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Stimuli-responsive fluorescent materials are ideal materials for paper anti-counterfeiting applications. However, the single responsiveness and the lacking of dynamics present the risk of being deciphered. Herein, we designed a series of cyanostilbene derivatives (ACNs) with fluorescence responses to acid or base. ACN1 with pyridine and hydroxyl groups exhibit dually responsive fluorescence "ON" in the solid state due to the ionization-enhanced intramolecular charge transfer (ICT) effect. Other ACNs with either pyridine or hydroxyl unit show only single responsiveness. Fluorescence papers (FPs) prepared by a simple dipping into the solutions of ACNs maintain the responsive fluorescence performance. FP1H with high ACN1 content exhibits time-dependent dynamic fluorescent colour changes by hydrogen chloride (HCl) vapour fumigation. The applications of paper anti-counterfeiting and information encryption are developed by combining ACN1 with other single-responsive ACNs. Moreover, a four-dimensional (4D) code with time-dependent information changes is designed. Our work provides new materials for the field of paper fluorescent anti-counterfeiting encryption. [ABSTRACT FROM AUTHOR]

A portable paper-based electrochemical sensor has been developed to determine 5-hydroxymethylfurfural (5-HMF). A screen-printed carbon electrode (SPCE) was facilely fabricated for the first time on poster paper which showed a very satisfactory electrochemical response. The analytical performance of the electrode was enhanced by electrochemical deposition of silver microdendrites (AgMDs). The cathodic peak of 5-HMF occurred at approximately −1.48 V, lower than that obtained from the bare poster-SPCE. Moreover, the modified electrode showed a higher current response than the bare electrode, revealing that the AgMDs not only exhibited highlighted electrocatalytic features but also improved the electrical conductivity and increased the electrode surface area. Afterward, some influencing conditions were optimized, including scan rate and the number of scan cycles for AgMD deposition, pH, temperature, and square wave voltammetric parameters. Under the optimal conditions, the analytical characteristics of the proposed sensor were evaluated. The cathodic peak current increased linearly according to 5-HMF concentration over the range of 3–100 ppm, and the detection limit was 1.0 ppm. This low-cost, disposable electrochemical sensor provided environmentally friendly, simple and rapid detection, acceptable precision, good stability, and high selectivity. Additionally, this method can be applied to quantify 5-HMF in honey samples with satisfying accuracy. [ABSTRACT FROM AUTHOR]

The integration of smartphones with visual-based paper strips has gained great attention because of the rapid, low-cost, and relible analysis. Herein, we report on the synthesis of a red luminescent europiumbased metal organic framework (Eu-MOF) for the detection of folic acid in pharmaceutical formulations. The Eu-MOF showed strong and stable red emission fluorescence (excited at 270 nm), and the emission was significantly quenched upon exposure to folic acid due to the inner filter effect. A fluorometric assay in solution and visual detection based on fluorescence on a paper strip were used independently to quantify folic acid. The paper strips were prepared using chromatography paper and with the aid of a smartphone, folic acid was visually detected. In solution, the calculated LOD was 0.3 mM with a dynamic linearity range from 1.0 to 12.50 mM. Meanwhile, in the visual detection based on a smartphone integrated with a paper test strip, the linearity was from 1.0 to 9.0 mM with 0.12 mM as the LOD. Color analysis, from the photographs taken with a smartphone, was performed via analyzing the RGB coordinates using the Image-J program. The luminescent probe was applicable to detect folic acid in various drug tablets with recovery data ranging from 95 to 103%. The application of smartphones and fluorescent paper strips provides reliable detection of folic acid for on-site analysis, particularly in remote rural areas. [ABSTRACT FROM AUTHOR]

The sustainable goal of technological advancement is to go from lab to site through the development of a sensitive, specific and portable sensor for pollution monitoring. Herein, we report a completely portable colorimetric prototype device for the selective monitoring of lead (Pb) pollution, mainly in air, which relies on a new aspect of analysing the colorimetric assays on paper strips by the direct measurement of the retroreflective information, other than the available tedious image analysis methods. Our indigenously developed citrate-functionalized silver nanoparticles (AgNPs) embedded in cellulose paper strips showed significant localized surface plasmonic resonance (LSPR) peaks in the blue region and with the increase in the Pb concentration, the LSPR band in the blue region decreased and a new peak appeared in the green region of the electromagnetic spectrum due to the formation of larger aggregates. The prototype device monitored these spectral changes and accordingly gave the Pb content present in the sample. In this work, we made the sample under study by the acid digestion of one of the widely present air-suspended particulates, i.e., PbO2. The prototype device is a suitable fielddeployable technique for environmental Pb sensing and will open up new perspectives for future advancement in low-cost paper-based sensing. [ABSTRACT FROM AUTHOR]

Surveillance of SARS-CoV-2 infection is critical for controlling the current pandemic. Antigen rapid tests (ARTs) provide a means for surveillance. Available lateral flow assay format ARTs rely heavily on nitrocellulose paper, raising challenges in supply shortage. Vertical flow assay (VFA) with cellulose paper as test material attracts much attention as a complementary test approach. However, current reported VFAs are facing challenges in reading the test signal from the bottom face of the test cassette, complicating the test workflow and hindering translation into rapid test application. Here, we address this gap with an enhanced VFA against SARS-CoV-2 N protein that adapts a cellulose pull-down test format allowing (1) one-step sample application at the top of the test cassette and (2) readout of the test signal from the top. We also demonstrate the feasibility of translating the enhanced VFA into a point-of-care application that can help in SARS-CoV-2 surveillance. [ABSTRACT FROM AUTHOR]

Chronic obstructive pulmonary disease (COPD) has become the third leading cause of global death. Insufficiency in early diagnosis and treatment of COPD, especially COPD exacerbations, leads to a tremendous economic burden and medical costs. A cost-effective and timely prevention requires decentralized point-of-care diagnostics at patients' residences at affordable prices. Advances in point-of-care (POC) diagnostics may offer new solutions to reduce medical expenditures by measuring salivary and blood biomarkers. Among them, paper-based analytical devices have been the most promising candidates due to their advantages of being affordable, biocompatible, disposable, scalable, and easy to modify. In this review, we present salivary and blood biomarkers related to COPD endotypes and exacerbations, summarize current technologies to collect human whole saliva and whole blood samples, evaluate state-of-the-art paper-based analytical devices that detect COPD biomarkers in saliva and blood, and discuss existing challenges with outlooks on future paper-based POC systems for COPD diagnosis and management. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (μPADs) are foundational devices for point-of-care testing, yet suffer from limitations in regards to their sensitivity and capability in handling complex assays. Here, we demonstrate an airflow-based, evaporative method that is capable of manipulating fluid flows within paper membranes to offer new functionalities for multistep delivery of reagents and improve the sensitivity of μPADs by 100–1000 times. This method applies an air-jet to a pre-wetted membrane, generating an evaporative gradient such that any solutes become enriched underneath the air-jet spot. By controlling the lateral position of this spot, the solutes in the paper strip are enriched and follow the air jet trajectory, driving the reactions and enhancing visualization for colorimetric readout in multistep assays. The technique has been successfully applied to drive the sequential delivery in multistep immunoassays as well as improve sensitivity for colorimetric detection assays for nucleic acids and proteins via loop-mediated isothermal amplification (LAMP) and ELISA. For colorimetric LAMP detection of the COVID-19 genome, enrichment of the solution on paper could enhance the contrast of the dye in order to more clearly distinguish between the positive and negative results to achieve a sensitivity of 3 copies of SARS-Cov-2 RNAs. For ELISA, enrichment of the oxidized TMB substrate yielded a sensitivity increase of two-to-three orders of magnitude when compared to non-enriched samples – having a limit of detection of around 200 fM for IgG. Therefore, this enrichment method represents a simple process that can be easily integrated into existing detection assays for controlling fluid flows and improving detection of biomarkers on paper. [ABSTRACT FROM AUTHOR]

Paper-based flexible sensors have attracted much attention due to their abundant resource, low cost and good degradability in the natural environment leaving no electronic waste (e-waste). However, the mechanical properties of paper still need to be strengthened and the output stability may be impacted by water or high humidity because of the hydrophilicity of cellulose fibers. In order to solve these problems, for the first time, a paper-based flexible sensor with available running data under water without encapsulation was fabricated using softwood cellulose fibers and graphite nanoplates through a papermaking technique in this work. The cellulose nanofibers (CNFs) were added to reinforce the paper and the alkyl ketene dimer (AKD) emulsion was coated on the paper to endow it with super-hydrophobicity. The sensor can be used for both strain and pressure detection. As a strain sensor, the gauge factor (GF) was 18.99 and the response time was 0.3 s. It can be used to monitor human motions such as the bending of fingers, the wrist, and elbow. Interestingly, it was proven to be able to monitor finger bending at high humidity and under water due to its super-hydrophobicity. As a pressure sensor, it exhibited sensitivity S1 = 0.019 kPa−1 in the range of 0 to 316.5 kPa, and S2 = 0.01 kPa−1 in the range of 316.5 to 1421 kPa, with the response time of 0.3 s. The detecting range is much wider than that of reported sustainable flexible pressure sensors. Furthermore, this sensor can be easily disposed of by burning, thus avoiding the production of e-waste. This multifunctional flexible paper-based sensor may find potential in sport and health monitoring, soft robotics and human–machine interfaces. [ABSTRACT FROM AUTHOR]

Paper microfluidics is a rapidly growing subfield of microfluidics in which paper-like porous materials are used to create analytical devices that are well-suited for use in field applications. 3D printing technology has the potential to positively affect paper microfluidic device development by enabling tools and methods for the creation of devices with well-defined and tunable fluidic networks of porous matrices for high performance signal generation. This critical review focuses on the progress that has been made in using 3D printing technologies to advance the development of paper microfluidic devices. We describe printing work in three general categories: (i) solid support structures for paper microfluidic device components; (ii) channel barrier definition in existing porous materials; and (iii) porous channels for capillary flow, and discuss their value in advancing paper microfluidic device development. Finally, we discuss major areas of focus for highest impact on the next generation of paper microfluidics devices. [ABSTRACT FROM AUTHOR]

In recent years, the development of multi-functional supercapacitors with high flexibility and strong environmental adaptability has gradually become a focus of attention. In this work, a multi-functional paper-based supercapacitor with excellent temperature adaptability, plasticity, tensile strength, strong adhesion, and self-healing properties is obtained by introducing PVA and ZnCl2 into carbonized paper-based materials (APC-PVA@ZnCl2). The as-obtained APC-PVA@ZnCl2 supercapacitor has excellent adaptability to the environment, even in a low-temperature environment below zero, still maintaining a high volumetric specific capacitance of 3438.45 mF cm−3 and high volumetric specific energy density of 44 mW h cm−3. Moreover, the APC-PVA@ZnCl2 supercapacitor can be stretched beyond 2400–2500% strain, indicating good tensile properties. In addition, the APC-PVA@ZnCl2 composite can also be used as a sensing material to detect current signals with different characteristics generated by the movement of different parts of the human body, showing excellent sensing performance. Besides, the APC-PVA@ZnCl2 composite also displays outstanding thermoelectric properties. It is hoped that this work can provide a reference for the development of green multi-functional supercapacitors. [ABSTRACT FROM AUTHOR]

This work presents the development of a green paper-based analytical device (Green-PAD) array for pH detection. The array was obtained with natural dyes extracted from red cabbage (Brassica oleracea) and butterfly pea flower (Clitoria ternatea); a filter paper was used as a substrate. The RGB indexes of the PADs' colors were extracted from the pictures taken using a smartphone or using a specifically developed RGB detector (Arduino-based) to obtain RGB indexes not affected by the light and the photocamera sensitivity. Multi-technique chemometric models were developed for calculating the pH value, starting from the RGB triplet of each sensing PAD. A preliminary and explorative chemometric analysis with PCA (partial component analysis) and TWPCA (3-way PCA) was carried out. Partial least square regression, PLS, was then applied to correlate the color of the PAD's picture with the solutions' pH. Different solutions at various pHs, ranging from 1 to 13, were obtained by titrating orthophosphoric acid with standardized NaOH, and they were used to create PLS models. Some real samples were examined as a test set, and the results were validated with pH-meter measurements. The ability of the PLS to model the experimental data was satisfactory since a good agreement between the experimental and fitted pH values was obtained. The proposed PADs were prepared with natural dyes and filter papers, so they are completely biodegradable and eco-friendly. Their fabrication does not require toxic or expensive reagents and sophisticated equipment. Also, the developed RGB detector, built-up with low-cost components and recycled batteries, adds value making the measurement cheap, easy and feasible also by non-expert people. [ABSTRACT FROM AUTHOR]

A chromone-based symmetrical dipodal Schiff base probe L was designed and synthesized for multi-analyte detection in both aqueous and organic media. L displayed a prominent 'turn-on' fluorescence response with Al3+ (LOD = 6.9 μM) via the chelation-enhanced fluorescence (CHEF) process in a fully aqueous medium based on the inhibition of the photoinduced electron transfer (PET) process. Moreover, the in situ generated [L-Al3+] system was able to detect pyrophosphate (PPi) under identical experimental conditions. The proposed sensing pathway is believed to be the complexation with aluminium, followed by the subsequent decomplexation of the system by PPi. Furthermore, as the probe was decorated with –NH functionalities, it attained fluorescence indications upon binding with a basic anion. The detection ability of the probe for fluoride ions (LOD = 6.8 × 10−8 M) in the organic medium was studied using the 'turn-off' emission change based on the formation of a N–H⋯F hydrogen bond and subsequent deprotonation, as well as a visual change in color from yellow to reddish-yellow under UV light. The in situ prepared [L-F−] adducts could potentially sense Zn2+ ions with a 'turn-on' response via the metal-induced release of the free probe. All of the spectroscopic analyses were recorded to support the recognition mechanism of the aforementioned analytes by the reported probe molecule L. The probe also found applications in testing real water samples. [ABSTRACT FROM AUTHOR]

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and viral RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67–3000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation. [ABSTRACT FROM AUTHOR]

The mechanical properties of thermally conductive composites are the key to realize their applications. Strength of materials is of significance, furthermore the toughness of materials also should attract more concern. Actually, few researchers have reported the simultaneous improvement of strength and toughness of anisotropic thermally and electrically conductive composites. Therefore, this study aims to obviously improve the in-plane thermal and electrical conductivities of nylon composites, which display superior tensile strength and toughness, compared to other thermally conductive composites. The nylon composite papers, prepared through a facile method involving vacuum-assisted filtration and compression molding processes, present a laminate structure and compact graphene nanoplatelet (GNP) stacks inside composites. On account of the special structure, the nylon composite papers show a super-high in-plane thermal conductivity of 16.0 W m−1 K−1 and electrical conductivity of 18.0 S cm−1 at a filler loading of 14.6 wt%. Surprisingly, the composite papers still exhibit a high strength of 48.3 MPa, which is comparable to that of a pure nylon film. In addition, the elongation at break of the composite paper with 14.6 wt% GNPs is as high as 34.2%, ultimately endowing the composite papers with a good toughness of 13.15 MJ m−3. The nylon composite papers successfully achieve the integration of excellent thermal and electrical conductivities, and superior strength and toughness, showing huge application values in the field of intelligent electronic device. [ABSTRACT FROM AUTHOR]

Snake bites are a neglected tropical disease, causing mortality and severe damage to various vital organs like the nervous system, kidneys and heart. There is increasing interest in designing new antivenom treatments that are more specific to particular groups (either taxonomic or regional) of species, given the increasing evidence that current polyvalent Indian antivenom is ineffective in many situations. Under these circumstances, being able to detect the species, or a group of species, responsible for the envenomation becomes important. Unfortunately, no such diagnostic tool is available in the Indian market. Such a tool will need to be rapid, sensitive and affordable. To address this need, we have combined the power of nanotechnology and paper microfluidics and herein report a device that has the ability to detect and differentiate viper venom from elapid and scorpion venom. In principle, this assay is based on the release of the dye from the stimuli-responsive glutaraldehyde cross-linked methylene blue-loaded gelatin (GMG) nanoparticles in the presence of snake venom metalloproteases and serine proteases. The developed equipment-free assay can detect and discriminate viper venom from that of elapids and scorpions. The low-end detection limit of the sensor is ∼3.0 ng for the saw-scaled viper Echis carinatus, while the same for Russell's viper Daboia russelii is ∼6.0 ng. The performance of the sensor remains unaltered for different batches of GMG nanoparticles. Altogether, this finding establishes the role of nanotechnology and paper microfluidics in the rapid and accurate detection of viper venom. [ABSTRACT FROM AUTHOR]

Recently, hydrogen peroxide (H2O2) has been used as a disinfectant in sanitizers for cleaning hands, and solid surfaces of hospitals, offices and homes to prevent the spread of the COVID-19 virus. The effluents from domestic, hospital and municipal waste should be monitored for their H2O2 content to avoid the entry of this toxic pollutant into the ecosystem. Therefore, we developed a low-cost graphene (Gr)-printed paper electrode for determination of H2O2 using cyclic voltammetry (CV). An office inkjet-printer and Gr nano-ink stabilized with ethyl cellulose (EC) were used for the fabrication of printed paper electrodes (PPEs) to determine H2O2 quantitatively. A stable Gr–EC nano-ink (2%) with viscosity and surface tension values of 12 mPa S−1 and 35 mN M−1, respectively, was formulated to obtain conductive electrodes. A wide linear range (2 μM–25 mM) with a better limit of detection (0.28 μM) for the determination of H2O2 was obtained when the Gr–EC/PPE was used as a working electrode. Further, the Gr–EC/PPE was successfully employed for analysis of H2O2 in wastewater. The electrochemical determination of H2O2 using the Gr–EC/PPE as an electrode in CV is rapid, economical, flexible and eco-friendly when compared with previously reported methods. [ABSTRACT FROM AUTHOR]

A single-step protocol was developed for the hydrolytic hydrogenation of microcrystalline cellulose into sorbitol over commercial carbon-supported Ru, in the presence of gaseous CO2 as an acid source and molecular hydrogen as a reductant. Under these conditions, cellulose was first hydrolysed to glucose by reversibly formed carbonic acid in water and then instantaneously hydrogenated on Ru/C. By tuning the reaction parameters, such as temperature, time and the relative pressure of CO2 and hydrogen gas, cellulose was fully converted at 220 °C in 18 h under 30 and 40 bar of H2 and CO2, respectively, with a sorbitol yield of 81%. Blank experiments revealed that without a catalyst and hydrogen, the reaction exhibited <5% conversion and glucose was the only detected product when the reaction was performed under CO2 pressure. XRD measurements on CO2-treated cellulose surprisingly revealed no noticeable changes in the crystallinity index (<10% with respect to microcrystalline cellulose), suggesting that hydrolytic hydrogenation took place on crystalline, not amorphous, cellulose. Furthermore, not only several cellulosic feedstocks, including filter paper, cotton wool, and cotton fiber, but also typical cellulose-based wastes such as a cardboard pizza box were also tested and under the optimized conditions sorbitol was obtained with yields ranging from 56% up to 72% in all cases. No less significant was the Ru/C catalyst stability, which could be recycled at least six times without any noticeable activity loss. [ABSTRACT FROM AUTHOR]

The electrocatalytic hydrogenation of aromatic rings in benzoic acid derivatives has arisen as a notionally engaging substitute for thermal catalysis under mild conditions. However, the utilization of organic solvents and low faradaic efficiency are incompatible with the principles of green chemistry and energy conservation. Herein, bimetallic PtRu supported on carbon paper developed by co-electrodeposition with optimized atomic ratios maintains an inspiring high conversion of 92.9%, high selectivity of 100% and a high faradaic efficiency of 62.2% for the hydrogenation of benzoic acid to cyclohexanecarboxylic acid in an acidic aqueous electrolyte without external H2, which is the best result to date. The optimized electrocatalyst also exhibits outstanding stability and universality for the electrocatalytic hydrogenation of benzoic acid derivatives. In situ Raman results and theoretical calculations prove that the synergistic effect generated by Ru modifying the electronic structure of Pt simultaneously enhances the capture of benzoic acid molecules and interfacial active hydrogen species and lowers the reaction energy barrier. After adsorbing benzoic acid, more accumulation of electrons around the Ru atom reduces the electron density of phenyl, thereby activating the reaction. Meanwhile, the uniform alloy nanoclusters anchored to the carbon paper surface ensure highly efficient electronic transmission and high dispersion of active components, reducing excessive agglomeration. A proton-exchange membrane reactor is also used to certify the potential of the electrocatalytic hydrogenation of benzoic acid derivatives for large-scale application. [ABSTRACT FROM AUTHOR]

Wood bark is a structurally complex by-product of the pulp and paper industry, which focuses primarily on the valorization of structurally more regular wood xylem components. The aim of this study was the elucidation of the less valorised willow wood counterparts (whole bark, inner bark, sclerenchyma bundles, and parenchymatous tissues) by NMR spectroscopic techniques. This allowed a better understanding of the structural features of macromolecular components of bark (i.e. pectin, hemicellulose, and lignin), thus providing a base for a more rational design of the customized biochemical processes prior to chemical processing of bark. This crucial knowledge contributed to the creation of a protocol/decision tool to select tailored enzymes (discarding the slightest substrate binding) for the biological pre-treatment of bark to a state suitable for chemical pulping. Such a protocol/decision-making tool would significantly improve the efficiency of enzyme selection by 60–70% due to the specific catalytic activity of the enzymes involved. [ABSTRACT FROM AUTHOR]

A series of Ti-doped W18O49 samples were prepared using a convenient solvothermal route. Due to the synergistic effect of doped Ti and oxygen vacancies, the samples showed excellent visible-light photochromic properties. Their performances as light-printable rewritable paper and smart windows showed great application value and promotion value. [ABSTRACT FROM AUTHOR]

Analyzing the components and contents of environmental gases is of great importance for industrial production, human health, and environmental safety. Carbon dioxide (CO2) has drawn great concern for its adverse effects on climate change and physical health. Simple, in situ, and selective methods for CO2 detection are thus highly demanded. This work presents a versatile and easily fabricated paper sensor for the selective detection of ambient CO2. The sensor consists of two components with a fluorescent molecule ANT-PPh3 as the sensing element and an ionic liquid [DBUH]+[Im]− for the absorption of CO2. Based on the photo-induced electron transfer (PET) between ANT-PPh3 and [DBUH]+[Im]−, the sensor exhibited fluorescence enhancement in the presence of CO2, and the response process is reversible. The sensor exhibits improved selectivity for CO2 over SO2 and NO2 compared with most reported works, with good stability and fast response to human breath. Without complex instrumentation and gas pre-collection processes, the early notification of high indoor CO2 concentrations was realized using this sensor. Taking advantage of its intuitive fluorescence changes, specific responsiveness, and convenience, we believe our designed CO2 sensor could be applied practically in monitoring and indicating high indoor CO2 concentrations in living scenarios. [ABSTRACT FROM AUTHOR]

This work reports a flexible yet robust Ti3C2Tx MXene/bamboo microfibril (BF) composite paper via a simple vacuum filtration process. Due to the excellent compatibility between MXene and BF, the MXene/BF composite paper demonstrates simultaneously an excellent tensile strength of 49.5 MPa, higher than that of both MXene sheet and BF film alone and also among the top values compared with those in the literature, an excellent electrical conductivity as high as 4.8 × 103 S m−1 which is also higher even at a lower MXene content than those reported in the literature, and outstanding electrical stability with no detectable deterioration after 1000 cycles of stretching, bending and compression. As a result, the MXene/BF composite paper shows versatility for making various high-performance wearable electronics. Specifically, the as-prepared flexible pressure sensor by stacking exhibits a high sensitivity of 0.153 kPa−1 and a linear sensing performance in the pressure range of 0 to 2.5 kPa; the as-fabricated electric heater displays outstanding electrothermal performance, giving a temperature difference of 20 °C in air at the lowest input voltage of 2.5 V compared with those of the literature; the produced wearable symmetric all-solid-state supercapacitor achieves large enhancements in volumetric capacitance and gravimetric capacitance compared with the neat MXene supercapacitor and outstanding energy storage stability upon varied deformations. The MXene/BF composite paper with the above virtues is appealing for wide applications in multifunctional wearable electronics. [ABSTRACT FROM AUTHOR]

The integration of paper-based devices with fluorescent nanomaterials as recognition elements has offered novel opportunities for biosensing with enhanced sensitivity and selectivity, as well as stable signals. This work innovatively designed a fluorescent paper-based device for enantioselective sensing of D -alanine (D -Ala), where carbon dots (CDs) grafted cellulose paper (PCD) was used as the fluorophore and the in situ generated gold nanoparticles (AuNPs) were used as quenchers. D -α-Amino acid oxidase (DAAO) stereo-selectively catalyzed D -Ala to produce hydrogen peroxide (H2O2), which mediated the in situ formation of PCD/AuNPs composites and quenched the fluorescence of PCD based on fluorescence resonance energy transfer (FRET). Under optimal conditions, the designed PCD/AuNPs demonstrated a reliable quenching response to D -Ala in the range of 1–100 μM and the limit of detection was 0.55 μM. Moreover, the platform was applied to detect D -Ala in serum, simulated gastric fluid samples, and was further employed to determine D -Ala in BGC-823 gastric cancer cells with satisfactory results. Ultimately, the PCD/AuNPs platform provided a novel strategy for the development of reliable and sensitive assays based on paper-based devices. It has great potential to be utilized in enantioselective sensing and clinical early diagnosis. [ABSTRACT FROM AUTHOR]

The practicality of portable fluorescent detectors has attracted widespread attention. Herein, a series of luminogens was obtained via integrating pyrrole/fluorinated-pyrrole with triphenylamine in high yield. The emission performance was modified via varying the F and CN substituents on the pyrrole ring. The compounds TPACHO and TPAFCHO, with aldehyde-group-substituted pyrrole, exhibit significant mechanochromic luminescence (MCL) behavior and typical AIEE properties. The compounds TPA2CN and TPA2FCN can efficiently detect liquid and gaseous hydrazine hydrate, and they can achieve paper-based detection through visually clear emission color switching from yellow/orange to blue. The minimum detectable concentration of hydrazine was 10 mM. Moreover, TPA2CN exhibits good inhibitory activity toward human nasopharyngeal tumor cells (CNE1) and it has application prospects in tumor cell detection and biological cell monitoring. Thus, such functionalized paper can be applied as highly selective discriminating test strips for hydrazine hydrate. [ABSTRACT FROM AUTHOR]

Detection and characterization of DNA damage plays a critical role in genotoxicity testing, drug screening, and environmental health. We developed a fully integrated origami paper-based analytical device (oPAD) for measuring DNA damage. This simple device allows on-paper cell lysis, DNA extraction, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) reaction and signal readout with simple operation steps, enabling rapid (within 30 min) and high throughput assessment of multiple DNA damages induced by exogenous chemical agents. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (μPADs) have been widely explored for point-of-care testing due to their simplicity, low cost, and portability. μPADs with multiple-step reactions usually require precise flow control, especially flow-delay. This paper reports the numerical, mathematical, and experimental studies of flow delay through wax valves surrounded by PDMS walls on paper microfluidics. The predried surfactant in the sample zone diffuses into the liquid sample which can therefore flow through the wax valves. The delay time is automatically regulated by the diffusion of the surfactant after sample loading. The numerical study suggested that both the elevated contact angle and the reduced porosity and pore size in the wax printed region could effectively prevent water but allow liquids with lower contact angles (e.g., surfactant solutions) to flow through. The PDMS walls fabricated using a low-cost liquid dispenser effectively prevented the leakage of surfactant solutions. By controlling the quantity, diffusion distance, and type of the surfactant predried on the chip, the system successfully achieved a delay time ranging from 1.6 to 20 minutes. A mathematical model involving the above parameters was developed based on Fick's second law to predict the delay time. Finally, the flow-delay systems were applied in sequential mixing and distance-based detection of either glucose or alcohol. Linear ranges of 1–100 mg dL−1 and 1–40 mg dL−1 were achieved for glucose and alcohol, respectively. The lower limit detection (LOD) of glucose and alcohol was 1 mg dL−1. The LOD of glucose was only 1/11 of that detected using μPADs without flow control, indicating the advantage of controlling fluid flow. The systematic findings in this study provide critical guidelines for the development and applications of wax valves in automatic flow delay for point-of-care testing. [ABSTRACT FROM AUTHOR]

Wearable displays with aesthetic design, durability, and washability are highly desired for communication and information gathering wherever and at any time. However, daily wear and washing might damage the characteristics of wearable displays with flexible plastic or extra elastomer substrate, and long-time repeated actuation could also lead to electric fatigue in the display. Here, we proposed a machine-washable, tailorable, and comfortable wearable textile-based electrophoretic electronic paper display (EPD) by encapsulating the electrophoretic ink microcapsules and hot pressing EPD into the daily textile. The gadget exhibited a contrast ratio of 13 and good stability after repeated harsh deformation (e.g., soaking, needling, tailoring, or machine washing). The optimal contrast ratio that benefited from the selected high- κ elastomer waterborne polyurethane (WPU) was achieved in human safety voltage. To demonstrate its potential application, the EPD prototypes of a patterned static display T-shirt and a lightweight dynamic display wristband watch were fabricated by screen printing and laser engraving. The as-fabricated textile-based EPDs with features, including simple fabrication with aesthetic design, excellent waterproofness, low energy consumption, and stretchability, provide important guidance for human and machine interaction for realizing truly wearable displays (i.e., wearing displays). [ABSTRACT FROM AUTHOR]

A well-designed support material between catalyst and substrate can always significantly enhance the performance of an electrode on water oxidation. In this work, a functional Ni and N-doped carbon layer (NNC) was designed on carbon paper (CP) via pyrolysis by using a controlled electrodeposited polyporphyrin as a precursor. Consequently, the fabricated NiFe-LDH/NNC/CP achieved a catalytic current density of 100 mA cm−2 at a small overpotential of 231 mV with a low Tafel slope of 26.0 mV dec−1, as well as high durability for more than 360 h. The insights are that N-doping reinforces the hydrophilicity and the catalyst binding capacity, while Ni-doping intensifies the conductivity. [ABSTRACT FROM AUTHOR]