Discrimination of gallbladder stone employing Laser-Induced Breakdown Spectroscopy (LIBS) and Photoacoustic Spectroscopy (PAS).

Compositional analysis of gallstone samples has been carried out, using Laser-Induced Breakdown Spectroscopy (LIBS) and Photoacoustic Spectroscopy (PAS). Classification of gallstone has been made on the basis of intensities of the inorganic and organic constituents present in the LIBS spectra. A regression plot is drawn between LIBS spectral intensities of organic & inorganic elements and the stoichiometric ratio of Cholesterol, Bilirubin and Calcium Carbonate. Atomic lines of various elements, as well as molecular signatures of CaO Orange band, CN Violet band, and C2 Swan band, are observed in LIBS spectra. The relative hardness of gallstones is estimated from the intensity ratio of ionic to neutral atomic lines of the species observed in LIBS spectra. PAS is used for detecting molecular constituents in the gallstones. Principal Component Analysis (PCA) is performed for the discrimination of gallstones. It is found that PAS data, in combination with LIBS provide a suitable method for the compositional analysis of gallstones.

Standoff pump-probe photothermal detection of hazardous chemicals.

A novel pump-probe Photothermal methodology using Quartz Tuning Fork (QTF) detector has been demonstrated for the first time. A tunable mid-IR Quantum Cascade Laser (QCL) and a CW fixed wavelength visible laser have been used as the pump and probe beam respectively. The developed Photothermal (PT) technique is based on Quartz Tuning Fork (QTF) detector for the detection of hazardous/explosive molecules adsorbed on plastic surface and also in aerosols form. PT spectra of various trace molecules in the fingerprinting mid- infrared spectral band 7-9 µm from distance of 25 m have been recorded. The PT spectra of explosives RDX, TNT and Acetone have been recorded at very low quantities. Acetone is the precursor of explosive Tri-Acetone Tri-Phosphate (TATP). The experimentations using pump and probe lasers, exhibit detection sensitivity of less than 5 µg/cm2 for RDX, TNT powders and of ~ 200 nl quantity for Nitrobenzene (NB) and Acetone (in liquid form) adsorbed on surfaces, from a distance of ~ 25 m. The sensitivity of the same order achieved from a distance of 15 m by using only a mid-IR tunable pump laser coupled to QTF detector. Thus the pump-probe PT technique is more sensitive in comparison to single tunable QCL pump beam technique and it is better suited for standoff detection of hazardous chemicals for homeland security as well as for forensic applications.

Ultrasensitive photoacoustic sensor based on quantum cascade laser spectroscopy.

The paper focuses on development of ultra-sonic detection system based on laser photoacoustic spectroscopic technique and processing of signal for detection of very low quantity chemicals, explosive materials, and mixtures of these hazardous molecules. The detection system has been developed for the first time with specially designed one side open photo-acoustic cell having high quality factor. Explosive and Hazardous materials like RDX, DNT, PETN, Gun Powder, TATP (Tri acetone tri-peroxide) and their simulants like Acetone were detected in 7 to 9µm wavelength band. Lock in amplifier electronic instrument was used for the detection of hazardous chemicals and mixture of explosives in very low quantity. Detection limit of the photoacoustic ultrasonic sensor was also carried out of powder, liquid and adsorbed on surfaces.

Vibrationally selective radiative and non-radiative transitions in gaseous hydrogen molecules.

An efficient vibrationally selective technique to build-up the v″=1 vibrational levels in gaseous hydrogen is demonstrated using stimulated Raman pumping (SRP). Both photo-acoustic Raman spectroscopy (PARS) and coherent anti-Stokes Raman spectroscopy (CARS) are used to study non-radiative and radiative (v″=0 and v″=1) transitions in gaseous H(2) molecules. The population fraction in the v″=1 vibrational level has been estimated using combined photo-acoustic and coherent anti-Stokes Raman spectroscopy with stimulated Raman pumping.

Detection sensitivity of laser-induced breakdown spectroscopy for Cr II in liquid samples.

The performance of laser-induced breakdown spectroscopy (LIBS) has been evaluated for detection of toxic metals such as Cr in water. Pure aqueous solutions (unitary matrix) with variable Cr concentration were used to construct calibration curves and to estimate the LIBS limit of detection (LOD). The calibration curves for Cr in a binary matrix (Cr plus Cd) and a tertiary matrix (Cr plus Cd and Co) were used to evaluate the matrix effect on the LOD. The LOD for Cr was found to be 1.1, 1.5, and 2.0 ppm (parts in 10(6)) in a unitary, binary, and tertiary matrix, respectively. Once calibrated, the system was utilized for the detection and quantification of the Cr in tannery wastewater collected from different locations in the industrial area of Kanpur, India, where Cr concentrations were determined to be far higher than the U.S. Environmental Protection Agency safe drinking water limit of 0.05 ppm.

Quantitative analysis of gallstones using laser-induced breakdown spectroscopy.

The utility of laser-induced breakdown spectroscopy (LIBS) for categorizing different types of gallbladder stone has been demonstrated by analyzing their major and minor constituents. LIBS spectra of three types of gallstone have been recorded in the 200-900 nm spectral region. Calcium is found to be the major element in all types of gallbladder stone. The spectrophotometric method has been used to classify the stones. A calibration-free LIBS method has been used for the quantitative analysis of metal elements, and the results have been compared with those obtained from inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurements. The single-shot LIBS spectra from different points on the cross section (in steps of 0.5 mm from one end to the other) of gallstones have also been recorded to study the variation of constituents from the center to the surface. The presence of different metal elements and their possible role in gallstone formation is discussed.