During emergency medical situations, where the patient has an obstructed airway or necessitates respiratory support, endotracheal intubation (ETI) is the medical technique of placing a tube into the trachea in order to facilitate adequate ventilation of the lungs. Complications during ETI, such as repeated attempts, failed intubation, or accidental intubation of the esophagus, can lead to severe consequences or ultimately death. Consequently, a need exists for a feedback mechanism to aid providers in performing successful ETI. Our study examined the spectral reflectance properties of the tracheal and esophageal tissue to determine whether a unique spectral profile exists for either tissue for the purpose of detection. The study began by using a hyperspectral camera to image excised pig tissue samples exposed to white and UV light in order to capture the spectral reflectance properties with high fidelity. After identifying a unique spectral characteristic of the trachea that significantly differed from esophageal tissue, a follow-up investigation used a fiber optic probe to confirm the detectability and consistency of the different reflectance characteristics in a pig model. Our results characterize the unique and consistent spectral reflectance characteristic of tracheal tissue, thereby providing foundational support for exploiting spectral properties to detect the trachea during medical procedures.
During emergency medical situations where the patient has an obstructed airway or necessitates respiratory support, endotracheal intubation (ETI) is the medical technique of placing a tube into the trachea in order to facilitate adequate ventilation of the lungs. In particular, the anatomical, visual and time-sensitive challenges presented in these scenarios, such as in trauma, require a skilled provider in order to successfully place the tube into the trachea. Complications during ETI such as repeated attempts, failed intubation or accidental intubation of the esophagus can lead to severe consequences or ultimately death. Consequently, a need exists for a feedback mechanism to aid providers in performing successful ETI. To investigate potential characteristics to exploit as a feedback mechanism, our study examined the spectral properties of the trachea tissue to determine whether a unique spectral profile exists. In this work, hyperspectral cameras and fiber optic sensors were used to capture and analyze the reflectance profiles of tracheal and esophageal tissues illuminated with UV and white light. Our results show consistent and specific spectral characteristics of the trachea, providing foundational support for using spectral properties to detect features of the trachea.
Efforts to develop a single solution for detecting hazardous chemicals and biological organisms for both military and civilian communities often produce conflicting requirements. The detection of biological threats, specifically spores, presents us with the most challenging problem. Raman spectroscopy is an excellent method for unique chemical and biological identification. The applicability of Raman spectroscopy to bacterial identification and analysis has been previously demonstrated. Surface-enhanced Raman scattering (SERS) is a well-known method for improving the signal level in Raman scattering. In order to form a uniform noble metal surface architecture, and therefore reproducible surface enhanced spectra, novel fabrication techniques have been developed. Here we report on our recent efforts using silver-shells around latex spheres as a SERS substrate for bacterial endospores.
Surface enhanced Raman spectroscopy (SERS) has been used as a tool to investigate spectral differences of bacterial endospores. Ultimately, this method could be used as a smart and rapid on-site detector for biological warfare agents. However, due to the spectral complexity and the relative size of spores to the substrate features, a rigidly defined substrate is necessary for reproducible characterization. We are investigating many of the reported substrate classes such as: Nano-sphere lithography (NSL), Film over nano-sphere (FONS), nano-shells, electrochemically roughened metals, and dispersed and immobilized colloids. The key aspects of this work include discerning what architectural pattern provides the largest enhancement and reproducibility when sampling the spore coat and whether some method of immobilization, or attraction, of the spores to the surface is necessary. We will present preliminary results of bacterial spore identification as well as a comparison of the substrates studied.
Raman spectroscopy has proven to be a plausible solution to the difficult challenge of on-site detection of biological threats. Adding to the challenge is the fact that many biological species, spores specifically, have relatively low scattering cross sections. The intrinsic need to detect these threats at low concentrations and in the presence of strong background signals necessitates the need for surface enhancement schemes. With an available technique to quickly identify bacterial spores, we hope to find spectral differences between target species in order to incorporate library technologies with the on-site sensor. We are investigating many of the reported substrate classes such as: Nano-sphere lithography (NSL), Film over nano-sphere (FONS), nano-shells, electrochemically roughened metals, and dispersed and immobilized colloids. The key aspects of this work include discerning what architectural features provide the largest enhancement and reproducibility. We will present preliminary results of bacterial spore identification as well as a comparison of the substrates studied.
The threat of biological agents to soldiers and the civilian community was amply demonstrated in the fall of 2001. We are examining the feasibility of using surface-enhanced Raman spectroscopy (SERS) to detect and identify bacteria. In order to use SERS for bacterial detection and identification, it is necessary to determine the most appropriate type of SERS substrate to use. We are examining gold colloids in suspension, immobilized gold colloids, electrochemically roughened gold, periodic particle arrays (PPA), and film over nanosphere substrates (FONS). Briefly, PPA’s are prepared by depositing gold or silver in the interstitial spaces in a close-packed array of polystyrene nanospheres, while FONS are prepared by depositing approximately half a nanosphere diameter of gold or silver on top of a close-packed array of polymer nanospheres. We are evaluating each of these substrate types to determine which will have a high affinity for bacteria, whether we need to modify the surface of the substrate to attract bacteria, and the degree to which each type of substrate enhances the Raman scattering from the bacterial targets. We will present the results of our initial evaluations of substrates and the spectra obtained for several species of bacteria.
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of several Bacillus species. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful biological agents. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of several bacterial spores in aqueous media have been measured using SERS substrates based on 60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 785-nm laser diode was used to capture/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the species identification of bacterial spores.
The use of surface-enhanced Raman spectroscopy (SERS) has recently seen a revitalization of interest with advances in surface coating technologies and other related areas. Recent reports have indicated that enhancement factors of up to 14 orders of magnitude can be achieved, providing the sensitivity requisite to trace level detection of target analytes. Due to the short range of the SERS effect, the interference of background materials may be reduced if the target analyte can be selectively brought near the SERS surface. SERS also holds the promise of providing the ability to determine the identity of bacterial species through recognition of the unique spectrum of a given species. The first major hurdle to its application to this problem is the design and optimization of appropriate surfaces for SERS of bacteria. This is complicated by the negative surface charge of the metal surface and the bacterium that results in a repulsive force that must be overcome. Our efforts have focused on selection of the best SERS substrate for this purpose. We are examining four potential SERS substrates: Au colloids in suspension with the bacteria, Au colloids immobilized on a surface, electrochemically roughened Au surfaces, and Ag periodic particle arrays provided by Prof. Richard van Duyne.
Photothermal interferometry has been demonstrated as a technique that can detect vapors with extremely high sensitivity (parts-per-trillion levels). Our present research uses a photothermal detection scheme that incorporates tunable sources and a modified Jamin interferometric design to provide high selectivity and sensitivity for organo-phosphate vapor detection. Two possible tunable excitation sources are being studied for this sensor technology, a tunable CO2 laser and difference frequency mixing of a tunable NIR laser with a fixed wavelength NIR laser in a nonlinear crystal. The modified Jamin design imparts superior vibrational immunity by ensuring both interferometer beams encounter common optical elements. Examining the two complementary optical outputs of the interferometer, phase shifts on microradian levels have been detected. Trace chemical vapor detection is accomplished by introducing the tunable excitation laser source across the path of one interferometer beam providing a phase shift due to absorptive heating. Preliminary results indicated parts-per-billion level detection of both DMMP and DIMP using ~ 400mW of CO2 laser power at appropriate wavelengths.
Our group has been developing a system for single-particle fluorescence detection of aerosolized agents. This paper describes the most recent steps in the evolution of this system. The effects of fluorophore concentrations, droplet size, and excitation power have also been investigated with microdroplets containing tryptophan in water to determine the effects of these parameters on our previous results. The vibrating orifice droplet generator was chosen for this study base don its ability to generate particles of well- known and reproducible size. The power levels required to reach saturation and photodegradation were determined. In addition, the collection of fluorescence emission was optimized through the use of a UV achromatic photographic lens. This arrangement permitted collection of images of the droplet stream. Finally, the use of a dual-beam, conditional firing scheme facilitated the collection of improved signal- to-noise single-shot spectra from individual biological particles.
Raman spectroscopy has been shown to be a useful tool for characterizing neat crystalline explosive samples and for identifying principle components in many propellant and explosive formulations. Recently, we have been investigating changes in Raman spectra of explosives and propellant formulations which occur as the temperature approaches the melting point of the sample. We report recent measurements of Raman spectra of explosives and propellant formulations during bulk heating, and recent measurements of laser heating of the samples during measurement of Raman spectra. The results of these measurements are important to investigators using Raman spectroscopy to measure vibrational spectra at the surface of burning propellant samples.
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