An easily transferable protocol for in-situ quasi-non-invasive analysis of protein binders in works of art

Advanced label-free electrochemical immunosensor for a minimally invasive detection of proteins in paintings

In recent decades, scientific methodologies applied in theCultural Heritage field have been growing, due to their pivotal role in guiding informed decisions concerning conservation strategies and daily maintenance. To achieve this goal, minimally/non-invasive quantitative and qualitative analyses are needed. However, the non-invasive and selective identification of proteinaceous binders and coatings in artworks represent an open issue in Cultural Heritage science. Herein, a novel miniaturized system is introduced, which consists of a label-free electrochemical immunosensor integrated with biocompatible Gellan gel. This method is intended to selectively and minimally invasively identify ovalbumin (OVA) on-site in paintings. The label-free immunosensor is made up on screen-printed electrodes (SPEs) by functionalizing the working electrode (WE) with a primary antibody (anti-ovalbumin) for the specific recognition of OVA. The presence of OVA produces antigen-antibody reaction, which results in the development of a bulky immunocomplex on the WE. This complex is quantified using square wave voltammetry (SWV) and a reversible redox probe: the current measured is inversely proportional to the OVA concentrations. The developed immunosensors showed good analytical performances when applied directly to painted mock-ups, exhibiting a limit of detection (LOD) of 1.6 ng mL-1, a limit of quantification (LOQ) equal to 16 ng mL-1, a working range between 0.01 and 0.4 μg mL-1 and selectivity for OVA over other protein components commonly present in painted artworks, including bovine serum albumin (BSA), collagen, and casein. The outcomes highlighted the dependability of the immunosensor in detecting OVA and the efficacy of Gellan gel as a streamlined method for extracting the target protein while preventing residue accumulation on the painting surface. This advancement suggests the potential of Gellan gel-coupled immunosensor systems as viable diagnostic alternatives for artwork management and preservation.

Look but don't touch: Non-invasive chemical analysis of organic paint binders - A review

Diagnostics on historical art samples are decisive for assessing degradation and understanding the chemical composition of supports and polychromies. These investigations help us in uncovering the artist's style and techniques and provide invaluable information for restoration, preservation and conservation. In paint formulation, the binder, also known as medium, disperses insoluble pigments and creates a homogeneous, adhesive mixture. Various analytical techniques, often used in combination, are usually employed to characterize binders with infrared (IR) and Raman spectroscopies being the most common choices. Recently, mass spectrometry (MS) has gained prominence for its ability to allow detailed structural characterization and identification, thanks to soft ionization sources such as matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI). However, MS typically requires micro-sampling, which is often prohibited for highly valuable artworks. This limitation has driven research toward the development of innovative minimally invasive sampling strategies like enzyme-functionalized gels applied to polychromies for in-situ protein digestion and peptide extraction. These quasi-non-invasive methods offer powerful solutions for extracting and characterizing organic painting binders, unlocking valuable insights into these elusive materials. This review aims to explore both the most common non-invasive analytical techniques used to characterize ancient and contemporary painting binders, and the most recent advancements in minimally invasive sampling strategies, which represent convenient and interesting approaches to enable the use of invasive analytical approaches while preserving the integrity of precious artworks.

A Study on the Materials Used in the Ancient Architectural Paintings from the Qing Dynasty Tibetan Buddhist Monastery of Puren, China

Situated in the village of Lama Temple on the eastern bank of the Wulie River in Chengde, Puren Temple stands as one of the few remaining royal temples of great importance from the Kangxi era (1662-1722 AD). This ancient edifice has greatly contributed to the advancement of our comprehension regarding the art of royal temple painting. The present study undertakes a comprehensive analysis and identification of nine samples obtained from the beams and ceiling paintings within the main hall of Puren Temple. Furthermore, a systematic examination of their mineral pigments and adhesives is conducted. The findings from polarized light microscopy (PLM), energy-type X-ray fluorescence spectrometer (ED-XRF), micro-Raman spectroscopy (m-RS), and X-ray diffractometer (XRD) analyses reveal that the pigments present in the main hall beams of Puren Temple are cinnabar, lead white, lapis lazuli, and lime green, while the pigments in the ceiling paintings consist of cinnabar, staghorn, lead white, lapis lazuli, and lime green. The use of animal glue as a binder for these pigments on both the main hall beams and ceiling paintings is confirmed via pyrolysis-gas chromatography-mass spectrometry (Py-Gc/Ms) results. These findings hold significant implications for the future restoration of Puren Temple, as they provide valuable guidance for the selection of appropriate restoration materials.

Artefact Profiling: Panomics Approaches for Understanding the Materiality of Written Artefacts

This review explains the strategies behind genomics, proteomics, metabolomics, metallomics and isotopolomics approaches and their applicability to written artefacts. The respective sub-chapters give an insight into the analytical procedure and the conclusions drawn from such analyses. A distinction is made between information that can be obtained from the materials used in the respective manuscript and meta-information that cannot be obtained from the manuscript itself, but from residues of organisms such as bacteria or the authors and readers. In addition, various sampling techniques are discussed in particular, which pose a special challenge in manuscripts. The focus is on high-resolution, non-targeted strategies that can be used to extract the maximum amount of information about ancient objects. The combination of the various omics disciplines (panomics) especially offers potential added value in terms of the best possible interpretations of the data received. The information obtained can be used to understand the production of ancient artefacts, to gain impressions of former living conditions, to prove their authenticity, to assess whether there is a toxic hazard in handling the manuscripts, and to be able to determine appropriate measures for their conservation and restoration.

Review of recent advances on the use of mass spectrometry techniques for the study of organic materials in painted artworks

The study of painted artworks using scientific methods is fundamental for understanding the techniques used in their creation and their appropriate conservation. The ethical constraints involved in the handling of, and sampling from, these objects has steered recent developments in the field of Heritage science towards a range of new non-invasive/non-destructive spectroscopic techniques capable of providing important insights into their elemental or bulk chemical compositions. Due to the inherent complexities of heritage artefacts, however, their organic components are especially difficult to study in this way and their identification and degradation pathways are thus often best investigated using mass spectrometric (MS) techniques. The versatility, sensitivity and specificity of MS techniques are constantly increasing, with technological advances pushing the boundaries of their use in this field. The progress in the past ten years in the use of MS techniques for the analysis of paint media are described in the present review. While some historical context is included, the body of the review is structured around the five most widely used or emerging capabilities offered by MS. The first pertains to the use of spatially resolved MS to obtain chemical maps of components in cross-sections, which may yield information on both inorganic and organic materials, while the second area describes the development of novel sample preparation approaches for gas chromatography (GC)-MS to allow simultaneous analysis of a variety of components. The third focuses on thermally assisted analysis (either with direct MS or coupled with GC-MS), a powerful tool for studying macromolecules requiring zero (or minimal) sample pre-treatment. Subsequently, the use of soft ionisation techniques often combined with high-resolution MS for the study of peptides (proteomics) and other macromolecules (such as oligosaccharides and triglycerides) is outlined. The fifth area covers the advances in radiocarbon dating of painting components with accelerator MS (AMS). Lastly, future applications of other MS techniques to the study of paintings are mentioned; such as direct analysis in real time MS (DART-MS) and stable isotope ratio MS (IRMS). The latter, having proven its efficiency for the study of lipids in archaeological artefacts, is envisioned to become a valuable tool for this area, whereas DART-MS is already being utilised to study the surface composition of various museum objects. Rapid technological advances, resulting in increased sensitivity and selectivity of MS techniques, are opening up new approaches for paintings analysis, overcoming the fundamental hurdle of sample size available for destructive analysis. Importantly, while the last decade has seen proteomics applications come to the fore, this review aims to emphasise the wider potential of advanced MS techniques for the study of painting materials and their conservation.

Paleoproteomics

Paleoproteomics, the study of ancient proteins, is a rapidly growing field at the intersection of molecular biology, paleontology, archaeology, paleoecology, and history. Paleoproteomics research leverages the longevity and diversity of proteins to explore fundamental questions about the past. While its origins predate the characterization of DNA, it was only with the advent of soft ionization mass spectrometry that the study of ancient proteins became truly feasible. Technological gains over the past 20 years have allowed increasing opportunities to better understand preservation, degradation, and recovery of the rich bioarchive of ancient proteins found in the archaeological and paleontological records. Growing from a handful of studies in the 1990s on individual highly abundant ancient proteins, paleoproteomics today is an expanding field with diverse applications ranging from the taxonomic identification of highly fragmented bones and shells and the phylogenetic resolution of extinct species to the exploration of past cuisines from dental calculus and pottery food crusts and the characterization of past diseases. More broadly, these studies have opened new doors in understanding past human-animal interactions, the reconstruction of past environments and environmental changes, the expansion of the hominin fossil record through large scale screening of nondiagnostic bone fragments, and the phylogenetic resolution of the vertebrate fossil record. Even with these advances, much of the ancient proteomic record still remains unexplored. Here we provide an overview of the history of the field, a summary of the major methods and applications currently in use, and a critical evaluation of current challenges. We conclude by looking to the future, for which innovative solutions and emerging technology will play an important role in enabling us to access the still unexplored "dark" proteome, allowing for a fuller understanding of the role ancient proteins can play in the interpretation of the past.

A primer for ZooMS applications in archaeology

Collagen peptide mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, also known as zooarchaeology by mass spectrometry (ZooMS), is a rapidly growing analytical technique in the fields of archaeology, ecology, and cultural heritage. Minimally destructive and cost effective, ZooMS enables rapid taxonomic identification of large bone assemblages, cultural heritage objects, and other organic materials of animal origin. As its importance grows as both a research and a conservation tool, it is critical to ensure that its expanding body of users understands its fundamental principles, strengths, and limitations. Here, we outline the basic functionality of ZooMS and provide guidance on interpreting collagen spectra from archaeological bones. We further examine the growing potential of applying ZooMS to nonmammalian assemblages, discuss available options for minimally and nondestructive analyses, and explore the potential for peptide mass fingerprinting to be expanded to noncollagenous proteins. We describe the current limitations of the method regarding accessibility, and we propose solutions for the future. Finally, we review the explosive growth of ZooMS over the past decade and highlight the remarkably diverse applications for which the technique is suited.

New baits for fishing in cultural heritage's Mare Magnum

We describe here a modern tool for exploring documents pertaining to the world Cultural Heritage while avoiding their contamination or damage. Known under the acronym EVA, it consists of a plastic foil of Ethylene Vinyl Acetate studded with strong cation and anion resins admixed with C₈ and C₁₈ hydrophobic beads. When applied to any surface such foils can harvest any type of surface material, which is then eluted and analyzed via standard means, such as GS/MS (typically for metabolites), MS/MS (for peptide and protein analysis), X-ray (for elemental analysis). We briefly review here a number of past data, such as screening of original documents by Bulgakov, Chekov, Casanova, Kepler, while dealing in extenso with very recent data, pertaining to Orwell and Stalin and analysis of the skin of an Egyptian mummy. The technique was also successfully applied to paintings, such as the Donna Nuda at the Hermitage in St. Petersburg, attributed to Leonardo and his school. This novel methodology represents a formidable tool for exploring the past life of famous authors, scientist and literates in that it can detect traces of their pathologies and even drug consumption left by saliva and sweat traces on their original hand-written documents.

Spectroscopic investigation and comprehensive analysis of the polychrome clay sculpture of Hua Yan Temple of the Liao Dynasty

This article shows the investigation results of the polychrome clay sculptures in Hua Yan Temple of the Liao Dynasty in Datong, China. The mineral pigments, adhesive and painting techniques used in these cultural relics were systematically analyzed in this project. Optical microscope (OM), Scanning electron microscope coupled with an energy-dispersive X-ray spectroscopy (SEM-EDS), micro-Raman, Fourier transform infrared spectrometer (FT-IR) and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses were selected as scientific micro-destructive analytical methods. The results show that the pigments in the polychrome clay sculptures include cinnabar, lead red, malachite, atacamite, azurite, orpiment and gold. Meanwhile, the presence of nitrogen-containing substances and glue-marker characteristic pyrolysis products clearly indicates that the adhesive used in most of the polychrome clay sculptures was glue-protein. Additionally, the combination of heat-bodied tung oil and glue-protein was also found in the golden areas.

In Situ Hydrogel Extraction with Dual-Enzyme Digestion of Proteinaceous Binders: the Key for Reliable Mass Spectrometry Investigations of Artworks

A novel strategy based on in situ dual-enzyme digestion of paint layer proteinaceous binders is introduced for faster and more confident identification, resulting in a bottom-up proteomics approach by MALDI-TOF mass spectrometry (MS). In situ sampling/extraction of proteinaceous binders using small pieces of a hydrophilic gel, previously loaded with trypsin and chymotrypsin proteolytic enzymes, was successfully exploited. Along with minimal invasiveness, the synergy of both enzymes was very useful to increase the number of annotated peptide peaks with their corresponding amino acid sequence by database search and subsequent MALDI-TOF/TOF analysis. The protocol was initially aimed at enhancing the identification of egg-based binders and then validated on fresh and aged model pictorial layers; an increased protein coverage was significantly attained regardless of the used painting binders. Optical microscope images and spectrophotocolorimetry analysis evidenced that the painting layers were not damaged or altered because of contact/sampling without leaving hydrogel residues. The proposed protocol was successfully applied on a painted altarpiece "Assumption of the Virgin" dated to the XVI century and on an angel statue of the Nativity crib dated to the XII century, both from Altamura's Cathedral (Apulia, Italy). The occurrence of various protein binders of animal origin was easily and reliably ascertained.

EVA Technology and Proteomics: A Two-Pronged Attack on Cultural Heritage

A novel way for exploring the world's cultural heritage in the absence of damage or contamination (such as removing pigments in paintings or chipping away pieces of bones) of the items under investigation is here reported, called the EVA technique. It is based on films of ethylene vinyl acetate (EVA) impregnated with strong anion and cation exchangers, admixed with hydrophobic resins, C₈ and C₁₈. When in contact with any surface these films can harvest nanomoles of macromolecules (proteins and DNA) as well as metabolites, which can then be identified by standard instrumentation. Some important applications are reported, such as the findings of the renal pathology and assumption of morphine in the original manuscript of Master I Margarita by Bulgakov, the presence of TBC bacterium in Chekhov's shirt and in a letter by Orwell, the Y. pestis and anthrax bacteria in the death registries of Milan's lazaretto in the 1630 plague bout, as well as ample traces of five metals in Kepler's manuscripts, suggesting his potential practice of alchemy. Also, in the pages of the Memoirs of Casanova, although the gonorrhea bacterium could not be found, spots of HgS could be measured, suggesting its use for curing the disease. A family of EVA films is described, enlarging its use to dedicated applications, such as the capture of drugs of abuse in the pages of famous writers and even in the paintings of fauvists. It is hoped that the present methodology could open the doors of museums, state archives, and private collections for detecting biological traces left by artists, literates, and men of culture in their masterpieces.

"1984": What Orwell could not predict. Proteomic analysis of his scripts

George Orwell, fighter for the Republican Army during the Spanish Civil War, was shot through the throat by a sniper on 20th May 1937 and nearly killed. After receiving only a summary external treatment, on the 29th, he was cured in a Barcelona hospital where he was infected by the Koch bacillus. After fleeing from Spain on 23rd June 1937, he repaired to his cottage in Wallington, Hertfordshire, wherefrom he wrote a letter to Sergey Dynamov, Editor of Soviet journal "Foreign Literature." This typewritten letter was analyzed by application of five EVA strips (ethylene vinyl acetate studded with strong cation and anion and with C₈ and C₁₈ resins; four on the corners and one over his signature), searching for biological traces. Upon elution of the captured biologicals, trypsin digestion and Orbitrap Fusion trihybrid mass spectrometer analyses, three of the five strips yielded clear traces of six unique proteins (via proteotypic peptides) of the tuberculosis bacterium. Additionally, MALDI TOF analysis of saliva of a tuberculosis patient and the EVA strip eluates gave a spectrum of 14 peptide bands (Mr 2700 to 6700 Da range) coincident between the two samples, thus, fully confirming Orwell's pathology. These results are attributed to saliva traces on Orwell's fingertips and to the fact that the letter was written on 2nd July 1937, when Orwell's pathology was at its peak.