Novel Probe for Thermally Controlled Raman Spectroscopy Using Online IR Sensing and Emissivity Measurements.

Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its characterization. Thus, such photothermal side effects can represent a serious problem to be carefully controlled in order to safeguard the integrity of the material and its spectral features. In this work, an innovative probe for thermally controlled portable Raman spectroscopy (exc. 785 nm) equipped with infrared sensing lines was developed. It included an infrared source and two thermopile sensors, which allowed to perform real-time measurements of the local emissivity of the material surface under laser excitation. The emissivity, which is needed in order to monitor the temperature of the irradiated surface through infrared radiation measurements, represents the complementary component of the reflectance in the radiative energy balance. Thus, total reflectance, temperature measurements and Raman spectroscopy were integrated in the present probe. After independently assessing the reliability of the former in order to derive the emissivity of variety of materials, the probe was successfully applied on pigments, paint layers, and a painting on canvas. The results achieved evidence the significant exploitation potential of the novel tool.

Quantitative Compositional Analyses of Calcareous Rocks for Lime Industry Using LIBS.

Here, the potential of laser-induced breakdown spectroscopy (LIBS) in grading calcareous rocks for the lime industry was investigated. In particular, we developed a system equipped with non-intensified detectors operating in scanning mode, defined a suitable data acquisition protocol, and implemented quantitative data processing using both partial least squares regression (PLS-R) and a multilayer perceptron (MLP) neural network. Tests were carried out on 32 samples collected in various limestone quarries, which were preliminarily analyzed using traditional laboratory X-ray fluorescence (XRF); then, they were divided into two groups for calibration and validation. Particular attention was dedicated to the development of LIBS methodology providing a reliable basis for precise material grading. The congruence of the results achieved demonstrates the capability of the present approach to precisely quantify major and minor geochemical components of calcareous rocks, thus disclosing a concrete application perspective within the lime industry production chain.

Nanoscopic insights into the surface conformation of neurotoxic amyloid ß oligomers.

Raman spectroscopy assisted by localized plasmon resonances generating effective hot spots at the gaps between intertwined silver nanowires is herein adopted to unravel characteristic molecular motifs on the surface of Aß42 misfolded oligomers that are critical in driving intermolecular interactions in neurodegeneration.

Terahertz Time-Domain Reconstruction of Coating Microstratigraphy on Gilded Surfaces.

Here, a systematic study in order to assess the potential of THz time domain reflectometry for measuring the thicknesses of overpaint layers applied on original gilded surfaces was carried out. The work is part of a thorough characterization campaign, which is going on at the Rijksmuseum for addressing the conservation problems of a set of 19th century gilded picture frames on which heavy coatings were applied in previous undocumented restoration interventions. To perform such non-invasive thickness measurements, an analytical protocol based on Gaussian fits of the THz pulse-echo temporal profiles was optimized through the preparation of suitable technical samples and the comparison with direct thickness measurements. Finally, the methodology was validated by characterizing the microstratigraphy of an original sculptural element from a gilded picture frame in the Rijksmuseum collection. The results achieved show the effectiveness of the present approach in revealing multi-layered dielectric microstructures with a spatial resolution of about 30 µm when using a spectral range up to 1.5 THz.

High Energy Double Peak Pulse Laser Induced Plasma Spectroscopy for Metal Characterization Using a Passively Q-Switched Laser Source and CCD Detector.

Here, the development and testing of a portable double peak pulse laser induced plasma spectroscopy (DPP-LIPS) based on passively Q-switched Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser excitation is reported. The latter delivered structured laser pulses at a repetition rate of up to 20 Hz, including two energy peaks of about 100 mJ each with a relative temporal spacing of about 80 µs. Plasma spectra were collected using a low-cost Czerny-Turner spectrometer equipped with a non-intensified CCD (Charge-Coupled Device) array. Such a DPP-LIPS setup is technologically simpler and cheaper than the usual ones. Despite the relatively large temporal separation between the mentioned laser peaks, significant spectral intensity enhancements with respect to the usual single peak pulse configuration were observed. The amplification factor measured ranged between 2 and 10, depending on the specific emission peaks and the Q-switched configuration, and a consequent significant improvement of the detection limit of trace elements was observed. The instrument was calibrated for the quantitative analysis of copper alloy through systematic measurements carried out on reference samples and was then tested in an example archaeometric characterization of a statuette from the Egyptian Museum of Florence.

1064-nm-resonant gold nanorods for photoacoustic theranostics within permissible exposure limits.

Therapeutic and diagnostic methods based on photomechanical effects are attracting much current attention in contexts as oncology, cardiology and vascular surgery, for such applications as photoacoustic imaging or microsurgery. Their underlying mechanism is the generation of ultrasound or cavitation from the interaction of short optical pulses with endogenous dyes or targeted contrast agents. Among the latter, gold nanorods are outstanding candidates, but their use has mainly been reported for photoacoustic imaging and photothermal treatments. Conversely, much less is still known about their value as a precision tool for photomechanical manipulations, such as to impart local damage with high spatial resolution through the expansion and collapse of microbubbles. Here, we address the feasibility of gold nanorods exhibiting a distribution of surface plasmon resonances between about 900 to above 1100 nm as a contrast agent for photoacoustic theranostics. After testing their cytotoxicity and cellular uptake, we discuss their photostability and use to mediate cavitation and the photomechanical destruction of targeted cells. We find that the choice of a plasmonic band peaking around 1064 nm is key to enhance the translational potential of this approach. With respect to the standard alternative of 800 nm, at 1064 nm, relevant regulations on optical exposure are less restrictive and the photonic technology is more mature.

Raman spectrometer for the automated scan of large painted surfaces.

In this work, a novel Raman scanner capable of performing point-to-point mapping of relatively large surface of paintings is presented. This device employs an excitation wavelength of 1064 nm, and it is equipped with a high efficiency probe in order to collect the back-scattered light from each point of analysis. The use of long depth-of-field optics as well as an autofocus system allowed maintaining the best conditions for the Raman signal acquisition during the scanning, regardless of the surface irregularities. The small dimension of the optical components and the reasonable size of mechanical parts made this instrumentation particularly suitable for on-site measurements. Finally, the Raman scanner was also equipped with an online temperature control using a thermal sensor, which allows modulating automatically the output power of the laser source in order to prevent overheating and alteration effects during the scanning process. The capabilities of the Raman scanner were evaluated scanning two valuable paintings one attributed to Ambrogio Lorenzetti and the other to Duccio da Buoninsegna of the fourteenth century.

Advances in laser cleaning of artwork and objects of historical interest: the optimized pulse duration approach.

Laser ablation has found numerous applications in biomedical and industrial settings but has not spread as quickly as a means of cleaning artwork. In this Account, we report recent advances in the study and application of laser cleaning to the conservation of cultural heritage. We focus on the solution of representative cleaning problems of encrusted stones, metals, and wall paintings that were achieved through the optimization of laser pulse duration. We begin by introducing the basic mechanisms involved in the laser ablation of stratified materials and the criteria for preventing undesired side effects to the substrate and then briefly present case studies for each of these materials. Laser interaction effects are reviewed in a schematic way, with a concise overview of the physical models needed to support intuitive interpretations of the phenomenology observed, both in laboratory tests and in practical applications on important artifacts. This approach aims to provide keys of generalization that will favor the rigorous application of laser cleaning, repeatability of the successful results reported in this work, and further dissemination and acceptance of the technique. The topics treated examine the ablation mechanisms along with the efficiency, gradualness, selectivity, and effectiveness of the technique as a function of the pulse duration of neodymium laser systems and the operating conditions. Physical modeling and experimental evidence support the selection of pulse durations of between several tens of nanoseconds and several tens of microseconds, making it possible to minimize the risk of photothermal and photomechanical effects and maximize the selectivity of the ablation process. The sections dedicated to stones and metals also deal with the important problem of discoloration, which has significantly slowed the spread of the laser cleaning technique. The well-known problem of a yellowish appearance after laser cleaning is shown to be closely related to the ablation process; it can therefore be prevented by a suitable selection of irradiation parameters. The metal surfaces investigated are amalgam gilding, gold leaf gilding, and, for the first time, silver artifacts. We also describe the criteria used for applying laser ablation techniques to restoring unique masterpieces, such as Lorenzo Ghiberti's Porta del Paradiso and Donatello's David. Furthermore, a novel and unusual cleaning approach for archaeological silver is reported. Based on underwater laser irradiation, it provides a way to prevent oxidative effects and amplify the photomechanical coupling to the hard, thick concretions that usually accompany archaeological pieces. Finally, the experimental extension of the laser cleaning approach to wall painting and its practical use in important restoration works is presented. The practical examples reveal a significant advance in perspective for the application, which was unthinkable until recently. In sum, this Account describes novel technological and methodological contributions of laser cleaning that are having a significant impact in the field of cultural heritage conservation.

Pirenoxine prevents oxidative effects of argon fluoride excimer laser irradiation in rabbit corneas: biochemical, histological and cytofluorimetric evaluations.

The production of reactive oxygen species (ROS) associated with excimer laser irradiation is recognized as a possible cause of corneal haze following photorefractive keratectomy (PRK). Our work was aimed at investigating in vitro the oxidative effects induced by subablative laser fluences and at demonstrating the protective effectiveness of pirenoxine. Comparative trials of subablative fluence on rabbit eyes with or without 10(-5) M pirenoxine were carried out. Superoxide anion (O(2)(-)), conjugated diene (CD), and thiobarbituric acid reagent substance (TBARS) formation were analyzed. Cellular death was evaluated by flow cytometry. Histological examinations were also performed. No appraisable differences in O(2)(-),CD,andTBARS formation were detected soon after irradiation, whereas they all increased following incubation. Pirenoxine inhibited such increases. Cytofluorimetric and histological observations gave coherent results. The experimental data indicate that oxidative and toxic effects are ascribable to ROS avalanches triggered by laser irradiation-induced photodissociation and are inhibited by pirenoxine.

A new method based on contact surface profilometry for quantitative measurement of resorbed bone volume.

Bone is a dynamic tissue. Its continuous remodeling depends on the balance between bone formation and bone resorption. These two processes are carried out by specialized cells called osteoblast and ostreoclast respectively. The osteoclastic bone resorption consists in degradation of the mineral and collagen components of bone. The study of bone turnover requires accurate assessment of osteoclastic bone resorption, that becomes even more important in pathologic bone loss due to the uncoupling between bone formation and bone resorption. Osteoclastic activity is diffucult to measure. Many techniques, generally based on the detection of the resorbing lacunae (lacunae (pits) due to the bone degradation, allow to estimate bone resorption, but none of them quantitatively and directly measures the volume of resorbed bone. We propose a reliable and relatively simple method, based on contact surfact profilometry, to evaluate directly and quantitatively the volume of resorbed bone. The method has the following advantages: