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Abstract This study aims to characterise the so-called Sialkoti paper used to produce Pahari drawings preserved today in the Wereldmuseum in Leiden (Netherlands) (WML). These works originate from the Punjab Hills in India (today Himachal Pradesh) and are commonly known as ‘Pahari miniature paintings’. The paper upon which these drawings are executed is said to have been produced in Sialkot during the eighteenth and nineteenth centuries when papermaking was an integral part of an overall regional economy correlated with other sectors such as agriculture and the textile industry. Although the term Sialkoti refers to identified papermills in Sialkot (now Pakistan), the paper from this region is yet to be subjected to a systematic study. This article therefore explores the paper(s) in question through macro- and microscopic observations of structure, pulp and fibres. The study of historical sources, complemented by the analysis of paper samples and fibre identification, has revealed that the pulp would have been prepared from a variety of manufactured products using different technologies, such as rags, cloth, mats, rope and other plant-based materials made from local bast fibres which, once tattered, were recycled to prepare the pulp. Microscopic study reveals that a variety of fibre combinations under different conditions and processing steps were used, in particular sunn hemp fibre (Crotalaria juncea L.), a plant species that has until now rarely been identified in historical paper. In addition, the presence of kenaf and jute fibres, as well as a significant quantity of cotton fibres, have also been demonstrated. To overcome the lack of comparative materials, our work was supported by a comparative study of several materials made from sunn hemp now held in the Ethnobotany Collection at Kew Gardens. Samples were taken from these materials and provided useful reference micrographs for the identification of the WML samples. The quality of the paper used by Pahari artists, as well as the raw materials available and their processing, are discussed in detail. Putting all the data, including technical and historical information into perspective, we conclude that the Pahari artists used a paper of inferior quality compared to other types of paper used for other purposes such as the creation of illuminated manuscripts in the Punjab plains. This study therefore provides useful analytical and material evidence that complements previous historical, technical and anthropological studies.

Abstract Paper bookbindings have been disregarded for centuries by scholars since they were only considered temporary covering materials for manuscripts and books. Recently, there is a willingness to reconsider these bindings and to evaluate their role. Thanks to the collaboration with the Marciana National Library in Venice, which stores an impressive collection of 849 detached bindings, the current research provides a chemical-physical elucidation about the composition and the manufacture of paper bookbindings realized between the 16th and the eighteenth century in the Venetian area. A selection of bookbindings was analysed by the means of complementary methods (thickness measurements, Attenuated Total Reflection—Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Pyrolysis–Gas Chromatography–Mass Spectrometry (Py-GC–MS) and X-Ray Fluorescence (XRF)). Data evidence the presence of cellulose as the main component of paper pulp; hemicellulose and lignin were identified too, probably related to the presence of linen/hemp rags in the paper production. Gelatine was detected muck likely related to paper sizing; among inorganic additives CaCO3 was found in all samples. The presence of waxy material may be due to past undocumented conservation treatments.

Abstract In the process of conservation mounting, starch paste made from wheat flour is the glue of choice to paste reinforcing strips and backing papers, often Xuan paper, for mending and decorating aged and damaged paper-based Chinese artworks. To keep objects intact and select appropriate conservation materials, this research explored the applicability of near-infrared (NIR) spectroscopy coupled with multivariate analysis for the characterization of contemporary unsized Xuan paper with and without starch. In particular, partial least squares (PLS) regression was used to predict the degree of polymerization (DP) of the paper, i.e., one of the most important properties of paper materials, and principal component analysis (PCA) was used to detect starch and to distinguish between papers with different amounts of starch. Using 12 contemporary unsized Xuan papers, the NIR-PLS method for DP prediction was validated, and the best-performed model was generated using the logarithmic transformation of DP−1 as a response variable, with root mean square error of prediction (RMSEP) of DP 128. The NIR-PCA method was also found to be applicable to separate starch-free papers and papers treated with starch, and the results indicate that the higher the content of starch, the better PCA classification performs. This research provides supporting data for the non-destructive characterization of Xuan paper-based objects and differentiates between Xuan paper before and after treatment with starch.

Abstract Purpose Paper-based artifacts hold significant cultural and social values. However, paper is intrinsically fragile to microorganisms, such as mold, due to its cellulose composition, which can serve as a microorganisms’ nutrient source. Mold not only can damage papers’ structural integrity and pose significant challenges to conservation works but also may subject individuals attending the contaminated artifacts to health risks. Current approaches for strain identification usually require extensive training, prolonged time for analysis, expensive operation costs, and higher risks of secondary damage due to sampling. Thus, in current conservation practices with mold-contaminated artifacts, little pre-screening or strain identification was performed before mold removal, and the cleaning techniques are usually broad-spectrum rather than strain-specific. With deep learning showing promising applications across various domains, this study investigated the feasibility of using a convolutional neural network (CNN) for fast in-situ recognition and classification of mold on paper. Methods Molds were first non-invasively sampled from ancient Xuan Paper-based Chinese books from the Qing and Ming dynasties. Strains were identified using molecular biology methods and the four most prevalent strains were inoculated on Xuan paper to create mockups for image collection. Microscopic images of the molds as well as their stains situated on paper were collected using a compound microscope and commercial microscope lens for cell phone cameras, which were then used for training CNN models with a transfer learning scheme to perform the classification of mold. To enable involvement and contribution from the research community, a web interface that actuates the process while providing interactive features for users to learn about the information of the classified strain was constructed. Moreover, a feedback functionality in the web interface was embedded for catching potential classification errors, adding additional training images, or introducing new strains, all to refine the generalizability and robustness of the model. Results & Conclusion In the study, we have constructed a suite of high-confidence classification CNN models for the diagnostic process for mold contamination in conservation. At the same time, a web interface was constructed that allows recurrently refining the model with human feedback through engaging the research community. Overall, the proposed framework opens new avenues for effective and timely identification of mold, thus enabling proactive and targeted mold remediation strategies in conservation.

Having economical, flexible, disposable and readily manufacturable devices for everyday sensing applications is of paramount importance. We report a novel and cost-effective technique for fabricating paper-based devices using an Advanced PAP (A-PAP) pen, which is capable of withstanding typical aqueous solutions and organic solvents. The quick fabrication process does not require any sophisticated instrumentation or a heating step, making it a promising technology for resource-limited settings. Using an A-PAP pen, we have fabricated two-dimensional (2D) paper-based devices for chemical detection of heavy metal and nitrite. We have also demonstrated the versatility of fabrication technique for biological sensing using 2D lateral flow paper-based devices for the detection of dopamine. Furthermore, the technique is also validated for fabricating complex three-dimensional (3D) paper-based devices using a paper origami technique for heavy metals sensing. The ready-to-use devices can be fabricated in seconds, making them convenient for on-the-spot testing. Overall, this technique provides a valuable tool for creating affordable, efficient, and accessible chemical and biological testing solutions.

Chloride (Cl−) is an anion widely distributed in nature. It is also an essential parameter to consider when assessing the water quality for ensuring drinking water safety, preventing infrastructure damage, mitigating environmental impact, identifying groundwater contamination. This work presents the first development of a diameter-based measurement paper sensor for chloride analysis using the reaction based on a Mohr's precipitation titration. The paper sensor that has a circular shape with 3-cm diameter was pre-coated with AgNO3 and CrO42− forming brown precipitates of the Ag2CrO4. The sensor was sealed using lamination films with 3-mm diameter hole-punched inlets on the top of the lamination film for sample delivery. To detect chloride, the sensor was simply immersed into the sample. The chloride solution flows into the central sample inlet and spreads radially to undergo the displacement reaction with Ag2CrO4 precipitate, forming AgCl white precipitate whose diameter proportional to the chloride that can be observed within 3 min. Concentration of AgNO3 used was found to impact the analytical figures of merit. The lower AgNO3 concentration yields lower limit of detection, narrower linear range but higher sensitivity. The sensor was applied for chloride analysis in tap water, drinking water and industrial water and the chloride concentration obtained from the developed sensors are not significant differences from those obtained from the standard titration method at 95% confidence interval (two tailed P = 0.08) indicating that the developed sensor provides accurate analysis of chloride in water samples from various sources. The developed sensor was used by the untrained staffs for on-site of analysis chloride in tap water collected at 26 locations in SaenSuk Municipality area, Chonburi, Thailand. The results showed that the chloride level in all samples is in range of 52.2–84.7 mg L−1 which is far below the acceptable range set by the Provincial Waterwork Authority of Thailand (< 250 mg L−1) indicating that the tap water used in this area is safe for consumers.

A novel design and set up of paper chromatography in the form of radial serpentine arms laying horizontally is proposed. The consumption of mobile phase is reduced to be 1 mL or less as compared to the tens of mL typically used in the conventional set ups for ascending paper chromatography, without any change in the order of the separated components. Greenness measurement based on the ChlorTox value is approximately 25, when comparing to a conventional system that consumes 25 mL of mobile phase. A digital image of the chemical separation makes data analysis more feasible as the image can be kept, and hence, extending the time for data analysis. The Retention Factor (Rf) value from a serpentine shaped stationary phase can be calculated based on measurement of linear distances of the solvent front and those travelled by each component, and converting them to arclengths using the mathematical equation of a catenary wave that produces that particular design. Proof of concept is demonstrated by the separation of food dyes using a two solvent system, where a nonvolatile salt solution is followed by a volatile organic solvent mixture of alcohols and base. Relationships between concentration, color intensity (RGB values), and zone arclength are also demonstrated which indicate possibility of quantitative study on the serpentine design using digital image analysis.

This work presents, for the first time, an exploitation of an argentometric Mohr's method for iodide detection using diameter-based measurement on laminated paper-based analytical device (LPAD). Our LPAD is simplified fabricated with no required hydrophobic barrier for patterning a detection flow channel. In the absence of a flow channel, the liquid is imbibed radially into the filter paper outward from the small center inlet hole. This imbibition leads to the measurement of diameter after the formation of the precipitation product. For LPAD, a rectangular piece of Whatman filter paper is cut and positioned between a top laminating sheet, which has a hole punched for inlet, and a bottom laminating sheet. The central inlet hole enables access to the liquid on the paper. For iodide analysis, silver nitrate is dispensed first, followed by the iodide standard/sample. This process leads to the formation of pale-yellow silver iodide solids on the paper. The chromate indicator solution is subsequently loaded to the paper. The color of the chromate solution imparts a tint to the circular band of silver iodide solids, resulting in an intense yellow color. When the silver iodide precipitates are stained, the chromate solution typically serves as an indicator, chemically reacting to an excess silver nitrate solution moistened on paper. This reaction generates an outer reddish-brown ring of silver chromate. The distinct color contrast between the intense yellow (tinted silver iodide) and reddish-brown (silver chromate) allows for clear observation of the measurement boundary, facilitating diameter-based measurements of the circular band of silver iodide. We demonstrate the applicability in analysis of pharmaceutical KI tablets. The quantitative results obtained from diameter-based measurement LPAD show good agreement with those obtained from the potentiometric method. Our hydrophobic barrier-free LPAD is rapid, cost-effective, low liquid consumption and applicable for onsite analysis.

Abstract Gels prepared from the polysaccharide gellan are used for aqueous poulticing treatments in paper conservation when the application of water must be restricted. Optimal use of the rigid, yet shapeable gel requires direct contact with the paper surface, which carries the risk of gel residues on the treated surface. We used acid methanolysis as a destructive analytical method to detect rhamnose as a component of gellan, which was undetectable with ATR-FTIR spectroscopy. We show that there is a significant probability of leaving gellan residues on the paper. Conservators should be aware of this potential side effect when considering the use of gellan poultices in direct contact with paper objects.

Environmental toxic pollutants and pathogens that enter the ecosystem are major global issues. Detection of these toxic chemicals/pollutants and the diagnosis of a disease is a first step in efficiently controlling their contamination and spread, respectively. Various analytical techniques are available to detect and determine toxic chemicals/pathogens, including liquid chromatography, HPLC, mass spectroscopy, and enzyme-linked immunosorbent assays. However, these sensing strategies have some drawbacks such as tedious sample pretreatment and preparation, the requirement for skilled technicians, and dependence on large laboratory-based instruments. Alternatively, biosensors, especially paper-based sensors, could be used extensively and are a cost-effective alternative to conventional laboratory testing. They can improve accessibility to testing to identify chemicals and pollutants, especially in developing countries. Due to its low cost, abundance, easy disposal (by incineration, for example) and biocompatible nature, paper is considered a versatile material for the development of environmentally friendly electrochemical/optical (bio) sensor devices. This review presents an overview of sensing platforms constructed from paper, pointing out the main merits and demerits of paper-based sensing systems, their fabrication techniques, and the different optical/electrochemical detection techniques that they exploit.

The presence of pharmaceuticals in water is a major problem worldwide. To alleviate this, this study produced carbon blends from avocado seeds and paper waste and activated them with hydrogen peroxide (H2O2), nitric acid (HNO3) and potassium permanganate (KMnO4). The effectiveness of the adsorbents was tested in removing ibuprofen (IBU) and paracetamol (PRC) from water. Characterization of the adsorbents by SEM, BET, FTIR and TGA revealed that the morphology was porous, with a large surface area and several functional groups bound to the surface. The concentration effect experiments showed that the uptake of IBU and PRC increased with an increasing initial concentration and that these data were consistent with the Freundlich model. The contact time effect showed that the uptake of PRC was rapid in the initial phase for all the adsorbents. However, the rate gradually slowed down and equilibrium was reached after 40 min for BCMN, 60 min for BCMH and BCMP and 120 min for BCM. IBU, on the other hand, showed that equilibrium was reached after 30 min for BCMN, BCMH and BCMP and after 120 min for BCM. These data complemented the PSOM. The model is based on chemisorption, where electrons are transferred and shared, and hydrogen bonding and π-π interactions. The △Ho value confirms that the sorption of IBU and PRC was endothermic. The △So was positive, indicating greater freedom at the solution interface during uptake.

Abstract Numerous natural dyes were used to dye mediaeval Islamic paper from the tenth to the nineteenth century, using a variety of techniques. The objective of this research is to develop an analytical method using high performance liquid chromatography with diode array detection (HPLC–DAD) to identify natural dyes in forty historical Islamic paper manuscripts from two collections. In addition, novel information was obtained from original treatises containing recipes for dyeing paper and the chronological use of dyes in dyeing mediaeval Islamic paper between the tenth and seventeenth centuries. The results show that thirty-four of the forty manuscripts examined contained dyes. Six natural dyes were detected, including henna, madder, lac, safflower, turmeric, and weld. This is the first study aimed at developing a method for determining various natural dyes in Islamic paper from a wide historical and geographical range in the mediaeval time and to fill significant gaps in the technical and historical knowledge of papermaking.

Abstract Soot stain from diverse sources is the most common stain that stains historical paper documents found in libraries, museums, and storage facilities. It is believed to be one of the types of deterioration that arises from the contact between stains and paper sheets. Therefore, in the present work, the effectiveness of the synthesized hybrid nanogel consisting of carbopol and nanoparticles (NPs) of ZnO, TiO2, or Fe3O4, in low and high-viscosity forms, for eliminating soot stains from historical paper manuscripts was conducted. The prepared hybrid nanogels were characterized utilizing the TEM, AFM, XRD, DLS, and Zeta Potential techniques. Following preparation, the soot-stained paper samples were heated to 105 °C for 6 days, a process known as accelerated thermal aging. Surface morphology, mechanical properties and the color change of the paper samples were investigated. The prepared hybrid nanogel had a spherical shape with well-defined edges and uniform size, with an average particle diameter ranging from 30 to 35 nm. There was no significant NPs agglomeration seen, suggesting uniform dispersion in the carbopol matrix. Additionally, the prepared gels' crystal structure and phase purity were revealed by the XRD analysis results. Paper fibers were visible in some parts of the treated sample with TiO2/carbopol hybrid nanogel at high-viscosity before aging. Cleaning soot-stained paper samples using high-viscosity Fe3O4/carbopol hybrid nanogel is more successful than using low-viscosity nanogel. the sample treated with high-viscosity ZnONPs/carbopol hybrid nanogel produced the highest total color differences (ΔE) (26.17). The paper sample treated with high-viscosity ZnO/carbopol hybrid nanogel exhibited the maximum tensile strength (61.8 N/mm2) and elongation at break (1.174%). The evaluation of the paper samples both before and after the cleaning process revealed that, the treatment with high-viscosity ZnO/carbopol hybrid nanogel gave the best results in removing soot stains from stained paper samples.

Abstract Presence of copying pencils in heritage objects poses a significant challenge for conservators due to their proneness to fading, sensitivity to solvents and difficulties in differentiation from regular graphite pencils. In this paper a method of copying pencils identification by means of ATR—FTIR spectroscopy is used. A protocol for spectra processing and dimensionality reduction of spectral data by means of principal component analysis has been developed, allowing for pencil types differentiation and providing an easy to read visual representation of the collected data. The protocol has been developed on mock-up samples and tested on objects from the archives of the State Museum Auschwitz – Birkenau.

Abstract Some ancient Chinese paper artifacts dyed with amur cork tree bark extracts are currently preserved to different extents in museums and libraries worldwide. As traditional natural plant dyes, the long-term performance of the amur cork tree bark extract-dyed handmade paper has been questioned under a preserved environment. The photodegradation process of the extract-dyed papers was examined under accelerating artificial UVA irradiation conditions according to China national standard-paper and board- accelerated aging (exposure to light). Changes during aging were analyzed by optical observation and scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), pH, and tensile strength and folding endurance tests. The results showed that the main components from extracted dyes played an important role in affecting the photodegradation properties of dyed paper. The changes in surface color, pH, morphology and mechanical properties after the artificial UVA accelerated degradation tests revealed that a suitable concentration of the extract dyes for maintaining the long-term irradiation stability of the paper is important.

Abstract Efficient removal of mold stains becomes an important research topic for paper conservation. In this study, a cleaning scheme based on the combination of bioenzymes and biosurfactants was explored. Morphological and molecular biology identifications were first jointly applied to identify the dominant strains sampled from five ancient books that are stored in the same environment. Cellulolytic experiments were then conducted to evaluate the cellulose degradation ability of the strains according to the cellulolytic digestive index. Finally, paper Mockups for the ancient books were constructed to investigate the most effective combination of bioenzymes and biosurfactants in removing mold stains as well as its effect on the paper’s physical properties. The result concluded that the combination of 3% papain, 7% of sophorolipid or 7% of betaine, and distilled water, achieved optimal stain removal effect with over 50% cleaning rate at 35 °C, after 30 min of infiltration. The maximum color difference of the paper material after cleaning was around 0.60, pH was between 7.45 and 7.79, and no significant changes in tensile strength were observed. At the same time, Sophorolipid and Betaine both have superior deacidification, anti-acidification, anti-aging, and reinforcement capabilities, which can provide extra support to the fibrous structure in addition to cleaning the paper materials. The microbial contamination cleaning agent proposed in this study shows promising application prospects in conserving mold-contaminated paper artifacts.

Abstract Traditional papermaking was a significant innovation that intrigued the information-sharing society in a wide range of the globe. The importance of finding the historical background hidden behind the historical traditional paper is critical to understanding societies in history. Advanced molecular biological research is applied to many forensic studies to identify the origin and criminal events. Yet, biological research refrained from the heritage science of traditional papers due to its damage to the samples. The current study explores the Pearson correlation between DNA in traditional paper and non-destructive measurement of characteristics of traditional paper. DNA concentration and purity were found to have a proportional relationship based on the CIEL*a*b* color system. The color of the traditional paper was assessed assessment shows green and yellow rather than red and blue. The DNA concentration demonstrated a positive linear correlation with the peaks of 992 cm−1, 1599 cm−1, and 1628 to 1638 cm−1 region, which were lignin-specific functional groups. The presence of lignin in traditional paper defines the colors green and yellow, which is related to the presence of a cell wall. The quantity of cell walls present is linked to DNA survival during the traditional papermaking process. Furthermore, the partial least square (PLS) regression model is established. The prediction model based on DNA, paper properties, and smoothing + the second derivative preprocessed attenuated total reflection-Fourier-transform infrared (ATR-FTIR) spectral data demonstrated valid purity predictions. The evaluation parameter of the cross-validated prediction model contains a low Root Mean Square Error of Cross-Validation (RMSECV) of 0.091 for DNA purity. The determination coefficient was close to 1. However, the further establishment of a validated DNA extraction methodology is required for the consistency of the prediction model for DNA concentration. The hierarchical clustering analysis demonstrated the agglomerative dendrogram on traditional paper samples. For the dendrogram, the Nasu paper mulberry (originating in northern Japan) was distinguished from another paper mulberry (originating in southwestern Japan) by clustering. By multivariate statistical analysis, the DNA presence and quality were predictable from the Japanese traditional papers. In addition, the clustering analysis provided the possible origin of paper mulberry materials for traditional papers. Based on the preliminary information, the need for DNA analysis on historical traditional paper can be determined.

Abstract There are many paper manuscripts at museums, stores, and libraries that have different stains. The dust stains and soil remains played an important role in the degradation of these manuscripts. Therefore, the cleaning process for these stains is important to process. Unfortunately, the removal of stains by some traditional techniques can be hazardous to the paper's fibers. Therefore, this study aims to evaluate innovative nanoparticle gels in the cleaning process of dust stains from paper manuscripts. The synthesized nanomaterials [Fe3O4, TiO2, and ZnO]/Carbopol hybrid nanogel were examined in order to investigate the surface morphology, determine the physio-chemical properties, for phase structure, using scanning electron microscope (SEM), transmission electron microscope (TEM), AFM, DLS, XRD, and Zeta potential. Some stained paper samples were prepared and exposed to accelerated thermal aging at 100 °C for 72 h. The evaluation of the cleaning by nanogel was performed by different analytical procedures containing investigation with a USB digital microscope, SEM, color change, mechanical properties, and ATR-FTIR analysis. The results of this study showed that ZnO/Carbopol hybrid nanogel at high viscosity gave the best results in the cleaning process of mud stains through the ability to dismantle mud particles and increase surface contact with the solvent. The aged treated sample with high viscosity form of ZnO NPs/carbopol hybrid nanogel gave the highest tensile strength value of (56.0 N). The treated samples with the high viscosity form of ZnO NPs/carbopol hybrid nanogel gave the highest value of elongation (1.398%) before aging. It also does not affect the chemical composition of the paper after cleaning it, but rather on the whole, it bites the hydration of the paper, which positively affects the properties of the treated paper.

Chemical wastes, such as synthetic dyes and coloring agents, pose significant concerns due to their detrimental impact on human health and ecosystems. As an eco-friendly alternative, the study of natural dyes and coloring agents has gained momentum over the last decade, owing to their biodegradability and reduced environmental and health risks. Here, we report a novel approach employing a butterfly pea anthocyanin paper-based sensor to quantify Fe(III) ions in water. Compared to previous green sensing techniques reliant on heavy instrumentations, this approach offers enhanced accessibility, cost-effectiveness, and user-friendliness. Notably, this study is the first example of natural dye sensing on a capillary microfluidics system. The capillary-driven microfluidic system ensures user-friendly operation and allows the sensing platform to be directly immersed in water without reagent loss. The device's design involves drying the butterfly pea-derived anthocyanin reagent within a pH-controlled paper substrate embedded in the capillary-driven microfluidic system. Smartphone-based colorimetric signal generation and quantification was achieved within seconds for a working range of 50–800 mg/L, with the device's detection limit of 43 mg/L using ImageJ and 55 mg/L using the smartphone app. This green sensing methodology has the potential to be used for groundwater sources with elevated Fe(III) levels. Additionally, this platform can be used in chemistry educational settings as an effective means to understand fundamental concepts such as acid-base reactions, base strength, ionic equilibrium, and metal complexation in a user-friendly microfluidic system.

Abstract Medieval paper, a handmade product, is made with a mould which leaves an indelible imprint on the sheet of paper. This imprint includes chain lines, laid lines and watermarks which are often visible on the sheet. Extracting these features allows the identification of the paper stock and gives information about the chronology, localisation and movement of manuscripts and people. Most computational work for feature extraction of paper analysis has so far focused on radiography or transmitted light images. While these imaging methods provide clear visualisation of the features of interest, they are expensive and time consuming in their acquisition and not feasible for smaller institutions. However, reflected light images of medieval paper manuscripts are abundant and possibly cheaper in their acquisition. In this paper, we propose algorithms to detect and extract the laid and chain lines from reflected light images. We tackle the main drawback of reflected light images, that is, the low contrast attenuation of chain and laid lines and intensity jumps due to noise and degradation, by employing the spectral total variation decomposition and develop methods for subsequent chain and laid line extraction. Our results clearly demonstrate the feasibility of using reflected light images in paper analysis. This work enables feature extraction for paper manuscripts that have otherwise not been analysed due to a lack of appropriate images. We also open the door for paper stock identification at scale.

Abstract Microorganisms, especially microscopic filamentous fungi, represent one of the most significant factors influencing the degradation of cultural heritage cellulosic objects. Early detection, identification and characterisation of microbial communities can help select a suitable conservation intervention and, in addition, allow possible control of its effectiveness. A combination of spectral methods and statistical data processing appears to be a suitable alternative to conventional methods for monitoring microbial contamination. The main goal of the presented research was the investigation of the spectral properties of vital and devitalised filamentous fungi Alternaria alternata, Aspergillus niger, Cladosporium herbarum, Penicillium chrysogenum, and Trichoderma atroviride, inoculated on a paper substrate Whatman in two phases—dormant (conidia) and active (mycelium). The combination of the UV-Vis-NIR and NIR Fibre Optics Reflection Spectroscopy (FORS) with the Principal Component Analysis (PCA) was set to determine whether the spectra of vital and devitalised forms of studied samples differ. The obtained results prove differences between the spectra of vital and devitalised forms of filamentous fungi, at least in one studied spectral region. Therefore, UV-Vis-NIR and NIR FORS combined with PCA seems to be a promising tool for monitoring paper-based objects' microbial contamination.

Many neonates’ manifest hyperbilirubinemia and jaundice during the first week following birth because of bilirubin accumulation in the blood. Newborns with severe hyperbilirubinemia develop neurotoxicity. Therefore, sensitive, accurate, cost-effective, and timely determination of bilirubin levels is highly desired. Herein, we present three simple systems of bilirubin assessment based on spectrophotometric, and digital imaging tools. Image-capturing devices pose a formidable challenge to sophisticated spectrophotometers and field-monitoring devices because of their simplicity and sensitivity. The first and second systems of bilirubin assessment, in solution, relied on spectrophotometric and conventional color responses of digital images collected with conventional or android smartphone camera, with LODs of 0.060–0.082 and LOQs of 0.200–0.273 ppm bilirubin. The third system utilized a microfluidic paper-based analytical device (μ-PAD) that is patterned with a wax printer on Whatman grade-1 chromatographic papers, with linear calibration graphs of up to 2.70,s and LODs of 0.035–0.040 and LOQs of 0.117–0.133 μg bilirubin/μ-PAD.

One-pot syntheses and in situ ultrasonication have been optimized to generate tunable and highly hydrophobic 2,7-octadienyl-ether (ODE) cellulose nanofibrils (CNFs). Using only butadiene sulfone to serve as dual reaction medium and precursor to 1,3-butadiene (1,3-BD) for telomerization with cellulose hydroxyls, the OH-to-ODE conversion significantly improved from ca. 0.7 to 1.2, 1.8, 3.1, and 4.1 mmol of ODE/g-cellulose at 103-110 °C for 1-2 h. Ultrasonication was highly effective and versatile in the direct disintegration of ODE-cellulose (ODE-cell) in nonpolar organic solvents and plant oils into ODE-CNFs as well as pretreating cellulose for improved functionalization. Mixing 2 wt % in situ ultrasonicated 1.2 mmol of ODE/g-cell improved the modulus of polybutadiene six times and the strength of poly(styrene-b-isoprene-b-styrene) three times, whereas in situ ultrasonication of 1.8 mmol/g-cell directly with linseed oil at merely 0.07 wt % created holistic biobased hydrophobic cellulose paper to resist water penetration while also significantly improving the tensile strength. This optimized telomerization and streamlined in situ ultrasonication approach has presented a sustainable synthesis and processing strategy to generate highly hydrocarbon-compatible nanocelluloses previously unattainable.

Abstract In paper degradation studies, the viscosity-average degree of polymerisation (DPv) is often used as a key indicator of the extent of degradation of cellulosic paper. DPv can be deduced from the viscosity of dilute paper solutions, as typically measured through glass capillary viscometry. The current study proposes an efficient, alternative method to evaluate DPv of cellulosic paper, which is based on rotational rheometry. The proposed methodology relies on the application of a shear flow in a thin film of cellulose solution to measure its dynamic viscosity, from which DPv can be subsequently derived in a straightforward fashion. Rheometry allows to measure the viscosity for a range of shear rates, which results in multiple DPv evaluations per sample, and thus in statistically representative data from an individual test. Further, rheometry typically requires considerably less paper mass per test than glass capillary viscometry, which makes the method attractive for paper degradation studies with limited sample availability. Also, rheometry measurements are less work-intensive than glass capillary viscometry measurements. The rheometry method has been applied to 4 hygrothermally aged cellulose paper samples and the unaged counterpart. The measurement results regarding the age-dependency of DPv and the number of cellulose chain scissions are compared to those obtained by glass capillary viscometry, showing a very good agreement. At a longer ageing time, both experimental methods reveal a non-linear decrease in time of DPv, and a non-linear increase in time of the number of cellulose chain scissions, which indicate that the cellulose ageing process is realistically captured. The agreement in measurement results further demonstrates that rheometry is an easy-to-use, accurate and efficient alternative for DPv measurements by glass capillary viscometry.

The development of highly specific biomimetic recognition material is a challenge for rapid detection of harmful residues in foodstuff. In this study, a paper-based boronate affinity metal-organic framework/molecularly imprinted polymer microfluidic chip (FZS-BA@MIP) was constructed based on the in situ construction strategy, which was also designed as a highly specific biomimetic recognition module. Here, the homogeneous zeolitic imidazole framework-8 (ZIF-8) membrane served as a great scaffold and enrichment layer. Besides, the recognition layer of MIP was prepared based on a highly oriented boronate affinity surface imprinting strategy. With the aid of the liquid flow channel, the highly specific enrichment and visual detection for antibiotic residues like kanamycin in actual products were achieved on the paper chip module of an integrated lateral flow platform. The whole analysis process could be accomplished within 30 min. In brief, this study offered a new integrated biomimetic recognition platform for visually detecting harmful veterinary residues containing cis-diols, which demonstrated promising commercial value in point-of-care testing of foodborne hazardous compounds.

Oxygen (O2) was discovered approximately 250 years ago (Contribution 1), a breakthrough accredited to at least three people: Antoine-Laurent de Lavoisier in France (Antoine Lavoisier), Carl Wilhelm Scheele in Sweden, and Joseph Priestley in England [...]

Condition assessment of works of art created with oil media on paper could be a complex matter when presenting problems of damage due to the absorption of oil binders by the paper support, since they depend on several factors and occur in variable conditions. The present work refers to the results of an investigation on the effect of linseed oils on the color, opacity, morphology, tensile strength, and chemical properties of lignocellulosic papers, in comparison to that of pure cellulosic papers. Lignocellulosic papers are involved in research on new, yet significant, parameters that might influence the behavior of the oil-impregnated areas of the supports upon aging. The research was applied to mock-ups, made of two types of lignocellulosic paper impregnated with three types of linseed oil and subjected to accelaratated ageing in specific conditions of relative humidity and temperature in closed environment. The research involved colorimetry, opacity, tensile strength, pH measurements, SEM, FTIR, and VOC analysis with GC-MS. The results indicated that thermal-humid ageing caused the gradual darkening of the oil-impregnated mock-ups, alterations in opacity, and decrease of pH values, depending mainly on the formulation of linseed oil, as well as a reduction in tensile strength. FTIR analysis results indicated that the chemical changes that occur upon ageing supported the recorded optical and mechanical alterations, while VOC emissions are both associated with the paper type and the kinetics of degradation of the different types of linseed oil.

The goal of green chemistry is to reduce the impact of chemical processes on the environment. In this context, it is important to develop new analytical tools that comply with the principles of green analytical chemistry (GAC) to contribute to the sustainable development of the planet. This study describes the development of an environmentally friendly methodology using paper-based analytical devices (µPADs) to perform acid-base titrations by distance-based measurements. The devices were composed of a circular zone defined with 5 mm diameter connected to a rectangular channel of 40 mm long × 3 mm wide. The titrations of acidic (strong and weak) and alkaline (strong and weak) solutions were successfully demonstrated using 10 µL of titrant solution and 10 µL of sample solution. The solution added into the zone travels different distances depending on the concentration of the titrated, thus promoting the channel coloration or discoloration. The distance measurements covered by the titrated solutions were obtained recorded with a digital caliper. As proof-of-concept for quantitative purposes, the µPAD was then used to determine the acetic acid content in commercial vinegar. The average distances ranged from to 32.0 to 32.5 mm and the concentration values ranged from 4.3 to 4.6% (m/v). Conventional acid-base volumetry was used as a control method, and the obtained results demonstrated no statistical difference at 95% confidence level. Lastly, the 12 principles of GAC were analyzed to evaluate the suitability of the proposed method. Considering a unified scale between 0 and 1, the final green value was 0.72. Titrations with distance-based detection on µPADs were found to be a technique with fast responses and low cost that can be used as a replacement for conventional practices in teaching laboratories or adapted for the detection of different analytes.

In the era of liquid biopsy, microRNAs emerge as promising candidates for the early diagnosis and prognosis of cancer, offering valuable insights into the disease's development. Among all the existing analytical approaches, even if traditional approaches such as the nucleic acid amplification ones have the advantages to be highly sensitive, they cannot be used at the point-of-care, while sensors might be poorly sensitive despite their portability. In order to improve the analytical performance of existing electroanalytical systems, we demonstrate how a simple chromatographic paper-based disk might be useful to rationally improve the sensitivity, depending on the number of preconcentration cycles. A paper-based electrochemical platform for miRNA detection has been developed by modifying a paper-based electrode with a methylene blue (MB)-modified single-stranded sequence (ssDNA) complementary to the chosen miRNA, namely miR-224 that is associated with lung cancer. A detection limit of ca. 0.6 nM has been obtained in spiked human serum samples. To further enhance the sensitivity, an external chromatographic wax-patterned paper-based disk has been adopted to preconcentrate the sample, and this has been demonstrated both in standard and in serum solutions. For each solution, three miR-224 levels have been preconcentrated, obtaining a satisfactory lowering detection limit of ca. 50 pM using a simple and sustainable procedure. This approach opens wide possibilities in the field of analytical and bioanalytical chemistry, being useful not only for electrochemistry but also for other architectures of detection and transduction. [ABSTRACT FROM AUTHOR]

Oil media on paper, such as oil paintings, sketches, prints, and books, occasionally present problems associated with the effect of oil medium on the paper support, raising a composite matter of condition assessment as it depends on several factors. The present work examines the effect of linseed oil on paper and, in particular, the changes caused by three types of linseed oil on the optical, morphological, mechanical, and chemical properties of pure cellulosic paper, employing mock-ups submitted to artificial ageing in controlled conditions of relative humidity and temperature in airtight vessels. The study involved colorimetry, opacity, tensile strength, pH measurements, SEM, FTIR, and VOC analysis with GC-MS. Processing of the results has so far indicated that thermal-humid ageing caused the gradual darkening of the oil-impregnated mock-ups, as well as alterations in opacity, intense fall of pH values, and severe reductions in tensile strength, while linseed oil processing during manufacture has a significant impact. FTIR spectra have indicated that chemical changes upon ageing are in accordance with those of optical and mechanical changes, while VOC emissions are mostly associated with the drying and degradation of the different types of linseed oil.

Abstract Extracts from amur cork tree barks contain some of the most important traditional natural dyes used, especially for functional production in ancient Chinese papers, due to religious reasons and their aesthetic aspects and antibacterial properties. Some ancient paper artefacts, dyed with this colourant and scattered around the world, are currently preserved to different extents. This study aims to characterize the thermal degradation process of amur cork tree bark extracts dyed papers to improve the knowledge and effectiveness of restoration practices. The properties of extracts dyed papers treated under dry-heat accelerating ageing conditions were investigated via optical observation and scanning electron microscopy as well as with pH, tensile strength and folding endurance analyses. The results showed that the main components from extracted dyes played important roles in affecting the properties of dyed paper. The changes in surface colour, pH, morphology and mechanical properties after the artificial dry-heat ageing tests revealed the most suitable concentration of extract dyes for maintaining the long-term thermal stability of the paper.

Abstract The Alessandrina Library was founded in 1667 by pope Alexander VII Chigi and is nowadays housed in the Campus of Sapienza University of Rome (Italy). Within its Ancient (mostly made of rag paper) and Modern (mostly made of contemporary paper) collections, it includes more than one million books produced from the XVI to the XXI century. In 2019, six thermo-hygrometers were deployed in its multi-storey repository to monitor temperature (T) and relative humidity (RH). Hourly T and RH data collected over 2 years allowed us to evaluate spatial and temporal thermo-hygrometric distributions and to carry out a comprehensive assessment of the climate-induced risks (mechanical, chemical, and biological deterioration mechanisms). Vertical temperature gradients associated with unstable conditions occurred in winter, resulting in upraising air flows up to the ceiling. The risky short-term RH fluctuations (EN 15757:2010) were determined to avoid mechanical stress in case of loans, relocation, and consultation. The Time Weighted Expected Lifetime (TWEL) index was used to evaluate the chemical risk for different paper-based collections as a function of their acidity and degree of polymerisation, also considering the typical response time of paper books to T and RH changes. The TWEL calculation estimated that the durability of acidic paper was around 300 years and highlighted that rag paper could be subject to cellulose hydrolysis only in summer and autumn, while contemporary paper was mostly at no risk. The risk of mould germination (Sedlbauer diagram) was possible on few days in Autumn, while the production of insect eggs (Brimblecombe empirical function) was favoured during approximately 42% of time over the year. In addition, illuminance and colorimetric measurements (performed on selected book covers) showed that light-sensitive objects could be exposed to the photodeterioration risk in the east-facing side of the repository. Although the investigation focussed on a specific case study, a similar approach could be effectively adapted to most library and archival repositories conserving paper-based collections.

In the ever-growing demand for agricultural production, the use of pesticides and the consequential health risks is an issue that remains in the spotlight. The biomonitoring of pesticides in biological matrices is a mandatory task to point out the adverse effects on those people that are particularly exposed (i.e., occupational exposure) and to customize the use of pesticides for safer and more aware agricultural practices (i.e., precision agriculture). To overcome the bottleneck of costs and long sample treatments, we conceived a paper-based analytical device for the fast and smart detection of glyphosate in human urines, which is still the most widespread pesticide. Importantly, we demonstrate how to face the analytical interference given by uric acid to develop an electrochemical sensor for glyphosate detection using paper as a multifunctional material. To this purpose, a sample treatment was pointed out and integrated into a paper strip to decrease the level of uric acid in urines, finally delivering a ready-to-use device that combines lateral and vertical flow. The effective decrease of uric acid after the paper-integrated treatment is verified by direct oxidation in differential pulse voltammetry, whereas glyphosate detection can be carried out by enzyme inhibition assay in chronoamperometry. The system showed a limit of detection for glyphosate of 75 μg/L and a linear range of 100 - 700 μg/L. Additionally, the sustainability of the paper device was assessed and compared with reference chromatographic methods. Overall, this work provides an example of how to design green sensing solutions for addressing analytical challenges in line with the White Analytical Chemistry principles.

Abstract This study applied various scientific analyses to one fragment of paper and three pigments excavated from earthenware found in the Hoeamsa Temple site at Yangju, Korea, which is believed to have been built in the early twelfth century. Radiocarbon dating of the paper fragment suggests a manufacture date between 1460 and 1646 (at a 95% confidence interval). It was estimated to have been used during the early and middle period of the Joseon dynasty (1391–1776), when the Hoeamsa Temple site was rebuilt. In addition, by staining the fiber of the paper fragment with Graff “C” stain, the paper’s raw material was identified as paper mulberry through dislocation, cross-marking, and transparent membrane, which are characteristics of the bast fiber. Efforts were made to identify their material properties and manufacturing techniques of the three types of pigments. Color difference analysis was performed by distributing the pigments in large areas to reveal characteristic differences according to the color difference of the pigment. We found that green-type pigments are malachite and atacamite, red-type pigments are hematite based on the element Fe, and white-type pigments are quartz and muscovite based on the elements Si and Al. In addition, as the size distribution of the three types of pigments is wide and has a multi-peak distribution curve, it was concluded that the pigments were used without purification.

Abstract Paper cultural relics such as double-sided printed newspapers and periodicals represent modern cultural heritage. Severe damage such as embrittlement, decay, and dreg generally occur to paper; hence, it urgently needs conservation and restoration. Therefore, herein, a new reinforcement method for the fragile double-sided printed paper cultural relics is proposed with cotton mesh and adhesive PVA217 as reinforcement materials. Using a computer measured and controlled folding endurance tester, a pendulum tensile strength tester, pH meter, pulp viscosimeter, and other instruments, the physical properties of newspaper samples before and after aging were evaluated. In addition, the mechanical properties, chromatic aberration and surface morphology of simulated samples before and after the cotton mesh reinforcement and Japanese washi paper reinforcement were assessed. The experimental results indicate that this new reinforcement method could effectively improve the physical strength, chromatic aberration and durability of the simulated samples. Widespread applications of this cotton mesh reinforcement method for the reinforcement and protection of the red revolutionary cultural relics such as double-sided printed newspaper and periodicals during the Republic of China era are foreseeable.

Abstract Paper degradation menaces the useful lifetime of books, manuscripts, and works on paper during storage, circulation, and display in libraries, archives, and museums. Severe damages such as embrittlement, decay, and mold often occur to the paper that might threaten to lose cultural heritage. However, the shelf life of papers stored in suitable conditions can be extended by hundreds of years. The most important external factors affecting the deterioration of paper-based materials include, in particular, changes in temperature and air humidity. In this study, the effects of accelerated aging under different conditions, including substantially different relative humidity, were considered relative to the strength properties of the paper sheets. These include the mechanical strength, such as breaking length, tear resistance, and bursting strength of the paper samples before and after dry heat aging and hydrothermal aging. Samples with various content of lignin produced in neutral pH were examined to exclude the adverse influence of acidity on paper properties. The results indicate that impact of moisture on tensile properties and pH-value of paper is much greater than the effect of increased temperature. The results of this work are intended to consolidate and expand the theoretical foundation and provide technical support for the conservators and library staff on the storage of paper cultural relics.

In this study, Melamine–formaldehyde (MF) resins were subjected to modification with benzoguanamine (BG) to produce MF-BG resins, followed by a comprehensive analysis of their chemical composition using advanced spectroscopic techniques such as Fourier transform infrared (FTIR), 1H-NMR, and 13C-NMR spectroscopy. The flame-retardant characteristics and thermal decomposition behavior of papers impregnated with MF-BG were examined and contrasted with those treated with standard MF. In particular, the optimized MF-BG5-treated paper exhibited a Limiting Oxygen Index (LOI) value exceeding 30%, and analysis using a cone calorimeter indicated a notable decrease in parameters such as the heat-release rate (P-HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) when compared to papers impregnated with standard MF. The findings from the scanning electron microscopy (SEM) analysis of the residual char following cone calorimeter experiments revealed that the MF-BG5-treated paper exhibited a denser and more uniform char formation. This phenomenon consequently limits the emission of combustion by-products and impedes the spread of flame. This study provides a feasible method for low-pressure laminates with better flame retardancy by using the BG additive up to a limit in MF resin. [ABSTRACT FROM AUTHOR]

In this research work, a coated paper was prepared with poly (butylene adipate-co-terephthalate) (PBAT) film to explore its use in eco-friendly food packaging. The paper was coated with PBAT film for packaging using hot pressing, a production method currently employed in the packaging industry. The coated papers were evaluated for their structural, mechanical, thermal, and barrier properties. The structural morphology and chemical analysis of the coated paper confirmed the consistent formation of PBAT bi-layered on paper surfaces. Surface coating with PBAT film increased the water resistance of the paper samples, as demonstrated by tests of barrier characteristics, including the water vapor transmission rate (WVTR), oxygen transmission rate (OTR), and water contact angle (WCA) of water drops. The transmission rate of the clean paper was 2010.40 cc m−2 per 24 h for OTR and 110.24 g m−2 per 24 h for WVTR. If the PBAT-film was coated, the value decreased to 91.79 g m−2 per 24 h and 992.86 cc m−2 per 24 h. The hydrophobic nature of PBAT, confirmed by WCA measurements, contributed to the enhanced water resistance of PBAT-coated paper. This result presents an improved PBAT-coated paper material, eliminating the need for adhesives and allowing for the fabrication of bi-layered packaging. [ABSTRACT FROM AUTHOR]

Abstract The cleaning of particles from smooth and rough paper surfaces using a high-speed CO2 snow jet was investigated. The measurements included characterization of the jet properties, determination of the cleaning efficiency, and evaluation of any possible adverse effects. The method was compared with nitrogen jet cleaning and dry cleaning by commercial materials. The results showed that the CO2 snow jet is able to effectively remove particles from the paper surface and did not cause any observable degradation. The CO2 snow jet cleaning compared with the mechanical dry cleaning showed similar effectiveness without any adverse effects on the paper surface. It was proved that the CO2 snow technique is a suitable method for cleaning common types of paper materials.

Abstract Once printed, books are always accompanied by the smells of volatile organic compounds (VOCs) which are continuously emitted not only by inks but also by papers themselves throughout their lives. Although the VOCs from papers may bring mild discomfort to readers, they are considered as very important factors that feature the degradation of papers and show potential applications in cultural relic appraisal. In this study, an analytical approach based on solid phase microextraction combined with gas chromatography-mass spectrometry (SPME-GC/MS) was proposed for the evaluation of volatile organic compounds (VOCs) emitted by Chinese traditional handmade papers. The VOCs evaluations and artificial aging processes were both applied to recent-made papers and naturally aged papers from a traditional Chinese calligraphy and painting scroll (collected by the National Museum of China). To be noticed, a large number of aliphatic acids, aldehydes, ketones, furan derivatives, benzene series and terpenoid substances indicated that the VOCs signals not only reveal the degradation of paper but also tentatively reflect the storage environment along hundreds of years ago. The semi-quantitative evaluation of markers indicated that the historical paper is under a serious degradation due to the high capacity it releases. Our results provided a path way to get the degradation information of ancient paintings as well as potential realistic applications such as the conservation of paper-based relics and the environmental protection in libraries and museums.

Abstract Quantification of the degradation behaviour of heritage objects is essential to manage the rate of degradation and hence optimise their lifetime. In this research, a 23 full factorial experiment was carried out to deepen the understanding of the photodegradation of historical rag paper induced by continuous polychromatic visible radiation. Oxygen concentration, relative humidity and illuminance were investigated as the three environmental factors of primary concern. The effects of these factors on the rate constant of change in diffuse reflectance and tristimulus discolouration were investigated by analysis of variance and multiple linear regression. The three main effects were found to contribute the most to the rate of photodegradation of historical paper, among which relative humidity played the most important role whereas illuminance played the least. This observation is likely to hold when extrapolating the experimental conditions to real conditions in collection storage and display.

In this work, we developed an alternative manufacturing paper-based microfluidics method through 3D printing and wax filament. Microfluidic paper-based analytical devices (µPADs) are low-cost and easy-to-manufacture tools used for various chemical and biological analyses and studies. Paper-based microfluidics with wax has been limited as the manufacturers have discontinued most wax printing equipment. We aim to develop a low-cost and accessible manufacturing method that can replace conventional wax-on paper-based microfluidic manufacturing methods. Using highly available commercial 3D printing technology and wax filament, we could create hydrophobic wax barriers on the surface of different paper types. The properties and limits of this manufacturing method were characterized. Moreover, using this paper-based microfluidic manufacturing method, we were able to measure dopamine electrochemically using µPAD as a passive flow-based method in concentrations as low as 1 nM using injections as small as 15 µL.

In this work, a new paper-based device (PAD) was developed for the colorimetric detection of multiple heavy metals. The sensing principle of this PAD is based on the analyte-regulated photocatalytic activity of quantum dots (QDs) to certain substrates. The PAD consisted of three filter paper layers, defining a sample area, three channels, and three testing areas. Three photocatalytic reactions between different QDs and their corresponding substrates could be performed in one device, achieving the simultaneous detection of Cu(II), Mn(II), and Hg(II). The detection limits are 7.3 nM for Cu(II), 5.4 nM for Mn(II), and 8.1 nM for Hg(II), respectively. This PAD was applied to analyze real samples and the results were consistent with those obtained by inductively coupled plasma-optical emission spectrometer. This approach may provide a promising colorimetric sensing platform for multi-target analysis.

The calcium monitoring in the body not only anticipates several potential diseases (osteoporosis, kidney stones or high blood pressure) but also helps to improve target therapies and follow-up the patient's health status. Calcium monitoring is essential for the diagnosis of one of the most common endocrine disorders worldwide, namely hyperparathyroidism. So, in this work, a new Point-of-care test (POC-test) using a microfluidic paper-based analytical device (μPAD) for calcium quantification in saliva samples is described. The developed μPAD was based on the colorimetric reaction between calcium and cresolphthalein complexone (CPC) which forms an intense purple colour product. The developed device enabled calcium quantification in the range of 0.27–4.50 mmol/L (11.0–180 mg/L) with a detection limit of 80 µmol/L (3.2 mg/L). The accuracy of the developed μPAD was confirmed by analysing saliva samples (#10) and comparing the results obtained with the atomic absorption spectrometry reference procedure; the relative deviation between the two sets of results was below 10 %. A correlation between salivary calcium content and calcium content in blood was established and it was possible to conclude that salivary calcium concentrations above 1.55 mmol/L is an indicator of hypercalcemia. The developed device was stable for 2 weeks when stored at room temperature in vacuum conditions.