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.

When Social Media Empowers Analytical Chemists to Explore Millions of Spectra Derived from a Complex Sample

Analytical chemistry has never yielded such a wealth of experimental data as it does today, and this exponential trend shows no sign of abating. We continually advance the capabilities of our instruments and conceive innovative concepts, all in a concerted effort to naturally push the boundaries of our understanding regarding intricate sample matrices. Spectroscopic imaging, in the broadest sense, is certainly the field where we observe this acceleration even more pronouncedly. Analytical chemistry swiftly grasped the significance of processing acquired data for comprehensive exploration through utilization of chemometrics or machine learning tools. One can assert today that chemometrics undeniably constitutes an integral facet in the advancement of an analytical approach. However, we are now faced with a new challenge, as the experimental data accumulated for certain analytical techniques are so vast and massive that exploring them with such tools has become unfeasible, and this is by no means a computational capacity issue. Analytical chemistry is far from being the sole field affected by this issue, and one could argue that others have grappled with it long before us, such as, for instance, social media, to name just one. The purpose of this paper is to demonstrate that such a domain, which may initially seem distant from our concerns, can offer novel tools capable of overcoming these barriers, even though we are not necessarily dealing with the same objects. More specifically, we delve into the clustering of over 10 million LIBS spectra acquired as part of an imaging experiment aimed at exploring a singular rock sample. This will serve to demonstrate that an open-source library developed by Meta (formerly known as Facebook) can enable us to conduct a comprehensive exploration of this sample, a feat deemed impossible with conventional data analysis approaches.

Trace Element Distribution in Zoned Kyanite of Thassos Island (Greece) Using Combined Spectroscopic Analyses

Comprehensive mineralogical and petrographic studies require analytical methods capable to report the distribution of major to trace elements within crystals in order to unravel their formation conditions and subsequent evolution. Additionally, the investigation of transition elements (e.g., Ti, V, Cr, Mn, Fe, and Zn) is essential for the comprehension of substitution processes within colored minerals. This study is conducted on a zoned kyanite crystal from a deformed quartz vein found within garnet-kyanite-biotite-hematite-plagioclase±staurolite±sillimanite paragneiss of Thassos Island, Greece. Herein, we show the efficiency of combining conventional, for example, cathodoluminescence, electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and new methods, for example, micro-laser-induced breakdown spectroscopy (µLIBS), micro-X-ray fluorescence (µXRF), and Raman spectroscopy, to determine the chemical and crystallographic features of minerals. The simple chemistry of this crystal offers an ideal case to compare and valuate the potential of combined spectroscopy techniques to analyze minerals. We demonstrate that µLIBS and µXRF are perfectly adapted to perform multi-element imaging of major to trace elements down to the ppm level within a pluricentimetric crystal (2.3 x 0.5 cm) prior to quantitative analyses. We also highlight the benefit of cathodoluminescence and Raman mapping in the investigation of crystallographic features within minerals. The multispectroscopic approach enabled us to correlate growth stages of kyanite with the polymetamorphic history of the sample. Our results also highlight the spatial dependence of Ti for the generation of blue zonation by Fe²⁺-Ti⁴⁺ substitutions with Al³⁺.

Archaeological Mortar Characterization Using Laser-Induced Breakdown Spectroscopy (LIBS) Imaging Microscopy

Lime mortar is a complex mixture resulting from hardening of lime, water, and aggregates. Lime mortar was used from the time of the Roman Empire until the Industrial Revolution. The recipes used differ according to the period, geographical area of preparation, craftsman, or function. This is why the study of archaeological mortars is of such great importance in building archaeology. In this study, we used laser-induced breakdown spectroscopy (LIBS) to characterize the elemental composition of three lime mortar samples with a µ-LIBS instrument, allowing elemental image compilation. These samples originate from three different geographical locations: Angers (France), Dardilly (France), and Pompeii (Italy), and were taken from buildings that had different functions: cathedral, aqueduct, and house, respectively. Thanks to image processing and the creation of masks, it was possible to extract not only the lime signature and nature of the aggregate but also its granulometry and circularity. All this information is essential for cultural heritage research. This study shows the potential of the LIBS technique in archaeometric analysis of archaeological mortars.

Visualizing the cerebral distribution of chemical elements: A challenge met with LIBS elemental imaging

Biological tissues contain various metals and metalloids ions with central role in the regulation of several pathophysiological functions. In parallel, the development and the evaluation of novel nanocompounds for biomedicine require the monitoring of their biodistribution in tissues of interest. Therefore, researchers need to use reliable and accessible techniques to detect and quantify major and trace elements in space-resolved manner. In this communication, we report how Laser-Induced Breakdown Spectroscopy (LIBS) can be used to image the distribution of chemical elements in brain tissues.

Measurement error due to self-absorption in calibration-free laser-induced breakdown spectroscopy

Self-absorption of spectral lines is known to lower the performance of analytical measurements via calibration-free laser-induced breakdown spectroscopy. However, the error growth due to this effect is not clearly assessed. Here we propose a method to quantify the measurement error due to self-absorption based on the calculation of the spectral radiance of a plasma in local thermodynamic equilibrium. Validated through spectroscopic measurements for a binary alloy thin film of compositional gradient, the method evidences that measurement performance lowering due to self-absorption depends on the spectral shape of the analytical transition and on the intensity measurement method. Thus, line-integrated intensity measurements of Stark broadened lines enable accurate analysis, even at large optical thickness, if line width and plasma size are precisely known. The error growth due to self-absorption is significantly larger for line shapes dominated by Doppler broadening and for line-center intensity measurements. The findings present a significant advance in compositional measurements via calibration-free laser-induced breakdown spectroscopy, as they enable straightforward selection of most appropriate analytical lines.

Aerosol analysis by micro laser-induced breakdown spectroscopy: A new protocol for particulate matter characterization in filters

Atmospheric aerosols (particulate matter - PM) affect the air quality and climate, even in remote areas, such as the Antarctic Region. Current techniques for continuous PM monitoring are usually complex, costly, time consuming and do not provide real-time measurements. In this work, based on micro laser-induced breakdown spectroscopy (LIBS), an innovative method with an optical design and multi-elemental scanning imaging, is presented to characterize PM collected in filters from Antarctica. After following a simple protocol and under atmospheric pressure, the new approach allows to obtain a global visualization of the elemental PM composition of the filters with a minimum sample destruction and preparation. For the first time, we were able to map the localization of pollutants in filters at high spatial resolution and speed. This recent method offers a new insight on the characterization of PM, particularly in isolated areas, where no complex equipment and real time measurements are demanded.

Saturated signals in spectroscopic imaging: why and how should we deal with this regularly observed phenomenon?

We have all been confronted one day by saturated signals observed on acquired spectra, whatever the technique considered. A saturation, also known as clipping in signal processing, is a form of distortion that limits a signal once it exceeds a threshold. As a consequence, clipped or saturated bands with their characteristic plateau present numerical values that do not correspond to the analytical reality of the analyzed sample. Of course, analysts know that they cannot consider these erroneous values and therefore reconsider either sample preparation or instrument settings. Unfortunately, there are many experiments today (and this is the case in spectroscopic imaging) for which we will not be able to fight against the saturation effect that will undeniably be observed on the acquired spectra. The aim of this article is first to show why it is important to correct these saturation effects at the risk of having a biased view of the sample and more specifically in the context of multivariate data analysis. In a second step, we will look at strategies for managing saturated bands. An original concept will then be presented by considering saturated values as missing ones. A statistical imputation strategy will then be implemented in order to recover the information lost during the measurement.

Short-Pulse Lasers: A Versatile Tool in Creating Novel Nano-/Micro-Structures and Compositional Analysis for Healthcare and Wellbeing Challenges

Driven by flexibility, precision, repeatability and eco-friendliness, laser-based technologies have attracted great interest to engineer or to analyze materials in various fields including energy, environment, biology and medicine. A major advantage of laser processing relies on the ability to directly structure matter at different scales and to prepare novel materials with unique physical and chemical properties. It is also a contact-free approach that makes it possible to work in inert or reactive liquid or gaseous environment. This leads today to a unique opportunity for designing, fabricating and even analyzing novel complex bio-systems. To illustrate this potential, in this paper, we gather our recent research on four types of laser-based methods relevant for nano-/micro-scale applications. First, we present and discuss pulsed laser ablation in liquid, exploited today for synthetizing ultraclean "bare" nanoparticles attractive for medicine and tissue engineering applications. Second, we discuss robust methods for rapid surface and bulk machining (subtractive manufacturing) at different scales by laser ablation. Among them, the microsphere-assisted laser surface engineering is detailed for its appropriateness to design structured substrates with hierarchically periodic patterns at nano-/micro-scale without chemical treatments. Third, we address the laser-induced forward transfer, a technology based on direct laser printing, to transfer and assemble a multitude of materials (additive structuring), including biological moiety without alteration of functionality. Finally, the fourth method is about chemical analysis: we present the potential of laser-induced breakdown spectroscopy, providing a unique tool for contact-free and space-resolved elemental analysis of organic materials. Overall, we present and discuss the prospect and complementarity of emerging reliable laser technologies, to address challenges in materials' preparation relevant for the development of innovative multi-scale and multi-material platforms for bio-applications.

Aza-BODIPY: A New Vector for Enhanced Theranostic Boron Neutron Capture Therapy Applications

Boron neutron capture therapy (BNCT) is a radiotherapeutic modality based on the nuclear capture of slow neutrons by stable ¹⁰B atoms followed by charged particle emission that inducing extensive damage on a very localized level (<10 μm). To be efficient, a sufficient amount of ¹⁰B should accumulate in the tumor area while being almost cleared from the normal surroundings. A water-soluble aza-boron-dipyrromethene dyes (BODIPY) fluorophore was reported to strongly accumulate in the tumor area with high and BNCT compatible Tumor/Healthy Tissue ratios. The clinically used ¹⁰B-BSH (sodium borocaptate) was coupled to the water-soluble aza-BODIPY platform for enhanced ¹⁰B-BSH tumor vectorization. We demonstrated a strong uptake of the compound in tumor cells and determined its biodistribution in mice-bearing tumors. A model of chorioallantoic membrane-bearing glioblastoma xenograft was developed to evidence the BNCT potential of such compound, by subjecting it to slow neutrons. We demonstrated the tumor accumulation of the compound in real-time using optical imaging and ex vivo using elemental imaging based on laser-induced breakdown spectroscopy. The tumor growth was significantly reduced as compared to BNCT with ¹⁰B-BSH. Altogether, the fluorescent aza-BODIPY/¹⁰B-BSH compound is able to vectorize and image the ¹⁰B-BSH in the tumor area, increasing its theranostic potential for efficient approach of BNCT.

Highly textured lead-free piezoelectric polycrystals grown by the micro-pulling down freezing technique in the BaTiO3–CaTiO3 system

Growth of highly textured lead-free piezoelectric polycrystals in the BaTiO₃–CaTiO₃ system by the micro-pulling down technique.

Doping nanoparticles using pulsed laser ablation in a liquid containing the doping agent

While doping of semiconductors or oxides is crucial for numerous technological applications, its control remains difficult especially when the material is reduced down to the nanometric scale. In this paper, we show that pulsed laser ablation of an undoped solid target in an aqueous solution containing activator ions offers a new way to synthesise doped-nanoparticles. The doping efficiency is evaluated for laser ablation of an undoped Gd₂O₃ target in aqueous solutions of EuCl₃ with molar concentration from 10^-5 mol L^-1 to 10^-3 mol L^-1. Thanks to luminescence experiments, we show that the europium ions penetrate the core of the synthesised monoclinic Gd₂O₃ nanoparticles. We also show that the concentration of the activators in the nanoparticles is proportional to the initial concentration in europium ions in the aqueous solution, and a doping of about 1% ([Eu]/[Gd] atomic ratio) is reached. On the one hand, this work could open new ways for the synthesis of doped nanomaterials. On the other hand, it also raises the question of undesired penetration of impurities in laser-generated nanoparticles in liquids.

[Elemental imaging using laser-induced breakdown spectroscopy: latest medical applications]

Multi-elemental imaging of soft tissues using Laser-induced breakdown spectroscopy, also known as LIBS, allows for the direct visualization of the distribution of endogenous or exogenous elements within tissues. LIBS was used to image the kinetics of metal nanoparticles in elimination organs, but also the physiological distribution of biological elements in situ and the topography of chemicals or metals in exposed human tissues. Based on our experience and recent literature in the field of imaging the elemental content of animal and human specimens, this review describes the principle and characteristics of the instrument, technical considerations for setting up experiments with LIBS, its advantages, limitations and possibilities for pre-clinical and medical applications.

Lead-free piezoelectric crystals grown by the micro-pulling down technique in the BaTiO3–CaTiO3–BaZrO3 system

Growth of lead-free piezoelectric single crystal fibres in the BaTiO₃–CaTiO₃–BaZrO₃ system by the micro-pulling down technique.

Seed orientation and pulling rate effects on bubbles and strain distribution on a sapphire crystal grown by the micro-pulling down method

Undoped sapphire rod crystals along different crystallographic orientations (a [112̄0], m [101̄0], c [0001] and c [0001] shifted 30° off axis) were successfully grown by the micro-pulling down (μ-PD) method.

Elemental and optical imaging evaluation of zwitterionic gold nanoclusters in glioblastoma mouse models

We report in this study the in vivo biodistribution of ultra-small luminescent gold (Au) particles (∼1.5 nm core size; 17 kDa), so-called nanoclusters (NCs), stabilized by bidentate zwitterionic molecules in subcutaneous (s.c.) and orthotopic glioblastoma mice models. Particular investigations on renal clearance and tumor uptake were performed using highly sensitive advanced imaging techniques such as multi-elemental Laser-Induced Breakdown Spectroscopy (LIBS) imaging and in-line X-ray Synchrotron Phase Contrast Tomography (XSPCT). Results show a blood circulation time of 6.5 ± 1.3 min accompanied by an efficient and fast renal clearance through the cortex of the kidney with a 66% drop between 1 h and 5 h. With a similar size range, these Au NCs are 5 times more fluorescent than the well-described Au₂₅GSH₁₈ NCs in the near-infrared (NIR) region and present significantly stronger tumor uptake and retention illustrated by an in vivo s.c. tumor-to-skin ratio of 1.8 measured by non-invasive optical imaging and an ex vivo tumor-to-muscle of 6.1. This work highlights the pivotal role of surface coating in designing optimum Au NC candidates for cancer treatment.

Characterization of foreign materials in paraffin-embedded pathological specimens using in situ multi-elemental imaging with laser spectroscopy

Pathologists typically encounter many disparate exogenous materials in clinical specimens during their routine histopathological examinations, especially within the skin, lymph nodes, and lungs. These foreign substances may be free extracellular deposits or induce several clinical abnormalities or histopathological patterns. However, pathologists almost never investigate or report the chemical nature of exogenous metals in clinical specimens due to a lack of convenient and available technologies. In this paper, a novel strategy based on laser-induced breakdown spectroscopy (LIBS) technology is evaluated for in situ multi-elemental tissue imaging. The improved procedures allow visualization of the presence of chemical elements contained within paraffin-embedded specimens of medical interest with elemental images that are stackable with conventional histology images. We selected relevant medical situations for which the associated pathology reports were limited to the presence of lymphohistiocytic and inflammatory cells containing granules (a granuloma and a pseudolymphoma) or to lymph nodes or skin tissues containing pigments or foreign substances. Exogenous elements such as aluminum, titanium, copper, and tungsten were identified and localized within the tissues. The all-optical LIBS elemental imaging instrument that we developed is fully compatible with conventional optical microscopy used for pathology analysis. When combined with routine histopathological analysis, LIBS is a versatile technology that might help pathologists establish or confirm diagnoses for a wide range of medical applications, particularly when the nature of external agents present in tissues needs to be investigated.

Megapixel multi-elemental imaging by Laser-Induced Breakdown Spectroscopy, a technology with considerable potential for paleoclimate studies

Paleoclimate studies play a crucial role in understanding past and future climates and their environmental impacts. Current methodologies for performing highly sensitive elemental analysis at micrometre spatial resolutions are restricted to the use of complex and/or not easily applied techniques, such as synchrotron radiation X-ray fluorescence micro-analysis (μ-SRXRF), nano secondary ion mass spectrometry (nano-SIMS) or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Moreover, the analysis of large samples (>few cm²) with any of these methods remains very challenging due to their relatively low acquisition speed (~1–10 Hz), and because they must be operated in vacuum or controlled atmosphere. In this work, we proposed an imaging methodology based on laser-induced breakdown spectroscopy, to perform fast multi-elemental scanning of large geological samples with high performance in terms of sensitivity (ppm-level), lateral resolution (up to 10 μm) and operating speed (100 Hz). This method was successfully applied to obtain the first megapixel images of large geological samples and yielded new information, not accessible using other techniques. These results open a new perspective into the use of laser spectroscopy in a variety of geochemical applications.

Laser-induced breakdown spectroscopy for elemental characterization of calcitic alterations on cave walls

Cave walls are affected by different kinds of alterations involving preservative issues in the case of ornate caves, in particular regarding the rock art covering the walls. In this context, coralloids correspond to a facies with popcorn-like aspect belonging to the speleothem family, mostly composed of calcium carbonate. The elemental characterization indicates the presence of elements that might be linked to the diagenesis and the expansion of the alterations as demonstrated by prior analyses on stalagmites. In this study, we report the use of laser-induced breakdown spectroscopy (LIBS) to characterize the elemental composition of one coralloid sample with a portable instrument allowing punctual measurements and a laboratory mapping setup delivering elemental images with spatial resolution at the micrometric scale, being particularly attentive to Mg, Sr, and Si identified as elements of interest. The complementarity of both instruments allows the determination of the internal structure of the coralloid. Although a validation based on a reference technique is necessary, LIBS data reveal that the external layer of the coralloid is composed of laminations correlated to variations of the LIBS signal of Si. In addition, an interstitial layer showing high LIBS signals for Fe, Al, and Si is interpreted to be a detrital clay interface between the external and the internal part of the coralloid. These preliminary results sustain a possible formation scenario of the coralloid by migration of the elements from the bedrock.

Advanced multimodal nanoparticles delay tumor progression with clinical radiation therapy

Radiation therapy is a major treatment regimen for more than 50% of cancer patients. The collateral damage induced on healthy tissues during radiation and the minimal therapeutic effect on the organ-of-interest (target) is a major clinical concern. Ultra-small, renal clearable, silica based gadolinium chelated nanoparticles (SiGdNP) provide simultaneous MR contrast and radiation dose enhancement. The high atomic number of gadolinium provides a large photoelectric cross-section for increased photon interaction, even for high-energy clinical radiation beams. Imaging and therapy functionality of SiGdNP were tested in cynomolgus monkeys and pancreatic tumor-bearing mice models, respectively. A significant improvement in tumor cell damage (double strand DNA breaks), growth suppression, and overall survival under clinical radiation therapy conditions were observed in a human pancreatic xenograft model. For the first time, safe systemic administration and systematic renal clearance was demonstrated in both tested species. These findings strongly support the translational potential of SiGdNP for MR-guided radiation therapy in cancer treatment.

Nanoparticle Mediated Tumor Vascular Disruption: A Novel Strategy in Radiation Therapy

More than 50% of all cancer patients receive radiation therapy. The clinical delivery of curative radiation dose is strictly restricted by the proximal healthy tissues. We propose a dual-targeting strategy using vessel-targeted-radiosensitizing gold nanoparticles and conformal-image guided radiation therapy to specifically amplify damage in the tumor neoendothelium. The resulting tumor vascular disruption substantially improved the therapeutic outcome and subsidized the radiation/nanoparticle toxicity, extending its utility to intransigent or nonresectable tumors that barely respond to standard therapies.

Ultrasmall Nanoplatforms as Calcium-Responsive Contrast Agents for Magnetic Resonance Imaging

The preparation of ultrasmall and rigid platforms (USRPs) that are covalently coupled to macrocycle-based, calcium-responsive/smart contrast agents (SCAs), and the initial in vitro and in vivo validation of the resulting nanosized probes (SCA-USRPs) by means of magnetic resonance imaging (MRI) is reported. The synthetic procedure is robust, allowing preparation of the SCA-USRPs on a multigram scale. The resulting platforms display the desired MRI activity—i.e., longitudinal relaxivity increases almost twice at 7 T magnetic field strength upon saturation with Ca(2+). Cell viability is probed with the MTT assay using HEK-293 cells, which show good tolerance for lower contrast agent concentrations over longer periods of time. On intravenous administration of SCA-USRPs in living mice, MRI studies indicate their rapid accumulation in the renal pelvis and parenchyma. Importantly, the MRI signal increases in both kidney compartments when CaCl2 is also administrated. Laser-induced breakdown spectroscopy experiments confirm accumulation of SCA-USRPs in the renal cortex. To the best of our knowledge, these are the first studies which demonstrate calcium-sensitive MRI signal changes in vivo. Continuing contrast agent and MRI protocol optimizations should lead to wider application of these responsive probes and development of superior functional methods for monitoring calcium-dependent physiological and pathological processes in a dynamic manner.

Long-term in vivo clearance of gadolinium-based AGuIX nanoparticles and their biocompatibility after systemic injection

We previously reported the synthesis of gadolinium-based nanoparticles (NPs) denoted AGuIX (activation and guiding of irradiation by X-ray) NPs and demonstrated their potential as an MRI contrast agent and their efficacy as radiosensitizing particles during X-ray cancer treatment. Here we focus on the elimination kinetics of AGuIX NPs from the subcellular to whole-organ scale using original and complementary methods such as laser-induced breakdown spectroscopy (LIBS), intravital two-photon microscopy, inductively coupled plasma optical emission spectrometry (ICP-OES), transmission electron microscopy (TEM), and electrospray ionization mass spectrometry (ESI-MS). This combination of techniques allows the exact mechanism of AGuIX NPs elimination to be elucidated, including their retention in proximal tubules and their excretion as degraded or native NPs. Finally, we demonstrated that systemic AGuIX NP administration induced moderate and transient effects on renal function. These results provide useful and promising preclinical information concerning the safety of theranostic AGuIX NPs.

Laser spectrometry for multi-elemental imaging of biological tissues

An increasing interest has arisen in research focused on metallic and organic ions that play crucial roles in both physiological and pathological metabolic processes. Current methods for the observation of trace elements in biological tissues at microscopic spatial resolution often require equipment with high complexity. We demonstrate a novel approach with an all-optical design and multi-elemental scanning imaging, which is unique among methods of elemental detection because of its full compatibility with standard optical microscopy. This approach is based on laser-induced breakdown spectroscopy (LIBS), which allows the elements in a tissue sample to be directly detected and quantified under atmospheric pressure. We successfully applied this method to murine kidneys with 10 µm resolution and a ppm-level detection limit to analyze the renal clearance of nanoparticles. These results offer new insight into the use of laser spectrometry in biomedical applications in the field of label-free elemental mapping of biological tissues.

Laser-induced breakdown spectroscopy: a new approach for nanoparticle's mapping and quantification in organ tissue

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) performed on thin sections of rodent tissues: kidneys and tumor, allows the detection of inorganic elements such as (i) Na, Ca, Cu, Mg, P, and Fe, naturally present in the body and (ii) Si and Gd, detected after the injection of gadolinium-based nanoparticles. The animals were euthanized 1 to 24 hr after intravenous injection of particles. A two-dimensional scan of the sample, performed using a motorized micrometric 3D-stage, allowed the infrared laser beam exploring the surface with a lateral resolution less than 100 μm. Quantitative chemical images of Gd element inside the organ were obtained with sub-mM sensitivity. LIBS offers a simple and robust method to study the distribution of inorganic materials without any specific labeling. Moreover, the compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of the same biological tissue with different types of response: elemental, molecular, or cellular.

Identification of polymer materials using laser-induced breakdown spectroscopy combined with artificial neural networks

A combination of laser-induced breakdown spectroscopy (LIBS) and artificial neural networks (ANNs) has been used for the identification of polymer materials, including polypropylene (PP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyoxymethylene (POM), polyethylene (PE), polyamide or nylon (PA), polycarbonate (PC) and poly(methyl methacrylate) (PMMA). After optimization of the experimental setup and the spectrum acquisition protocol, successful identification rates between 81 and 100% were achieved using spectral features gathered from single spectra without averaging (1 second acquisition time) over a wide spectral range (240-820 nm). Furthermore, ten different materials based on PVC were tested using the identification procedure. Correct identifications were obtained as well. Sorting of the materials into sub-categories of PVC materials according to their charges (concentration in trace elements such as Ca) was performed. The demonstrated capacities fit, in practice, the needs of plastic-waste sorting and of producing high-grade recycled plastic materials.

Measuring, in solution, multiple-fluorophore labeling by combining fluorescence correlation spectroscopy and photobleaching

Determining the number of fluorescent entities that are coupled to a given molecule (DNA, protein, etc.) is a key point of numerous biological studies, especially those based on a single molecule approach. Reliable methods are important, in this context, not only to characterize the labeling process but also to quantify interactions, for instance within molecular complexes. We combined fluorescence correlation spectroscopy (FCS) and photobleaching experiments to measure the effective number of molecules and the molecular brightness as a function of the total fluorescence count rate on solutions of cDNA (containing a few percent of C bases labeled with Alexa Fluor 647). Here, photobleaching is used as a control parameter to vary the experimental outputs (brightness and number of molecules). Assuming a Poissonian distribution of the number of fluorescent labels per cDNA, the FCS-photobleaching data could be easily fit to yield the mean number of fluorescent labels per cDNA strand (approximately = 2). This number could not be determined solely on the basis of the cDNA brightness, because of both the statistical distribution of the number of fluorescent labels and their unknown brightness when incorporated in cDNA. The statistical distribution of the number of fluorophores labeling cDNA was confirmed by analyzing the photon count distribution (with the cumulant method), which showed clearly that the brightness of cDNA strands varies from one molecule to the other. We also performed complementary continuous photobleaching experiments and found that the photobleaching decay rate of Alexa Fluor 647 in the excited state decreases by about 30% when incorporated into cDNA, while its nonradiative decay rate is increased such that the brightness of individual Alexa labels is decreased by 25% compared to free Alexa dyes.