Raman and Laser Induced Fluorescence (LIF) spectroscopic techniques were used for studying Azotobacter vinelandii- a genus of free-living diazotrophic soil bacteria. Azotobacter has generated a great deal of interest owing to their unique mode of metabolism. It is a large, obligately aerobic soil bacterium, which has one of the highest respiratory rates known among living organisms and is able to grow on a wide variety of carbohydrates, alcohols and organic acids. The Raman Scattering of Azotobacter, incubated with gold nanoparticles, was examined with 532-nm as an excitation laser wavelength. The basic instrumentation for characterizing the bacteria by Raman spectroscopy employed a continuous wave (CW) frequency doubled Nd: YAG laser (532-nm) and a modified In-Photonics fiber optic state-of-art miniaturized Raman Probe. The surface enhancement effects allowed the observation of Raman spectra of such bacterial cells, and were excited in the visible region of wavelength at low incident power for minimum sample degradation. LIF spectra of Azotobacter were measured with a 410-nm CW diode laser as an excitation source, and a reflection probe to deliver laser beam on the sample and collect the LIF signal from the sample. Spectral contrast observed in gold particles conjugated bacteria, from nitrogen fixing and non-nitrogen fixing condition was analyzed for characterizing the bacteria cells, and the results are presented in the paper.
A Photomultiplier Tube (PMT) based optical fiber Raman sensor was developed for online
monitoring of nitrogen/oxygen concentration ratios in gaseous mixtures. The sensor employed a frequency
doubled 532 nm continuous wave (CW) Nd:YAG laser and a modified In-Photonics fiber optic state-of-art
miniaturized Raman Probe. The gaseous mixture was enclosed in a high pressure cell and subjected to
varying degrees of pressure. Raman signal of gaseous nitrogen and oxygen were first analyzed with a
miniature spectrometer. The detection system was then replacing by a Labview interfaced PMT module for
fast data acquisition and real time monitoring of relative Raman signals of nitrogen and oxygen.
Instrumentation features and sensor performances with different detection systems (i.e. spectrometer and
PMT) is presented in the paper.
A novel fiber optic prototype sensor based on Raman spectroscopy for qualitative and quantitative monitoring of various chemicals in the sample was developed. The sensor employs a high power 670nm laser diode as an excitation light source and a specially designed fiber optic Raman probe with launching and collecting fibers. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. The uniqueness of the sensor lies in its compact and stable design configuration, that includes carefully aligned optical components, viz. laser diode, filter holder, and miniature spectrometer. Developed sensor is immune to ambient light fluctuation and offers a cost effective solution for probing several species in harsh environment. Various issues like system fabrication, optimization, functional stability, signal/noise ratio, repeatibility etc are well addressed and presented in this paper.
Ethanol and methanol form the essential components in the hydrocarbon-based fuels, serving as transportation fuels also; and will likely play an increasingly important role in the future as crucial fuel components. The motivation of the present work is to differentiate such hydrocarbons from their mixture sample on the basis of their spectrum analysis for various ratios of their composition. A fiber optic Spontaneous Raman sensor is developed as a probe indicator for component detection of such hydrocarbon mixtures. The sensor employs a frequency doubled 532 nm continuous ND:YAG laser and a specially designed fiber optic Raman probe. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. Attractiveness of our scheme lies in the online determination of sample constituents without employing specially designed IR fiber with much-complicated and expensive IR spectroscopy and, with no alteration in sample physico-chemical structure. Spectral analysis techniques based on spectral shape band intensities and areas and some multi-component analysis are being tested to find the most effective tool for measuring ethanol and methanol from the mixture. The analysis results from these tests will be presented in the paper.