Standoff infrared and Raman spectroscopy (SIRS and SRS) detection systems were designed from commercial instrumentation and successfully tested in remote detection of high explosives (HE). The SIRS system was configured by coupling a Fourier-transform infrared interferometer to a gold mirror and detector. The SRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HE samples were detected on stainless steel surfaces as thin films (2-30 microg/cm(2)) for SIRS experiments and as particles (3-85 mg) for SRS measurements. Nitroaromatic HEs: TNT, DNT, RDX, C4, and Semtex-H and TATP cyclic peroxide homemade explosive were used as targets. For the SIRS experiments, samples were placed at increasing distances and an infrared beam was reflected from the stainless steel surfaces coated with the target chemicals at an angle of approximately 180 degrees from surface normal. Stainless steel plates containing TNT and RDX were first characterized for coverage distribution and surface concentration by reflection-absorption infrared spectroscopy. Targets were then placed at the standoff distance and SIRS spectra were collected in active reflectance mode. Limits of detection (LOD) were determined for all distances measured for the target HE. LOD values of 18 and 20 microg/cm(2) were obtained for TNT and RDX, respectively, for the SIR longest standoff distance measured. For SRS experiments, as low as 3 mg of TNT and RDX were detected at 7 m source-target distance employing 488 and 514.5 nm excitation wavelengths. The first detection and quantification study of the important formulation C4 is reported. Detection limits as function of laser powers and acquisition times and at a standoff distance of 7 m were obtained.
We have developed a rapid, sensitive, and quantitative method for identification of microRNA (miRNA) sequences in multicomponent mixtures using surface-enhanced Raman spectroscopy (SERS). The method uses Ag nanorod array substrates prepared by oblique angle vapor deposition as the SERS platform. We show that Ag nanorod-based SERS spectra are uniquely characteristic for each miRNA sequence studied, and that the spectral reproducibility is sufficient for quantitative analysis of miRNA profiles in multicomponent mixtures using partial least squares (PLS) regression analysis. This method was applied to individual sample mixtures consisting of two, three, and five miRNAs. Separate PLS models were generated for the two-, three-, and five-component mixtures from >150 calibration spectra covering a concentration range of 6 to 150 microM for each miRNA. The PLS models were externally validated with independent test samples resulting in root mean square errors of prediction (RMSEP) of 7.4, <7.4, and <10 microM for the two-, three-, and five-component models, respectively. These results demonstrate the applicability of SERS for quantitative detection and profiling of miRNAs and suggest that SERS may prove to be a novel, label-free method for identification of disease biomarkers.
Fiber Optic Coupled Reflection/Absorption Infrared Spectroscopy (RAIRS) has been investigated as a potential technique for developing methodologies of detection and quantification of explosive residues on metallic surfaces. TNT, DNT, HMX, PETN, and Tetryl were detected at loading concentrations less than 400 ng/cm 2 . Data were analyzed using Chemometrics statistical analysis routines. In particular, partial least squares multivariate analysis (PLS) was used for quantification studies. Peak areas were also used for data analysis to compare with linear multivariate analysis. The measurements resulted in intense absorption bands in the fingerprint region of the infrared spectrum that were used to quantify the target threat chemicals and to calculate the limit of detection for each compound. Micro-RAIRS vibrational imaging was also used for characterization of the distribution and form of layers of explosives deposited on stainless steel sheets. The degree of homogeneity depended strongly on the method of deposition. The images were generated by calculating the area under vibrational signals of 15 lm 9 15 lm grids with a separation of 15 lm. Histograms of the maps were generated and the homogeneity was evaluated by using standard deviations, mean kurtosis, skewness, and moments of distributions obtained. Methanol solutions of High Explosives (HE) resulted in the optimum distributions on the stainless steel surfaces tested and therefore, Methanol selected as the preferred solvent for the Fiber Optics Coupled-RAIRS experiments.
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