Alan C. Samuels

Laser-induced breakdown spectroscopy of bacterial spores, molds, pollens, and protein: initial studies of discrimination potential

Laser-induced breakdown spectroscopy (LIBS) has been used to study bacterial spores, molds, pollens, and proteins. Biosamples were prepared and deposited onto porous silver substrates. LIBS data from the individual laser shots were analyzed by principal-components analysis and were found to contain adequate information to afford discrimination among the different biomaterials. Additional discrimination within the three bacilli studied appears feasible.

The Conformational Structures and Dipole Moments of Ethyl Sulfide in the Gas Phase

The pure rotational spectrum of ethyl sulfide has been measured from 12 to 21 GHz in a 1 K jet-cooled expansion using a Fourier-transform microwave (FTMW) spectrometer. Prominent features in the spectrum are assigned to transitions from three conformational isomers. Additional assignments of the 13C and 34S isotopomer spectra of these conformers effectively account for all of the remaining transitions in the spectrum. Accurate “heavy-atom” substitution structures are obtained via a Kraitchman analysis of 14 rotational parameter sets, permitting definitive identification of the molecular structures of the three conformers. Two of the structures designated as the gauche–gauche (GG) and trans–trans (TT) conformers have symmetric forms with C2 and C2v symmetries, respectively, and the third trans–gauche (TG) configuration is asymmetric. The components of the electric dipole moment along the principal inertial axes have been determined from Stark measurements and are consistent with these structural assignment...

THZ-FREQUENCY SPECTROSCOPIC SENSING OF DNA AND RELATED BIOLOGICAL MATERIALS

The terahertz frequency absorption spectra of DNA molecules reflect low-frequency internal helical vibrations involving rigidly bound subgroups that are connected by the weakest bonds, including the hydrogen bonds of the DNA base pairs, and/or non-bonded interactions. Although numerous difficulties make the direct identification of terahertz phonon modes in biological materials very challenging, recent studies have shown that such measurements are both possible and useful. Spectra of different DNA samples reveal a large number of modes and a reasonable level of sequence-specific uniqueness. This chapter utilizes computational methods for normal mode analysis and theoretical spectroscopy to predict the low-frequency vibrational absorption spectra of short artificial DNA and RNA. Here the experimental technique is described in detail, including the procedure for sample preparation. Careful attention was paid to the possibility of interference or etalon effects in the samples, and phenomena were clearly differentiated from the actual phonon modes. The results from Fourier-transform infrared spectroscopy of DNA macromolecules and related biological materials in the terahertz frequency range are presented. In addition, a strong anisotropy of terahertz characteristics is demonstrated. Detailed tests of the ability of normal mode analysis to reproduce RNA vibrational spectra are also conducted. A direct comparison demonstrates a correlation between calculated and experimentally observed spectra of the RNA polymers, thus confirming that the fundamental physical nature of the observed resonance structure is caused by the internal vibration modes in the macromolecules. Application of artificial neural network analysis for recognition and discrimination between different DNA molecules is discussed.

Classification of Select Category A and B Bacteria by Fourier Transform Infrared Spectroscopy

Fourier transform infrared (FT-IR) spectroscopy historically is a powerful tool for the taxonomic classification of bacteria by genus, species, and strain when they are grown under carefully controlled conditions. Relatively few reports have investigated the determination and classification of pathogens such as the National Institute of Allergy and Infectious Diseases (NIAID) Category A Bacillus anthracis spores and cells (BA), Yersinia species, Francisella tularensis (FT), and Category B Brucella species from FT-IR spectra. We investigated the multivariate statistics classification ability of the FT-IR spectra of viable pathogenic and nonpathogenic NIAID Category A and B bacteria. The impact of different growth media, growth time and temperature, rolling circle filter of the data, and wavelength range were investigated for their microorganism differentiation capability. Viability of the bacteria was confirmed by agar plate growth after the FT-IR experimental procedures were performed. Principal component analysis (PCA) was reduced to maps of two PC vectors in order to distill the FT-IR spectral features into manageable, visual presentations. The PCA results of the strains of BA, FT, Brucella, and Yersinia spectra from conditions of varying growth media and culture time were readily separable in two-dimensional (2D) PC plots. FT spectra were separated from those of the three other genera. The BA pathogenic spore strains 1029, LA1, and Ames were clearly differentiated from the rest of the dataset. Yersinia rhodei, Y. enterocolitica, and Y. pestis species were distinctly separated from the remaining dataset and could also be classified by growth media. Different growth media produced distinct subsets in the FT, BA, and Yersinia spp. regions in the 2D PC plots. Various 2D PC plots provided differential degrees of separation with respect to the four viable bacterial genera including the BA sub-categories of pathogenic spores, vegetative cells, and nonpathogenic vegetative cells. This work provided evidence that FT-IR spectroscopy can indeed separate the four major pathogenic bacterial genera of NIAID Category A and B biological threat agents including details according to the growth conditions and statistical parameters.

Mid-Infrared Emission from Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a powerful analytical technique for detecting and identifying trace elemental contaminants by monitoring the visible atomic emission from small plasmas. However, mid-infrared (MIR), generally referring to the wavelength range between 2.5 to 25 μm, molecular vibrational and rotational emissions generated by a sample during a LIBS event has not been reported. The LIBS investigations reported in the literature largely involve spectral analysis in the ultraviolet–visible–near-infrared (UV-VIS-NIR) region (less than 1 μm) to probe elemental composition and profiles. Measurements were made to probe the MIR emission from a LIBS event between 3 and 5.75 μm. Oxidation of the sputtered carbon atoms and/or carbon-containing fragments from the sample and atmospheric oxygen produced CO2 and CO vibrational emission features from 4.2 to 4.8 μm. The LIBS MIR emission has the potential to augment the conventional UV-VIS electronic emission information with that in the MIR region.

Long-wave, infrared laser-induced breakdown (LIBS) spectroscopy emissions from energetic materials.

Laser-induced breakdown spectroscopy (LIBS) has shown great promise for applications in chemical, biological, and explosives sensing and has significant potential for real-time standoff detection and analysis. In this study, LIBS emissions were obtained in the mid-infrared (MIR) and long-wave infrared (LWIR) spectral regions for potential applications in explosive material sensing. The IR spectroscopy region revealed vibrational and rotational signatures of functional groups in molecules and fragments thereof. The silicon-based detector for conventional ultraviolet–visible LIBS operations was replaced with a mercury–cadmium–telluride detector for MIR–LWIR spectral detection. The IR spectral signature region between 4 and 12 μm was mined for the appearance of MIR and LWIR–LIBS emissions directly indicative of oxygenated breakdown products as well as dissociated, and/or recombined sample molecular fragments. Distinct LWIR–LIBS emission signatures from dissociated-recombination sample molecular fragments between 4 and 12 μm are observed for the first time.

Mid-Infrared Laser-Induced Breakdown Spectroscopy Emissions from Alkali Metal Halides

CLAYTON S.-C. YANG,* E. BROWN, UWE HOMMERICH, SUDHIR B. TRIVEDI, ALAN C. SAMUELS, and A. PETER SNYDER Battelle Eastern Science and Technology Center, Aberdeen, Maryland 21001 (C.S.-C.Y.); Department of Physics, Hampton University, Hampton, Virginia 23668 (E.B., U.H.); Brimrose Corporation of America, Baltimore, Maryland 21152 (S.B.T.); and Edgewood Chemical Biological Center, Aberdeen Proving Ground, Maryland 21010-5424 (A.C.S., A.P.S.)

Mid-Infrared, Long Wave Infrared (4–12 μm) Molecular Emission Signatures from Pharmaceuticals Using Laser-Induced Breakdown Spectroscopy (LIBS)

In an effort to augment the atomic emission spectra of conventional laser-induced breakdown spectroscopy (LIBS) and to provide an increase in selectivity, mid-wave to long-wave infrared (IR), LIBS studies were performed on several organic pharmaceuticals. Laser-induced breakdown spectroscopy signature molecular emissions of target organic compounds are observed for the first time in the IR fingerprint spectral region between 4–12 μm. The IR emission spectra of select organic pharmaceuticals closely correlate with their respective standard Fourier transform infrared spectra. Intact and/or fragment sample molecular species evidently survive the LIBS event. The combination of atomic emission signatures derived from conventional ultraviolet–visible-near-infrared LIBS with fingerprints of intact molecular entities determined from IR LIBS promises to be a powerful tool for chemical detection.

Ion pair formation in water clusters: a theoretical study

Abstract Two hydrated ion pairs of the formula (H3O+)(H2O)3 (OH−) are studied using Hartree-Fock and MP2 wavefuctions with a 6-311 + + G∗∗ basis set. Two neutral water pentamers are also studied for comparison. Thermodynamics, IR spectra, dipole moments, rotational constants and spatial extent of the four clusters are examined in detail. Agreement of calculated thermodynamic quantities and IR spectra with experimental values is significant. The hydrated ion pairs are stablized more by electron correlation than the neutral species. This can be partially explained in terms of the strained configuration of these hydrated ion pairs. The hydrated ion pairs also have a suprisingly small calculated dipole moment.

THz absorption signature detection of genetic material of E. coli and B. subtilis

The development of efficient biological agent detection techniques requires in-depth understanding of THz absorption spectral features of different cell components. Chromosomal DNA, RNAs, proteins, bacterial cell wall, proteinaceous coat might be essential for bacterial cells and spores THz signature. As a first step, the DNAs contribution into entire cell THz spectra was analyzed. The experimental study of cells and DNAs of E. coli and cells/spores and DNA of Bacillus subtilis was conducted. Samples were prepared in the form of water solutions (suspension) with the concentrations in the range 0.01-1 mg/ml. The measurable difference in the THz transmission spectra of E. coli and Bacillus subtilis DNAs was observed. The correlation between chromosomal DNA signature and a corresponding entire spore/cell signature was observed. This correlation was especially pronounced for spores of Bacillus subtilis and their DNA. These experimental results justify our approach to develop a model for THz signatures of biological simulants and agents. In parallel with the experimental study, for the first time, the computer modeling and simulation of chromosome DNAs of E. coli and Bacillus subtilis was performed and their THz signatures were calculated. The DNA structures were optimized using the Amber software package. Also, we developed the initial model of the DNA fragment poly(dAT)-poly(dTA) solvated in water to be used in the simulations of genetic material (DNA and RNA) of spores and cells. Molecular dynamical simulations were conducted using explicit solvent (3-point TIP3P water) and implicit solvent (generalized Born) models. The calculated THz signatures of E. coli and Bacillus subtilis DNAs and poly(dAT)-poly(dTA) reproduce many features of our measured spectra. The results of this study demonstrate that THz Fourier transform infrared spectroscopy is a promising tool in generating spectral data for complex biological objects such as bacterial cells and spores.