Laser-Induced Breakdown Spectroscopy Imaging Research Articles

Identification of Relevant Spectral Ranges in Laser-Induced Breakdown Spectroscopy Imaging Using the Fourier Space.

Laser-induced breakdown spectroscopy (LIBS) imaging has now a well-established position in the subject of spectral imaging, leveraging multi-element detection capabilities and fast acquisition rates to support applications both at academic and technological levels. In current applications, the standard processing pipeline to explore LIBS imaging data sets revolves around identifying an element that is suspected to exist within the sample and generating maps based on its characteristic emission lines. Such an approach requires some previous expert knowledge both on the technique and on the sample side, which hinders a wider and more transparent accessibility of the LIBS imaging technique by non-specialists. To address this issue, techniques based on visual analysis or peak finding algorithms are applied on the average or maximum spectrum, and may be employed for automatically identifying relevant spectral regions. Yet, maps containing relevant information may often be discarded due to low signal-to-noise ratios or interference with other elements. In this context, this work presents an agnostic processing pipeline based on a spatial information ratio metric that is computed in the Fourier space for each wavelength and that allows for the identification of relevant spectral ranges in LIBS. The results suggest a more robust and streamlined approach to feature extraction in LIBS imaging compared with traditional inspection of the spectra, which can introduce novel opportunities not only for spectral data analysis but also in the field of data compression.

Enhancing Diagnostic Capabilities for Occupational Lung Diseases Using LIBS Imaging on Biopsy Tissue.

Laser-induced breakdown spectroscopy (LIBS) imaging continues to gain strength as an influential bioanalytical technique, showing intriguing potential in the field of clinical analysis. This is because hyperspectral LIBS imaging allows for rapid, comprehensive elemental analysis, covering elements from major to trace levels consistently year after year. In this study, we estimated the potential of a multivariate spectral data treatment approach based on a so-called convex envelope method to detect exotic elements (whether they are minor or in trace amounts) in biopsy tissues of patients with occupational exposure-related diseases. More precisely, we have developed an approach called Interesting Features Finder (IFF), which initially allowed us to identify unexpected elements without any preconceptions, considering only the set of spectra contained in a LIBS hyperspectral data cube. This task is, in fact, almost impossible with conventional chemometric tools, as it entails identifying a few exotic spectra among several hundred thousand others. Once this detection was performed, a second approach based on correlation was used to locate their distribution in the biopsies. Through this unique data analysis pipeline to processing massive LIBS spectroscopic data, it was possible to detect and locate exotic elements such as tin and rhodium in a patient's tissue section, ultimately leading to a possible reclassification of their lung condition as an occupational disease. This review will thus demonstrate the potential of this new diagnostic tool based on LIBS imaging in addressing the shortcomings of approaches developed thus far. The proposed data processing approach naturally transcends this specific framework and can be leveraged across various domains of analytical chemistry, where the detection of rare events is concealed within extensive data sets.

Characterization of lithium phosphorus oxide thin film libraries by laser-induced breakdown spectroscopy imaging: A step towards high-throughput quantitative analyses

Elemental analysis is a challenge for the development of High Throughput Experimentation (HTE) on thin film materials, and an even greater one when it comes to screening lithium-containing battery materials. In this regard, Laser-Induced Breakdown Spectroscopy has been evaluated here for the quantitative analysis of lithium in libraries of Li2.3PO3.65 amorphous solid electrolyte films. The LIBS analysis of multiple samples with the same composition, but with thicknesses ranging from 50 to 700 nm, has revealed a linear trend in the intensity ratio of the Li I 610.35 nm and P I 214.91 nm emission lines, opening the way to rapid quantitative analysis of material libraries. The sensitivity of the technique finally allowed the detection of the Li I 670.79 nm emission line for film thicknesses down to 4 nm, corresponding to 0.2% of the ablated volume, or about 0.15 pg of Li.

High-Resolution High-Speed LIBS Microscopy

Laser-induced breakdown spectroscopy (LIBS) imaging instruments typically utilize lasers with repetition rates below 100 Hz since in most cases this regime provides a good balance of sampling frequency and laser pulse energy. However, measuring large sample areas of a several cm2 with high spatial resolution (<10 μm), at this frequency rate would be very time consuming since millions of spectral data points need to be collected in order to create a high-resolution image (3 h–15 h per cm2). In this work, we explore the approach to reduce, the acquisition time for high resolution LIBS imaging, or so-called μ-LIBS imaging, by using a laser operating in the kHz pulse repetition frequency (PRF) range. As a result, we describe and demonstrate a μ-LIBS imaging microscope which can image >6 cm2 sample areas with about 10 μm resolution in significantly shorter time (<20 min/cm2). The developed system opens a potential for variety of application fields where knowledge of elemental composition and elemental distribution is needed to perform conclusive analysis.

Characterization of Functional Coatings on Cork Stoppers with Laser-Induced Breakdown Spectroscopy Imaging.

Evaluating the efficiency of surface treatments is a problem of paramount importance for the cork stopper industry. Generically, these treatments create coatings that aim to enhance the impermeability and lubrification of cork stoppers. Yet, current methods of surface analysis are typically time-consuming, destructive, have poor representativity or rely on indirect approaches. In this work, the use of a laser-induced breakdown spectroscopy (LIBS) imaging solution is explored for evaluating the presence of coating along the cylindrical surface and in depth. To test it, several cork stoppers with different shaped areas of untreated surface were analyzed by LIBS, making a rectangular grid of spots with multiple shots per spot, to try to identify the correspondent shape. Results show that this technique can detect the untreated area along with other features, such as leakage and holes, allowing for a high success rate of identification and for its performance at different depths, paving the way for future industry-grade quality control solutions with more complex surface analysis.

Diagnosis and correction methods for spectral interference in the framework of LIBS imaging

Laser-Induced Breakdown Spectroscopy (LIBS) has become a powerful imaging technique for elemental characterization in analytical chemistry due to its advantages over other techniques. Major, minor, and trace elements are detected with high measurement dynamic, a low limit of detection and a high acquisition rate, allowing for the quick analysis of large sample surfaces. Today, chemometric tools are commonly used to ensure the most comprehensive and unbiased exploration of such spectroscopic data. However, the integration of the signal from a wavelength assumed to be specific to the element of interest remains the basic tool for generating a chemical distribution map from a hyperspectral dataset. This classical approach is based on a strong assumption, the specificity of the chemical information on the spectral domain being considered. Any spectral interference inevitably result in the generation of a biased distribution image. In this publication, we demonstrate how Principal Component Analysis (PCA) can diagnose the potential presence of a spectral interference and how Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) can ultimately correct it if necessary using a LIBS imaging dataset obtained from the analysis of a complex rock sample. The proposed approach combines the simplicity and effectiveness of the integration method with the diagnostic and correction capabilities of chemometric tools, providing a comprehensive solution for spectral interference in LIBS imaging.

Rapid and high-resolution visualization elements analysis of material surface based on laser-induced breakdown spectroscopy and hyperspectral imaging

It is extremely important for material analysis to visualize the elemental distribution of the sample surface quickly, sensibly, and high-resolution. Most point-to-point methods, such as laser-induced breakdown spectroscopy (LIBS), are incapable of achieving high spatial resolution at a reasonable time cost, while surface scanning methods such as hyperspectral imaging (HSI) is insensitive to concentration and material composition. In this work, we proposed a method coupling LIBS with HSI for rapid and high-resolution elemental distribution analysis of material surface. The method of point-to-point laser ablation and region of interest (ROI) segmentation were primarily employed. We further processed the LIBS and HSI spectra and distinguished different ROIs of material surface using principal component analysis. Significant LIBS and HSI lines that contributed to the classification of ROIs were also identified. Moreover, we examined the relationship between the principal component scores of LIBS and HSI spectra based on the Spearman correlation coefficient. Finally, the element visualization images of LIBS and LIBS-HSI were presented and compared. Compared with LIBS imaging, LIBS-HSI imaging offers a better spatial resolution that is at least 90.75 folds higher and a scanning time that is at least 6 times shorter. These results, together with the experimental process, indicate that LIBS-HSI appears to be a promising contender for rapid and high-resolution visual element analysis of material surface.

LIBS and Raman image fusion: An original approach based on the use of chemometric methodologies

Laser-induced breakdown spectroscopy (LIBS) imaging is a powerful and innovative technique with a constant increasing success and interest in many scientific fields. Using LIBS imaging, it is possible to highlight the presence of atoms in complex samples of different nature to achieve important spectral and spatial information. Simple preparation of the sample, an acquisition rate that can reach a speed of 1 kHz, a high spatial resolution (in the order of μm scale) and a sensitivity in the order of ppm are among the assets of this technique. An additional valuable aspect in the current LIBS setups is the possibility to acquire with the same LIBS platform spectroscopic responses resulting from another radiation-matter interaction, such as Raman measurements. The most common data treatment approach to LIBS imaging data is still univariate, i.e., the observation of maps at certain representative LIBS wavelength, but this prevents extracting all the useful information contained in the acquired spectra and obtaining an integral understanding of the correlation between the spatial and spectral information. Chemometrics and multivariate analysis in the framework of spectral unmixing can lead to these outcomes. Therefore, the aim of this work is to show the potential of investigating simultaneously LIBS and Raman imaging spectral data acquired on the same sample with the assistance of the unmixing method Multivariate Curve resolution – Alternating Least Squares (MCR-ALS). To illustrate the value of the thorough interpretation of fused LIBS and Raman images by unmixing analysis and the steps to take place in this kind of study, a real sample of a complex polymetallic mineral formed by several mineral phases incorporating carbonates, silicates and sulphides has been used. In this paper we will show that using a pipeline analysis already validated in another work of our group, it is possible to extract pure chemical contributions of the heterogeneous aforementioned minerals. The data analysis protocol presented is valid for the investigation of LIBS and Raman spectroscopies separately, but becomes much more valuable when the two acquired data sets for the same sample are simultaneously examined, leading to new aspects that would be hindered if not investigated at the same time with a suitable fusion approach.

Laser-induced breakdown spectroscopy-guided synergistic phototherapy: A theranostic platform mediated by a single laser wavelength

Currently, cancer theranostic studies have only focused on integrating existing medical imaging techniques with therapeutic modalities. Obviously, this strategy is not a real theranostic method, as diagnosis and therapy are based on different principles and require independent operation. Here, a cancer theranostic method was established by laser-induced breakdown spectroscopy (LIBS)-mediated synergistic photothermal/photodynamic therapy, which was activated by a single 1064-nm light for simultaneous tumor localization and treatment. PEGylated cobalt phosphate (CoP@PEG) nanoparticles (NPs) with strong near-infrared (NIR)-II absorbance, high photothermal conversion efficiency and a reactive oxygen species generation effect were fabricated, and they produced excellent antitumor outcomes under 1064-nm excitation, as evidenced by the substantial increase in HepG2 cell death in vitro and complete tumor elimination in vivo. Meanwhile, the diagnostic method of the LIBS imaging system used in the present study also uses 1064-nm light. The LIBS imaging system can provide fast, real-time analysis and imaging of elements and facilitate the localization of the tumor site by monitoring the distribution of CoP@PEG NPs for precise tumor treatment. We postulate that this theranostic platform will promote the development of further theranostic research.

Data fusion of LIBS and PIL hyperspectral imaging: Understanding the luminescence phenomenon of a complex mineral sample

Laser-induced breakdown spectroscopy (LIBS) imaging is an innovative technique that associates the valuable atomic, ionic and molecular emission signals of the parent spectroscopy with spatial information. LIBS works using a powerful pulse laser as excitation source, to generate a plasma exhibiting emission lines of atoms, ions and molecules present in the ablated matter. The advantages of LIBS imaging are potential high sensitivity (in the order of ppm), easy sample preparation, fast acquisition rate (up to 1 kHz) and μm scale spatial resolution (weight of the ablated material in the order of ng). Despite these positive aspects, LIBS imaging easily provides datasets consisting of several million spectra, each containing several thousand spectral channels. Under these conditions, the current chemometric analyses of the raw data are still possible, but require too high computing resources. Therefore, the aim of this work is to propose a data compression strategy oriented to keep the most relevant spectral channel and pixel information to facilitate, fast and reliable signal unmixing for an exhaustive exploration of complex samples. This strategy will apply not only to the context of LIBS image analysis, but to the fusion of LIBS with other imaging technologies, a scenario where the data compression step becomes even more mandatory. The data fusion strategy will be applied to the analysis of a heterogeneous kyanite mineral sample containing several trace elements by LIBS imaging associated with plasma induced luminescence (PIL) imaging, these two signals being acquired simultaneously by the same microscope. The association of compression and spectral data fusion will allow extracting the compounds in the mineral sample associated with a fused LIBS/PIL fingerprint. This LIBS/PIL association will be essential to interpret the PIL spectral information, which is nowadays very complex due to the natural overlapped signals provided by this technique.

Direct multi-elemental imaging of freshly impregnated catalyst by Laser-Induced Breakdown Spectroscopy

The preparation step of a catalyst is of primary importance as it may govern its performance. We report here the first direct multi-elemental imaging of an alumina-supported catalyst during the maturation process. Alumina extrudate support was impregnated with a nickel nitrate solution in the presence of citric acid as an organic additive. Wet extrudates were sampled, cut in half and imaged by Laser-Induced Breakdown Spectroscopy (LIBS) for varying maturation times. Results were validated by comparison with more conventional techniques such as Raman and Magnetic Resonance Imaging. This communication demonstrates the speed of acquisition, low detection limits and multi-elemental capabilities of LIBS to provide valuable information to understand the phenomena occurring during catalyst impregnation. The proposed approach allows one to shorten drastically the analysis time (by a factor of 30) and emphasizes LIBS imaging potential as a unique characterization technique able to simultaneously monitor the distribution of the metallic precursor, organic additive and support impurities.

Study on the Molecular Mechanisms Against Human Breast Cancer from Insight of Elemental Distribution in Tissue Based on Laser-Induced Breakdown Spectroscopy (LIBS).

The role of elements in physiological and pathological metabolic processes remains an unmet challenge in biomedical research and clinical applications. Herein, a visual elemental imaging of tumor tissue platform of a laser-induced breakdown spectroscopy (LIBS) was developed to initially understand anti-tumor mechanisms. The relative enrichment degree and heterogeneous spatial distributions of four elements (calcium, sodium, copper, and magnesium) of tumor tissue from different treated could be easy to visualize. In particular, significant differences in the distribution of elements were observed in tumor tissue from drug-loading complex (hydrogel/DOX) treatment group. Correspondingly, the analysis of histopathological morphology showed that the morphology and density of tumor tissue in hydrogel/DOX treatment group changed obviously by using hematoxylin and eosin (H&E) staining assay, meanwhile cleaved caspase-3 (caspase-3) and tumor necrosis factor (TNF-α) were expressed at high levels tumors tissue in hydrogel/DOX treatment group by using immunohistochemical (IHC) staining. These results would endow different biological elements with incredible potential to study the mechanisms of anti-tumor, which opens new direction and perspectives for the multi-elemental mapping of biological tissues, especially in clinic application. The integrated platform of DNA nanohydrogel drug carrier-based anti-tumor treatment combined with LIBS elemental imaging, via tail intravenous injection of saline, hydrogel, DOX, and hydrogel/DOX in breast cancer xenograft tumor mice. (A) The workflow is outlined starting from nanohydrogel drug carrier-based anti-tumor treatment. (B) Schematic diagram of LIBS imaging platform.

Fast High-Resolution Multi-Elemental Mapping of Phosphate Pellets Using Laser Induced Breakdown Spectroscopy

Recent years have seen a growing trend towards analytical techniques capable of conducting spatially resolved analyses of surfaces for industrial, nanotechnology, geological and biomedical applications. Depending on the application, spatially resolved measurements are required to provide a better understanding of the sample surface composition with significant advantages over conventional bulk analyses. The recent developments of the LIBS technique and its simplicity of use have allowed the development of systems capable of performing multi-element imaging analyses of major and trace elements with ~50 μm (or lower) spatial resolution at fast acquisition speeds up to kHz per pixel. LIBS technology enables systematic and selective ways based on the physics of atomic emission spectroscopy (AES). Complex structures are revealed by LIBS imaging at ultrafast speed. This paper presents results on laser-induced breakdown spectroscopy (LIBS) performing fast high-resolution multi-elemental mappings of Phosphate samples. Phosphate Pellets samples were laser scanned at a repetition rate of 1 kHz with a spatial resolution of 50 μm, using the Mission: Coriosity platform from ELEMISSION Inc. The elemental mappings of the 10 mm2 surfaces for 6 elements were obtained, revealing high levels of detail and complexity in the elements distributions. Advanced graphical algorithms allow direct visualization of the distribution of several elements on the same image. In particular, LIBS imaging has been used for multi-elements surface mapping of Phosphate Pellets, and show specific clustering composition, indicating that line intensity of a given analyte element is not only related to that analyte, but also to other elements present in the samples. This last statement has been verified using multivariate approach for calibration and prediction of elemental concentration in Phosphate Pellets.

Detection of minor compounds in complex mineral samples from millions of spectra: A new data analysis strategy in LIBS imaging

Today, Laser-Induced Breakdown Spectroscopy (LIBS) imaging is in full change. Indeed, always more stable instrumentations are developed, which significantly increases the signal quality and naturally the analytical potential of the technique for the characterization of complex and heterogeneous samples at the micro-scale level. Obviously, other intrinsic features such as a limit of detection in the order of ppm, a high field of view and high acquisition rate make it one of the most complete chemical imaging techniques to date. It is thus possible in these conditions to acquire several million spectra from one single sample in just hours. Managing big data in LIBS imaging is the challenge ahead. In this paper, we put forward a new spectral analysis strategy, called embedded k-means clustering, for simultaneous detection of major and minor compounds and the generation of associated localization maps. A complex rock section with different phases and traces will be explored to demonstrate the value of this approach.

Nanoscale laser-induced breakdown spectroscopy imaging reveals chemical distribution with subcellular resolution.

Understanding chemical compositions is one of the most important parts in exploring the microscopic world. As a simple method for elemental detection, laser-induced breakdown spectroscopy (LIBS) is widely used in materials, geological and life science fields. However, due to the long-existing limitation in spatial resolution, it is difficult for LIBS to play an analytical role in the field of micro-world. Herein, we first report a reliable nanoscale resolution LIBS imaging technique by introducing a sampling laser with a micro-lensed fiber. Through the emission enhancement using the double-pulse laser, we obtained the spectral signal from a sampling crater of less than 500 nanometers in diameter, and visualized the chemical distribution of the self-made grid sample, SIM chip and nano-particles in single cells. The relative limits of detection (RLODs) of In and absolute limits of detection (ALODs) of Al can reach 0.6% and 18.3 fg, respectively.

Investigation of signal extraction in the frame of laser induced breakdown spectroscopy imaging

Laser-induced breakdown spectroscopy (LIBS)-based imaging techniques have become well known among spatially resolved elemental approaches due to their mature instrumentation and outstanding advantages and applications. Data processing and in particular signal extraction are key in all LIBS-based imaging analyses to provide robust and reliable results. To date, there has not been a statistical evaluation of this issue when processing large and complex LIBS datasets. In this work, we aimed to test the performance of three extraction methods applied to micro-LIBS-based imaging. We also proposed a new conditional data extraction procedure relying on the statistical uncertainty associated with the extracted signal. We built a synthetic spectral dataset with controlled spectral features and tested the linearity, dynamic range and operating speed of different extraction approaches. The results of this study demonstrate the importance of data extraction and provide evidence for its optimization. This procedure is of particular relevance for the extraction of weak line intensities and in cases where the presence or absence of certain elements is critical (i.e., biomedical applications or trace analysis). In addition, the proposed conditional approach offers new insights into the means of providing LIBS imaging results.

Introduction to laser induced breakdown spectroscopy imaging in food: Salt diffusion in meat

This study illustrates the ability of laser induced breakdown spectroscopy (LIBS) to detect and map minerals in food. A LIBS system was used to spatially collect spectra of beef samples. Samples were brined in a 6% salt solution for 2 h and 24 h along with a control sample. Samples were measured by scanning the cross-section of each sample in a 90 × 90 square grid. Sodium (Na) distribution images with respect to emission peak at 589.05 nm were generated after pre-processing the spectral data which directly corresponds to salt levels. As expected, the control sample showed the lowest Na distribution whereas 2 h brined sample showed distribution along the sample's edges decreasing towards the centre. The 24 h brined sample showed increased diffusion. Overall, results show the ability of LIBS to map salt diffusion in meat via Na LIBS imaging, which could be used to optimize brining conditions.

An exploratory study of the potential of LIBS for visualizing gunshot residue patterns

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800μm, using a stage displacement velocity of 4mm/s and a laser frequency of 5Hz was employed (e.g. an area of 130×165mm2 was measured in less than 3h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258–289 and 446–463nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area.

High-resolution three-dimensional compositional imaging by double-pulse laser-induced breakdown spectroscopy

In this paper we present a new instrument specifically realized for high-resolution three-dimensional compositional analysis and mapping of materials. The instrument is based on the coupling of a Double-Pulse Laser-Induced Breakdown Spectroscopy (LIBS) instrument with an optical microscope. The compositional mapping of the samples is obtained by scanning the laser beam across the surface of the sample, while the in depth analysis is performed by sending multiple laser pulses on the same point. Depths of analysis of several tens of microns can be obtained. The instrument presented has definite advantages with respect to Laser Ablation-ICP Mass Spectrometry in many applications related to material analysis, biomedicine and environmental diagnostics. An application to the diagnostics of industrial ceramics is presented, demonstrating the feasibility of Double-Pulse LIBS Imaging and its advantages with respect to conventional single-pulse LIBS imaging.

A new diagnostic for volume fraction measurement of metal-oxide nanoparticles in flames using phase-selective laser-induced breakdown spectroscopy

A new diagnostic has been developed for measuring nanoparticle volume fraction by using phase-selective laser-induced breakdown spectroscopy (LIBS) for TiO2 nanoparticles generated during flame synthesis. The volume fraction is determined from Ti atomic spectra by exciting all the nanoparticle-phase matter to the plasma state, while keeping the gas-phase unexcited, based on the selectivity of breakdown thresholds between gas phase and particle phase. The measurement is performed with no detection delay, as no Bremsstrahlung background is detected. The nonvisible nanoplasmas are likely confined around each nanoparticle, differing from the continuously expanding plasmas produced in conventional LIBS. The intensity of the atomic spectra increases proportionally with laser fluence and reaches a saturation regime above 35J/cm2, facilitating the measurement of volume fraction. It is found that smaller nanoparticles decrease in absorption efficiency due to the size-dependent band gap. Nevertheless, this effect diminishes for nanoparticle sizes above 8nm. In the saturation regime, a fairly-good linear relation exists between signal intensity and nanoparticle volume fraction, for volume fractions above 140ppb. Benefitting from locally-confined nanoplasmas without detectable sparks, two-dimensional planar measurements of TiO2 nanoparticle volume fraction is accomplished, resulting in the visualization of the rapid formation of nanoparticles across the flame sheet and conservation of their volume fraction in the post-flame region. When an impinged-upon substrate is added, the two-dimensional phase-selective LIBS imaging shows good resolution of nanoparticle volume fraction variation in the boundary layer, influenced by diffusion and thermophoresis.