Jagdish P. Singh

Characterization of malignant tissue cells by laser-induced breakdown spectroscopy

Cancer diagnosis and classification is extremely complicated and, for the most part, relies on subjective interpretation of biopsy material. Such methods are laborious and in some cases might result in different results depending on the histopathologist doing the examination. Automated, real-time diagnostic procedures would greatly facilitate cancer diagnosis and classification. Laser-induced breakdown spectroscopy (LIBS) is used for the first time to our knowledge to distinguish normal and malignant tumor cells from histological sections. We found that the concentration of trace elements in normal and tumor cells was significantly different. For comparison, the tissue samples were also analyzed by an inductively coupled plasma emission spectroscopy (ICPES) system. The results from the LIBS measurement and ICPES analysis were in good agreement.

Laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is an emerging technique for materials analysis that is rapidly maturing and is becoming increasingly accepted as an important tool in analytical chemistry. LIBS is also advancing as a technology as new commercial instruments are becoming available. The core attributes of (1) real-time analysis; (2) no sample preparation; (3) high sensitivity; (4) high specificity for materials identification; (5) sensitivity to all chemical elements in each laser shot; as well as (6) uncommon versatility of point, standoff, as well as underwater-sensing provides a strong argument that LIBS will make a significant impact on science and society. A bibliometric study of the LIBS literature shows clearly that the importance and the number of application areas related to LIBS and laser-based techniques continues to grow. The driving force for this growth appears to be its rapid and remote analysis capabilities for a wide variety of sample types, including the analysis where the requirement for little or no sample preparation is important and the consumption of very small amounts of the sample is critical. Additionally, the relative ease with which LIBS can be combined with other techniques, particularly molecular techniques such as Raman spectroscopy is an advantage. For proof of the impact that LIBS is already making, one needs to go no further than to learn about the next Mission toMars scheduled for 2011/2012 where LIBS is the prime chemical analytical tool of choice. This special issue on LIBS presents the latest progress in this rapidly evolving spectroscopic technique. The 18 articles represent a good balance between fundamental research on the LIBS phenomenology and the applied use of this technique. The papers presented indicate to the reader the active areas in the LIBS field. For example, research is focused on improving the sensitivity of the technique shows that the approach of double-pulse is still of interest. The understanding of physical phenomenon at the early stage of the plasma or the comparison between singleand double-pulse is still attracting further research. While Nd:YAG lasers operating at the fundamental wavelength 1,064 nm or its harmonics are most used for the laser-induced plasma generation in LIBS applications; some papers are focused on the use of the CO2 laser at 10.6 μm. In some cases, the use of this infrared laser may present benefits which can be further exploited. The analysis of slurries is a field of application where LIBS can offer a powerful tool for real-time analysis as the current analytical approaches in this field by conventional This article was published in the special issue Laser-Induced Breakdown Spectroscopy with Guest Editors Jagdish P. Singh, Jose Almirall, Mohamad Sabsabi, and Andrzej Miziolek.

Laser-induced breakdown spectrometry as a multimetal continuous-emission monitor

Laser-induced breakdown spectrometry (LIBS) has been used to detect atomic and molecular species in various environments. LIBS has the capability to be used as a continuous-emission monitor to monitor toxic-metal concentrations in stack emissions. Recently a mobile LIBS system was calibrated in our laboratory and tested as a multimetal continuous-emission monitor during a joint U.S. Department of Energy-Environmental Protection Agency (EPA) test. LIBS measurements were performed with three sets of metal concentrations at the EPA Rotary Kiln Incinerator Simulator. The LIBS system successfully measured concentrations of Cr, Pb, Cd, and Be in near real time in this test. Real-time LIBS data were averaged and compared with data obtained from an EPA reference method that was conducted concurrently with LIBS. The details of the LIBS calibration and results of these LIBS measurements are described.

Gold-nanoparticle-based miniaturized laser-induced fluorescence probe for specific DNA hybridization detection: studies on size-dependent optical properties

A compact, highly specific, inexpensive and user friendly optical fibre laser-induced fluorescence (LIF) sensor based on fluorescence quenching by nanoparticles has been developed to detect single-strand (ss-) DNA hybridization at femtomolar level. The fluorescence of fluorophore-tagged ss-DNA increases by a factor of 80 when it binds to a complimentary DNA, while the addition of single-base mismatch DNA had no effect on the fluorescence efficiency. We present theoretical and experimental results on dye fluorescence quenching induced by gold nanoparticles having different particle sizes. Fluorescence spectra clearly show that the quenching efficiency decreases with increasing size of the gold nanoparticles and increasing the distance between dye and nanoparticles. The mechanism of size- and distant-dependent fluorescence quenching has been discussed. Effects of various influential experimental parameters and configurations were investigated in order to optimize and miniaturize the sensor performance.

Optical emission from laser-induced breakdown plasma of solid and liquid samples in the presence of a magnetic field

The optical properties of laser-induced plasma generated firm solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an approximately 5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3-10-micros time delay after plasma formation in the laser energy range 10-50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3-25 micros the energy range 50-200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.

Parametric study of a fiber-optic laser-induced breakdown spectroscopy probe for analysis of aluminum alloys

Abstract In the present work we demonstrate a fiber-optic laser-induced breakdown spectroscopy (FO LIBS) system for delivering laser energy to a sample surface to produce a spark as well as to collect the resulting radiation from the laser-induced spark. In order to improve the signal/background (S/B) ratio, various experimental parameters, such as laser energy, gate delay and width, detector gain, lenses of different focal lengths and sample surface, were tested. In order to provide high reliability and repeatability in the analysis, we also measured plasma parameters, such as electron density and plasma temperature, and determined their influence on the measurement results. The performance of FO LIBS was also compared with that of a LIBS system that does not use a fiber to transmit the laser beam. LIBS spectra with a good S/B were recorded at 2-μs gate delay and width. LIBS spectra of six different Al alloy samples were recorded to obtain calibration data. We were able to obtain linear calibration data for numerous elements (Cr, Zn, Fe, Ni, Mn, Mg and Cu). A linear calibration curve for LIBS intensity ratio vs. concentration ratio reduces the effect of physical variables (i.e. shot-to-shot power fluctuation, sample-to-surface distance, and physical properties of the samples). Our results reveal that this system may be useful in designing a high-temperature LIBS probe for measuring the elemental composition of Al melt.

2,4,6-Trinitrotoluene detection by laser-photofragmentation-laser-induced fluorescence.

Photofragmentation (PF) and subsequent nitric oxide (NO) laser-induced fluorescence (LIF) is being developed to measure the concentration of energetic materials (EMs) in soil and other media. Laser radiation near 226 nm photodissociates gas-phase EM to NO(2), which predissociates into NO that gives an intense luminescence. The EM concentration is inferred from the intensity of the NO fluorescence. We have studied the factors that affect the PF-LIF signal intensity, including the effect of buffer gas on the LIF spectrum of pure NO, the effect of 2,4,6-trinitrotoluene (TNT) pressure on the PF-LIF spectrum, the effect of buffer-gas pressure on the PF-LIF signal intensity of pure TNT, and the effect of temperature on the PF-LIF spectra of pure TNT and of TNT in simulated soil. Heating of the TNT sample above 343 K was found to increase the magnitude of the PF-LIF signal intensity significantly, but also was found to cause physical and chemical changes in the TNT sample. The effects of heating and evacuating on the TNT sample were investigated. TNT concentration calibration curves were obtained for TNT in simulated soil mixtures. The limit of detection of TNT in soil was estimated to be 40 parts in 10(9).

Evaluation of the potential of laser-induced breakdown spectroscopy for detection of trace element in liquid.

Abstract The analytical figure of merit of the potential of laser-induced breakdown spectroscopy (LIBS) has been evaluated for detection of trace element in liquid. LIBS data of Mg, Cr, Mn, and Re were studied. Various optical geometries, which produce the laser spark in and at the liquid sample, were tested. The calibration curves for Mg, Cr, Mn, and Re were obtained at the optimized experimental conditions with bulk liquid and in liquid jet. It was found that measurements using a liquid jet provide better detection limits than bulk liquid measurements. The limits of detection (LOD) of Mg, Cr, Mn, and Re in the present liquid jet measurement are found to be 0.1, 0.4, 0.7, and 8 ppm, respectively. The LOD of Mg using Mg 279.55 nm was compared with the values found in other liquid work.

Laser-induced breakdown spectroscopy of molten aluminum alloy.

We have demonstrated that a fiber-optic laser-induced breakdown spectroscopy (LIBS) probe is suitable for measuring the concentration of minor constituents of a molten Al alloy in a laboratory furnace. For the first time to our knowledge we are able to record the LIBS spectra in several spectral regions of seven different molten Al alloy samples by inserting the LIBS probe inside the molten alloys, allowing us to obtain a ratio calibration curve for minor constituents (Cr, Mg, Zn, Cu, Si, etc.), using Fe as a reference element. A ratio calibration curve for Fe with a major element (Al) can also be obtained with which the concentration of Fe in the alloy can be determined. The effects of the surrounding atmosphere on the LIBS spectra of the molten alloy were investigated. Effects of focal length of the lens on the LIBS signals were also studied. LIBS spectra of a solid Al alloy recorded with the same LIBS probe were compared with the LIBS spectra of the molten alloy. Our results suggest that the LIBS probe is useful for monitoring the elemental composition of an Al melt in an industrial furnace at different depths and different positions inside the melt.

Study of laser-induced breakdown emission from liquid under double-pulse excitation.

The application of laser-induced breakdown spectroscopy to liquid samples, by use of a Nd:YAG laser in double-pulse excitation mode, is described. It is found that the line emission from a magnesium ion or atom is more than six times greater for double-pulse excitation than for single-pulse excitation. The effect of interpulse separation on the emission intensity of a magnesium ion and a neutral atom showed an optimum enhancement at a delay of 2.5-3 micros. The intensity of neutral atomic line emission dominates the ion emission from the plasma for higher interpulse (>10 micros) separation. A study of the temporal evolution of the line emission from the plasma shows that the background as well as line emission decays faster in double-pulse excitation than in single-pulse excitation. The enhancement in the emission seems to be dominated by an increase in the volume of the emitting gas. The limit of detection for a magnesium solution improved from 230 parts per billion (ppb) in single-pulse mode to 69 ppb in double-pulse mode.