 10−9 cm2/endospore was calculated for the amide A band at the frequency of its peak absorbance, 3278 cm−1. The absorption cross-section of the amide A band in reflection is estimated to be σabs ≈ (2.10 ± 0.12) × 10−9 cm2/endospore.

Fine-Structure Measurements of Oxygen A Band Absorbance for Estimating the Thermodynamic Average Temperature of the Earth's Atmosphere. An Experiment in Physical and Environmental Chemistry

The rotational fine structure observable in a forbidden electronic absorbance of diatomic oxygen in the earths atmosphere can be observed as a series of minima in the solar spectrum near 762 nm wavelength. The relative intensities of these rotational fine-structure lines can be used quantitatively to estimate the average temperature of the atmosphere along the path taken by sunlight to the observer. Measured values for temperature vary from day to day and season to season and are generally far lower than ambient temperatures because of averaging over the depth of the atmosphere. These experimentally determined thermodynamic temperatures can be compared to Web-based atmospheric models for particular locations and times to illustrate the fact that they are average values.