Copper Soaps Formation in Verdigris-Linseed Oil Painting Mixtures: A Multispectroscopic Characterization.

Copper acetate (also known as verdigris) is a bimetallic Cu(II) greenish pigment widely used in oil paintings. Since ancient times, this pigment has been known as a degradation-prone compound, especially when combined with lipidic binders. However, the degradation mechanism and the involved species have not yet been disclosed. In this article, we study verdigris interactions with linseed oil in painting mock-ups, stressing out the formation of copper-based complexes and proposing reaction routes. Such complex systems are studied by applying a complementary multispectroscopic approach: a combination of continuous-wave (CW) electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM), and Raman and attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopies. Based on the experimental evidence, we propose the following mechanism: the neutral copper acetate shifts to a basic verdigris-promoting triglyceride hydrolysis, aided by the coordination of Cu(II) cations toward the carboxylic functions. The increased amount of free fatty acids in the mixtures triggers the formation of monomeric Cu(II) complexes. Afterward, the oil polymerization reaction occurs, and secondary oxidation species, containing OH groups in the alkyl chain, act as further ligands for copper nuclei. This is the first time, to the best of our knowledge, that a comprehensive view is proposed.

Application of Multispectral Imaging and Portable Spectroscopic Instruments to the Analysis of an Ancient Persian Illuminated Manuscript.

Illuminated manuscripts are, in general, the final products of a wise and complex interaction of different competencies. In particular, each manuscript reflects uses and techniques rooted in the historical and geographical traditions of the area of realization. Defining the characteristics and the materials in these valuable artefacts is an essential element to reconstruct their history and allow a more precise collocation and a possible comparison with other works in similar periods and areas. Non-invasive methods, mainly using portable instruments, offer undoubtedly good support in these studies. Recent analyses of an ancient Persian illuminated manuscript, combining multispectral imaging and spectroscopic measurements made with portable instruments (XRF, FORS, micro-Raman, IR-ATR) on selected points, provided new data for an improved understanding of this rare book. This study details the possibilities offered by combining these non-invasive methods for an in-depth understanding of the techniques and practices behind the realization of Middle Eastern illuminated manuscripts and provided new perspectives for multidisciplinary approaches to research in this field.

Surface Enhanced Raman Spectroscopy for Quantitative Analysis: Results of a Large-Scale European Multi-Instrument Interlaboratory Study.

Surface-enhanced Raman scattering (SERS) is a powerful and sensitive technique for the detection of fingerprint signals of molecules and for the investigation of a series of surface chemical reactions. Many studies introduced quantitative applications of SERS in various fields, and several SERS methods have been implemented for each specific application, ranging in performance characteristics, analytes used, instruments, and analytical matrices. In general, very few methods have been validated according to international guidelines. As a consequence, the application of SERS in highly regulated environments is still considered risky, and the perception of a poorly reproducible and insufficiently robust analytical technique has persistently retarded its routine implementation. Collaborative trials are a type of interlaboratory study (ILS) frequently performed to ascertain the quality of a single analytical method. The idea of an ILS of quantification with SERS arose within the framework of Working Group 1 (WG1) of the EU COST Action BM1401 Raman4Clinics in an effort to overcome the problematic perception of quantitative SERS methods. Here, we report the first interlaboratory SERS study ever conducted, involving 15 laboratories and 44 researchers. In this study, we tried to define a methodology to assess the reproducibility and trueness of a quantitative SERS method and to compare different methods. In our opinion, this is a first important step toward a "standardization" process of SERS protocols, not proposed by a single laboratory but by a larger community.

Spotting aged dyes on paper with SERS.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive technique for the non- or minimally invasive identification of molecules at very low concentrations. In this work, SERS is exploited using naked laser-ablated gold nanoparticles (AuNPs) for the detection of dyes on artificially aged paper inked with a ballpoint pen. Although several studies on inks with SERS are present in the literature, most of them report on the investigations on freshly prepared products, and less information is present on the detection of aged dyes and inks using SERS. Ballpoint inks are commonly used in daily activities, but have also been employed by several contemporary artists. These inks are very sensitive to light, and they discolor rapidly, making their detection demanding. In the present work, the SERS spectra of a ballpoint pen ink on two types of paper were analyzed after light-induced ageing, and the importance of the dye-AuNP interaction is discussed. The results show that the interpretation of the SERS spectra of the aged samples, such as those of interest in the Cultural Heritage field, is a tricky and delicate operation and that the diffusion of the dyes to the hot spot regions of the plasmonic nanoparticles plays a pivotal role in the detection of degraded ink components. Therefore, appropriate evaluation of the factors affecting the molecule-plasmonic nanoparticle interactions and of the history of the artwork to be analyzed is fundamental to avoiding the misinterpretation of the spectra and, consequently, of the original composition of the analyzed artwork.

Predictions on the SERS enhancement factor of gold nanosphere aggregate samples.

Colloidal gold nanostructures are nowadays widely involved in sensor applications. One of the most interesting techniques that takes advantage of them is certainly the Surface Enhanced Raman Scattering (SERS) effect, even if it is often considered a tricky technique due to structural constraints required by the nanostructured substrates to obtain high enhancement factors (EFs), i.e. the presence of hot spots. Because of the easy preparation and high number of hot spots, aggregated gold nanospheres seem to be the most efficient through the SERS colloids, but their characteristic high disorder makes them unpredictable and difficult to compare between different batches. For this reason, less SERS effective, but more regular and organized substrates are usually preferred. In this study, a method based on Boundary Element Method (BEM) simulation is used to accurately predict the colloidal SERS EFs of gold nanoparticle (AuNP) aggregates, starting from their experimental extinction spectra. Surprisingly, it was found that larger aggregates do not exhibit stronger hot spots, but rather higher amounts of them, influencing the overall predicted EFs, which well reflect the results obtained experimentally.

Detection of low-quantity anticancer drugs by surface-enhanced Raman scattering.

Ultrasensitive detection of low-quantity drugs is important for personalized therapeutic approaches in several diseases and, in particular, for cancer treatment. In this field, surface-enhanced Raman scattering (SERS) can be very useful for its ability to precisely identify analytes from their unique vibrational spectra, with very high sensitivity. Here, we report a study about SERS detection of sunitinib, paclitaxel and irinotecan, i.e. three commonly used antineoplastic drugs, and of SN-38, i.e. the metabolite of irinotecan, dissolved in methanol solutions. By using commercial Klarite substrates, we found that sunitinib, irinotecan and SN-38 have detection limits of 20-70 ng, which is below the threshold for applications in cancer therapy. Conversely, the SERS signal was not appreciable with paclitaxel, and this is explained by the absence of optical resonances in the visible range. Overall, our results show that ultrasensitive SERS detection of sunitinib, irinotecan and SN-38 is feasible, encouraging further development of this technology also for other drugs with similar molecular structure especially for those analytes with absorption bands in the visible range.

Magneto-plasmonic Au-Fe alloy nanoparticles designed for multimodal SERS-MRI-CT imaging.

Diagnostic approaches based on multimodal imaging are needed for accurate selection of the therapeutic regimens in several diseases, although the dose of administered contrast drugs must be reduced to minimize side effects. Therefore, large efforts are deployed in the development of multimodal contrast agents (MCAs) that permit the complementary visualization of the same diseased area with different sensitivity and different spatial resolution by applying multiple diagnostic techniques. Ideally, MCAs should also allow imaging of diseased tissues with high spatial resolution during surgical interventions. Here a new system based on multifunctional Au-Fe alloy nanoparticles designed to satisfy the main requirements of an ideal MCA is reported and their biocompatibility and imaging capability are described. The MCAs show easy and versatile surface conjugation with thiolated molecules, magnetic resonance imaging (MRI) and computed X-ray tomography (CT) signals for anatomical and physiological information (i.e., diagnostic and prognostic imaging), large Raman signals amplified by surface enhanced Raman scattering (SERS) for high sensitivity and high resolution intrasurgical imaging, biocompatibility, exploitability for in vivo use and capability of selective accumulation in tumors by enhanced permeability and retention effect. Taken together, these results show that Au-Fe nanoalloys are excellent candidates as multimodal MRI-CT-SERS imaging agents.

SERS nanostructures with engineered active peptides against an immune checkpoint protein.

The immune checkpoint programmed death ligand 1 (PD-L1) protein is expressed by tumor cells and it suppresses the killer activity of CD8+ T-lymphocyte cells binding to the programmed death 1 (PD-1) protein of these immune cells. Binding to either PD-L1 or PD1 is used for avoiding the inactivation of CD8+ T-lymphocyte cells. We report, for the first time, Au plasmonic nanostructures with surface-enhanced Raman scattering (SERS) properties (SERS nanostructures) and functionalized with an engineered peptide (CLP002: Trp-His-Arg-Ser-Tyr-Tyr-Thr-Trp-Asn-Leu-Asn-Thr), which targets PD-L1. Molecular dynamics calculations are used to describe the interaction of the targeting peptide with PD-L1 in the region where the interaction with PD-1 occurs, showing also the poor targeting activity of a peptide with the same amino acids, but a scrambled sequence. The results are confirmed experimentally since a very good targeting activity is observed against the MDA-MB-231 breast adenocarcinoma cancer cell line, which overexpresses PD-L1. A good activity is observed, in particular, for SERS nanostructures where the CLP002-engineered peptide is linked to the nanostructure surface with a short charged amino acid sequence and a long PEG chain. The results show that the functionalized SERS nanostructures show very good targeting of the immune checkpoint PD-L1.

LDI-MS assisted by chemical-free gold nanoparticles: enhanced sensitivity and reduced background in the low-mass region.

Gold nanoparticles (AuNPs) assisted laser desorption ionization mass spectrometry (LDI-MS) emerged as an effective technique for the detection of analytes with high sensitivity. The surface chemistry and the size of AuNPs are the crucial parameters for lowering the detection limits and increasing the selectivity of LDI-MS. Here we show that chemical-free size selected AuNPs, obtained by laser ablation synthesis in solution (LASiS), have very low background in the low mass region (<500 Da), contrary to citrate stabilized AuNPs (citrate-AuNPs) and dihydroxyacetophenone (DHAP). This allowed better performances for the picomole detection of low mass analytes like arginine, fructose, atrazine, anthracene and paclitaxel. The results suggest that chemical-free LASiS-AuNPs can be an excellent matrix for nanoparticle-assisted LDI-MS.

Degradation products from naturally aged paper leaves of a 16th-century-printed book: a spectrochemical study.

In this work, we present a wide-range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de-acidification treatment of leaves from a 16th-century-printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X-ray fluorescence (XRF) spectroscopy and HPLC-MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water-soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de-acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by-products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by-products from naturally aged paper.

Alternative SERRS probes for the immunochemical localization of ovalbumin in paintings: an advanced mapping detection approach.

In the field of analytical chemistry, many scientific efforts have been devoted to develop experimental procedures for the characterization of organic substances present in heterogeneous artwork samples, due to their challenging identification. In particular, performances of immunochemical techniques have been recently investigated, optimizing ad hoc systems for the identification of proteins. Among all the different immunochemical approaches, the use of metal nanoparticles - for surface enhanced Raman scattering (SERS) detection - remains one of the most powerful methods that has still not been explored enough for the analysis of artistic artefacts. For this reason, the present research work was aimed at proposing a new optimized and highly efficient indirect immunoassay for the detection of ovalbumin. In particular, the study proposed a new SERRS probe composed of gold nanoparticles (AuNPs) functionalised with Nile Blue A and produced with an excellent green and cheap alternative approach to the traditional chemical nanoparticles synthesis: the laser ablation synthesis in solution (LASiS). This procedure allows us to obtain stable nanoparticles which can be easily functionalized without any ligand exchange reaction or extensive purification procedures. Moreover, the present research work also focused on the development of a comprehensive analytical approach, based on the combination of potentialities of immunochemical methods and Raman analysis, for the simultaneous identification of the target protein and the different organic and inorganic substances present in the paint matrix. An advanced mapping detection system was proposed to achieve the exact spatial location of all the components through the creation of false colour chemical maps.

What controls the composition and the structure of nanomaterials generated by laser ablation in liquid solution?

Laser ablation synthesis in liquid solution (LASiS) is a "green" technique that gives access to the preparation of a library of nanomaterials. Bare noble metal spherical particles, multiphase core-shell oxides, metal-semiconductor heterostructures, layered organometallic compounds and other complex nanostructures can be obtained with the same experimental set up, just by varying a few synthetic parameters. How to govern such versatility is one of the current challenges of LASiS and requires a thorough understanding of the physical and chemical processes involved in the synthesis. In this perspective, the fundamental mechanisms of laser ablation in liquids are summarized, organized according to their temporal sequence and correlated with relevant examples taken from the library of nanomaterials disclosed by LASiS, in order to show how synthesis parameters influence the composition and the structure of products. The resulting framework suggests that, to date, much attention has been devoted to the physical aspects of laser-matter interaction and to the characterization of the final products of the synthesis. Conversely, the clarification of chemical processes active during LASiS deserves more research efforts and requires the synergy among multiple investigation techniques.

Large excited state two photon absorptions in the near infrared region of surprisingly stable radical cations of (ferrocenyl)indenes.

Multiphoton absorptions are important non-linear optical processes which allow us to explore excited states with low energy photons giving rise to new possibilities for photoinduced processes. Among these processes, multiphoton absorptions from excited states are particularly interesting because of the large susceptibilities characteristic of excited states. Here we explore the nonlinear transmission measurements recorded with 9 ns laser pulses at 1064 nm of the radical cations of (2-ferrocenyl)indene and of (2-ferrocenyl)-hexamethylindene, two interesting very stable molecules. The non-linear transmission data can be interpreted with a multiphoton sequence of three photon absorptions, the first being a one photon absorption related to the intramolecular charge transfer and the second a two photon absorption from the excited state created with the first process. The two photon absorption cross section is found to be several orders of magnitude larger than those usually found for two photon absorbing systems excited from the ground state.

High performance multi-purpose nanostructured thin films by inkjet printing: Au micro-electrodes and SERS substrates.

Nanostructured thin metal films are exploited in a wide range of applications, spanning from electrical to optical transducers and sensors. Inkjet printing has become a compliant technique for sustainable, solution-processed, and cost-effective thin films fabrication. Inspired by the principles of green chemistry, here we show two novel formulations of Au nanoparticle-based inks for manufacturing nanostructured and conductive thin films by using inkjet printing. This approach showed the feasibility to minimize the use of two limiting factors, namely stabilizers and sintering. The extensive morphological and structural characterization provides pieces of evidence about how the nanotextures lead to high electrical and optical performances. Our conductive films (sheet resistance equal to 10.8 ± 4.1 Ω per square) are a few hundred nanometres thick and feature remarkable optical properties in terms of SERS activity with enhancement factors as high as 107 averaged on the mm2 scale. Our proof-of-concept succeeded in simultaneously combining electrochemistry and SERS by means of real-time tracking of the specific signal of mercaptobenzoic acid cast on our nanostructured electrode.

Efficient and reliable encapsulation for perovskite/silicon tandem solar modules.

Perovskite/silicon tandem solar cells have a tremendous potential to boost renewable electricity production thanks to their very high performance combined with promising cost structure. However, for actual field deployment, any solar cell technology needs to be assembled into modules, where the associated processes involve several challenges that may affect both the performance and stability of the devices. For instance, due to its hygroscopic nature, ethylene vinyl acetate (EVA) is incompatible with perovskite-based photovoltaics. To circumvent this issue, we investigate here two alternative encapsulant polymers for the packaging of perovskite/silicon tandems into minimodules: a thermoplastic polyurethane (TPU) and a thermoplastic polyolefin (TPO) elastomer. To gauge their impact on tandem-module performance and stability, we performed two internationally established accelerated module stability tests (IEC 61215): damp heat exposure and thermal cycling. Finally, to better understand the thermomechanical properties of the two encapsulants and gain insight into their relation to the thermal cycling of encapsulated tandems, we performed a dynamic mechanical thermal analysis. Our understanding of the packaging process of the tandem module provides useful insights for the development of commercially viable perovskite photovoltaics.

Simple and sustainable synthesis of perovskite-based optoelectronic material: CsPbBr3 nanocrystals via laser ablation in alcohol.

All-inorganic lead halide perovskite nanocrystals (NCs) have shown great potential as emerging semiconducting materials due to their excellent optoelectronic properties. However, syntheses in solution commonly use high temperatures and toxic solvents, which are obstacles for safety and sustainability of the process. In this work, laser ablation in alcohol is proposed as a simple and sustainable, ligand-free, top-down approach to synthesize CsPbBr3 nanocrystals in ambient conditions. The effects of different low boiling point commercial alcohols used as solvents on the optical properties of CsPbBr3 NCs colloidal solutions are investigated. Although in traditional bottom-up synthesis alcohols are usually found to be not appropriate for the synthesis of perovskite NCs, here it is demonstrated that CsPbBr3 orthorhombic nanocrystals with narrow full width half maximum (FWHM < 18 nm), long photoluminescence lifetimes (up to 17.9 ns) and good photoluminescence quantum yield (PLQY up to 15.5%) can be obtained by selecting the dielectric constant and polarity of the alcohol employed for the synthesis.

Mechanical and Tribological Properties of Ta-N and Ta-Al-N Coatings Deposited by Reactive High Power Impulse Magnetron Sputtering.

In this article, the depositions and functional characterizations of Ta-N and Ta-Al-N coatings for protection purposes, grown by reactive high-power impulse magnetron sputtering onto silicon substrates, are described. Nitride films were grown while changing the substrate polarization voltage (i.e., the applied bias voltage) during the process. Moreover, the effects of adding Al to form a ternary system and the resulting variation of the coatings' mechanical and tribological properties have been widely investigated by nanoindentation, scratch, and wear tests. Micro-Raman characterization has been applied to the wear tracks to explore the comprehensive tribo-environment and wear mechanism. Interestingly, Ta-Al-N films, despite significantly improved mechanical properties, show a premature failure with respect to Ta-N coatings. The wear mechanisms of Ta-N and Ta-Al-N systems were revealed to be very different. Indeed, Ta-Al-N films suffer higher oxidation phenomena during wear, with the formation of an oxidized surface tribofilm and a reduced wear resistance, while Ta-N coatings undergo plastic deformation at the wear surface, with a slightly adhesive effect.

Enhancement of Magnetic Surface-Enhanced Raman Scattering Detection by Tailoring Fe3O4@Au Nanorod Shell Thickness and Its Application in the On-site Detection of Antibiotics in Water.

Surface-enhanced Raman scattering (SERS) has become a promising method for the detection of contaminants or biomolecules in aqueous media. The low interference of water, the unique spectral fingerprint, and the development of portable and handheld equipment for in situ measurements underpin its predominance among other spectroscopic techniques. Among the SERS nanoparticle substrates, those composed of plasmonic and magnetic components are prominent examples of versatility and efficiency. These substrates harness the ability to capture the target analyte, concentrate it, and generate unique hotspots for superior enhancement. Here, we have evaluated the use of gold-coated magnetite nanorods as a novel multifunctional magnetic-plasmonic SERS substrate. The nanostructures were synthesized starting from core-satellite structures. A series of variants with different degrees of Au coatings were then prepared by seed-mediated growth of gold, from core-satellite structures to core-shell with partial and complete shells. All of them were tested, using a portable Raman instrument, with the model molecule 4-mercaptobenzoic acid in colloidal suspension and after magnetic separation. Experimental results were compared with the boundary element method to establish the mechanism of Raman enhancement. The results show a quick magnetic separation of the nanoparticles and excellent Raman enhancement for all the nanoparticles both in dispersion and magnetically concentrated with limits of detection up to the nM range (∼50 nM) and a quantitative calibration curve. The nanostructures were then tested for the sensing of the antibiotic ciprofloxacin, highly relevant in preventing antibiotic contaminants in water reservoirs and drug monitoring, showing that ciprofloxacin can be detected using a portable Raman instrument at a concentration as low as 100 nM in a few minutes, which makes it highly relevant in practical point-of-care devices and in situ use.

Ball-milling modification of single-walled carbon nanotubes: purification, cutting, and functionalization.

Single-walled carbon nanotubes (SWNTs) can be successfully cut with relatively homogeneous sizes using a planetary mill. The optimized conditions produce highly dispersible SWNTs that can be efficiently functionalized in a variety of synthetic ways. As clearly shown by Raman spectroscopy, the milling/cutting procedure compares very favorably with the most common way of purifying SWNTs, namely, treatment with strong oxidizing acids. Moreover a similar milling process can be used to functionalize and cut pristine SWNTs by one-step nitrene chemistry.

Anti-Kasha's rule fluorescence emission in (2-ferrocenyl)indene generated by a twisted intramolecular charge-transfer (TICT) process.

A twisted intramolecular charge-transfer (TICT) process has been identified in (2-ferrocenyl)indene. This photochemical process explains the anti-Kasha's rule fluorescence emission observed for this system. Experimental and model investigations on (2-ferrocenyl)tetramethylindene and (2-ferrocenyl)-hexamethylindene were also performed, in order to evaluate the effect of a steric hindrance on the TICT mechanism. The energy of the lowest main excited states was computed with a TD-DFT approach, as a function of the rotation of the dihedral angle between the indene and the cyclopentadienyl planes. To the best of our knowledge, this is the first example of TICT generated by metal-to-ligand charge transfer (MLCT) in a ferrocene-containing complex and, more generally, the first case of complexes in which a metal center is directly involved.