This paper describes a compact, self-contained, cost effective, and portable Raman Integrated Tunable Sensor (RAMiTs) for screening a wide variety of chemical and biological agents for homeland defense applications. The instrument is a fully-integrated, tunable, "point-and-shoot" Raman monitor based on solid-state acousto-optic tunable filter (AOTF) technology. It can provide direct identification and quantitative analysis of chemical and biological samples in a few seconds under field conditions. It also consists of a 830-nm diode laser for excitation, and an avalanche photodiode for detection. Evaluation of this instrument has been performed by analyzing several standard samples and comparing the results those obtained using a conventional Raman system. In addition to system evaluation, this paper will also discuss potential applications of the RAMiTs for detection of chemical and biological warfare agents.
This paper describes a self-contained, portable Raman instrument that has been developed for environmental and homeland defense applications. The instrument consists of a 830-nm diode laser for excitation, an acousto-optic tunable filter (AOTF) for wavelength discrimination, and an avalanche photodiode for detection. The primary component of this system is the AOTF and it has been selected based on its spectral range along with its high resolution, ~7.5 cm-1. Software has been developed in house using C programming language for controlling the instrument (i.e. the AOTF frequency, the signal acquisition, etc.). Evaluation of this instrument has been performed by analyzing several standard samples and comparing to a conventional Raman system. In addition to system evaluation, this paper will also discuss potential applications of this instrument to trace detection of hazardous chemicals using the Raman Integrated Tunable Sensor (RAMiTs) coupled with surface-enhance Raman scattering process.
An integrated multi-functional biochip based on integrated circuit complementary metal oxide semiconductor (CMOS) sensor array for use in medical diagnostics and pathogen detection has been described. The usefulness and potential of the biochip as a rapid, inexpensive screening tool for detection of bioenvironmental pathogens will be demonstrated. Detection of aerosolized spores was achieved by coupling the miniature system to a portable bioaerosol sampler, and the performance of the antibody-based recognition and enzyme amplification method was evaluated. The bioassay performance was found to be compatible with the air sampling device, and the enzymatic amplification was found to be an attractive amplification method for detection of low spore concentrations. The combined portable bioaerosol sampler and miniature biochip system detected 100 B. globigii spores, corresponding to 17 aerosolized spores/L of air.
This work provides an overview of progress made, in our laboratory, towards the development of a practical biochipbased technology with a biofluidics system for the detection of E. coli and other pathogens. Efforts have been devoted towards efficient coupling between a compact biofluidics sample/reagent delivery system and an integrated circuit (IC) biochip, consisting of a 2-dimensional photosensor array, for on-chip monitoring of bioassays. The complementary
metal-oxide semiconductor (CMOS) technology has been implemented to design and produce the IC biochip, which features a 4x4 array of independently addressable photodiodes that are integrated with amplifiers, discriminators and logic circuitry on a single platform. The CMOS-based biochip offers the advantages of compactness and low power consumption, making it better suited for field use than other array detectors, including CCDs. The biofluidics system includes a 0.4 mL hybridization chamber, which accommodates disposable sampling platforms embedded with bioreceptors for selective capture of pathogen DNA, proteins, or antibodies in discrete zones. The independently operating photodiodes of the IC biochip offer the capability of monitoring of multiple assays. Highlights of this work
include highly sensitive detection of E. coli (<50 organisms) and quantitative capability with a linear dynamic range of 3-5 orders of magnitude for various assays.
In this work, we examine a system that exploits the photoacoustic effect to act as an ultrasonic pulse generator and an optical detector. At the core of the system are a solid substrate and an optical absorber. To test the performance as an ultrasonic generator, several substrate- absorber (SA) combinations are examined. The pulses generated by these systems are evaluated based on their bi- directional symmetry and characteristics of their Fourier spectra. To demonstrate the use of the SA system as an optical detector, a linearity study was performed for one specific choice of substrate and absorber. These substrate- absorber systems exhibit a variety of behaviors and form a versatile set of tools for ultrasound, optical and hybrid use.
In this work, we discuss data acquired in a clinical investigation to evaluate the utility of transcranial ultrasound for monitoring/detecting brain injury. Using a portable ultrasonic data acquisition system, over one thousand transcranial waveforms were captured from five subjects, including three head-injured patients. Several representative waveforms are shown to demonstrate the feasibility of the ultrasonic detection scheme and to illustrate the similarities and variabilities among the signals acquired in this study.
This paper describes a self-contained, portable Raman instrument that has been developed for biomedical analyses. The instrument consists of a 785-nm diode laser for excitation, an acousto-optic tunable filter (AOTF) for wavelength discrimination, and an avalanche photodiode for detection. The primary component of this system is the AOTF and it has been selected based on its spectral range along with its high resolution, approximately 7.5 cm-1. Software has been developed in-house in the programming language of C for controlling the instrument (i.e., the AOTF frequency, the signal acquisition, etc.). Evaluation of this instrument has been performed by analyzing several standard samples and comparing their spectra to spectra acquired using a conventional laboratory system. In addition to system evaluation, this paper will also discuss potential applications of this instrument to multiplexed genechip types of analyses.
The development of a field-portable Raman instrument for environmental analyses is described. It is based on the use of a near-infrared frequency-stabilized diode laser for excitation, an acousto-optic tunable filter for wavelength selection, and an avalanche photodiode for detection. Evaluation of this instrument for the monitoring of environmentally important species will be discussed as well as its ability to be operated in room light without significantly increasing the background signal. In addition, we will also describe a baseline removal procedure based on second derivative approach that simplifies and increases the accuracy of the instrument' s automated identification algorithm
The development of a field-portable Raman instrument for environmental analyses is described. It is based on the use of a near-infrared frequency-stabilized diode laser for excitation, an acousto-optic tunable filter for wavelength selection, and an avalanche photodiode for detection. Evaluation of this instrument for the monitoring of environmentally important species will be discussed as well as its ability to be operated in room light without significantly increasing the background signal. In addition, we will also describe a baseline removal procedure based on second derivative approach that simplifies and increases the accuracy of the instrument's automated identification algorithm.
In this work, we examine the orientation-dependent scattering and attenuation properties of white mater from mammalian brain tissue. We find that both the backscatter and attenuation of ultrasound in these tissues exhibit anisotropy. Furthermore, when extrapolated down to 1 MHz, it appears that the attenuation differences will be small but the backscatter differences are potentially resolvable. From a tissue characterization context, this means that the impact of changes due to the rotation of overlying tissues will be small compared to the changes in the strength of the backscatter signals from the regions of interest.
In this work, we examine the role of diffraction in the design of ring-shaped ultrasonic receivers for photoacoustic probes. The sensitivity patterns of ultrasonic receiving rings are calculated at 1 MHz using the angular spectrum technique. Three separate series of simulations are considered: flat ring with a fixed outer diameter and a variable inner diameter, flat ring with a fixed inner diameter and variable outer diameter, and a spherically focused ring with a variable inner diameter. From these results the focal zone characteristic and sensitivities are calculated. For the planar rings, we find that the spatial sensitivity varies markedly with ring width but the overall sensitivities are comparable. For the focused (spherically curved) rings, the focal distances and beam volumes were similar while the sensitivity grew with ring thickness.
12 In this work, we present the fluorescence spectra of anthracene and pyrene vapors at different elevated temperatures (from 150 to 650 degree(s)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.
12 We report for the first time, the development of a 3D optical random access memory material for neutron dosimetry. Detection of energetic neutrons is important in many applications, spanning from radioactive waste monitoring to space exploration. These anthracene-based photochromic dosimeters show a decrease in fluorescence intensity following exposure to energetic neutrons. Unlike current neutron dosimeters, where foreknowledge of the neutron energy is necessary to determine an exposure dose, these materials can be used in unknown environments (e.g. space exploration). A readout system has also been developed to determine the radiation characteristics (e.g. neutron energy) necessary for estimating dose. The results presented in this work, demonstrate the potential of these novel materials for space exploration and other applications where foreknowledge of neutron energy is unknown and current dosimeters are incapable of providing accurate dose information.
The interaction of light with tissue has ben used to recognize disease since the mid-1800s. The recent developments of light sources, detectors, and fiber optic probes provide opportunities to measure these interactions, which yield information for tissue diagnosis at the biochemical, structural, or physiological level. In this paper, we describe a bioimaging system designed for biomedical applications and show laser-indued fluorescence (LIF) images mammalian brain tissue. The LIF imaging of tissue was carried out in vitro using two laser excitations: 488 nm and 514 nm. Images were recorded through an acousto- optic tunable filter over the range 500 nm-650 nm with a charged coupled device camera. Background subtracted images were generated across the fluorescent wavelength. Subtraction allowed a safe comparison to be made with well- contrasted images. Of the two tested excitation wavelengths, 488 nm excitation gave the more distinctive contrast.
In this work, we present a novel method for the simultaneous acquisition of ultrasonic attenuation and optical absorption using photoacoustically-generated ultrasound. We discuss the theory behind the technique and apply the method to measurements in mammalian tissue samples. We show that the frequency dependence of ultrasonic attenuation measured with this technique is consistent with conventionally determined values and thus holds promise for future work.
The development of an optical-based dosimeter for neutrons and heavy charged particles is described. It is based on the use of three dimensional (3-D) optical memory materials, used in optical computing applications, and multiphoton fluorescence of photochromic dyes. Development and characterization of various types of dosimeter materials are described as well as the optical readout system. In addition, various excitation geometries for 'reading' and 'writing' to the optical memories are also discussed.
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 NIR scanning methods which may have some utility for the detection problem. For the scanning method, we acquire data point-by-point over a two- dimensional grid with a single emitter/detector probe. The soil (or sand) above a shallow buried object can be differentiated from the surrounding soil by detecting the difference in relative water content. Moist soil absorbs more near-infrared (NIR) incident light than dry soil. A light- emitting diode (LED) operating at 900 nm and a photodiode sensitive to NIR radiation formed the emitter/detector (ED) probe used in this study. The ED probe was mounted side-by- side and scanned over a surface in a two-dimensional grid as readings were collected point-by-point. The results indicated that this simple NIR emitter/detector probe discriminated between soils of varying water contents with an imaging resolution of 4 millimeters. To illustrate how imaging techniques can be used in this application, the fluorescence image of a landmine casing is presented. The results illustrate the potential of these two approaches for detection of landmines and buried objects.
In this work, we evaluate methods for detecting brain injury using ultrasound. We have used simulations of ultrasonic fields in the head to model the phase distortion of the skull. In addition we present experimental data from the crania of large animals. The experimental data help us understand and evaluate the performance of different transducers in acquiring the backscatter data from the brain through the skull. Both the simulations and acquired data illustrate the superiority of lower-frequency (<EQ 1 MHz) ultrasonic fields for transcranial acquisition of signals from inside the brain. Additionally, the experimental work shows that the higher-frequency (5 MHz) ultrasound can also be useful in acquiring clean nearfield data to help detect the position of the inner boundary of the skull.
In this work, we develop and evaluate the photoacoustic technique for recording spectra of white and gray mammalian brain tissues. In addition to the experimental work, we also discuss the geometric aspects of photoacoustic signal generation using collimated light. Spectral constructed from the peak-to-peak amplitude of the photoacoustic waveforms indicate differences in the two tissue types at wavelengths between 620 and 695 nm. The potential of the technique for non-invasive diagnosis is discussed.
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.
Three-dimensional optical memories which utilize two-photon processes have been proposed for use as a radiation dosimeter. The 'bits' stored by the optical memory are altered by the passage of radiation and can yield information about the dose and energy. In this work, the 'write' process of a two-photon optical memory is examined. This process uses a crossed-beam excitation scheme. By considering the spatial and temporal properties of the excitation sources used to drive the two- photon transitions, conditions are derived under which the number of absorption events due to the crossed-beams acting together outnumber the background events.
In this work, we examine the physics underlying wave propagation in the head to evaluate various ultrasonic transducers for use in a brian injury detection device. The results of measurements of the attenuation coefficient and phase velocity for ultrasonic propagation in samples of brain tissue and skull bone from sheep are presented. The material properties are then used to investigate the propagation of ultrasonic pressure fields in the head. The ultrasound fields for three different transducers are calculated for propagation in a simulated brain/skull model. The model is constructed using speed-of-sound and mass density values of the two tissue types. The impact of the attenuation on the ultrasound fields is then examined. Finally, the relevant points drawn from these discussions are summarized. We hope to minimize the confounding effects of the skull by using sub-MHz ultrasound while maintaining the necessary temporal and spatial resolution to successfully detect injury in the brain.
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