Laser Induced Breakdown Spectroscopy (LIBS) is an appealing technique to study laser-induced plasmas(LIPs), both from the basic diagnostics point of view and for analytical applications. LIPs are complexdynamic systems, expanding at supersonic velocities and undergoing a transition between differentplasma regimes. If the Local Thermodynamic Equilibrium (LTE) condition is valid for such plasmas, severalanalytical methods can be employed and fast quantitative analyses can be performed on a variety ofsamples. In the present paper, a discussion about LTE is carried out and an innovative application to theanalysis of the alexandrite gemstone is presented. In addition, a study about the influence of plasmaparameters on the performance of LTE-based methods is reported for bronze and brass targets.

The interaction of nanoparticles with proteins has emerged as a key issue in addressing the problem of nanotoxicity. We investigated the interaction of silver nanoparticles (AgNPs), produced by laser ablation with human ubiquitin (Ub), a protein essential for degradative processes in cells. The surface plasmon resonance peak of AgNPs indicates that Ub is rapidly adsorbed on the AgNP surface yielding a protein corona; the Ub-coated AgNPs then evolve into clusters held together by an amyloid form of the protein, as revealed by binding of thioflavin T fluorescent dye. Transthyretin, an inhibitor of amyloid-type aggregation, impedes aggregate formation and disrupts preformed AgNP clusters. In the presence of sodium citrate, a common stabilizer that confers an overall negative charge to the NPs, Ub is still adsorbed on the AgNP surface, but no clustering is observed. Ub mutants bearing a single mutation at one edge ? strand (i.e. Glu16Val) or in loop (Glu18Val) behave in a radically different manner. Human ubiquitin forms amyloids on the surface of silver nanoparticles produced by laser ablation, which induce clustering of the nanoparticles and thioflavin T fluorescence. In the presence of sodium citrate as a stabilizer, ubiquitin only forms a protein corona. A single mutation (Glu16Val) at one edge ? strand of the protein can deeply influence the amyloid transition (see figure). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An ultrashort (100 fs) Ti:Sapphire pulsed laser has been employed in order toproduce nanostructures by pulsed ablation of a graphite target in water. Different (10-100-1000 Hz) repetition rates have been used, and the features of material produced have beeninvestigated by surface enhanced Raman spectroscopy (SERS) and scanning electron micro-scopy (SEM). SERS spectra show that a broad asymmetric band associated with diamond-likecarbon (DLC) is observed when repetition rates of 10 or 100 Hz are used. On the contrary,ablated species produced with 1 kHz pulses present a narrow peak at 1333 cm -1 , the typicalmode of diamond, which is, however, embedded in a DLC band centered at 1540 cm -1 . SEMimages show the presence of dispersed octahedral-shaped structures having a size from 1 to 5 ?m,in the case of 10 or 100 Hz repetition rates, and agglomerates of particles having a dimensionbelow 300 nm, when 1 kHz pulses are used.

Although the first nanoseconds to microseconds rule the resulting process yield of laser ablation in liquid, a comprehensive view involving combination of time-resolved measurement techniques is still lacking. In this paper, fundamental aspects of laser ablation of metals in water during the production of nanoparticles are discussed. Three fast diagnostic methods have been applied simultaneously. These are Optical Emission Spectroscopy for the plasma characterization, fast shadowgraph for plasma and cavitation bubble dynamics and laser scattering for the mechanisms of delivery of the produced materials in the liquid. Moreover, in order to validate the discussion, the effect on cavitation dynamics of the ablation of bulk and wire-shaped targets has been investigated together with the relative nanoparticles production yield. Unusual arrow-bow ejection phenomena between the cavitation bubble and the wire result in suppressed material back-deposition, causing efficient ejection of ablated matter into the liquid. The presented nanosecond and microsecond-resolved analysis allows estimating the timescale and role of the basic mechanisms involved in laser ablation in liquids as well as the thermodynamic characteristics of the processes.

Laser-induced breakdown spectroscopy (LIBS) is a fast and reliable technique suitable for the simultaneous qualitative and quantitative analysis of major and trace elements in samples of various nature and origin. In last decades, the use of metal accumulator plants, in combination with compost, has become a cheap and sustainable alternative technique to lower soil contamination by toxic heavy metals. In the present work, theLIBS technique has been applied to measure the concentrations of selected elements, including Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Sr, and Zn, in two composts of different origin and nature and four accumulator plant species (Atriplex halimus, Brassica alba, Brassica napus, and Eruca vesicaria). The plant samples were analyzed either as bulk plant material or as specific organs (i.e. shoots and roots). The concentrations measured by LIBS were assessed by complementary induced coupled plasma-optical emission spectroscopy. The significant correlation found between the data obtained by the two techniques (R=0.732-0.999) supports the feasibility of LIBS for fast screening of major, trace and toxic elements in plant and compost samples. In conclusion, the LIBS technique shows promising for further applications in soil remediation as well as in agriculture.

In the present work, laser ablation of a graphite target submerged inpure water was tested as a methodology for the production of carbon-basednanoparticles. The effect of varying the external pressure imposed to the liquidwas investigated for the first time, in the range from 1 to 146 atm. Single or doublelaser pulses were used to ablate the target and the produced nanoparticles werecharacterized by atomic force microscopy (AFM) and by Raman spectroscopy. Aspectroscopic study of the laser induced plasma features was carried out with a Titarget and interpreted in terms of laser-induced cavitation phenomena. Tubularnanoparticles of 25 nm average diameter were obtained only by single pulse (SP)ablation of graphite, while particles formed with the double pulse (DP) techniquemainly consisted of graphite particulates. At 1 atm, these tubular nanoparticles were few and mixed with diamondlike carbon,while at 146 atm they were produced in a larger amount, suggesting that the high density effect induced by pressure plays a keyrole for their generation.

A fast procedure for chemical analysis of different meteorites is presented, based on LIBS (Laser Induced Breakdown Spectroscopy). The technique is applied to several test cases (Dhofar 019, Dhofar 461, Sahara 98222, Toluca, Sikhote Alin and Campo del Cielo) and can be useful for rapid meteorite identification providing geologists with specific chemical information for meteorite classification. Concentration profiles of Fe, Ni and Co are simultaneously detected across the Widmanstatten structure of the iron meteorite Toluca with a view to determining cooling rates. The LIBS analysis of meteorites is also used as a laboratory test for analogous studies on the respective parent bodies (Mars, asteroids) in space exploration missions where one clear advantage of the proposed technique is that no direct contact with the sample is required.

Laser-Induced Breakdown Spectroscopy (LIBS) is a fast and reliable technique suitable for the simultaneous qualitative and quantitative analysis of major and trace elements in samples of various nature and origin. In last decades, the use of compost as an organic amendment has become a very common, cheap and sustainable agricultural practice to provide soil with organic matter and nutrients, although the content of heavy metals in compost may often represent a risk for its agronomic use. In the present work, the detection and concentration of selected macro- and micronutrients and heavy metals, including Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Sr, and Zn, in two commercial composts of different origin have been measured comparatively by LIBS and conventional Induced Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) techniques. In general LIBS data are in good agreement with the corresponding ICP-OES data. The best correlation of LIBS values with ICP-OES values are obtained at the laser wavelength of 532 nm for Al, Ca, K, Mg, Mn and Na, and at the wavelength of 355 nm for Cr, Cu, Fe, Pb, Sr and Zn. In conclusion, our results confirm the feasibility of LIBS for the quantitative analysis of several elements in composts with several advantages including no need of (or minimal) sample preparation, rapidity and relatively low costs, showing promising for further applications. However, a number of instrumental and substrate factors still need to be optimized to obtain a better performance for accuracy and precision of LIBS analysis for each element.

Analytical applications of Laser Induced Breakdown Spectroscopy (LIBS), namely optical emission spectroscopy of laser-induced plasmas, have been constantly growing thanks to its intrinsic conceptual simplicity and versatility. Qualitative and quantitative analysis can be performed by LIBS both by drawing calibration lines and by using calibration-free methods and some of its features, so as fast multi-elemental response, micro-destructiveness, instrumentation portability, have rendered it particularly suitable for analytical applications in the field of environmental science, space exploration and cultural heritage. This review reports and discusses LIBS achievements in these areas and results obtained for soils and aqueous samples, meteorites and terrestrial samples simulating extraterrestrial planets, and cultural heritage samples, including buildings and objects of various kinds.

This paper presents an evaluation of Laser Induced Breakdown Spectroscopy (LIBS) as a technique for gathering data relevant to Solar System geophysics. Two test cases were demonstrated: elemental analysis of chondrules in a chondrite meteorite, and space- resolved analysis of the interface between kamacite and taenite crystals in an octahedrite iron meteorite. In particular most major and minor elements (Fe, Mg, Si, Ti, Al, Cr, Mn, Ca, Fe, Ni, Co) in Sahara 98222 (chondrite) and its chondrules, as well as the profile of Ni content in Toluca (iron meteorite), were determined with the Calibration Free (CF) method. A special attention was devoted to exploring the possibilities offered by variants of the basic technique, such as the use of Fe I Boltzmann distribution as an intensity calibration method of the spectroscopic system, and the use of spatially resolved analysis. © 2014 Elsevier B.V. All rights reserved.

A modified version of the calibration-free (CF) method was applied to the analysis of a set of archaeological brooches made of various copper-based alloys and coming from the archaeological site of Egnatia (Apulia, Southern Italy). The developed methodology consists in determining the plasma temperature by reversing the set of equations employed in the usual CF algorithm, and it is thus referred to as "inverse method". The plasma temperature is determined for one certified standard, by using its known elemental composition as an input data, and then applied to the set of unknown samples to evaluate their composition in a CF mode. The feasibility of such an approach is demonstrated by comparing the results obtained with classical LIBS (drawing calibration lines with a series of matrix-matched certified standards) and with independent measurements performed with a conventional technique (LA-ICP-MS). © 2014 Elsevier B.V.

The excitation temperature of Laser Induced Plasmas (LIPs) of copper-based alloys was determined with an alternative approach, which reverses the procedure of calibration-free methods for quantitative analysis through Laser Induced Breakdown Spectroscopy (LIBS).The inverse method here proposed is based on the Local Thermodynamic Equilibrium (LTE) equations, which were applied to simulate the elemental composition of certified samples at different temperatures, assuming that the actual plasma temperature was the one providing the best agreement with certified data. This procedure was validated for a set of bronze and brass standard samples and in different experimental conditions, by changing laser pulse width (7 ns and 250 fs) and laser wavelength (1064 nm, 532 nm and 355 nm). The temperature determined with the inverse method was then employed to determine the elemental composition of archeological findings of different copper-based alloys from Southern Italy sites (from VII century B.C. to VII A.D.), in order to test its validity for the analysis of actual unknown samples. The obtained weight percentages showed a good correlation with those obtained with the calibration line method, which provided a further confirmation of the assumptions made. (C) 2012 Elsevier B.V. All rights reserved.

In the Laser-Induced Breakdown Spectroscopy (LIBS) technique, the existence of Local Thermodynamic Equilibrium (LTE) is the essential requisite for meaningful application of theoretical Boltzmann–Maxwell and Saha–Eggert expressions that relate fundamental plasma parameters and concentration of analyte species. The most popular criterion reported in the literature dealing with plasma diagnostics, and usually invoked as a proof of the existence of LTE in the plasma, is the McWhirter criterion [R.W.P. McWhirter, in: Eds. R.H. Huddlestone, S.L. Leonard, Plasma Diagnostic Techniques, Academic Press, New York, 1965, pp. 201–264]. However, as pointed out in several papers, this criterion is known to be a necessary but not a sufficient condition to insure LTE. The considerations reported here are meant to briefly review the theoretical analysis underlying the concept of thermodynamic equilibrium and the derivation of the McWhirter criterion, and to critically discuss its application to a transient and non-homogeneous plasma, like that created by a laser pulse on solid targets. Specific examples are given of theoretical expressions involving relaxation times and diffusion coefficients, as well as a discussion of different experimental approaches involving space and timeresolved measurements that could be used to complement a positive result of the calculation of the minimum electron number density required for LTE using the McWhirter formula. It is argued that these approaches will allow a more complete assessment of the existence of LTE and therefore permit a better quantitative result. It is suggested that the mere use of the McWhirter criterion to assess the existence of LTE in laser-induced plasmas should be discontinued.

In this paper the use of metallic nanoparticles (NPs) for improving Laser Induced Breakdown Spectroscopy (LIBS) is discussed. In the case of conductors an emission signal enhancement up to 1-2 orders of magnitude was obtained depositing NPs on the sample surface by drying a micro-drop of colloidal solution. The basic mechanisms of Nanoparticle Enhanced LIBS (NELIBS) were studied and the main causes of this significantly large enhancement were found to be related to the effect of NPs on the laser ablation process, in terms of a faster and more efficient production of seed electrons with respect to conventional LIBS. The characteristics of NELIBS-produced plasma were investigated by emission spectroscopy and spectrally resolved images. In spite of similar plasma parameters, the NELIBS plasma was found to have larger emission volume and longer persistence than the LIBS one. A method to determine NP concentration and size was also proposed, which involved depositing NPs on non-interacting substrates, and proved the feasibility of LIBS as a fast detection tool for a preliminary characterization of NPs. © 2014 Elsevier B.V.

In this paper emission spectra of the plasma produced by laser-matter interaction are discussed in terms of the correlation between the elementary plasma processes and the evolution of plasma parameters during the expansion. Three main stages have been identified and discussed in details: high density plasma, near equilibrium plasma and non-equilibrium plasma including molecular formation. In order to develop a comprehensive point of view on the correlation between plasma mechanisms and spectral emission features several concepts already discussed and elucidated in the plasma science have been adapted to the description of the laser induced plasma and to its ionizing and recombining character.

This paper focuses on the interpretation of the origin of the continuum radiation in Laser Induced Plasma(LIP) emission spectra, a subject that has received little consideration in the literature when compared to theanalysis of the line emission spectrum. The understanding of the spectral peculiarities observed immediatelyafter the laser pulse, when the continuum radiation prevails on discrete emission lines, can be extremelyimportant to retrieve the initial conditions of LIP and to correlate the produced plasma to the ablationmechanism. In this work, in addition to a qualitative interpretation of the LIP continuum in the initial stage ofexpansion, a methodology is proposed for a better measurement of the atomic temperature in the expansionstage of the LIP. Such methodology is based on the analysis of the combined Boltzmann and Planck plots. Theresults obtained stress once again the importance of considering non equilibrium effects in the initial stage ofLIP expansion.

Laser Induced Breakdown Spectroscopy (LIBS) is an analytical technique based on the optical emission spectroscopy of the plasma generated by high energy laser pulse and solid sample. LIBS allows to perform stand-off and in situ analysis with immediate response and a limit of detection (in the range of mgkg-1), and for these peculiarities is particularly suitable for analysis in the environmental field. In this work is presented a case of study where the elemental analysis of some polluted soils are obtained either with the classical calibration curve (CC) method or with a Local Thermodinamic Equilibrium (LTE)-based Calibration-Free (CF) method, in order to demonstrate the capability of this technique. It is important to underline that the latter methodology does not require the use of preliminary experiments with standard samples and so it does not have any limitation due to the matrix effect.Several polluted soil samples were analyzed by drawing calibration lines to determine the concentration of some trace metals (e.g., Cr, Pb, Cu, Zn, Sr, Ni), as well as those of some major elements (e.g., Fe, Mn, Mg). The elemental concentration (normalized by Fe concentration) was measured with ICP-OES and LIBS techniques respectively. For what concern LIBS measurements, a comparison was done between two different data treatment: the LTE-CF based method and the classical CC method. For some elements a comparison was tried between calibration lines and calibration-free data, in order to validate the latter techniques also for complex matrices such as soils.

Laser Induced Breakdown Spectroscopy (LIBS) is a fast and multi-elemental analytical technique particularly suitable for the qualitative and quantitative analysis of several elements in solid samples including metal alloys for metallurgy and jewellery, and cultural heritage materials. Due to negligible or virtually absent pre-treatments of samples, high sensitivity, simultaneous multielemental detection of major and trace elements, and especially capability for microanalysis with low sample consumption, LIBS has been recently used also for analysis of environmental samples, i.e., meteorites, soils, sediments, and vegetables.In the present work, the authors test the feasibility of the LIBS technique to be used during the remediation/restore of soils by plants (phytoremediation) and compost application. In detail, Cr, Cu, Fe, Pb, and Zn content were investigated in four plant species (i.e., Atriplex halimus, Brassica napus, Rucola sativa, and Sorghum bicolor) and two different composts, and concentration values compared with those obtained by ICP-OES.Although the LODs for the LIBS-detected elements were sometimes quite higher if compared with other analytical techniques, data obtained underline the capability of LIBS method for the monitoring of the studied elements in plants growing in polluted soils, also allowing to calculate a "translocation" factor between roots and leaves. Good results were obtained also for composts.Furthermore, as some metals like Cu and Fe have to be considered, below certain concentrations, micronutrients, the authors propose the application of the LIBS in investigating deficit in plant uptake (e.g., Fe-chlorosis), and/or to evaluate the concentration of nutrients (e.g., Ca, Mg, Mn) in amendments/fertilizers.