Immunodetection of proteins in ancient paint media

The potential of aptamers for the analysis of ceramic bound proteins found within pottery

Archaeological pottery are the most numerous objects found during excavations and reflect the culinary practices of the past. However, their functionality for cooking/storing specific foods or drinks cannot be deduced solely from comparing their shapes and sizes. Analysis of protein residues bound to ceramics can reveal the protein/animal type through their amino acid sequence, thus enabling direct identification of food types. Therefore, the aim of our experimental study was to test sixteen aptamers for the analysis of proteinaceous organic residues found within the porous structure of pottery. Traditionally prepared archaeological ceramic replicas were cooked for 5 days in various food/protein suspensions, were UV aged, buried for a year, excavated, and extensively cleaned. Their shards were analysed using immunofluorescence microscopy with aptamers. Results show that eight aptamers (Clone1 and Kirby for egg residuals; seqU5 and BLG14 for milk residuals; HA for blood residuals; Gli4 for gluten residuals; Par1 for fish residuals; and D1 for collagen residuals) produced a successful/specific immunofluorescence microscopy result when they were hybridised to shards containing target protein residuals. Interestingly, on whole egg control samples, when the egg lysozyme-targeting aptamer Kirby was used, fluorescence intensity was 3.1 times greater compared to that observed with anti-ovalbumin antibodies.

In situ detection of silk fibroin using a dual recognition strategy with a flexible pressure immunosensor

Silk is a symbol of ancient Chinese civilization that has made an indelible contribution to the development of world civilization. However, because ancient artifacts are often contaminated or degraded, it is difficult to detect the presence of silk therein, and the true origin of silk thus remains a mystery. Therefore, this work presents a flexible pressure immunosensor that was designed based on 3D polypyrrole (PPy) foams for the trace detection of silk fibroin at archaeological sites. Initially, silk fibroin (SF) was conjugated with antibody-functionalized copper oxide nanoparticles (CuO NPs) and carboxylated magnetic beads (MBs) to form a sandwich immune complex. Then, the sandwich immune complex was added to hydrogen peroxide (H2O2) by magnetic separation to catalyse the generation of oxygen (O2), which converted the antigen-antibody specific recognition signal to gas pressure. As the pressure within the device increases, the 3D PPy foam, as the sensing layer resistance was 150 Ω, undergoes extrusion and deformation. This deformation leads to alterations in the foam resistance. The flexible pressure immunosensor can sensitively monitor the change in electrical resistance in the system and quantitatively detect silk fibroin. With optimization, the flexible pressure immunosensor demonstrates a dynamic range of operation spanning from 10 ng mL-1 to 100 μg mL-1, exhibiting a remarkable detection limit of 10.58 ng mL-1 specifically for silk fibroin. Notably, this immunosensor surpasses enzyme-linked immunosorbent assay (ELISA) in terms of superior reproducibility, specificity, and accuracy. Therefore, this application provides a new method and technical support for silk detection.

A new method for shellac binder detection in ancient building mortars

Shellac, also known as lac, is composed mainly of aleuritic acid.

Time-of-flight secondary ion mass spectrometry imaging in cultural heritage: A focus on old paintings

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging is a surface analysis technique that identifies and spatially resolves the chemical composition of a sample with a lateral resolution of less than 1 μm. Depth analyses can also be performed over thicknesses of several microns. In the case of a painting cross section, for example, TOF-SIMS can identify the organic composition, by detecting molecular ions and fragments of binders, as well as the mineral composition of most of the pigments. Importantly, the technique is almost not destructive and is therefore increasingly used in cultural heritage research such as the analysis of painting samples, especially old paintings. In this review, state of the art of TOF-SIMS analysis methods will be described with a particular focus on tuning the instruments for the analysis of painting cross sections and with several examples from the literature showing the added value of this technique when studying cultural heritage samples.

Rapid Enrichment and Detection of Silk Residues from Tombs by Double-Antibody Sandwich ELISA Based on Immunomagnetic Beads

The extraction and identification of silk residues in tombs is of great significance for studying the distribution and spread of early silk. However, the complex organic matter in the tomb hinders the accurate identification of silk. In this study, a double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) based on immunomagnetic beads (IMBs) was developed for the rapid enrichment and detection of silk residues. The double-antibody sandwich ELISA method established by pairing the IMBs prepared by the silk fibroin monoclonal antibody SF-3 and the silk fibroin monoclonal-labeled antibody bio-SF-1 had the highest detection sensitivity, with a linear detection range of 10 to 10⁴ ng mL^-1 and a detection limit of 5.12 ng mL^-1. This method was excellent in the extraction and analysis of silk residues from archaeological imprints and soil samples and successfully identified silk residues in samples at the final stage of silk degradation (physical invisible silk). The proteomics analysis results demonstrated the feasibility and practicability of this method.

Analytical Techniques for the Preservation of Cultural Heritage: Frontiers in Knowledge and Application

Chemistry is considered as the heart of preservation science. The archaeological objects are an organic-inorganic system and need comprehensive techniques to investigate the different materials with a high resolution and accuracy. The characterization process of archaeological materials is a useful guide to develop the right strategy for the conservation and intervention of the objects. In analytical chemistry practice, there are many techniques to employ the characterization process of the artworks: molecular, elemental, imaging, surface, thermal, separation, nuclear, dating, electrochemical, and miscellaneous techniques. It highlights the potential of chemical investigations to present reliable information to the conservators and art historians.

Detection and analysis of sources of lime mineral in ancient buildings

Among the eight detected archaeological samples, one was burned from oyster shells, and others were all burned from limestone and dolomite.

Development of an Enzyme-Linked Immunosorbent Assay and Gold-Labelled Immunochromatographic Strip Assay for the Detection of Ancient Wool

The identification of ancient wool is of great importance in archaeology. Despite lots of meaningful information can be achieved by conventional detection methods, that is, light and electron microscopy, spectroscopy, and chromatography, the efficacy is likely to be limited in the detection of ancient samples with contamination or severe degradation. In this work, an immunoassay was proposed and performed for the identification of ancient wool. First, a specific antibody, which has the benefits of low cost, easy operation, and extensive applicability, was developed directly through immunizing rabbits with complete antigen (keratin). Then, an enzyme-linked immunosorbent assay (ELISA) and a colloidal gold-labelled immunochromatographic strip (ICS) were developed to qualitatively identify the corresponding protein in ancient wool samples unearthed from Kazakhstan and China. The anti-keratin antibody exhibited high sensitivity and specificity for the identification of modern and ancient wool. The limit of detection (LOD) of the ELISA method was 10 ng/mL, and no cross-reactions with other interfering antigens have been noted. It is concluded that the immunoassays are reliable methods for the identification of ancient wool.

Miniaturized Biosensors to Preserve and Monitor Cultural Heritage: from Medical to Conservation Diagnosis

The point-of-care testing concept has been exploited to design and develop portable and cheap bioanalytical systems that can be used on-site by conservators. These systems employ lateral flow immunoassays to simultaneously detect two proteins (ovalbumin and collagen) in artworks. For an in-depth study on the application of these portable biosensors, both chemiluminescent and colorimetric detections were developed and compared in terms of sensitivity and feasibility. The chemiluminescent system displayed the best analytical performance (that is, two orders of magnitude lower limits of detection than the colorimetric system). To simplify its use, a disposable cartridge was designed ad hoc for this specific application. These results highlight the enormous potential of these inexpensive, easy-to-use, and minimally invasive diagnostic tools for conservators in the cultural heritage field.

Lanthanide-Labeled Immunochromatographic Strip Assay for the On-Site Identification of Ancient Silk

The on-site identification of ancient silks has long been a key challenge in archeology. Therefore, a rapid, cost-effective, sensitive analytical approach is highly desirable. In this paper, a lanthanide-labeled immunochromatographic strip which is suitable for the on-site identification of ancient silks is described. Compared with the conventional colloidal gold-based immunochromatographic strip, this strip shows much higher analytical sensitivity and better quantitative discrimination. The limit of detection (LOD) of the strip for silk fibroin (SF) was calculated as 8.09 ng/mL, approximately 185 times lower than that of the colloidal gold-based immunochromatographic strip. No cross-reactions with other possible interfering antigens were observed. Moreover, the strip also shows good reproducibility, with a mean recovery of 94.15-102.55% and coefficient of variation of 5.22-17.57% in the repeated tests. Based on the advantages of portability and cost-effectiveness, as well as sensitivity, specificity, and reproducibility, the lanthanide-labeled immunochromatographic strip is a promising tool for on-site detection of ancient relics in archeological fieldwork.

Determination of lacquer contained in samples of cultural relics by enzyme-linked immunosorbent assay

As an environmentally friendly natural polymer material, lacquer is durable, anti-bacterial, corrosion-resistant and decorative.

Coupling non invasive and fast sampling of proteins from work of art surfaces to surface plasmon resonance biosensing: Differential and simultaneous detection of egg components for cultural heritage diagnosis and conservation

Despite the wide application of surface plasmon resonance (SPR) to a broad area of interests, from environment to food analysis, from drug discovery to diagnostics, its exploitation in cultural heritage conservation is still unexplored. Water-based highly viscous polymeric dispersions (HVPD) composed by partially hydrolyzed polyvinyl acetate (PVA), borax, and water, were recently developed and successfully applied for the selective removal of surface degradation patinas (i.e. protein materials, natural resins etc.) from paintings of historical and artistic interest. This approach is here coupled for the first time to a SPR biosensor to simultaneously recognize albumen, yolk, or their mixtures in HVPD extracts. Ovalbumin and immunoglobulin Y are selected as analytes for egg white and yolk recognition, respectively. The biosensor was first characterized on standard analytes within the range 0-400mgL(-1) and then on fresh and dried egg albumen and yolk down to 2·10(^4) and 1·10(^5) dilution factors, respectively. Once optimized, the biosensor was combined to the HVPD application on simulated and real art samples for the evaluation of hen egg presence in the extract, i.e. albumen, yolk, or their co-presence in the matrix. For a contemporary 'sacred icon', realized by the traditional egg tempera procedure described by Cennino Cennini, the biosensor successfully distinguished different uses of egg components for the realization of painted and gilded areas, i.e. yolk and albumen, respectively. Finally, a XVIII century italian painting whose the realization technique is unknown, was tested confirming its egg tempera-based realization technique.

Immunochemical Methods Applied to Art-Historical Materials: Identification and Localization of Proteins by ELISA and IFM

Despite the large diffusion of natural organic substances in art-historical materials, their characterization presents many challenges due to the chemical complexity and instability with respect to degradation processes. Among natural products, proteins have been largely used in the past as binders but also as adhesives or additives in coating layers. Nevertheless, biological identification of proteins in art-historical objects is one of the most recent achievements obtained in heritage science thanks to the development of specifically tailored bio-analytical strategies. In the context of this active emerging discipline, immunological methods stand out for sensitivity, specificity and versatility for both protein recognition and localization in micro-samples. Furthermore, the growing use of immunological techniques for advanced diagnostics and clinical applications ensures continuous improvement in their analytical performance. Considering such, this review provides an overview of the most recent applications of enzyme linked immunosorbent assay and immunofluorescence microscopy techniques in the field of heritage materials. Specifically, the main strengths and potentials of the two techniques as well as their limits and drawbacks are presented and discussed herein.

Immunochemical Micro Imaging Analyses for the Detection of Proteins in Artworks

The present review is aimed at reporting on the most advanced and recent applications of immunochemical imaging techniques for the localization of proteins within complex and multilayered paint stratigraphies. Indeed, a paint sample is usually constituted by the superimposition of different layers whose characterization is fundamental in the evaluation of the state of conservation and for addressing proper restoration interventions. Immunochemical methods, which are based on the high selectivity of antigen-antibody reactions, were proposed some years ago in the field of cultural heritage. In addition to enzyme-linked immunosorbent assays for protein identification, immunochemical imaging methods have also been explored in the last decades, thanks to the possibility to localize the target analytes, thus increasing the amount of information obtained and thereby reducing the number of samples and/or analyses needed for a comprehensive characterization of the sample. In this review, chemiluminescent, spectroscopic and electrochemical imaging detection methods are discussed to illustrate potentialities and limits of advanced immunochemical imaging systems for the analysis of paint cross-sections.

Microchemical Study of Pigments and Binders in Polychrome Relics from Maiji Mountain Grottoes in Northwestern China

In this study, an integrated analytical method was developed to investigate the composition of both the inorganic pigments and organic binders of polychrome relics in Maiji Mountain Grottoes in northwestern China. Cross-sections of each sample were prepared at the beginning of the study, and all experiments were carried out on these cross-sections. Polychromic structures were revealed by optical microscopy and scanning electron microscopy-backscattered electron imaging. Inorganic materials were determined by using SEM coupled with an energy dispersive spectrometer and μ-Raman spectrometer, whereas organic materials were identified by staining techniques and highly sensitive and specific immunofluorescence microscopy. Data showed that the red colors are attributed to one or two pigments of red ochre, cinnabar, and minium; the blue pigment is natural lazurite; the green pigment is ascribed to atacamite; the white color is attributed to potassium feldspar; and the black surface is formed by the discoloration of minium to plattnerite under the influence of environmental factors. Regarding organic binders used in painting and preparation layers, mammalian animal glue and chicken egg white were both found alone or in mixture. Finally, the conclusion is made that the Secco technique is employed in polychrome relics from Maiji Mountain Grottoes.

Identification of Proteinaceous Binders in Ancient Tripitaka by the Use of an Enzyme-linked Immunosorbent Assay

Proteinaceous materials, such as ovabumin and collagen, were commonly used as binding media, and as adhesives and protective coatings. However, the identification of ancient proteinaceous binders is a great challenge for archaeologists, due to their limited sample size, complex combinations of various ingredients and reduced availability of the binder during the process of protein degradation. In this paper, an enzyme-linked immunosorbent assay (ELISA) provides to be a particularly promising method for the detection of proteinaceous binding materials in ancient relics. The present work focused on the specific identification of proteins in archaeological binders, which was brushed on the Tripitaka. Two samples, the adhesion area (S1) and the ink area (S2), were tested by ELISA. The results showed that both S1 and S2 reacted positively when treated with an anti-collagen-I antibody. It proved the existence of proteinaceous binders in Ancient Tripitaka, and the percentage of collagen in S1 and S2 was 61.44 and 15.4%, respectively. Compared with other conventional techniques, ELISA has advantages of high specificity, sensitivity, rapidity and low cost, making it especially suitable for the protein detection in the archaeological field.

Identification of Organic Binders in Ancient Chinese Paintings by Immunological Techniques

The identification and localization of organic binders in artworks are big challenges in archaeology and conservation science. Immunological techniques, such as enzyme-linked immunosorbent assay (ELISA) and immunofluorescence microscopy (IFM) have the potential to become powerful tools for the analysis of organic materials in ancient samples. In this study, ELISA and IFM techniques were combined to identify chicken ovalbumin, glue from several mammalian species, bovine milk, and fish glue in ancient Chinese painting samples. As binders, egg ovalbumin was found in two painting samples and animal glue was found in three samples, which were dated from the 4th to 8th centuries. The results clearly demonstrate that ELISA and IFM can be used to validate results from ancient samples.

Synchrotron DUV luminescence micro-imaging to identify and map historical organic coatings on wood

Collagen-based materials in historical coatings were characterised and imaged at the sub-micrometer scale using synchrotron DUV luminescence microspectroscopy and spectro-imaging.

Carboxy-terminated immuno-SERS tags overcome non-specific aggregation for the robust detection and localization of organic media in artworks

Surface-enhanced Raman scattering (SERS) nano-tags with a carboxy-terminated PEG surface coating overcome non-specific aggregation when applied for the immunological detection and localization of proteinaceous binding media in art samples.

Electrospray ionization linear trap quadrupole Orbitrap in analysis of old tempera paintings: application to nineteenth-century Orthodox icons

Proteomic approach in combination with mass spectrometry demonstrates a great potential for identification of proteinaceous materials in works of art. In this study we used a linear trap quadrupole Orbitrap (LTQ-Orbitrap), a state-of-the-art mass spectrometer for parts per million accuracy analyses of peptides behind tryptic hydrolysis. After the efficiency of the proteomic method was confirmed for reference and model samples, micro-samples from historical paintings were for the first time analysed using this technique. Superior performances of the liquid chromatography-mass spectrometry approach using a LTQ-Orbitrap mass spectrometer allowed identification of egg yolk peptides in two samples from nineteenth-century Orthodox icons, indicating egg tempera as the painting technique. Accurate precursor ion masses, in the range of ±2 ppm, and retention times of tryptic peptides strengthen protein identification. Additionally, in all historical samples the presence of animal glues suggested that the ground layer was likely bound using bovine collagen. Comparing to results acquired using matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry in our previous study, here we achieved higher ion scores and protein scores, better sequence coverage and more identified proteins. In fact, a combination of the two mass spectrometric techniques provided overlapping and complementary data, related to the detection of peptides with different physicochemical properties.

Cross-section and staining-based techniques for investigating organic materials in painted and polychrome works of art: a review

The article presents a review of the use of cross-section and staining techniques for investigating natural organic materials (mainly proteinaceous and oil-based binders/varnishes) in painted and polychrome artworks, considering the requirements of conservation practice and routine diagnostics. The reviewed literature calls attention to the importance of using cross sections to prepare samples for optical microscopy and to different properties of embedding resins; the most appropriate instrumental conditions for optical microscopy; and the advantages and disadvantages of the most common staining techniques. A few case studies were selected to illustrate the use of autofluorescence (intrinsic fluorescence) and induced fluorescence (using specific staining tests and fluorophore-labeled antibodies) for mapping and identifying organic paint materials in cross sections. New directions of research in cross-section analyses and fluorescence-based techniques for the identification and mapping of artistic materials are presented. The complementary use of different stains on the same cross section, further exploration of intrinsic and induced fluorescence of aged versus fresh materials, and applicability of cross-section observation and staining as complementary methods for assessing the effectiveness of restoration treatments, such as cleaning and consolidation, are discussed in the last section of the article.

An improved method of protein localization in artworks through SERS nanotag-complexed antibodies

There are several analytical techniques currently in use in conservation science to identify proteins in artworks. However, as is often the case, the determination of the exact location of a protein in a complex layer structure is challenging due to difficulty in separating layers. Localization of the protein in a cross-section has been demonstrated through attenuated total reflectance-Fourier transform infrared mapping and imaging as well as chemiluminescent and fluorescent-labeled antibodies; however, these techniques either require expensive instrumental setups or produce results that can be challenging to interpret. This paper will present research using surface-enhanced Raman scattering (SERS) nanotags complexed to secondary antibodies in conjunction with primary antibodies for the localization of ovalbumin, collagen, and casein in cross-sections from replicas and artworks containing avian egg, animal glue, or casein binders. The advantages of this technique over the others are (1) the detection method is a Raman microscope, equipment found in several museum laboratories; (2) the distinctive SERS signal from the nanotag increases the detection limit of the protein and decreases the interference from other colorants present in the cross-section layers; and finally, (3) the large (120 nm) SERS-labeled antibodies do not appear to penetrate into the cross-section, eliminating the risk of spurious signal and misidentification. Any agglomerations due to surface texture are clearly visible under normal illumination and can be avoided easily during analysis or removed with a light polish. This technique not only allows protein localization in multilayered samples while preserving the stratigraphic information but also retains the protein specificity of the antibody approach.

Tracing the biological origin of animal glues used in paintings through mitochondrial DNA analysis

We report the development of a suitable protocol for the identification of the biological origin of binding media on tiny samples from ancient paintings, by exploitation of the high specificity and high sensitivity offered by the state-of-the art DNA analysis. In particular, our aim was to molecularly characterize mitochondrial regions of the animal species traditionally employed for obtaining glues. The model has been developed using aged painting models and then tested to analyze the organic components in samples from the polychrome terracotta Madonna of Citerna by Donatello (1415-1420), where, by GC-MS and FTIR spectroscopy, animal glues and siccative oils were identified. The results obtained are good in terms of both sensibility and specificity of the method. First of all, it was possible to confirm that Donatello used animal glue for the preparation of the painted layers of the Madonna of Citerna and, specifically, glue derived from Bos taurus. Data obtained from sequencing confirm that each sample contains animal glue, revealing that it was mostly prepared from two common European taurine lineages called T2 and T3. There is one remarkable exception represented by one sample which falls into a surviving lineage of the now extinct European aurochs.