Philip J. Hargis

Ultraviolet fluorescence identification of protein, DNA, and bacteria

Recent food poisoning incidents have highlighted the need for inexpensive instrumentation that can detect food pathogens. Instrumentation that detects the relatively strong ultraviolet (UV) fluorescence signal from the aromatic protein amino acids in bacteria could provide a solution to the problem of real-time pathogen measurements. The capabilities of UV fluorescence measurements have, however, been largely ignored because of the difficulty in identifying pathogens in the presence of interfering backgrounds. Implementation of fluorescence measurements thus requires methodologies that can distinguish fluorescence features associated with pathogens from those associated with proteins, harmless bacteria, skin, blood, hair follicles, pesticide residue, etc. We describe multispectral UV fluorescence measurements that demonstrate the feasibility of detecting and identifying protein, DNA, and bacteria using a relatively simple UV imaging fluorometer and a unique multivariate analysis algorithm.

Development of an unattended ground sensor for ultraviolet laser-induced fluorescence detection of biological agent aerosols

A prototype of an unattended ground sensor has been developed for detection of biological agent aerosols. This point sensor uses ultraviolet laser induced fluorescence (UV LIF) to detect aerosol biological microorganisms collected on filter media. The concept can be designed to be compact, low power, and hardened to survive harsh delivery environments such as airdrop. The prototype consists of an air sampling system, a filter exchange mechanism, an Nd:YAG microlaser that is frequency tripled and quadrupled to generate 355-nm and 266-nm excitation wavelengths, a spectrometer, an intensified CCD detector, and a data acquisition and control system. The analysis utilizes a spectral database of fluorescence signatures of biological organisms and common interferents measured by Sandia for the Armys Edgewood Research and Development Engineering Center (ERDEC) and the Department of Energys Chemical and Biological Non-proliferation (DOE CBNP) program. The analysis algorithms are based on algorithms developed by Sandia for an airborne UV LIF lidar system.

Laser Diagnostic Studies of Plasma Etching and Deposition

Laser excited fluorescence spectroscopy was used to determine that CF2 radicals control the silicon dioxide to silicon etch ratio in fluorocarbon discharges used to etch silicon and silicon dioxide. CF2 was found to control the etch ratio through polymer formation which selectively inhibits the silicon etch rate.

Plasma-Initiated Laser Deposition of Polycrystalline and Monocrystalline Silicon Films

This paper reports a new method of silicon deposition using the interaction between the radiation from a pulsed ultraviolet excimer laser and the plasma species produced in a glow discharge in silicane (SiH/sub 4/). Examination of the deposited film by laser Raman spectroscopy and by transmission electron microscopy revealed that the morphology ranged from polycrystalline silicon at laser fluences of 0.13 to 0.17 J/cm/sup 2/ to epitaxial silicon at fluences of 0.4 to 0.6 J/cm/sup 2/. Growth rates of 100 nm/min for polycrystalline silicon and 30 nm/min for monocrystalline silicon were achieved.

Multispectral ultraviolet fluorescence lidar for environmental monitoring

We describe a multispectral ultraviolet (UV) fluorescence laser remote sensing system developed to detect and identify airborne pollutants. The system uses a UV laser source that is continuously tunable from 250 to 400 nm in conjunction with a database of fluorescence signatures and multivariate analysis algorithms to obtain species concentrations from multispectral UV fluorescence measurements. As presently configured, the system is designed to operate with sequentially transmitted laser wavelengths between 250 and 400 nm at a pulse repetition rate of 10 Hz and is designed to map chemical concentrations with a range resolution of approximately 1 m. We describe the optical detection, associated data acquisition and control electronics, and tunable UV laser transmitter. We also describe a unique software package used for instrument setup and control. Based on sensitivity calculations, 1 ppm-m of toluene can be detected at a range of approximately 2.0 km with a range resolution of 1 m and a signal-to-noise ratio of approximately 3.

Chemical recognition software

We have developed a capability to make real time concentration measurements of individual chemicals in a complex mixture using a multispectral laser remote sensing system. Our chemical recognition and analysis software consists of three parts: (1) a rigorous multivariate analysis package for quantitative concentration and uncertainty estimates, (2) a genetic optimizer which customizes and tailors the multivariate algorithm for a particular application, and (3) an intelligent neural net chemical filter which pre-selects from the chemical database to find the appropriate candidate chemicals for quantitative analyses by the multivariate algorithms, as well as providing a quick-look concentration estimate and consistency check. Detailed simulations using both laboratory fluorescence data and computer synthesized spectra indicate that our software can make accurate concentration estimates from complex multicomponent mixtures, even when the mixture is noisy and contaminated with unknowns.