Gordon H. Miller

Surface-active substrates for Raman and luminescence analysis.

This paper describes the development of active materials for optically enhanced Raman and fluorescence spectroscopy. The substrates for surface-enhanced Raman scattering investigated in this study involved silver-coated microspheres on glass plates. The effect of various experimental parameters, such as angle of incidence and excitation wavelength, were investigated. The substrate used for surface luminescence analysis consisted of a cellulose membrane coated with fumed silica microparticles, to enhance the sensitivity of analysis. Examples of analysis of benzo[a]pyrene and its derivatives are used to illustrate the efficacy of the analytical techniques.

Development of a compact, handheld Raman instrument with no moving parts for use in field analysis

This article describes a lightweight, self-contained, field portable Raman instrument that has been developed for rapid on-site determination of primary mixture components. The instrument consists of a helium neon (HeNe) laser for excitation, an acousto-optic tunable filter (AOTF) for wavelength discrimination, and an avalanche photodiode for detection. The AOTF is the primary component of this system and has been selected based on its spectral range (600–900 nm) along with its high resolution, ∼7.5 cm−1. Labview™ based software for controlling the AOTF frequency and the signal acquisition has also been developed. Several different samples were analyzed (both solids and liquids) using this instrument for the evaluation of parameters such as spectral resolution, sensitivity, and data acquisition speed for certain environmentally important compounds. The results from these measurements are compared with those using a conventional laboratory Raman system consisting of a grating-based spectrograph and a charg...

Laser-induced fluorescence studies of polycyclic aromatic hydrocarbons (PAH) vapors at high temperatures.

In this work, we present the fluorescence spectra of anthracene and pyrene vapors at different elevated temperatures (from 150 to 650 degrees C) excited with the 337 nm line of a nitrogen laser. We describe the high temperature effects on the resulting spectral properties including spectral intensity, spectral bandwidth and spectral shift. We found that the PAH fluorescence spectral bandwidths become very broad as the temperature increases. The broadening is mainly due to thermal vibrational sequence congestion. We also have found that the fluorescence intensity of pyrene vapor increases with increasing temperature, which results from the increase of the pyrene vapor absorption cross section at 337 nm.

Simultaneous detection of the tumor suppressor FHIT gene and protein using the multi-functional biochip

The tumor suppressor gene, fragile histidine triad (FHIT), encompasses the most common human chromosomal fragile site, at 3pl4.2. Detection of FHIT gene is important in cancer diagnostics since its alterations have been associated with several human cancers. A unique multi-functional biochip for simultaneous detection of FHIT DNA and FHIT protein on the same platform was applied. The design of the biochip is based on miniaturization of photodiodes, where functioning of multiple optical sensing elements, amplifiers, discriminators, and logic circuitry are integrated on a single IC board. Performance of biochip is based on biomolecular recognition processes using both DNA and protein bioreceptors, Cy5-labeled probes and laser excitation. Application of biochip for concurrent detection of various immobilized target DNA and protein molecules and multiplex of DNA and protein on the same microarray was accomplished. Linearity of biochip for quantitative measurements was demonstrated. Results demonstrated utility of this multi-functional biochip as a useful detection technology with applications in biological and clinical laboratories.

High-temperature vapor detection of polycyclic aromatic hydrocarbon fluorescence

Polycyclic aromatic hydrocarbons (PAHs) are generated from the incomplete combustion of organic matters in a wide variety of natural and man-made materials, such as fuels. It is important to develop an analytical technique for rapidly monitoring PAH generation at high temperatures during pyrolysis processes. This work describes a real-time and in situ technique using laser-induced fluorescence to detect PAH vapors at elevated temperatures. We report fluorescence spectra of several typical PAH model compounds, such as pyrene, phenanthrene and chrysene. We have also examined the temperature effects on PAH fluorescence spectra such as spectral shift, intensity and band width.

Passive dosimeter for monitoring ammonia vapor

Abstract A method is presented for ammonia detection in the vapor phase that exploits the reaction between fluorescamine and ammonia on a sodium lauryl sulfate (NaLS)-treated paper substrate. The fluorescence intensity of the aquamarine fluorescence product is used as a measure of the air vapor concentration (AVC) of ammonia. The substrate treatment with NaLS enhances the intensity of the fluorescent product and improves the reproducibility of the determination of ammonia. The paper substrate is mounted on a dosimeter and used to monitor exposure to ammonia vapor. The developed dosimeter is a self-contained, badge-sized device that passively collects ammonia on a precoated filter-paper at a rate determined by molecular diffusion. The dosimeter can detect ammonia AVC at the ppm level after only 1 min of exposure. For an 8-h exposure period the limit of detection is ca. 1 ppb.

Coherent imaging with two-dimensional focal-plane arrays: design and applications.

Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images.

Fiber optic sensor probe for in-situ surface-enhanced Raman monitoring

In this paper we report on the development of a fiberoptic sensor using a new detection method based on the Surface-Enhanced Raman Scattering (SERS) technique. The SERS effect is based on recent experimental observations which have indicated enhancement of the Raman scattering efficiency by factors up to 108 when a compound is adsorbed on rough metallic surfaces having submicron protrusions. In this report we describe the development of the SERS probes for in situ remote sensing.

Luminescence determination of benzoquinoline isomers in complex samples

Abstract The room-temperature phosphorescence (r.t.p.) and fluorescence spectra of benzoquinoline isomers are investigated. The isomers can be resolved into the linear or angular subgroups on the basis of their fluorescence and r.t.p. spectra by using conventional fixed excitation. Second-derivative and synchronous scanning techniques can be combined to improve the selectivity of the r.t.p. and fluorescence methods. These simple luminescence techniques were used to estimate three benzoquinoline isomers in a coal tar fraction. Direct analysis of this complex sample allowed acridine to be estimated and upper limits to be provided for benzo(h)quinoline and phenanthridine; the presence of three other isomers was not detected. Comparative studies with data obtained by high-performance liquid chromatography are reported.

Hyperspectral imaging using AOTF and NIR sensing of buried objects and landmines

The detection of landmines and buried objects requires methods that can cover large areas rapidly while providing the required sensitivity to detect the optical and spectroscopic contrasts in soil properties that can reveal their presence. These conditions on contrast and coverage can be met by capturing images of the soil at wavelengths which are sensitive to the properties modified by the presence of buried objects. In this work we investigate both imaging and scanning methods which may have some utility for the detection problem. In the imaging approach, we capture hyperspectral reflection images using an acousto-optic tunable filter (AOTF) and fluorescence images using a long-pass filter. For the scanning method, we acquire data point-by-point over a two-dimensional grid with a single emitter/detector pair. The results illustrate the potential of these two approaches for detection of landmines and buried objects.