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This study investigates the ammonium (NH 4 ) adsorption capabilities of hydrochar derived from paper waste sludge (PWSH) and its modified variant with ZnO (PWSH@ZnO).This study investigates the ammonium (NH + ) adsorption capabilities of hydrochar derived from paper waste sludge (PWSH) and its modified variant with ZnO (PWSH@ZnO). The adsorption behaviors were analyzed by varying parameters such as pH, contact time, initial NH 4 + ) adsorption capabilities of hydrochar derived from paper waste sludge (PWSH) and its modified variant with ZnO (PWSH@ZnO). The adsorption behaviors were analyzed by varying parameters such as pH, contact time, initial NH 4 + concentration, and ZnO modification ratios. The results indicate that ZnO modification significantly enhances the NH 4 + adsorption capacity, with PWSH@ZnO achieving a maximum capacity of 23.08 mg g -1 , compared to 20.09 mg g -1 for unmodified PWSH. The optimal pH for NH 4 + removal was found to be 8, at which PWSH@ZnO demonstrated a superior removal efficiency of 80%, compared to 68.03% for PWSH. Kinetic studies revealed that the adsorption process followed a pseudo-first-order model for both materials, with PWSH@ZnO exhibiting faster adsorption rates. Isotherm analysis further indicated that the adsorption is best represented by the Langmuir model, suggesting monolayer adsorption on a homogeneous surface. Overall, the incorporation of ZnO nanoparticles enhanced the adsorption capacity and improved the material's stability, positioning PWSH@ZnO as a promising candidate for NH 4 + removal in wastewater treatment applications. The synthesized PWSH@ZnO also demonstrates commendable reusability, maintaining nearly 50% of its initial adsorption capacity after five cycles., Competing Interests: The authors have not disclosed any competing interests., (This journal is © The Royal Society of Chemistry.)

Biogenic amines are organic nitrogen compounds that play key roles in various biological processes and are produced through amino acid decarboxylation. Among these, histamine stands out as a toxic biogenic amine with the potential to cause serious health issues when present at elevated levels in food, highlighting the importance of effective detection methods. However, current histamine detection approaches are often hindered by high costs, lengthy analysis times, and intricate procedures. This research introduces a novel, label-free method for detecting histamine in meat samples using highly conductive nano-silver inks to develop miniaturized sensors based on paper microdevice technology. The proposed paper-based electrochemical sensors offer significant advantages, including affordability, reproducibility, and environmental sustainability. A newly designed paper-based microsensor was developed for label-free histamine detection employing conductive nano-silver ink via a pen-on-paper technique. The fabrication process of the microsensor was thoroughly characterized through methods like field emission scanning electron microscope (FE-SEM), Energy Dispersive X-ray (EDAX), and Atomic Force microscopy (AFM). Key findings indicate that the microsensor successfully detects histamine concentrations across a broad dynamic range of 10 to 1000 nM, with a lower limit of quantification set at 10 nM. Validation of the sensor's performance was conducted using electrochemical tools such as cyclic voltammetry and square wave voltammetry, confirming its efficacy for real-time histamine monitoring in food products and biological environments. Additionally, the study underscores the sensor's excellent selectivity, long-term stability, and lightning-fast responsiveness, positioning it as a highly promising tool to enhance food safety and quality assurance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Developing high-efficiency, cost-effective, and long-term stable nanostructured catalysts for electrocatalytic water splitting remains one of the most challenging aspects of hydrogen fuel production. Urea electrooxidation reaction (UOR) can produce hydrogen energy from nitrogen-rich wastewater, making it a more sustainable and cheaper source of hydrogen. In this study, we have developed Ni/NiS hybrid structures with cauliflower-like morphology on carbon paper electrodes through the application of dimethylsulfoxide solvents. These electrodes serve as highly efficient and long-lasting electrocatalysts for the hydrogen evolution reactions (HER) and UOR. In particular, the Ni/NiS cauliflower-like morphology is confirmed via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Furthermore, electrochemical characterization of the Ni/NiS@CP catalyst showed a 1.35 V onset potential versus RHE for the UOR in 1.0 M KOH and superior electrocatalytic performance compared to bare Ni@CP. Additionally, the Ni/NiS@CP catalyst also exhibits a low overpotential of 125 mV at 10 mA cm -2 for HER in 0.5 M H 2 SO 4 with excellent durability, which is apparently lower than bare Ni@/CP (397 mV). Based on the results obtained, the synthesized Ni/NiS@CP catalyst may be a promising electrode candidate for handling urea-rich wastewater and generating hydrogen., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

A root-like waterborne hyperbranched polymer, synthesized from diethylenetriamine (DETA) and methyl acrylate (MA) monomers, was inspired by the effect of solidifying soil with tree roots. This polymer was then blended with aqueous isocyanate SK615, known as MD-HBP-NH 2 , to serve as a surface modifier for blockboards. The blockboards were treated with a modifier to enhance the interfacial adhesion with melamine-formaldehyde (MF) resin-impregnated decorative paper, thereby preventing surface cracks. The polycondensation reaction temperatures of the modifiers were compared. These results indicated that a hyperbranched root-structured polymer emulsion was formed through Michael addition reactions. Following this modification, the blockboards demonstrated enhanced planeness and dimensional stability. Furthermore, the isocyanate groups reacted with the exposed hydroxyl groups, and the amino groups reacted with the aldehyde groups in the MF resin, thereby enhancing the interfacial bonding strength between the wood and the impregnated decorative paper. At a polycondensation temperature of 155 °C, optimal overall performance was attained, with the ability to penetrate the wood surface to a depth of 1.28 mm, and exhibited superior surface crack resistance. Moreover, this waterborne hyperbranched polymer modifier is eco-friendly, green, and non-toxic, with lower levels of volatile organic compounds. This presents a promising avenue for the development of eco-friendly modifiers to prevent surface cracking in wood-based panels with impregnated decorative paper., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Surface-enhanced Raman scattering (SERS) is a powerful, highly efficient analytical technique capable of providing label-free, non-invasive, rapid, and ultrasensitive molecular detection down to the single-molecule level. Despite its advantages, SERS remains largely confined to laboratory settings due to the complexities of substrate fabrication and challenges in analyzing real-world samples. Developing flexible SERS substrates that achieve both high fabrication efficiency and high sensing performance, while being practical for field applications, is critical for advancing SERS toward broader, real-world use. In this study, we present a novel paper-based Ag dendritic SERS chip, fabricated via a simple chemical reduction process that directly forms Ag dendritic nanostructures on cellulose fibers. This chip substrate demonstrates exceptional sensitivity for the detection of thiram pesticide, with a detection limit as low as 7.76 × 10 -11 M. The chip substrate also exhibits outstanding reliability, with reproducibility and repeatability both less than 5%. Furthermore, the flexible nature of the paper substrate enables it to conform to curved surfaces and be in direct contact with analytes, exemplified by its ability to adhere to and retrieve thiram from pear skin using a novel "paste-and-peel-off" technique. The substrate shows remarkable performance for thiram detection on pear skin, with sharp recovery rates ranging from 90% to 105%. With its facile fabrication, excellent sensitivity, high reliability, and practical applicability in non-invasive sampling, the paper-based Ag dendritic SERS substrate offers significant potential as an advanced substrate to bring SERS out of the laboratory and closer to real-world applications., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

Distance-based detection (DbD) on paper-based microfluidic analytical devices (μPADs) has emerged as a promising, cost-effective, simple, and instrumentation-free assay method. Broadening the applicability of a new way of immobilization of reagent for DbD on μPADs (DμPADs) is presented, employing an ion exchange (IE) interaction of an anionic metallochromic reagent, 2-(5-bromo-2-pyridylazo)-5-[ N-n -propyl- N -(3-sulfopropyl)amino]phenol (5-Br-PAPS), on the anion-exchange filter paper. The IE DμPADs demonstrate superiority over standard cellulose filter paper in terms of the degree of reagent immobilization, detection sensitivity, and clear detection endpoints due to the strong retention of 5-Br-PAPS. The study investigated various parameters influencing DbD, including 5-Br-PAPS concentrations (0.25-1 mM), buffer types (acetic acid-Tris, MES), buffer concentrations (20-500 mM), and auxiliary complexing agents (acetic, formic, and glycolic acids). Subsequently, the performance of 17 metals (Ag + , Cd 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 2+ , Hg 2+ , La 2+ , Mn 2+ , Ni 2+ , Pb 2+ , Ti 2+ , Zn 2+ , Al 3+ , As 3+ , Fe 3+ , and V 4+ ) was evaluated, with color formation observed for 12 metals. Additionally, the paper surface was examined using SEM and SEM-EDX to verify the suitability of certain areas in the detection channel for reagent immobilization and metal binding. This method demonstrates quantitation limits of metals in the low μg mL -1 range, showing great potential for the rapid screening of toxic metals commonly found in herbal supplements and cosmetics regulated by the Food and Drug Administration (FDA). Thus, it holds promise for enhancing safety and regulatory compliance in product quality assessment. Furthermore, this method offers a cost-effective, environmentally sustainable, and user-friendly approach for the rapid visual quantification of heavy metals for in-field analysis, eliminating the need for complex instrumentation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Diabetes ketoacidosis (DKA) is a life-threatening complication and requires immediate medical attention in the case of diabetes subjects, especially in the case of type 1 diabetes mellitus. In the condition of DKA, the body produces an excess amount of ketone bodies after unregulated fat degradation, causing blood to become acidic and hampering the regular metabolic activities of the body. The current diagnostic technique for DKA condition is based on monitoring ketone bodies, especially β-hydroxybutyric acid, from human urine and blood samples. The detection of serum ketone bodies in pathology is sometimes limited due to false positive results and the lack of standardization for precise quantification of analytes. In this study, a paper-based patch operating on the thin film solid-phase microextraction (TF-SPME) principle was developed and it was coupled with gas chromatography-mass spectrometry for simple quantification of β-hydroxybutyric acid (BHB) ketone body from a phosphate-buffered saline matrix. To fabricate the paper-based TF-SPME patches, a regular A4 sheet paper sheet was utilized as the substrate and uniform coating by multiwalled carbon nanotubes (MWCNT), polydimethylsiloxane (PDMS) and divinyl benzene (DVB) compounds was performed with an automatic film applicator. The 70 μm paper-based coated sheet was trimmed into 4 cm × 1 cm dimension pieces to obtain multiple patches from a single sheet. Extraction of the BHB ketone body into the closed vials was performed by exploiting the individual DVB/PDMS and DVB/CNT/PDMS paper patches followed by desorption with acetonitrile before quantification by gas chromatography-mass spectrometry analysis. Our study showed that the BHB extraction efficiency of DVB/PDMS-coated patches was higher than that of DVB/CNT/PDMS. The outcome showed a good linearity ( R 2 concentration range of BHB by paper-based DVB/PDMS patches. This study demonstrated the feasibility of utilizing simple, cost-effective paper-based disposable TF-SPME patches as a sampling kit for future screening of diabetes ketoacidosis without the need for prolonged traditional sample preparation in pathology.-1 concentration range of BHB by paper-based DVB/PDMS patches. This study demonstrated the feasibility of utilizing simple, cost-effective paper-based disposable TF-SPME patches as a sampling kit for future screening of diabetes ketoacidosis without the need for prolonged traditional sample preparation in pathology., Competing Interests: All authors acknowledged no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

The development of novel rare earth fluorescent materials and the exploration of their applications have consistently been focal points of research in the fields of materials science and chemistry. In this work, a novel rare earth composite material with good photo-fluorescence properties and self-supporting has been prepared via a simple ultrasonic solvent reaction method. Initially, the Phen moieties is immobilized onto the surface of a self-supporting fiberglass paper using ICPTES, followed by the coordination of Eu(TTA) 3 moieties with Phen moieties through a convenient ultrasonic solvent reaction. The resulting GF-Phen-Eu(TTA) 3 has been characterized using FTIR, UV-Vis DRS, fluorescence measurements, and so on. The results indicate that the composite material exhibits strong fluorescent emission and presents a vivid red color under ultraviolet light. Further research has shown that the fluorescence of GF-Phen-Eu(TTA) 3 strips demonstrated a pronounced quenching effect in response to some transition metal ions (1 mM). Hence, the rare earth composite materials presented here can be utilized not only for the production of optical materials, but also for the development of fluorescence sensing strips., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

Paper-based sensors or paper-based analytical devices (PADs) have recently emerged as the cost-efficient, and portable, on-site detection tools for various biological and environmental analytes. However, paper-based sensors often suffer from poor selectivity. Here, a single-step paper-based flexible sensor platform has been developed for the on-site detection of paraquat (PQ) pesticide in real samples, utilizing chitosan and citrate-capped silver nanoparticles integrated with a flexible paper. The nanocomposite paper film was thoroughly characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The composite paper platform demonstrated a color change with a reaction time within a few minutes (6-7 min) in the presence of PQ pesticide. The trace level PQ pesticide has been detected with a limit of detection (LOD) of 10 μM and a linear range (LR) of 10-100 μM. The sensor shows 3× more selective signal towards PQ pesticide compared to other similar pesticides. The relative standard deviation (RSD) was found to be 5% for repeatability, 4% for reproducibility, 2% for interference, and 3.5% for real sample analysis, indicating high precision sensing and within the WHO limit of RSD (20%). The present work will open up new avenues for the advancements in flexible paper sensors; cost-effective, portable, on-site sensors, and sustainable device development., Competing Interests: The authors have no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Lumpy skin disease (LSD) is a contagious viral disease caused by the Lumpy Skin Disease virus (LSDV), a member of the Capripoxviridae family. Traditional LSDV diagnostic procedures proved to have challenges in terms of cross reactivity as well as limited sensitivity and specificity. Herein, we combined molecularly imprinted polymers (MIPs) and quantum dots (QDs) technology to develop a paper-based turn on fluorescence sensor for rapid, sensitive and selective detection of LSDV. Under optimal conditions, the sensor showed linear enhancement in fluorescence intensity with the increase of LSDV concentration and exhibited a detection limit of 10 1 log 10 TCID50 per ml. It also presented high specificity towards LSDV compared to other viruses viz sheep pox virus (SPV). Furthermore, the proposed sensor was successfully tested with spiked and real LSDV samples, proving its potential to serve as a sensitive selective sensor for LSDV diagnosis. Based on our knowledge, this is the first record of a paper-based diagnostic sensor for LSDV utilizing a CQDs-MIPs turn-on mechanism., Competing Interests: Authors declared no conflict of interest., (This journal is © The Royal Society of Chemistry.)

We investigate the adsorption behavior of polar and nonpolar molecules on carbon nanotube interfaces through computational simulations. Gaussian 16 was utilized to calculate the total energy of each possible molecular structure and analyze the adsorption mechanisms in stacked and inline configurations. The study reveals that nonpolar molecules favor stacked adsorption on two graphene interfaces, while polar molecules prefer inline adsorption. The findings suggest that inline adsorption of polar molecules results in minimal changes to the local dielectric constant, which may explain the absence of multi-step adsorption isotherms. The research examines the stability and energetics of molecular adsorption on graphene layers simulating CNT interfaces. Different types of molecules (polar and nonpolar) exhibit distinct adsorption behaviors, with nonpolar molecules aligning with the IUPAC type VI isotherm model and polar molecules following the Langmuir isotherm model (IUPAC type I). This study provides insight into how molecules are likely to adsorb on CNT surfaces and the impact on the local dielectric constant. This understanding has implications for the design and optimization of CNT-based sensors, particularly in detecting organic solvents and gases in various environments., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Pancreatitis is a life-threatening inflammatory disease of the pancreas. In 2019, 34.8 out of 100 000 people suffered from acute pancreatitis globally. In humans, the level of α-amylase increases three times the normal value during pancreatitis. α-Amylase is an enzyme that hydrolyses α-1,4 glycosidic bonds of starch. In this study, we investigated a novel distance-based sensing method. We exploited the existing starch triiodide method, where the blue colour of starch-triiodide fades away and becomes colourless when α-amylase breaks the starch chain at the α-1-4 glycosidic bond. A hydrophilic channel was made on paper using a simple laser printer to create hydrophobic barriers. This channel was impregnated with starch triiodide, where α-amylase can turn it colourless. This distance covered by the change in colour is directly proportional to the concentration of α-amylase in a sample. Simulated samples with different concentrations of porcine α-amylase and pancreatin were used for testing using the developed paper-based chemometer device. The paper-based chemometer device was also tested with artificial blood serum with different concentrations of α-amylase. The R 2 of this device was found to be 0.9905, and the accuracy of the device when compared with a 2-chloro-4-nitrophenyl-α-d-maltotrioside method was found to be 95.54% with a sensitivity of 0.131 U L -1 . Correlation test also showed that the paper-based chemometer device for α-amylase can be used as a testing device for artificial blood serum. This is a preliminary investigation that shows promising results. The chemometer devices stored in air-tight packets at 4-8 °C in a refrigerator did not lose the colour intensity until day 90 and retained an accuracy of 94.5%. However, the device needs to be evaluated in clinical settings prior to using it for measuring α-amylase in patients.-1 . Correlation test also showed that the paper-based chemometer device for α-amylase can be used as a testing device for artificial blood serum. This is a preliminary investigation that shows promising results. The chemometer devices stored in air-tight packets at 4-8 °C in a refrigerator did not lose the colour intensity until day 90 and retained an accuracy of 94.5%. However, the device needs to be evaluated in clinical settings prior to using it for measuring α-amylase in patients., Competing Interests: There is no conflict of interest., (This journal is © The Royal Society of Chemistry.)

The United Nations estimates that by 2030, agricultural production must increase by 70% to meet food demand. Precision agriculture (PA) optimizes production through efficient resource use, with soil fertility being crucial for nutrient supply. Traditional nutrient quantification methods are costly and time-consuming. This study introduces a rapid (15 min), user-friendly, paper-based platform for determining four essential macronutrients-nitrate, magnesium, calcium, and ammonium-using colorimetric methods and a smartphone for data reading and storage. The sensor effectively detects typical soil nutrient concentrations, showing strong linearity and adequate detection limits. For nitrate, the RGB method resulted in an R 2 of 0.992, a detection range of 0.5 to 10.0 mmol L -1 , and an LOD of 0.299 mmol L -1 . Calcium quantification using grayscale displayed an R 2 of 0.993, a detection range of 2.0 to 6.0 mmol L -1 , and an LOD of 0.595 mmol L -1 . Magnesium was best quantified using the hue color space, with an R 2 of 0.999, a detection range of 1.0 to 6.0 mmol L -1 , and an LOD of 0.144 mmol L -1 . Similarly, ammonium detection using the hue color space had an R 2 of 0.988, a range of 0.5 to 2.5 mmol L -1 , and an LOD of 0.170 mmol L -1 . This device enhances soil fertility assessment accessibility, supporting PA implementation and higher food production., Competing Interests: The authors have no competing interests to declare that are relevant to the content of this article., (This journal is © The Royal Society of Chemistry.)

Bacterial infections have become a serious global health problem due to the misuse of antibiotics which causes the emergence of antibiotic-resistant strains. Photothermal therapy (PTT) has been widely studied in recent years as a method to combat the development of bacterial resistance. However, PPT may cause damage to the human body due to excessive laser power. Therefore, it is important and urgent to develop a multifunctional platform that can sensitively detect bacteria and effectively inhibit or kill bacteria at low laser power. Herein, a novel multifunctional paper substrate of Ti 3 C 2 T x -AuNP was successfully synthesized by a self-assembly and freeze-drying method for bacterial detection and photothermal sterilization at low laser power. The typical Gram-negative Escherichia coli ( E. coli ) and the Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA) were used as models to perform label-free, rapid and sensitive detection of bacteria based on the surface-enhanced Raman spectroscopy (SERS) method with detection limits as low as 10 5 CFU mL -1 and 5 × 10 5 CFU mL -1 , respectively, demonstrating the paper substrate's ability to detect bacteria with sensitivity and accuracy. The paper substrate of Ti 3 C 2 T x -AuNP exhibits significant antibacterial effects when irradiated with 808 nm light at a low laser power of only 300 mW cm -2 and a short irradiation time of 5 minutes, and the germicidal rates for E. coli and MRSA were 99.94% and 92.71%, respectively. At the same time, the paper substrate of Ti 3 C 2 T x -AuNP also produces a variety of reactive oxygen species under 808 nm laser irradiation, resulting in photodynamic therapy (PDT). Accordingly, this paper substrate of Ti 3 C 2 T x -AuNP can not only sensitively detect bacteria, but also has photothermal and photodynamic sterilization, providing a promising countermeasure for the clinical treatment of diseases caused by multidrug-resistant bacteria., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In the search for pharmaceutically active compounds from natural products, it is crucial and challenging to develop separation methods that target not only structurally similar compounds but also a class of compounds with desired pharmaceutical functions. To achieve both structure-oriented and function-oriented selectivity, the choice of functional monomers with broad interactions or even biomimetic roles towards targeted compounds is essential. In this work, an imidazole (IM)-functionalized paper membrane was synthesized to realize selectivity. The IM was selected based on its capability to provide multiple interactions, participation in several bioprocesses, and experimental verification of adsorption performance. Using gallic acid as a representative component of Pomegranate Peel , the preparation conditions and extraction parameters were systematically investigated. The optimal membrane solid-phase extraction (MSPE) method allowed for enrichment of gallic acid from the complex matrix of Pomegranate Peel , enabling facile quantitative analysis with a limit of detection (LOD) of 0.1 ng mL -1 . Furthermore, with the aid of cheminformatics, the extracted compounds were found to be similar in both their structures and pharmaceutical functions. This work offers a novel approach to preparing a readily synthesized extraction membrane capable of isolating compounds with similar structures and pharmaceutical effects, and provides an MSPE-based analytical method for natural products., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dapoxetine (DPX) belongs to the selective serotonin reuptake inhibitor (SSRI) class and functions by blocking the serotonin transporter and increasing serotonin activity, thereby delaying ejaculation. Therefore, monitoring of the concentration of DPX in human biofluids is important for clinicians. In this study, application of silver nanoparticles with the morphology of prisms (AgNPrs) for the sensitive measurement of DPX using colorimetric chemosensing and the spectrophotometric method was investigated. Also, DPX was determined in real samples using the spectrophotometry method. Based on the obtained results, all of the detection process in colorimetric assay is related to morphological reform of AgNPrs after it's specific electrostatic and covalent interaction with DPX as analyte. The UV-vis results indicate that the proposed AgNPrs-based chemosensing system has a wide range of linearity (0.01 μM to 1 mM) with a low limit of quantification of 0.01 μM in human urine samples, which is suitable for clinical analysis of this drug in human urine samples. It is important to point out that, this chemosensing strategy showed inappropriate analytical results for the detection of DPX in human urine samples which is a novelty of this platform. Finally, the optimized microfluidic paper-based analytical device (μPAD) was integrated with the colorimetric analysis of DPX to provide a time/color system for estimating analyte concentration by a portable substrate toward in situ and on-site biomedical analysis. Interestingly, the analytical validation tests showed appropriate results with great stability, which may facilitate commercialization of the engineered substrate. For the first time, in order to provide a simple and portable colorimetric/spectrophotometric recognition system to sensitive determination of DPX, an optimized pump-less microfluidic paper-based colorimetric device (μPCD) was introduced and validated for the real-time biomedical analysis of this analyte. According to the obtained results, this alternative approach is suitable for therapeutic drug monitoring (TDM) and biomedical analysis by miniaturized and cost-beneficial devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The Cu(i)-catalyzed Huisgen cycloaddition click chemistry reaction is of particular interest in the production of paper sheets or natural fiber composites since it leads to the formation of chemically stable bonds between two fibers. This study focuses on the click chemistry modification of kraft pulp fibers. We based our approach on prior research that treated kraft fibers using click chemistry, including propargylation and tosylation reactions. Our focus was on enhancing these treatments to achieve better final sheet properties. After the azidation of tosylated fibers, the crosslinking is carried out with and without a catalyst using water as a solvent to form enhanced kraft fiber sheets. The chemical characterization and the mechanical properties of fibers obtained at intermediate stages confirmed the presence of various functions on the surface of the modified fibers, with a very high degree of substitution and the inter-fiber cross-linking by click chemistry. The presence of inter-fibers covalent bonds led to significant improvements in the mechanical strength and tensile stiffness of the sheets., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Parkinson's disease (PD), the second most frequent neurodegenerative illness, is a neurological ailment that produces unintentional or uncontrolled body movements, which should be diagnosed in its early stages to hinder the progression. Monitoring the concentration of α-synuclein (α-Syn) in body fluids can be one of the most efficient ways for PD early detection. In this work, a paper-based electrochemical immunosensor was designed for α-Syn bio-assay in human plasma samples based on encapsulation of the biotinylated antibody on novel dendritic fibrous nanosilica ((KCC-1- nPr -CS 2 )-Ab). For this purpose, a three-electrode system was prepared using stabilization of silver nano-ink on photographic paper. Then, the (KCC-1-NH-CS 2 )-Ab was immobilized on its surface and used to detect the target antigen (α-Syn). After characterization of the prepared substrate by FE-SEM and EDS, the redox behavior of the biosensor was evaluated using chronoamperometry techniques. Under optimal experimental conditions and using a label-free strategy, the engineered immunosensor showed a linear relationship between peak current and antigen concentration in the linear range from 0.002 to 128 ng mL -1 with the lower limit of quantification of 0.002 ng mL -1 . Moreover, this work involves unprecedented use of conductive nano-inks for the manufacture of α-Syn immunosensor, which is aided by the use of a mesoporous silicate dendrimer in encapsulating the α-Syn antibody, thus offering a robust and simple point-of-care device for early PD diagnosis. The ability of the proposed platform to detect small amounts of α-Syn offers a promising approach to developing low-cost, sensitive, and transportable biosensors for Parkinson's disease screening in its early stages., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Biogenic amines (BAs) are a group of organic compounds that are produced through the decarboxylation of amino acids by microorganisms. These compounds are commonly found in a variety of foods and are known to cause adverse health effects if consumed in high concentrations. Therefore, the development of sensitive and rapid detection methods for detection and determination of BAs is essential for ensuring food safety. In this study, a novel colorimetric affordable test strip (CATS) was developed for the colorimetric and naked-eye detection of two BAs of ethylenediamine (EDA) and histamine (HIS) in meat samples. Also, triangular silver nanoparticles (AgNPrs) were used as a diagnostic optical probe, and CATS used as a simple, environmentally friendly, inexpensive diagnostic substrate for on - site recognition of meat spoil. The AgNPrs-based optosensor demonstrated high sensitivity and selectivity towards EDA and HIS, allowing for the detection of low concentrations of the BAs in real food samples such as raw chicken and beef. The system presented a UV-vis technique for HIS and EDA analysis in the linear range of 0.1 μM to 0.01 mM, with an LLOQ of 0.1 μM, and 0.05 to 1 μM, with an LLOQ of 0.05 μM, respectively. Additionally, the performance of the designed CATS in the analysis of produced gases was evaluated, highlighting the potential of this simple and cost-effective strategy for the development of BAs diagnostic kits. This approach provides a simple and cost-effective method for detecting BAs in food, which could be beneficial for ensuring food safety and preventing the harmful effects associated with their consumption., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A novel, simple, affordable, and reliable colorimetric paper-based analytical device (PAD) was developed for the point-of-use quality testing of ethanol-based hand sanitizers, mainly against adulteration by water. The principle was based on the novel solvatochromism of methylparaben (MPB)-Fe 3+ complex, where water is essential for complex formation and ethanol is necessary for MPB solubility. The intensity of the formed violet color, measured at 528 nm, showed a good correlation ( R 2 ions and MPB on chitosan-modified filter paper. The developed PAD was successfully applied for the quality testing of ethanol-based hand sanitizers using an established color index, where clearly distinct colors were observed as a function of the percentage ethanol (0-100%). The developed test strips could achieve on-site lab-quality results without expensive or sophisticated instruments using a few milligrams of FeCl 3+ and MPB in addition to regular filter paper. Accordingly, it can be used as a test strip for the quality checking of ethanol-based hand sanitizers by end users.3 and MPB in addition to regular filter paper. Accordingly, it can be used as a test strip for the quality checking of ethanol-based hand sanitizers by end users., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have influenced this work., (This journal is © The Royal Society of Chemistry.)

In the present work, four CaCO 3 -rich solid residues from the pulp and paper industry (lime mud, green liquor sludge, electrostatic precipitator dust, and lime dregs) were assessed for their potential as co-sequestrating agents in carbon capture. Carbonic anhydrase (CA) was added to promote both CO 2 hydration and residue mineral dissolution, offering an enhancement in CO 2 -capture yield under atmospheric (up to 4-fold) and industrial-gas mimic conditions (up to 2.2-fold). Geological CO 2 storage using olivine as a reference material was employed in two stages: one involving mineral dissolution, with leaching of Mg 2+ and SiO 2 from olivine; and the second involving mineral carbonation, converting Mg 2+ and bicarbonate to MgCO 3 as a permanent storage form of CO 2 . The results showed an enhanced carbonation yield up to 6.9%, when CA was added in the prior CO 2 -capture step. The proposed route underlines the importance of the valorization of industrial residues toward achieving neutral, or even negative emissions in the case of bioenergy-based plants, without the need for energy-intensive compression and long-distance transport of the captured CO 2 . This is a proof of concept for an integrated strategy in which a biocatalyst is applied as a CO 2 -capture promoter while CO 2 storage can be done near industrial sites with adequate geological characteristics., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Sodium (Na) metal batteries such as Na-ion batteries and Na-CO 2 batteries are considered to be excellent alternatives to lithium batteries in terms of their potential applications because of their high specific capacity and low cost. However, the sodium anode showed low efficiency and poor cycling in Na-metal battery performance due to the formation of sodium dendrites and serious corrosion. In this work, nitrogen (N), phosphorus (P) co-doped carbon paper (NP-CP) modified with cobalt tetroxide (Co 3 O 4 ) nanoparticles was prepared as the Na anode carrier (Co 3 O 4 @NP-CP), and a sodium-based composite anode (Na-Co@NP-CP) was further prepared by electrodepositing sodium. The experimental results indicate that the N, P and Co 3 O 4 multi-doped carbon paper has good sodiophilicity, which can induce the uniform plating/stripping of Na + ions and inhibit the growth of Na dendrites. The N, P doped carbon paper provides a high surface area and tremendous three-dimensional (3D) framework to effectively reduce the areal current density, facilitate the transfer of electrons, and enhance battery life. Therefore, Na-Co@NP-CP based symmetric cells exhibit stable cycling of over 1100 hours at current densities of 1 mA cm -2 and fixed capacity of 1 mA h cm -2 . When the Na-Co@NP-CP anode couples with CO 2 , the assembled batteries can deliver a stable cycling of 165 cycles at current densities of 500 mA g -1 and limited capacity of 500 mA h g -1 . When Na-Co@NP-CP anode couples with Na 3 V 2 (PO 4 ) 3 (NVP) cathode, the assembled cells exhibit lower hysteresis and batter cycling performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

π-Conjugated polymers such as polythiophene provide intramolecular wire effects upon analyte capture, which contribute to sensitive detection in chemical sensing. However, inherent aggregation-induced quenching causes difficulty in fluorescent chemical sensing in the solid state. Herein, we propose a solid-state fluorescent chemosensor array device made of a paper substrate (PCSAD) for the qualitative and quantitative detection of metal ions. A polythiophene derivative modified by dipicolylamine moieties (1 poly ), which shows optical changes upon the addition of target metal ions ( i.e. , Cu 2+ , Cd 2+ , Ni 2+ , Co 2+ , Pb 2+ , Zn 2+ , and Hg 2+ ), was highly dispersed on the paper substrate using office apparatus. In this regard, morphological observation of the PCSAD after printing of 1 poly suggested the contribution of the fiber structures of the paper substrate to the homogeneous dispersion of 1 poly ink to suppress aggregation-induced quenching. The optical changes in the PCSAD upon the addition of metal ions was rapidly recorded using a smartphone, which was further applied to imaging analysis and pattern recognition techniques for high-throughput sensing. Indeed, the printed PCSAD embedded with 1 poly achieved the accurate detection of metal ions at ppm levels contained in river water. The limit of detection of the PCSAD-based sensing system using a smartphone (48 ppb for Cu 2+ ions) is comparable to that of a solution-based sensing system using a stationary spectrophotometer (16 ppb for Cu 2+ ions). Therefore, the methodology based on a combination of a paper-based sensor array and a π-conjugated polymer will be a promising approach for solid-state fluorescent chemosensors., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

A paper-based ratiometric fluorescent sensing platform has been developed for glucose detection based on a dual-emission fluorescent probe consisting of carbon quantum dots (C QDs) and CdTe QDs. When the two kinds of QDs are mixed, the fluorescence of C QDs is reversibly quenched by CdTe QDs. However, in the presence of glucose, the fluorescence of CdTe QDs is quenched by H 2 O 2 catalyzed by glucose oxidase (GOx), which restores the fluorescence of C QDs. The proposed paper-based ratiometric fluorescent sensing platform exhibited good sensitivity and selectivity towards glucose. The working linear range was 0.1 mM to 50 mM with a limit of detection (LOD) of 0.026 mM. Additionally, the proposed paper-based sensor possesses viability for the determination of glucose in actual urine samples., Competing Interests: The authors have no conflict to declare., (This journal is © The Royal Society of Chemistry.)

Multienzyme systems are essential for utilizing di-, oligo-, and polysaccharides as fuels in enzymatic fuel cells effectively. However, the transfer of electrons generated by one enzymatic reaction in a multienzyme cascade at the electrode may be impeded by other enzymes, potentially hindering the overall efficiency. In this study, carbon paper was first modified by incorporating single-walled carbon nanotubes (SWCNTs) and gold nanoparticles (AuNPs) sequentially. Subsequently, glucose oxidase (GOx) and a trehalase-gelatin mixture were immobilized separately on the nanostructured carbon paper via layer-by-layer adsorption to mitigate the electron transfer hindrance caused by trehalase. The anode was first fabricated by immobilizing GOx and trehalase on the modified carbon paper, and the cathode was then fabricated by immobilizing bilirubin oxidase on the nanostructured electrode. The SWCNTs and AuNPs were distributed adequately on the electrode surface, which improved the electrode performance, as demonstrated by electrochemical and morphological analyses. An enzymatic fuel cell was assembled and tested using trehalose as the fuel, and a maximum power density of 23 μW cm -2 was obtained at a discharge current density of 60 μA cm -2 . The anode exhibited remarkable reusability and stability., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Conductive papers made from carbon nanotubes and wood fibers exhibit a p-type character. N 2 plasma treatment converts paper into n-type and conversion is verified by elemental analyses, work function and Hall-effect measurements. By screening one face of p-type paper in plasma, the p-n junctions are successfully created along the thickness direction and electrical rectification is evident by current-voltage measurement., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

In experiments, printing paper is imprinted with three different ink micropatterns (square, grid, and stripe). The wetting contact angle of water droplets on a heterogeneous surface is then investigated using a proportionate scaling molecular dynamics (MD) simulation, where the water droplets and the ink-patterned printing paper are both shrunk by a factor of 200 000 collectively. The errors from the theoretical values are always less than 1°, which is much less than the bias of experimental measurement data, according to the modeling contact angles. It has been demonstrated that this proportionate scaling approach works well to appropriately explain the interaction between micro-/nanostructures and liquids., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A simple and portable paper-based analytical device was developed for visual and semiquantitative detection of ferric ion in real samples using green emitting carbon dots (CDs), which were prepared via microwave method using sodium citrate, urea and sodium hydroxide as raw materials and then loaded on the surface of paper substrate. When Fe 3+ exists, the green fluorescence of CDs was quenched and significant color change from green to dark blue were observed, resulting the visual detection of Fe 3+ with a minimum distinguishable concentration of 100 μM. By analyzing the intensity changes of green channels of test paper with the help of smartphone, the semiquantitative detection was realized within the range of 100 μM to 1200 μM. The proposed paper-based analytical devices have great application prospects in on site detection of Fe 3+ in real samples., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Malondialdehyde (MDA) is a critical product of polyunsaturated adipose acid peroxidation and represents a common biomarker of oxidative stress. The effect of different MDA concentrations on human biofluids reflects pathological changes, which has been seen in diverse types of sickness, such as leukemia, diabetes, cancer, cardiovascular disease, and age-related macular degeneration and liver disease. In this study, different types of silver nanoparticles, including silver nanoprism (AgNPrs), silver nanowires (AgNWs), and silver nanospheres (AgNSs), were synthesized and used for the chemosensing of MDA by colorimetric and spectrophotometric methods. Colorimetric tests were performed to identify malondialdehyde in the solution as well as the one-droplet-based microfluidic paper substrate as a miniaturization device for the monitoring of analytes in human real samples. The analytical quantification of the MDA was done using the UV-Vis method. Also, the utilization of the designed chemosensor for the analysis of MDA in real sample was evaluated in human urine samples. Using the spectrophotometric method, MDA was deformed in the linear range of 0.01192 to 1.192 mM with a low limit of quantification of 0.12 μM. Essential significant features of this study include the first application of AgNPrs with high stability and great optical properties without any reagent as an optical sensing probe of MDA and optimized OD-μPCD toward on-site and on-demand MDA screening in real samples diagnosis and the innovative time/color semi-analytical recognition strategy. Moreover, the prepared OD-μPCD decorated by AgNPrs could be a prized candidate for commercialization due to the benefits of the low-cost materials used, like paper and paraffin, and portability. This innovative process led to uniform hydrophilic micro-channels on the surface of cellulose, without the use of a UV lamp, clean room, and organic solvents. This report could be a pioneering work, inspiring simple and effective on-site semi-analytical recognition devices for harmful substances or illegal drugs, which simply consist of a piece of lightweight paper and one drop of the required reagent., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Ascorbic acid (AA) or vitamin C plays multiple crucial roles, particularly as an antioxidant. This essentially biologically active molecule was selectively detected over other reductants by the synthesized profluorescent nitroxide probe ProN6 via a switch-on method. After either a hydrogen atom or single electron transfer from AA to nitroxide, the resulting diamagnetic hydroxylamine was rapidly cyclized to form a fluorescent O -acylalkoxyamine. This cyclization prevented the reoxidation of the corresponding hydroxylamine to the nitroxide, leading to a high precision of detection. A kinetic fluorescence study indicated that ProN6 exhibited higher reactivity than ProN7. Density functional theory (DFT) calculations indicated that the Gibbs free energy of the AA-induced cascade reductive lactonization of ProN6 was lower than that of ProN5 and ProN7. The designed probe achieved the sensitive and specific detection of AA with detection limits of 77.9 nM and 195.9 μM in solution and on paper, respectively. The utilization of the probe as a paper-based fluorescent sensor demonstrated the good accuracy of the quantitative analysis of AA in commercial supplements., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Heavy metals emanate from natural and man-made sources, such as agricultural chemicals including fertilisers and pesticides, medical waste, and chemicals released from industries. Detection and monitoring toxic metal ions is one of the challenges confronting scientists in biological, environmental, and chemical systems. This study describes the design and synthesis of a new imidazole-based fluorescent and colourimetric chemosensor (DPICDT) for highly selective sensing of Hg 2+ and Cu 2+ ions in aqueous acetonitrile medium. The probe was synthesised by coupling benzil and substituted aldehyde using ethanolic ammonium acetate. The structure of DPICDT was confirmed via IR spectra, NMR, and HR-MS spectra. The DPICDT probe displayed a rapid naked-eye response towards Cu 2+ ions from colourless to red-purple and significant fluorescence quenching response towards Hg 2+ over other competitive metal ions in both solution and solid support. The binding modes of DPICDT with Cu 2+ and Hg 2+ ions were found to be at a 1 : 1 ratio as determined using Job plot, ESI HR-MS, and the sensing mechanism was evolved by 1 H NMR titrations, HR-MS spectra, and DFT calculations. The lower detection limit was 15.1 nM for Cu 2+ , eventually far less than the World Health Organization guideline for drinking water (Cu 2+ - 31.5 μM) and 1.17 μM for Hg 2+ (permissible concentration 2 ppb). Promisingly, the tissue paper-based DPICDT test strips and silica-supported DPICDT were developed and demonstrated for on-site application without resorting to expensive instruments., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)