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High per- and polyfluorinated alkyl substance (PFAS) concentrations have been detected in agricultural soils in Southwest Germany. Discharges of PFAS-contaminated paper sludge and compost are suspected to be the cause of the contamination. Perfluorinated carboxylic acids (PFCAs) have been detected also in groundwater, drinking water, and plants in this area. Recently, previously unknown compounds have been identified by high-resolution mass spectrometry (HRMS). Major contaminants were polyfluorinated dialkylated phosphate esters (diPAPs) and N-ethyl perfluorooctane sulfonamide ethanol–based phosphate diester (diSAmPAP). In this study, HRMS screening for PFAS was applied to 14 soil samples from the contaminated area and 14 impregnated paper samples which were from a similar period than the contamination. The paper samples were characterized by diPAPs (from 4:2/6:2 to 12:2/12:2), fluorotelomer mercapto alkyl phosphates (FTMAPs; 6:2/6:2 to 10:2/10:2), and diSAmPAP. In soil samples, diPAPs and their transformation products (TPs) were the major contaminants, but also FTMAPs, diSAmPAP, and their TPs occurred. The distribution patterns of the carbon chain lengths of the precursor PFAS in soil samples were shown to resemble those in paper samples. This supports the hypothesis that paper sludge is a major source of contamination. The presence of major degradation products like PFCAs, FTSAs, or PFOS and their distribution of carbon chain lengths indicate the activity of biotic or abiotic degradation processes and selective leaching processes from the upper soil horizons. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03463-9.

Graphical abstract Enzyme-linked immunosorbent assay (ELISA) is widely used for the detection of disease biomarkers. However, it utilizes time-consuming procedures and expensive instruments, making it infeasible for point-of-care (POC) analysis especially in resource-limited settings. In this work, a multicolorimetric ELISA biosensor integrated on a paper/polymer hybrid microfluidic device was developed for rapid visual detection of disease biomarkers at point of care, without using costly equipment. This multicolormetric ELISA platform was built on multiple distinct color variants resulted from the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) and the etching of gold nanorods (AuNRs). The vivid color changes could be easily distinguished by the naked eye, and their red mean values allowed quantitative biomarker detection, without using any sophisticated instruments. When this multicolorimetric ELISA was integrated on a paper/polymer hybrid analytical device, it not only provided integrated processing and high portability but also enabled fast assays in about 50 min due to the unique advantages of paper/polymer hybrid devices. The limit of detection of 9.1 ng/μL of the hepatitis C virus core antigen, a biomarker for hepatitis C, was achieved using this multicolorimetric ELISA platform. This multicolor ELISA analytical device provides a new versatile, user-friendly, affordable, and portable immunosensing platform with high potential for on-site detections of various viruses, proteins, and biomarkers for low-resource settings such as at home, public venues, rural areas, and developing nations. Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03359-8.

In this study, Taguchi experimental design was used to the optimize operating parameters for the degradation of paper mill effluent using electrochemical (EC) process with two-dimensional concentric aluminum tube electrodes (CATE). For this purpose, four significant experimental factors were used in four levels pH (6–9), electrolysis time (10–40 min), voltage (6–12 V) and surface area (357–624 cm(2)). The process parameters were optimized, through performing L16 orthogonal array of Taguchi technique, for the removal of chemical oxygen demand (COD) and turbidity. The percent COD and turbidity reductions were transferred into an accurate S/N ratio for a larger value is the better (LBT) response. The study presents a unique method of finding optimum combination of process parameters to illustrate their effect on the turbidity and COD reduction. The treatment conditions for the maximum elimination of the pollutants were second level of pH (7), third level of ET (30 min), fourth level of voltage (12 V) and second level of surface area (446 cm(2)). The confirmation experiment results were within the confidence intervals (CI) indicating an acceptable agreement between predicted and observed values. Based on the p-values, the electrolysis time and voltages were found to be the most significant factors for both COD and turbidity reduction. The findings of research indicated, that the Taguchi method can be used successfully for the treatment of paper industry effluent by electrochemical technique.

Currently, most of the collected waste medium-density fiberboards (MDF) is incinerated or landfilled, as economically viable recycling methods are yet to be developed. By steam refining waste medium-density fiberboards (MDF), it is possible to hydrolyze the incorporated resins and isolate a high yield fiber fraction. Further refining of the steam treated fibers might enable the fibers to be utilized in applications such as paper packaging, facilitating a cascading use of the waste material stream. To this end, intimate knowledge of the material is needed. In this study, the steam refined fibers of two waste MDF samples containing differing amounts of softwood and hardwood underwent refining and beating. The resulting fibers were characterized regarding their morphology and paper test sheets were produced to evaluate their strength (compression-, tensile- and tear-strength). Distinct differences in response to refining between the MDF samples were apparent. For the sample with the higher hardwood share an increase in strength properties with increasing steam treatment severities could be observed and it was possible to produce test sheets with comparable compression strength to recycled pulp for industrial corrugated paperboard. For the sample with a higher share of softwood, the steam treatment severity did not show any influence on fiber morphology or paper properties, and the resulting paper strength was low in comparison to the other steam refined waste MDF sample. Graphic Abstract

Synthetic cannabinoid receptor agonists (SCRAs) are a class of varied compounds that mimic the effects of natural cannabinoids found in cannabis. Because they have a wide range of diverse structures, they vary widely in their potency. The abuse of new psychoactive substances (NPS) in prisons was reported in many European countries and in the USA. In the present study, we have described the identification of SCRAs in 56 infused paper sheet samples, seized mainly in Brazilian prisons between 2016 and 2020. The materials were seized by local or federal law enforcement and analyzed by Sao Paulo State Police or Brazilian Federal Police using gas chromatography–mass spectrometry, attenuated total reflection-Fourier transform infrared spectroscopy, liquid chromatography–high-resolution mass spectrometry or nuclear magnetic resonance spectrometry. Most of these samples (87.5%) were seized in 2019–2020; seven different SCRAs were identified in samples, and the most frequently identified substances were MDMB-4en-PINACA (23.6%) and 5F-MDMB-PICA (36.4%), the newest SCRAs emerging recently. As observed in Europe and the USA, Brazil also shows the prevalence of indazole-3-carboxamides and indole-3-carboxamides among SCRAs seizures in the prison system. This phenomenon is spreading all over the world at this moment. These data on the prevalence could help to alert judicial authorities to shutting down the introduction of NPS, including SCRAs, into prisons to ensure safety and security for avoiding health risks of prisoners and staff, leading to positive effects in this population. To our knowledge, this is the first demonstration of SCRAs smuggling into prisons in Latin America.

This study evaluates the use of fermentation to increase nutrient availability in pulp and paper bio-sludge (PPBS) as feed for black soldier fly larvae (BSFL). Rearing of BSFL on fermented PPBS was carried out in a climate chamber in order to assess nutrient availability and larvae survival and growth. The PPBS used came from a chemo-thermomechanical pulp/groundwood pulp mill. The PPBS was fermented at 35 °C and 55 °C, respectively, at initial pH of 10. The effects of sediment and liquid from fermented PPBS on larvae dry weight, survival rate until the prepupae stage, bioconversion, and reduction rate of PPBS were measured. The bioconversion of the liquids (4.1–6.6%) was substantially higher than for both the sediments and untreated PPBS (≤ 0.4%). The survival rate, on the other hand, was substantially lower (26.3–30.9 %) than for the sediments and untreated PPBS (49.5–52.6%). Neither the sediments nor the liquids had significant effects on the larvae weight or on the PPBS reduction rate. The sediments had no significant effect on the survival rate or the bioconversion. This study demonstrates that fermentation dissolves a part of the PPBS and that dissolved substances in the fermentation liquid readily convert to larvae biomass. However, the bulk of the lignocellulose is not dissolved, and most of PPBS nutrients remain unavailable for growth of the larvae. Further research should focus on improved pretreatment of PPBS to increase availability of nutrients and thereby improve the feasibility of BSFL as a recycling method for PPBS.

Microfluidic paper-based analytical devices (μPADs) have developed rapidly in recent years, because of their advantages, such as small sample volume, rapid detection rates, low cost, and portability. Due to these characteristics, they can be used for in vitro diagnostics in the laboratory, or in the field, for a variety of applications, including food evaluation, disease screening, environmental monitoring, and drug testing. This review will present various detection methods employed by μPADs and their respective applications for the detection of target analytes. These include colorimetry, electrochemistry, chemiluminescence (CL), electrochemiluminescence (ECL), and fluorescence-based methodologies. At the same time, the choice of labeling material and the design of microfluidic channels are also important for detection results. The construction of novel nanocomponents and different smart structures of paper-based devices have improved the performance of μPADs and we will also highlight some of these in this manuscript. Additionally, some key challenges and future prospects for the use of μPADs are briefly discussed.

In China, Xuan paper has been the paper of choice as artwork support and for conservation, for several centuries. However, little is known about its material properties, especially given the many grades of sized and unsized Xuan paper. In addition, there is a lack of information on its degradation. In this research, a selection of contemporary unsized Xuan papers was investigated, representing diverse raw materials. Seven out of twelve contemporary unsized Xuan papers were determined to be approximately neutral and contain > 2% alkaline reserve, indicating good durability. Viscometry was used to determine the degree of polymerisation (DP) as none of the samples gave significant reactions to the phloroglucinol spot test. The average DP of ten contemporary unsized Xuan papers is ~ 1700, excluding two papers that have presumably been sun-bleached, and that exhibit significantly lower DP. Using X-ray fluorescence, it can be demonstrated that Ca and Si are the dominant elements and interestingly, Ca content is directly correlated with ash content and with alkaline reserve. Accelerated degradation was performed at two sets of environmental conditions, i.e. 90 °C, 30% RH and 60 °C, 70% RH, and the established degradation rates agreed with the Collections Demography model of paper degradation meaning that degradation of Xuan papers proceeds in the same way as other types of paper. This research gives fundamental insights into contemporary unsized Xuan papers, which exhibit good stability during accelerated degradation despite the low starting DP in the context of the samples used in this study. Our findings may inform methods of Xuan paper production, selection of Xuan paper for conservation purposes, as well as preventive conservation of Xuan paper-based artefacts.

Process-monitoring laboratories in the pulp and paper industry generally use a combination of wet chemical analyses and physical measurements to certify the fitness of a production pulp for a specific end-use. These laboratory tests require time and the effort of trained personnel, limiting their utility for real-time process control. Here we show that Raman probes of unrefined cellulosic pulps, well-suited to the online measurement of in-process materials, can predict the quality attributes of manufactured papers. The accuracy of prediction improves when the covariance is modelled in a reduced measurement space selected by a data-driven, feature-selection technique referred to as a Template Oriented Genetic Algorithm (TOGA). TOGA, combined with discrete wavelet transform (DWT), isolates functional-group features that correlate best with mechanical properties paper derived from refined pulp. Paper makers refine market pulps to build sheet strength using a beating process that decreases freeness as it increases fibre-fibre bonding. Methods demonstrated here predict manufactured sheet properties obtainable after any specified degree of refining from the Raman spectrum of an unrefined pulp. This analysis capacity will enable both vendors of market pulp and makers of sheet paper to specify in advance the amount of beating required to produce a desired product, thereby saving cost and conserving resources.

An industry compatible chemo-refining approach was tested for preparation of micro-nanofibrillated cellulose (MNFC) from bleached softwood pulp using sodium meta-periodate and sodium chlorite as oxidizers followed by refining in Valley beater. SEM and FTIR analyses confirmed micro-nano scale fibrillation and chemical functional group modification in laboratory prepared MNFC, respectively. The water retention value, carboxyl content and viscosity of MNFC were found comparable with imported NFC as reference (R-NFC). To evaluate MNFC as strength enhancer for paper properties, 5% MNFC addition to bleached mixed hardwood pulp showed 6% reduction in bulk with 36%, 24% and 97% increment in breaking length, burst index and double fold of the handsheets, respectively without affecting tear index and optical properties than the control. Surface properties were also improved. Pulp drainability (37°SR) after MNFC addition was found suitable for papermaking. These laboratory results confirmed the potential of MNFC as a suitable strength additive for paper quality improvement.

In this study, a microfluidic paper-based analytical device (mu PAD) was integrated with a smartphone app capable of offline (without internet access) image processing and analysis for the rapid colorimetric detection of glucose. A self-inking stamp was used to form hydrophobic channels on a piece of paper-towel due to its superior water absorption efficiency. As demonstrated, the developed sensor was employed for the colorimetric detection of glucose in artificial saliva in the linear scope of 0 - 1 mM with a calculated detection limit of 29.65 mu M. The experimental results show that the quantitative analysis of glucose with the proposed smartphone platform could be completed in less than one minute. The app developed for the smartphone platform is capable of extracting the color-changing area with an embedded image processing tool which could address the problem of color uniformity in the detection zones of mu PAD. The integrated platform has great potential to be used for non-invasive measurements of glucose in body fluids, like tears, sweat and saliva.

Lightweight yet strong paper with high toughness is desirable especially for impact protection. Herein we demonstrated electrically conductive and mechanically robust paper (AP/PB-GP) made of reduced graphene oxide via interfacial crosslinking with 1-aminopyrene (AP) and 1-pyrenebutyrat (PB) small molecules. The AP/PB-GP with thickness of over ten micrometer delivers a record-high toughness (∼69.67 ± 15.3 MJ m−3 in average), simultaneously with superior strength (close to 1 GPa), allowing an impressive specific penetration energy absorption (∼0.17 MJ kg−1) at high impact velocities when used for ballistic impact protection. Detailed interfacial and structural analysis reveals that the reinforcement is synergistically determined by π-π interaction and H-bonding linkage between adjacent graphene lamellae. Especially, the defective pores within the graphene platelets benefit the favorable adsorption of the pyrene-containing molecules, which imperatively maximizes the interfacial binding, facilitating deflecting crack and plastic deformation under loading. Density functional theory simulation suggests that the coupling between the polar functional groups, e.g., −COOH, at the edges of graphene platelets and −NH2 and −COOH of AP/PB are critical to the formation of hydrogen bonding network.

Reproductive conflicts are expected in societies where nonbreeding helpers retain the ability to produce offspring. Despite potential competition from reproductively capable nestmates in social wasps, egg laying tends to be monopolised by a single or relatively few queens. Genetic studies on reproductive partitioning in Polistes paper wasps suggest high reproductive skew in the genus. Conflict is thought to be minimal due to nestmate relatedness or the possibility of inheriting a reproductive monopoly on a nest; consequently, there are inclusive fitness opportunities for nonreproductive helpers. However, most studies are limited to temperate wasp species. Given the cosmopolitan distribution of Polistes, genetic data on group conflicts are required for a broader range of tropical species to determine whether these trends apply across climatic zones. We examined female reproductive skew in the Neotropical paper wasp Polistes lanio, genotyping a selection of adults and pupae from established post-emergence nests using single-nucleotide polymorphisms (SNPs). SNP-based pedigree analyses indicate a reproductive monopoly held by a single queen, with queen replacement from natal nestmates and evidence of possible multiple mating. Relatedness between pupal offspring was high (r = 0.71). It is likely that high reproductive skew among females is a founding trait of Polistes societies, conserved among species that have spread into new environments from Indomalayan origins.

Pathogen detection is crucial for human, animal, and environmental health; crop protection; and biosafety. Current culture-based methods have long turnaround times and lack sensitivity. Nucleic acid amplification tests offer high specificity and sensitivity. However, their cost and complexity remain a significant hurdle to their applications in resource-limited settings. Thus, point-of-need molecular diagnostic platforms that can be used by minimally trained personnel are needed. The nuclease protection assay (NPA) is a nucleic acid hybridization-based technique that does not rely on amplification, can be paired with other methods to improve specificity, and has the potential to be developed into a point-of-need device. In traditional NPAs, hybridization of an anti-sense probe to the target sequence is followed by single-strand nuclease digestion. The double-stranded target-probe hybrids are protected from nuclease digestion, precipitated, and visualized using autoradiography or other methods. We have developed a paper-based nuclease protection assay (PB-NPA) that can be implemented in field settings as the detection approach requires limited equipment and technical expertise. The PB-NPA uses a lateral flow format to capture the labeled target-probe hybrids onto a nitrocellulose membrane modified with an anti-label antibody. A colorimetric enzyme-substrate pair is used for signal visualization, producing a test line. The nuclease digestion of non-target and mismatched DNA provides high specificity while signal amplification with the reporter enzyme-substrate provides high sensitivity. We have also developed an on-chip sample pretreatment step utilizing chitosan-modified paper to eliminate possible interferents from the reaction and preconcentrate nucleic acids, thereby significantly reducing the need for auxiliary equipment. Graphical abstract.

The study is a first investigation of the feasibility to preserve recycled fillers (e.g. calcium carbonate, kaolin) from deinking paper sludge for newspaper production using an alternative approach respect to the actual methods. Deinking paper sludge was incinerated at 575 °C. The thermal stability of the incinerated sludge (ash) was evaluated by infrared analysis. Subsequently, the resulting ash was bleached by sodium dithionite. The particle size of the ashes was analysed by laser diffraction. The effect of recycled fillers on recycled paper pulp, after blending, was evaluated by the analysis of the physical and optical properties of the obtained paper sheets. Analysis showed the conservation of the calcium carbonate and other fillers’ molecular structure, both after incineration of the sludge and after bleaching. The dithionite treatment of the ashes resulted in ISO brightness levels of more than 70. The brightness was stable over one month. Paper sheets made by blending the bleached ashes with recycled paper showed an improvement of brightness and opacity but a decrease in terms of porosity and breaking length compared to paper sheets made without any filler. The proposed method still requires further studies to evaluate the economical application but offers an opportunity for the recycling of inorganic materials and valorisation of the sludge.

The study describes the preparation of pulp and nanocellulose from non-wood plant materials, as well as an improved properties of paper and cardboard for mass production. The pulps from wheat straw, kenaf and flax fibers were prepared by the environmentally friendly organosolv method—cooking in a solution of isobutanol or peracetic acid. The organosolv pulps used to prepare nanocellulose had traces of lignin and mineral substances. The process of hydrolysis of the investigated organosolv pulps was optimal when carried out under the following conditions: 43% sulfuric acid, temperature 60 °C, hydrolysis time 90 min and ultrasonic treatment 60 min. Using the methods of SEM, XRD, TEM, AFM and TGA, the structure and properties of organosolv pulps and nanocellulose were studied. The use of nanocellulose in bulk and on the surface of mass types of paper and cardboard—paper for corrugation, offset paper, recycled containerboard and cardboard for flat layers of corrugated cardboard were investigated. We established the positive effect of nanocellulose application on the physical and mechanical properties of paper and cardboard. Low consumption of nanocellulose allows production of the paper and cardboard with properties that meet the requirements to appropriate standards and replacement of synthetic reinforcing materials.

The main objective of this study is the evaluation of RPPW anaerobic digestion feasibility at laboratory scale under Mesophilic condition. The experiment is conducted using a two-stage biofilm digester of 5 L capacity with mobile support material. Anaerobic treatment of wastewater from recycled pulp and paper industry in Morocco was tested using a laboratory-scale anaerobic biofilm digester that operated under mesophilic conditions over a 70-day. Chemical oxygen demand (COD) efficiency, volatile and total solid (VS, TS) elimination of the substrate during the process were: 78%, 52% and 48% respectively. The system was stable throughout its operating cycle with an optimum pH (7.24), alkalinity (1750 mg CaCO3/L) and a volatile fatty acid value (760 mg/L). The experimental daily biogas production measured reaches a value of 5 L/day with a composition of 71% methane, 27.6% carbon dioxide, 0.2 oxygen and 7713 ppm of the H2S. The study results show that the anaerobic biofilm reactor is a suitable technique for recycled pulp and paper wastewater (RPPW) treatment. The reactor shows high performances in terms of process stability, removal efficiency (> 70%) and biogas production. Anaerobic digestion is an efficient waste treatment technology that uses natural anaerobic decomposition to reduce the volume of waste while producing biogas. However, research is needed to strengthen microbial metabolism, biochemistry and the functioning of the rector to improve biogas production. The RPPW AD experiment with biofilm digester technology was stable throughout the operation period. The digester knows an overloaded in the last phase of the experiment which leads to an inhibition of biogas production.

In order to improve the efficiency of disease diagnosis and environmental monitoring, it is desirable to detect the concentration of proteins and metal ions simultaneously, since the current popular diagnostic platform can only detect proteins or metal ions independently. In this work, we developed a colorimetric microfluidic paper-based analytical device (µPAD) for simultaneous determination of protein (bovine serum albumin, BSA) and metal ions [Fe(III) and Ni(II)]. The µPAD consisted of one central zone, ten reaction zones and ten detection zones in one device, in which reaction solutions were effectively optimized for different types of chromogenic reactions. Fe(III), Ni(II) and BSA can be easily identified by the colored products, and their concentrations are in good accordance with color depth based on the established standard curves. The detection limits are 0.1 mM for Fe(III), 0.5 mM for Ni(II) and 1µM for BSA, respectively. Best of all, we demonstrated the efficiency of the µPAD with accurate detection of Fe(III), Ni (II) and BSA from river water samples within 15 minutes. The µPAD detection is efficient, instrument-free, and easy-to-use, holding great potential for simultaneous detection of cross type analytes in numerous diagnostic fields.

Propofol is a widely used intravenous anesthetic agent in sedation and general anesthesia. To improve the safety and maintain the depth of anesthesia, it is important to develop a rapid, sensitive, and reliable method to monitor the concentration of propofol in blood during anesthesia continuously. Here, we present a novel strategy based on paper spray ionization-mass spectrometry (PSI-MS) to detect propofol. Samples (in 10 μL) were mixed with methanol as protein precipitation solvent and 2,6-dimethylphenol as internal standard. Protein micro-precipitation was achieved with methanol by vortexing and centrifuging for 5 s each, and propofol was extracted to the supernatant. PSI-MS was performed in negative ionization mode, and MS signal lasted for 1 min. The analysis of a single sample was completed within 2 min. The area ratios of propofol to internal standard were calculated for quantification. Limit of detection of 5.5 ng mL−1 and limit of quantification of 18.2 ng mL−1 were achieved for propofol in whole blood. Calibration curve was linear in the range of 0.02–10 μg mL−1. The developed method was used successfully in monitoring the propofol concentration in 3 patients’ whole blood during anesthesia, showing its further application in controlling and feeding-back target concentration infusion.

Microfluidic paper-based analytical devices (μ-PADs) fabricated in Japan were employed for the determination of total chromium (Cr) in water, soil, and lettuce irrigated with wastewater in Ethiopia. The μ-PADs, which were printed by wax printing in Japan, were transported to Ethiopia and prepared for the determination of total Cr by adding appropriate reagents to the pretreatment and detection zones. Soil and lettuce samples were determined by the μ-PADs and a UV-Vis spectrophotometer in Ethiopia. A paired t-test showed that the mean total Cr concentrations determined in the soil and lettuce samples were not significantly different between μ-PADs and UV-Vis spectrophotometric analysis at the 5% level of significance. This implies that the μ-PADs have good accuracy and reliability, and could be employed to monitor Cr in environmental samples. We found that the total Cr concentrations in all soil and lettuce samples were above the permissible limit. Moreover, evaluating Cr contamination level using the geo-accumulation index indicated that the soils were contaminated with Cr moderately to heavily. Thus, the present work successfully demonstrated the potential of remote investigations of pollution in a less-equipped laboratory by transporting the μ-PADs fabricated in another laboratory.

The sensitive quantitative analysis of trace heavy metallic elements (Cd, Mn, Cr, and Cu) in aqueous solutions was achieved successfully through the combination of filter paper enrichment with laser-induced breakdown spectroscopy. Filter paper was enriched with 0.4 mL aqueous solutions to form a homogeneous sample layer on the surface of the metallic target. Considering the limits of detection, the values deduced with calibration curves already exhibited the high performance of the proposed method at several hundred or 10 μg/L (Cd 0.165, Mn 0.035, Cr 0.012, and Cu 0.078 mg/L), lower than or comparable to those using other similar methods. The LIBS results agreed reasonably well with those from ICP-MS for real samples. All results showed that our method was suitable and accurate for rapid on-site detection of trace metals in aqueous solutions. This indicates that filter paper enrichment combined with laser-induced breakdown spectroscopy is a feasible approach to wastewater quality monitoring.

Abstract Tissue paper softness relies on two major factors, the bulk softness, which can be indicated by the elasticity of the sheet, and surface softness. Measurement of surface softness is complicated and often requires a multi-step process. A key parameter defining surface softness is the topography of the surface, particularly the crepe structure and its periodicity. Herein, we present a novel approach to measure and quantify the tissue paper surface crepe structure and periodicity based on the detection of waviness along the sample using laser scanning confocal microscopy (LSM) and X-ray tomography (XRT). In addition, field emission scanning electron microscope (FESEM) was used to characterize the tissue paper surface. We demonstrate that surface topography is directly correlated to the erosion of the doctor blade, which is used to remove the dry tissue paper from the Yankee cylinder. Because of its accuracy and simplicity, the laser confocal microscopy method has the potential to be used directly on the production line to monitor the production process of the tissue paper. XRT revealed more structural details of the tissue paper structure in 3D, and it allowed for the reconstruction of the surface and the internal structure of the tissue paper. Graphic abstract

A superhydrophobic paper with excellent robustness was fabricated by roll coating with modified nano-TiO2. First, nano-TiO2 particles were hydrophobically modified by γ-aminopropyltriethoxysilane and 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS). Then the paper coating composed of modified nano-TiO2 particles as pigments and epoxy resin (EP) as adhesives was coated on a paper surface to create the desired surface morphology and surface energy. Compared with the uncoated filter paper, the prepared paper showed an improved rough surface morphology owing to the uniform layer of TiO2 microclusters deposited on the fiber network. The superhydrophobic paper exhibited water contact angles (WCA) about 153° ± 1.5°, and water sliding angles (WSA) about 3.5° ± 0.5°, low surface adhesion and excellent bounce ability. The superhydrophobic paper can withstand a variety of wear and tear, such as tape stripping and knife scraping. The as-prepared superhydrophobic paper showed mechanical durability even after 20 wear cycles with sandpaper,thus sustaining excellent superhydrophobicity on the filter paper surface. Moreover, it remains fully functional even in environments with high concentrations of acid and alkali for 96 h. The superhydrophobicity was not affected after storage for 6 months in a natural environment. It was confirmed that the superhydrophobic paper surface exhibited excellent chemical stability, long-term stability and self-cleaning properties. The entire production process was operated under normal environment, without complex equipment; and, as such, has the possibility for large-scale production and application in industry.

We present a high resolution, ultra-frugal printing of paper microfluidic devices using in-house paraffin formulation on a simple filter paper. The patterns printed using an office inkjet printer formed a selective hydrophobic barrier of 4 ± 1 µm thickness with a hydrophilic channel width of 275 µm. These printed patterns effectively confine common aqueous solutions and solvents, which was verified by solvent compatibility studies. SEM analysis reveals that the solvent confinement is due to pore blockage in the filter paper. The fabricated paper-based device was validated for qualitative assessment of Candida albicans (pathogenic fungi) by using a combination of L-proline β-naphthylamide as the substrate and cinnamaldehyde as an indicator. Our studies reveal that the pathogenic fungi can be detected within 10 min with the limit of detection (LOD) of 0.86 × 106 cfu/mL. Owing to its simplicity, this facile method shows high potential and can be scaled up for developing robust paper-based devices for biomarker detection in resource-limited settings. Graphic abstract

The use of nanocelluloses is being conducted for the most diverse applications. Their performance as coating agent has been mainly explored to improve barrier properties, as they emerge as perfect candidate for plastic substitution, but it is also important to explore their potential to improve printing quality. In the present work, the influence of different nanocelluloses, obtained through mechanical, enzymatic, TEMPO-mediated oxidation and carboxymethylation treatments, in the coating process and inkjet printability of office papers was assessed. The results revealed that the cellulose nanofibrils are better for printability than the microfibrils. But the size and charge of the former must be taken into account, since fibrils of very small size penetrate the paper structure, dragging the pigments from the surface, and very anionic nanofibrils can also have negative influence on the optical density. Besides, an interesting synergy between surface-sizing starch and the cellulose nanofibrils was found to occur as the latter closed the paper structure, which prevented starch from penetrating, while potentiating both of their positive effects on ink pigment entrapment. An additional study of characterization of inkjet pigments was also performed.

This article identifies the technological characteristics of the paper manufacturing industry in the Valley of Mexican Basin (VMB)—a densely populated region characterized by absolute water scarcity—in order to quantify the intensity with which water is used. The method consisted of modeling the paper industry’s technology estimating Cobb-Douglas production functions at two moments in time. The comparison of both functions makes it possible to identify water saving technologies during this period, and to evaluate whether the industry has made adjustments to deal with water restrictions. The data is obtained from the Economic Censuses of the National Institute of Statistics Geography and Informatics 2009 and 2014. While our work must be considered preliminary owing to the somewhat irregular nature of the data, certain clear conclusions do stand out. The paper industry located in the VMB has drastically reduced its water usage during the period of time analyzed. This is explained by the adoption of water saving technologies in the industry. In the process, an increase in capital is the main variable to explain such a technical change. This is expressed in the manner in which water and capital inputs appear to be highly suitable substitutes in paper manufacturing.

The diagnosis of dengue infection is still a critical factor determining success in the clinical management and treatment of patients. Here, the development of microfluidic paper-based analytical devices (μPADs) utilizing a sandwich immunoassay on wax patterned paper functionalized with anti-dengue NS1 monoclonal antibodies for point-of-care detection of dengue NS1 (DEN-NS1-PAD) is reported. Various assay conditions, including the length of the channel and diluent, were optimized, and the response detected by the naked eye and digitized images within 20–30 min. The DEN-NS1-PAD was successfully tested in the field for detecting dengue NS1 in buffer, cell culture media, and human serum. The limit of detection (LoD) of the DEN-NS1-PAD obtained with the naked eye, scanner, and a smartphone camera was 200, 46.7, and 74.8 ng mL−1, respectively. The repeatability, reproducibility, and stability of the DEN-NS1-PAD were also evaluated. High true specificity and sensitivity in the serum of pediatric patients were observed. These evaluation results confirm that the DEN-NS1-PAD can potentially be used in point-of-care dengue diagnostics, which can significantly impact on the spreading of mosquito-borne diseases, which are likely to become more prevalent with the effects of global warming.

We report a smartphone–paper-based sensor impregnated with cetyltrimethylammonium bromide modified silver nanoparticles (AgNPs/CTAB) for determination of Fe3+ in water and blood plasma samples. The methodology for determination of Fe3+ is based on the change in signal intensity of AgNPs/CTAB fabricated on a paper substrate after the deposition of analyte, using a smartphone followed by processing with ImageJ software. The mechanism of sensing for detection and determination of Fe3+ is based on the discoloration of AgNPs which impregnated the paper substrate. The discoloration is attributed to the electron transfer reaction taking place on the surface of NPs in the presence of CTAB. Fe3+ was determined when the paper was impregnated with 1 mM AgNPs for 5 min of reaction time and the substrate was kept under acidic conditions. The linear range for determination of total iron in terms of Fe3+ was 50–900 μg L−1 with a limit of determination (LOD) of 20 μg L−1 and coefficient of variation (CV) of 3.2%. The good relative recovery of 91.3–95.0% and interference studies showed the selectivity of the method for determination of total iron in water and blood plasma samples. Smartphone–paper-based sensors have advantages of simplicity, rapidity, user-friendliness, low cost, and miniaturization of the method for on-site determination of total iron compared to methods that require sophisticated analytical instruments.

Rumen fluid has been applied to lignocellulosic biomass digest for methane production, and various feed supplements have been shown to improve ruminant digestion of lignocellulosic biomass. Therefore, we investigated the effects of sodium dodecyl sulfate (SDS) on the pretreatment of lignocellulosic biomass with rumen fluid and subsequent methane fermentation. SDS was mixed with rumen fluid at concentrations of 0.1, 0.2, 0.4, and 0.8 g/L. After SDS addition, the waste paper was pretreated with rumen fluid at 37 °C for 6 h. SDS addition decreased the number of surviving rumen ciliates after pretreatment. SDS addition increased the dissolved chemical oxygen demand during pretreatment; however, SDS addition did not increase the volatile fatty acid concentration. After pretreatment, batch methane fermentation of pretreated waste paper was performed at 35 °C for 45 days. SDS addition at 0.1 and 0.2 g/L shortened the waste paper digestion time and enhanced methane gas production compared to the control. By contrast, SDS addition at 0.4 and 0.8 g/L remarkably inhibited methane production from waste paper. These findings suggest that low concentrations of SDS can improve the efficiency of lignocellulosic biomass pretreatment with rumen fluid, and can enhance methane production from waste paper.

Korean hand papermaking is a renowned cultural tradition in the Korean peninsula. It is still practiced while scientific analysis of paper itself from a large data set is rare. In this study, a set of more than three hundred Korean handmade papers, collected in a reference collection book Hanji: Korean handmade paper, were chemically investigated, and their property data such as colour, pH, grammage, thickness, tensile strength, folding endurance were statistically analysed in order to determine general features for Korean papers. The influence of different paper sheet formation methods (Heullimtteugi vs Gadumtteugi) were revealed by multivariate data analysis and the chemical profiles of raw materials were studied by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The Korean handmade paper samples display colour gamut in the colour space L* (69.9–95.9), a* [(−3)-3], b* (0–20), most have neutral/alkaline pH values. Paper density, fiber orientation and physical properties are influenced by the sheet formation techniques. For instance, Gadumtteugi tends to produce papers with strong fiber orientation while Heullimtteugi produces papers with more evenly distribution of fibers. In addition, Py-GC/MS analysis results show that paper mulberry fibers contain less intensity lignin monomers and more terpenic compounds in comparison with gampi and mitsumata fibers. This study provides paper analysis from large sample set, statistics reveal that the material preparing and making craft determined the paper structure which reflected in their physical properties. These properties influenced paper performance and applications in art creations as well as relics conservation and restoration. The characterized paper sample database could be used for handmade paper studies in East Asian region. Consequently, this study contributes to a better understanding of contemporary Hanji properties as well as improves knowledge on handmade papers from the Korean peninsula.

Due to the important role of oil source in our life, the separation of water-in-oil emulsion is urgent and necessary. Membrane seperation technology has been an efficient and widely used method in separating oil-water separation. Herein, we report a versatile approach to fabricate surface carbonized membranes with self-standing property from biomass-derived precursor by synergistic charring of phytic acid, arginine and filter paper. The obtained membrane exhibited superhydrophobicity in oil, excellent fouling resistance, and self-supporting ability. The membrane can be cycle-used at least 12 times with high permeation flux (up to 1380 L·m−2·h−1) and separation efficiency (up to 99.4%).

The use of dielectric nanofluids has been recently proposed as a method to improve the insulation system of transformers. It has been widely reported that these liquids present superior dielectric properties than conventional dielectric liquids and have a better behavior as cooling agents. Nevertheless some aspects need to be addressed before these materials are applicable to real equipment. This paper analyzes the interaction between dielectric nanofluids and the cellulose materials that constitute the solid insulation of transformers. The impregnation process of a transformer has been emulated in order to obtain samples of solid insulation impregnated with a Fe3O4 based nanofluid. The samples have been subjected to ICP testing and CryoSEM observation, complemented with the determination of the EDX sprectrum. The interaction between the nanoparticles and the cellulose fibers has been investigated finding that bonds are established between them when cellulose is impregnated with nanofluids. This research was funded by the Spanish Ministry of Economy and Competitiveness. Grant Number DPI2015-71219-C2-2-R and Spanish Ministry of Innovation. Grant Number PID2019-107126RB-C21.

There is a growing interest on recycling of waste fibres as an alternative to landfill disposal. The aim of the study was to investigate the durability and mechanical properties of waste paper–cement composite panels reinforced with varying kenaf fibre content (FC, 2–10%). The panels produced were evaluated for properties including modulus of rupture (MOR) and apparent modulus of elasticity (MOE). The resistance of the panels was tested in the field for both termite damage and fungi decay for a period of 24 weeks. Accelerated decay test was also performed on selected samples. The results showed that the mean MOR ranged from 3.17 MPa for samples with 10% FC to 4.84 MPa for samples with 8% FC. The mean MOE ranged from 248 MPa for samples with 10% FC to 1298.1 MPa for samples with 8% FC. Statistical analysis showed that the effect of the fibre content was significant on the properties evaluated (p

Infections caused by foodborne microorganisms are a great threat to the global environment and public healthcare today. Thus, rapid, portable and sensitive assays that can realize the identification of foodborne bacteria are highly desired. In this study, a smart fluorescent and colorimetric dual-readout sensing system has been established for simple and rapid E. coli determination by utilizing the Cu2+-triggered oxidation of o-phenylenediamine (OPD). Initially, Cu2+ can oxidize OPD to OPDox, resulting in an orange-yellow fluorescence and visible pale-yellow color. However, E. coli can effectively reduce Cu2+ into Cu+, inhibiting the Cu2+-triggered oxidation of OPD to OPDox. Consequently, the introduction of E. coli can turn off both the fluorescence and the UV-vis absorbance signals of the OPD-Cu2+ system, illustrating an original mechanism for fluorescent and colorimetric dual-channel detection of E. coli. Moreover, a filter paper-based visual sensor was built and coupled with OPD-Cu2+ solution under the assistance of a UV lamp. The as-prepared sensor can detect E. coli quantitatively with the help of a typical smartphone color-scanning application (APP). Thus, this study offers a valid dual-mode assay for sensitive and on-site visible detection of E. coli, guaranteeing the reliability of the results and is more attractive for practical use. Graphical Abstract Schematic illustration of the smartphone-integrated sensing system for fluorescent and colorimetric dual-channel detection of E. coli based on the Cu2+-OPD system.

Background Microfluidic chip detection technology is considered a potent tool for many bioanalytic applications. Rapid detection of foodborne pathogens in the early stages is imperative to prevent the outbreak of foodborne diseases, known as a severe threat to human health. Conventional bacterial culture methods for detecting foodborne pathogens are time-consuming, laborious, and lacking in pathogen diagnosis. To overcome this problem, we have created an embedded paper-based microchip based on isothermal loop amplification (LAMP), which can rapidly and sensitively detect foodborne pathogens. Results We embed paper impregnated with LAMP reagent and specific primers in multiple reaction chambers of the microchip. The solution containing the target pathogen was injected into the center chamber and uniformly distributed into the reaction chamber by centrifugal force. The purified DNA of Escherichia coli O157:H7, Salmonella spp., Staphylococcus aureus, and Vibrio parahaemolyticus has been successfully amplified and directly detected on the microchip. The E. coli O157:H7 DNA was identified as low as 0.0134 ng μL− 1. Besides, the potential of this microchip in point-of-care testing was further tested by combining the on-chip sample purification module and using milk spiked with Salmonella spp.. The pyrolyzed milk sample was filtered through a polydopamine-coated paper embedded in the inside of the sample chamber. It was transported to the reaction chamber by centrifugal force for LAMP amplification. Then direct chip detection was performed in the reaction chamber embedded with calcein-soaked paper. The detection limit of Salmonella spp. in the sample measured by the microchip was approximately 12 CFU mL− 1. Conclusion The paper embedded LAMP microchip offers inexpensive, user-friendly, and highly selective pathogen detection capabilities. It is expected to have great potential as a quick, efficient, and cost-effective solution for future foodborne pathogen detection.

构建基于有机材料的高性能柔性储钠电极面临诸多挑战. 本 工作通过可控组装及还原的方式, 实现了铁基配位聚合物纳米线/还原氧化石墨烯柔性薄膜的构筑. 多维复合薄膜可直接用作钠离 子电池自支撑负极, 且具有较高的储钠容量(200 mA g−1电流密度 下可逆容量为319 mA h g−1)和优异的倍率性能(3000 mA g−1大电 流密度下比容量可保持在∼120 mA h g−1). 研究表明有机配体(氨 三乙酸)中的羧基及氨基为储钠活性位点, 而配位金属离子(Fe2+)不 参与电化学反应.

Pollutants emerging from the effluents of paper mills eventually destroy the environment of our ecosystem. To find a proper solution of it, a cost-effective and environmentally benign technique is proposed here to remediate contaminants present in the effluent of paper mill in a sequential steps using advanced oxidation processes including Fenton reaction (FO) (Fe(II)/H2O2), modified Fenton oxidation (MFO) (Fe(II)/Zn(II)/H2O2) and biological flocculation process. A comparison and compilation among these techniques were carried out on the basis of the percentage removal of chemical oxygen demand (COD) as well as the observed degradation pattern in gas chromatography–mass spectrometry. Results revealed that MFO could remove ≥ 90% of COD at ~ 90 min, whereas FO could eliminate ≥ 80% COD at ~ 120 min. Further, the bioflocculation technique was found to reduce the heavy metal contents such as Fe, Mn, Zn, Co, Cd and Pb by ≥ 60%. In the sequential treatment process, lignin, phenolic and colour contents were also found to be reduced by ~ 84% ~ 97% and ~ 96%, respectively. Again, the bioassay tests were performed to verify the toxicity reduction in the industrial effluent after the application of the sequential treatment process. This study demonstrates that the sequential treatment technique could be an effective alternative for the treatment of paper mill effluent.

Huge quantity of paper mill wastes are dumped at the outskirt of factory as unwanted materials. Vermicomposting is an eco-friendly technique for beneficial conversion of different biodegradable/organic wastes into useful organic manure utilizing earthworms. Solid wastes generated in paper mills contain appreciable quantity of organic matter. Attempt was made for bio-conversion of Emami paper mill wastes with different numbers of Eisenia fetida (5–30 earthworms/2 kg substrate) for studying its influence on vermi-conversing time and quality of prepared vermicompost. Vermicomposting was carried out in trays following heap method and quality of final product was determined following both chemical analysis and bioassay on wheat seedlings. Application of more earthworms up to 20 numbers per 2 kg substrate made bio-conversion quicker but further addition of earthworm, however, delayed the process as some earthworms came out of beds and died probably due to competition for food among earthworms inside beds. Ten earthworms per kg paper mill wastes–saw dust–cow dung mixture (1:0.5:0.5 weight wise) was found as optimum earthworm population for preparing quality vermicompost having more major and secondary plant nutrients. Bioassay of this manure on wheat seedlings also confirmed the analytical findings. It is confirmed that earthworm population in vermibed played vital role in faster decomposition of paper mill wastes and releasing of more nutrients, which ultimately helped in better growth of wheat seedlings. Successful demonstration of vermicomposting technique will encourage local farmers for beneficial utilization of paper mill wastes in their agriculture.

Carbonization of biomasses is an effective and important approach to recycle biomass waste. The tissue papers are one of the most common household trash and waste lots of natural resources and energies. Herein, the one-step carbonization and activation treatment was applied on two kinds of tissue papers to transform them into porous carbons. It was found the precursor structure and composition as well as the calcination temperatures play key roles to control the pore structures. As the active materials of supercapacitor electrodes, the resultant porous carbons obtained from different paper precursors and calcination temperatures (700–900 °C) presented different electrochemical performances. The microporous carbons derived from the 700 °C calcination of the tissue paper using the wood pulp as the raw material showed high capacitance up to ~ 200 F/g, providing a simple but effective way to recycle biomasses.

Analytical strategies to ensure the quality and safety of food products without the need for skilled personnel are highly required. The simplicity of glucose strips for diabetes monitoring should be translated to the agri-food sector, ensuring easy evaluation of certain molecules and/or the freshness of a beverage/foodstuff. In addition to the well-known advantages that are characteristic of electroanalytical methods over other methods, paper-based materials are being used to further reduce the gap between complex laboratory testing and simple point-of-need testing. This article highlights some of the most recent advances in the development of paper-based electrochemical approaches for food surveillance, specifically focusing on the use of novel paper-based materials. Two examples are discussed: the development of a miniaturized biosensor realized on copy paper for the quantification of ethanol in commercial beers, and the measurement of ascorbic acid in food supplements within printed electronics supports. Paper-based materials have the potential to lower economic costs, simplify the operative tasks, and most importantly reduce waste generation. The continued combination of manufacturing methods and functional (smart) materials will facilitate the implementation of food analysis at the point of need.

Recycled paper and some hardwood paper often display poorer mechanical properties, which hinder its practical applications and need to be addressed. In this work, cellulose nanofibrils (CNFs) obtained by a combined process of enzymatic hydrolysis and grinding (EG-CNFs), grinding and microfluidization (GH-CNFs) or TEMPO-mediated oxidation and grinding (TE-CNFs) were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, CNFs were made into films on which some characterizations including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–Vis transmittance spectroscopy were implemented. Results showed that CNF fibrillation was promoted as times of passes increased in microfluidization, and CNFs pretreated by enzyme possessed shorter length. Crystallinity of CNFs was related to CNF manufacturing methods, while CNF films’ transparency was correlated to CNF diameter distributions. Moreover, CNFs were applied with different dosages on recycled and hardwood paper. Lengths of CNFs, strength of CNF network, and pulp properties were critical factors affecting the mechanical strength of CNFs-enhanced paper. GH-CNFs showed better strengthened effect on tensile strength of paper than TE-CNFs and EG-CNFs. The best overall improvement was achieved at GH-CNF10 dosage of 5.0 wt% on hardwood paper. The increment of tensile index, burst index, and folding endurance were 108.32%, 104.65%, and 600%, respectively. This work aims to find out the relationship between production methods and morphologies of CNFs and how the morphological characteristics of CNFs affecting the mechanical performance of paper when they are added as strength additives.

This paper describes the design and development of miniaturized microfluidic paper-based analytical devices (μPADs) for biological assays and enzyme storage instruments. Here, a glucose assay utilizing glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) is used as the model system. The efficacy of the miniaturized devices is further examined by assessing the activity of acetylcholinesterase (AChE). Two types of μPADs were developed: one, "strip" chips of detection zones of area 0.5, 0.1 cm2 and, two, "grid" chips of detection zone 0.05 cm2. The devices are easily fabricated via a wax printing process whereby lines of wax are deposited onto chromatographic paper and heated to create rows of hydrophobic barriers. The "strip" chips were subjected to three different temperature environments (-20, 0, and 20°C) over 30 days and glucose assays conducted at intermittent times yielding a correlation between corrected average inverse yellow intensity, days, and glucose concentration. Calculated and experimentally derived color intensity values for 1, 4, and 9 mM glucose concentrations after a 7-day storage study showed a good correlation (0.89 - 15.76% error). Both types of μPADs are effective platforms as potential point-of-care (POC) diagnostic devices and display minimal enzyme denaturation. μPADs of this size show promise as alternative devices for resource-limited regions and especially those areas where materials and instrumentation are not always available.

Respiratory viral infections often mimic the symptoms of infections caused by bacteria; however, restricted and targeted administration of antibiotics is needed to combat growing antimicrobial resistance. This is particularly relevant in low-income settings. In this work, we describe the use of isothermal amplification of viral DNA at 37 °C coupled to a paper-based vertical flow microarray (VFM) setup that utilizes a colorimetric detection of amplicons using functionalized gold nanoparticles. Two oligonucleotide probes, one in-house designed and one known adenoviral probe were tested and validated for microarray detection down to 50 nM using a synthetic target template. Furthermore, primers were shown to function in a recombinase polymerase amplification reaction using both synthetic template and viral DNA. As a proof-of-concept, we demonstrate adenoviral detection with four different adenoviral species associated with respiratory infections using the paper-based VFM format. The presented assay was validated with selected adenoviral species using the in-house probe, enabling detection at 1 ng of starting material with intra- and inter-assay %CV of ≤ 9% and ≤ 13%. Finally, we validate our overall method using clinical samples. Based on the results, the combination of recombinase polymerase amplification, paper microarray analysis, and nanoparticle-based colorimetric detection could thus be a useful strategy towards rapid and affordable multiplexed viral diagnostics. Electronic supplementary material The online version of this article (10.1007/s00216-018-1503-y) contains supplementary material, which is available to authorized users.

Rapid and reliable identification of bacteria is an important issue in food, medical, forensic, and environmental sciences; however, conventional procedures are time-consuming and often require extensive financial and human resources. Herein, we present a label-free method for bacterial discrimination using surface-enhanced Raman spectroscopy (SERS) and partial least squares discriminant analysis (PLS-DA). Filter paper decorated with gold nanoparticles was fabricated by the dip-coating method and it was utilized as a flexible and highly efficient SERS substrate. Suspensions of bacterial samples from three genera and six species were directly deposited on the filter paper-based SERS substrates before measurements. PLS-DA was successfully employed as a multivariate supervised model to classify and identify bacteria with efficiency, sensitivity, and specificity rates of 100% for all test samples. Variable importance in projection was associated with the presence/absence of some purine metabolites, whereas confidence intervals for each sample in the PLS-DA model were calculated using a resampling bootstrap procedure. Additionally, a potential new species of bacteria was analyzed by the proposed method and the result was in agreement with that obtained via 16S rRNA gene sequence analysis, thereby indicating that the SERS/PLS-DA approach has the potential to be a valuable tool for the discovery of novel bacteria. Graphical abstract This paper describes the discrimination of bacteria at the genus and species levels, after minimal sample preparation, using paper-based SERS substrates and PLS-DA with uncertainty estimation.

Valvasor's library is a unique example of a Seventeenth century personal library, including over 7300 prints and 1530 books. Today, it is kept in the Metropolitan Library of the Zagreb Archdiocese which is part of the Croatian State Archives. In this study, we analysed a selection of papers from Valvasor's collection (VC) of unknown origin and composition. We used a dual approach, combining the results of the analyses of two sets of samples to find the most useful tools for the characterization of historical handmade papers. 144 randomly selected papers were included in the study. As the VC is a cultural heritage, only non-destructive analyses were used, such as visual inspection, surface imaging, measurements of thickness and the determination of optical properties (brightness, yellowness, opacity and gloss). According to the optical properties, papers from the VC could be characterized as yellowish and opaque, without gloss. Due to the fact that the VC papers could not be destroyed, we took another set of samples consisting of 10 historical papers (HP) from archival materials, dating from the 16th to nineteenth century, and subjected them to non-destructive, as well as micro-destructive analyses. This was done to supplement the findings of non-destructive analyses of the original collection. Initially, spot tests were performed to determine water absorbency and to identify the presence of lignin and starch in the paper samples. SEM–EDS and XRF were applied for the identification of inorganic elements. FTIR analyses were used to identify the chemical structures of the paper components. Microscopic analyses were performed in two ways: the paper surface was imaged with a digital microscope, and the morphological characteristics of the fibres were studied using an optical microscope. The dominant fibres present were flax and hemp, with a smaller proportion of cotton. Additionally, thick and thin light brown fibres resembling straw were detected. The presence of calcium-containing components, gelatine and alum could be confirmed with SEM–EDS, XFR and FTIR analysis. Comparing the results of analyses performed on two sets of samples a connection was explored by which it was possible to define the characterization of VC papers. The main goal of the study was to document and characterize a specific collection for the future use of researchers of handmade paper or paper conservators. Furthermore, the study may serve as a model approach for other researchers who seek to document the characteristics of paper in their collections.

The copper(II) ion (Cu2+) has played an indispensable role in diverse kinds of functional physiological processes of organisms, which has become of growing interest. Despite the fact that numerous Cu2+ test papers using fluorescent probes have been fabricated, sensors featuring the ratiometric property that integrates quenched probes and an inner standard dye are rarely reported. Herein, a two-component ratiometric sensor in a paper-based device is proposed to realize highly selective Cu2+ detection. To overcome shortcomings such as low signal-to-noise ratio and incorrect response of the quenching probe, a novel BODIPY-based turn-off probe (P2017) is designed and introduced into the paper-based device with better water solubility and selectivity for Cu2+ detection. Furthermore, a reference dye (B001), exhibiting an emission at 690 nm when the excitation wavelength is 480 nm, is also introduced into the paper-based device. These two components can enhance the quality of the signal as P2017 is sensitively quenched by Cu2+, while B001 with a photostable property, serving as an internal benchmark, is unable to react with Cu2+. The results indicated that the two components provided a new concept for optimizing paper-based device fabrication and developing accurate, simple, and inexpensive Cu2+ detection methods, which could be potentially applied to monitor human health and the environment in remote areas.

In this early study, new cement-bonded bi-composite fibreboard (FB) was made from water hyacinth (WaHy) and waste paper (WP). Ordinary Portland cement (PdCe) used as a binder was mixed with other two additives: gypsum plasters (GyPl) and wood ash (WdAh), in defined proportions to form bonding matrices. The WP and WaHy were pre-treated and a linked process was developed for the mixing and consolidation steps. The FBs produced were based on different proportions of composites, binder, and additives mixed. The FBs produced were made from different proportions of composites, binders, and additives. Improved tensile strength was observed for bi-composite FB from WaHy mixed with WP. In general, FBs having densities in the range of 0.50–0.57 g cm−3 were compared favourably with the ASTM and ANSI standards (95%), thus making the FBs a potential alternative for building and construction purposes. More elaborate research with advanced analytical techniques is hereby suggested.

Microfluidic paper-based devices (μPADs) and wearable devices have been highly studied to be used as diagnostic tools due to their advantages such as simplicity and ability to provide instrument-free fast results. Diseases such as periodontitis and diabetes mellitus can potentially be detected through these devices by the detection of important biomarkers. This study describes the development of μPADs through craft cutter printing for glucose and nitrite salivary diagnostics. In addition, the use of μPADs integrated into a mouthguard as a wearable sensor for glucose monitoring is also presented. μPADs were designed to contain two detection zones for glucose and nitrite assays and a sampling zone interconnected by microfluidic channels. Initially, the analytical performance of the proposed μPADs was investigated and it provided linear behavior (r2 ≥ 0.994) in the concentration ranges between 0 to 2.0 mmol L−1 and 0 to 400 μmol L−1 for glucose and nitrite, respectively. Under the optimized conditions, the limits of detection achieved for glucose and nitrite were 27 μmol L−1 and 7 μmol L−1, respectively. Human saliva samples were collected from healthy individuals and patients previously diagnosed with periodontitis or diabetes and then analyzed on the proposed μPADs. The results found using μPADs revealed higher glucose concentration values in saliva collected from patients diagnosed with diabetes mellitus and greater nitrite concentrations in saliva collected from patients diagnosed with periodontitis, as expected. The results obtained on μPADs did not differ statistically from those measured by spectrophotometry. With the aim of developing paper-based wearable sensors, μPADs were integrated, for the first time, into a silicone mouthguard using a 3D-printed holder. The proof of concept was successfully demonstrated through the monitoring of the glucose concentration in saliva after the ingestion of chocolate. According to the results reported herein, paper-based microfluidic devices offer great potential for salivary diagnostics, making their integration into a silicone mouthguard possible, generating simple, low-cost, instrument-free, and powerful wearable sensors.

In this work, a novel holey graphene oxide bonded with sulfonic acid groups (S-HGO) was developed using a facile and eco-friendly strategy: erosion and oxidation of graphene oxide (GO) by H2O2 and sulfonation by 4-benzenediazoniumsulfonate. The freestanding paper fabricated by S-HGO shows a high proton conductivity of 4.97 × 10−2 S cm−1 at 60 °C and 100% relative humidity (RH), which is comparable to Nafion 115 (7.67 × 10−2 S cm−1) at the same condition. The holes on S-HGO provide shortcut channels for proton transfer across the GO nanosheet. The chemical-linked sulfonic acid groups afford additional hop sites for proton conduction and endow itself an enhanced thermostability. Under 100% RH and ambient pressure, the freestanding S-HGO deliver a peak power density of 103 mW cm−2 at a load current density of 273 mA cm−2, which is about three times more than that of GO at 35 °C. The results demonstrate that this S-HGO paper is a promising nanoscale inorganic material for proton exchange membranes.

Coated paper is an example of a multi-layer porous medium, involving a coating layer along the two surfaces of the paper and a fibrous layer in the interior of the paper. The interface between these two media needs to be characterized in order to develop relevant modeling tools. After careful cutting of the paper, a cross section was imaged using focused ion beam scanning electron microscopy. The resulting image was analyzed to characterize the coating layer and its transition to the fibrous layer. Such image analysis showed that the coating layer thickness is highly variable, with a significant fraction of it being thinner than a minimum thickness required to keep ink from invading into the fibrous layer. The overall structure of the coating and fibrous layers observed in this analysis provide insights into how the system should be modeled, with the resulting conclusion pointing to a specific kind of multi-scale modeling approach.