Valeria Spizzichino

Laser-induced breakdown spectroscopy for semi-quantitative and quantitative analyses of artworks—application on multi-layered ceramics and copper based alloys ☆

Abstract In the present work, we report on the analyses of different types of artworks, such as medieval glazed Umbrian pottery and copper based alloys from Roman and modern periods, performed by means of Laser Induced Breakdown Spectroscopy (LIBS). The semi-quantitative analyses on the multi-layered ceramic findings regard glaze, luster and pigment decorations present on the surface. The composition for each decorative layer was determined by estimating the contribution of the ceramic layer beneath the examined one to the whole plasma emission. Two types of ancient luster have been considered: red and gold, while the pigments examined include painted decorations of different blue tonalities. The measured elemental composition of the decorative layers resulted partially correlated with the color of the painted surface, measured by a standard UV-VIS spectrometer. In LIBS analyses of bronze samples, a procedure was developed, which improves data repeatability and extends quantitative measurements to minor elemental constituents. Results of the quantitative analyses gave indications about the manufacturing process of the artwork, its actual degree of conservation and the presence of residual surface decorations.

Scanning flow cytometer modified to distinguish phytoplankton cells from their effective size, effective refractive index, depolarization, and fluorescence

A laser flow cytometer based on scanning flow cytometry has been assembled. The unpolarized and linearly polarized light-scattering profiles, as well as the side emitted light in different spectral bands, were measured, allowing the simultaneous and real-time determination of the effective size and the effective refractive index of each spherelike particle. Additionally, each particle could be identified from depolarization and fluorescence measured simultaneously. The tests with aqueous samples of polystyrene spheres, fluorescent or nonfluorescent, and phytoplankton cells demonstrate that the system is able to retrieve size and refractive index with an accuracy of 1% and that the depolarization and fluorescence measurements allow the classification of particles otherwise indistinguishable.

Quantitative elemental analyses of archaeological materials by laser-induced breakdown spectroscopy (LIBS): an overview

LIBS is one of the most promising techniques for rapid, in-situ elemental analyses of artworks. It does not require sample preparation, it is almost non destructive (micro sampling) and information both about major and trace elements could be obtained simultaneously. LIBS has been used to recognize the elements present in different archaeological materials and has been also proposed for on-line monitoring during the object cleaning by lasers. Quantitative determination of the material composition can supply useful information to restorers and help the object cataloguing. However, the analytical LIBS measurements on the archaeological materials were rarely reported, mainly due to difficulties to obtain the corresponding matrix-matched standards, required for the initial calibration. Alternatively, Calibration-Free (CF) approach could be used on some class of materials if all the major sample elements are detected and if the laser plasma preserves the material stochiometry. The latter condition is sometimes missing, as in the case of bronzes under nanosecond pulse laser ablation. We have developed a theoretical model for laser ablation of quaternary copper alloys, which allows for correction of the missing plasma stochiometry in CF approach. The model also predicts the optimal calibration for this type of material. In our recent work, we also obtained quantitative LIBS results on marbles by realizing the calibration standards starting from doped CaCO3 powders and by applying the corrections on the plasma parameters, different for the laboratory standards and marbles. Semi-quantitative LIBS results have been also obtained on multi-layered renaissance ceramics by subtraction of the contribution to plasma of each ceramic layer.

In situ study of modern synthetic materials and pigments in contemporary paintings by laser-induced fluorescence scanning

Abstract Laser-induced fluorescence (LIF) has found, in the recent years, widespread application to the field of material study and characterization. In particular, LIF has been applied to the assessment of damage, biological growth, and the analysis of specific materials on various surfaces in cultural heritages. Only a few papers deal with the application of LIF to the study of modern synthetic materials (mostly plastics) and pigments, and the analysis of contemporary works of art. Preliminary laboratory measurements on a wide range of plastic and cellulose-based materials, solvents, resins, and varnishes have been performed for rapid material characterization during in situ measurement campaigns in cultural heritage, security, and forensic contexts. Four paintings by Gastone Novelli, in the National Gallery of Modern and Contemporary Art, Rome, have been investigated by a compact LIDAR fluorosensor scanning system developed at the Laboratory of Diagnostic and Metrology in the ENEA Centre of Frascati (UTAPRAD-DIM Laboratory) for LIF measurements. Results and the relative data processing have provided fluorescence images, false color images, and punctual spectral information. The comparison with data and spectra from purpose-built reference databases has enabled recognition of materials on the paintings, and provided information on their production.

Characterization and Discrimination of Plastic Materials Using Laser-Induced Fluorescence

The most meaningful spectral components in laser-induced fluorescence (LIF) spectra for several different commercial plastics have been individuated and used to automatically discriminate among different plastic materials and between plastics and complex organic materials, such as woods. Starting from LIF measurements on known samples, a number of significant wavelengths have been identified by principal component analysis (PCA). These have been used to produce intensity ratios functional to the discrimination. Threshold values for such ratios have been individuated in order to obtain an automatic recognition of plastics. The work done has been preparatory to the design and development of a multispectral imaging LIF system for fast detection of plastic debris in a post-blast scene.

Laser‐induced plasma spectroscopy: principles, methods and applications

Principles of the Laser Induced Plasma Spectroscopy and its advances are reported. Methods for obtaining quantitative analyses are described, together with discussion of some applications and the specific problems.

Nanomaterials for Conservation of Artistic Stones: Performance and Removal Tests by Laser Cleaning

In this work, nanomaterials were used as consolidants and protective layers for artistic stones. Synthetized nanocomposites were applied on marble and their performances as protective and water repellent coating were characterized. For the preparation of the novel nanocomposites, SiO2 and TiO2 nanoparticles were synthesized by laser pyrolysis and were dispersed in acrylic polymer and silicon-based resin. To evaluate the retreatability of water repellent treatments, the capability of laser to remove protective layers was explored. Laser cleaning tests with different working parameters have been carried out to optimize the effectiveness of the process. The effects of laser treatments on stone surfaces and on the applied nanocomposites were estimated by using confocal optical microscopy and Laser-Induced Fluorescence (LIF).

Selectivity evaluation of label-free detection of Bacillus spp spores using functionalized SERS substrates (Conference Presentation)

Several bacteria evolve in spore if the environmental conditions get to adverse e.g. for nutrient deprivation. The bacteria of genus Bacillus are Gram-positive aerobic bacteria and they are able to produce endospores (physiological inactive and resistant form), usually dispersed as aerosols. Endospores can survive for long time, until the conditions get back favourable. The genera Bacillus include pathogens, as Bacillus anthracis, used in the past as biological weapon. Prompt, accurate and sensitive detection is crucial for its control as pathogens or bioterrorism attacks. In case of the contamination with spores of B. anthracis, the time is essential to assure success in rescue. So, in this context, the early and fast analytical techniques, that need no or negligible sample preparation, is strongly required. Raman spectroscopy, and in particular Surface Enhanced Raman Spectroscopy (SERS), that can amplify nonlinearly the inherently weak Raman signal by several orders of magnitude, have become recognized and versatile analytical techniques also in microorganisms detection. These techniques can be used as sensitive tools for the detection and classification of biological threats, they can provide the chemical fingerprint of samples without complex and time-consuming pre-treatment samples preparation. Furthermore the development of in-field portable compact Raman platforms allows for using SERS for routine analysis. In the framework of the RAMBO (Rapid Air particle Monitoring against BiOlogical threats) project the feasibility of the SERS technique for the rapid identification and classification of few units of Bacillus spp (B. atrophaeus and B. thuringiensis) spores was investigated. B. atrophaeus and B. thuringiensis are harmless but genetically similar to the deadly B. anthracis. The RAMBO project purpose is the development of an advanced sensor with high performances, capable of detecting few spores or bacilli, with high selectivity and reliability, by means of two sensing techniques: SERS for early warning of bioagents dispersed in air or in water, and Polymerase Chain Reaction (PCR) technique for final recognition and validation. SERS and PCR will work in a microfluidic chip. In order to bind selectively the endospores, specific peptide receptors for B. thuringiensis have been selected to functionalize SERS substrates. To characterize the substrates, with and without spores to assess the effective immobilization of target, microscopy inspections, by optical microscope and Scanning Electron Microscope (SEM), were also carried out. The results show up the poor selectively of these peptides for B. thuringiensis, used as target, compared with the non specific Bacillus control. The performance of the system seems to be quite similar for both of them: the data processing by Principal Component Analysis and the following clustering analysis suggest the presence of indistinct answers for any bound endospore on the surface, and this is confirmed by microscope inspection. It could decrease the discrimination power of the sensor. Despite of such poor receptor selectivity, the SERS spectra of B. thuringiensis endospores show characteristic signals that can be related to DNA fragments or, much more probably, to the peptidoglycan (component of the external coat). This spectral feature could be used to detect the presence of B. thuringiensis endospores.

Characterization of Bacilli Spores by Surface-Enhanced Raman Spectroscopy, a Fast and Reliable Technique for Early Warning of Biological Threats

It is demonstrated that Raman Spectroscopy is a fast and sensitive tool for the detection and classification of molecular species. The vibrational spectrum inherently serves as fingerprint of the chemical composition of each sample a thus makes identification and early warning of threats possible. Also microorganisms in areas susceptible to bacterial contamination can be sensed. However, to increase the sensitivity and selectivity of the technique various solutions have been studied such as Resonant Raman Spectroscopy or Surface-Enhanced Raman Spectroscopy (SERS). In this work we present our results on the application of the SERS technique for the characterization of Bacillus atrophaeus spores, a biological and genetic simulant of the deadly bacterium Bacillus anthracis, already used in terroristic attacks in 2001 against U.S. media and government offices causing the death of five people and the infection of other 22. This work is part of the RAMBO project (Rapid Air particle Monitoring against Biological threats) whose ultimate goal is the development of an advanced sensor with high performances, capable of detecting few spores or bacilli of dangerous species with good selectivity and reliability so as to be used as an early warning sensor. In this context, the SERS technique allows to recognize the characteristics vibrational bands of the spores with a scan duration of only few seconds, on amounts of few tenths of spores or less, demonstrating how it can be considered an effective and fast technique for early warning of biological threats as it has been considered in the RAMBO project.

Rapid and label-free screening and identification of Anthrax simulants by Surface Enhanced Raman Spectroscopy

In the framework of RAMBO (Rapid-Air Monitoring particle against biological threats) project of the European Defense Agency (EDA), the feasibility of an unattended Surface Enhanced Raman Spectroscopy (SERS) sensor for biological threats detection was investigated. Its main goal concern Bacillus anthrax detection, both as vegetative cells and endospores. However since such bacteria are classified in Risk Group 3 (very dangerous microorganism), Bacillus thuringiensis and Bacillus atrophaeus were used as simulants. In order to bind selectively the target bacilli, Phages properly selected were immobilized on an active commercially available SERS substrate (functionalization). The Phages are a type of virus that infect selectively, by means of receptors, specific bacteria. Moreover they can resist on water or air environments without losing their binding capabilities. The sensing surface was characterized by standard micro-Raman equipments to assess the background Raman features. The Raman measurements have been carried out from 10X to 100X of magnification to differentiate between average and local features. Moreover the fast response was acquired by limiting the measure time at less than 1 minute. Samples of vegetative cells and endospores of Bacilli were randomly dispersed on the functionalized SERS substrates. The results obtained are promising: samples with and without bacilli could be distinguished one from the other. This is a step toward the use of SERS as an effective and fast technique for early warning of biological threats.