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We report a simple and cost-effective paper-based and colorimetric dual-mode detection of As(iii) and Pb(ii) based on glucose-functionalized gold nanoparticles under optimized conditions. The paper-based detection of As(iii) and Pb(ii) is based on the change in the signal intensity of AuNPs/Glu fabricated on a paper substrate after the deposition of the analyte using a smartphone, followed by processing with the ImageJ software. The colorimetric method is based on the change in the color and the red shift of the localized surface plasmon resonance (LSPR) absorption band of AuNPs/Glu in the region of 200-800 nm. The red shift (Δ

Silver nanoparticle (AgNP)-decorated cellulose filter paper (FP), a low-cost point-of-use (POU) water disinfection system, can supply affordable and safe drinking water for people in desperate need, especially in rural areas in developing countries. However, owing to the unstable immobilization of AgNPs, silver can leach into the treated drinking water from the FP and exceed the World Health Organization (WHO) drinking water limit (

This paper describes a method to fabricate microfluidic paper-based analytical devices (μPADs) using a toner laser printer. Multiple methods have been reported for the fabrication of μPADs for point-of-care diagnostics and environmental monitoring. Despite successful demonstrations, however, existing fabrication methods depend on particular printers, in-house instruments, and synthetic materials. In particular, recent discontinuation of the solid wax printer has made it difficult to fabricate μPADs with readily available instruments. Herein we reported the fabrication of μPADs using the most widely available type of printer: a toner laser printer. Heating of printed toner at 200 °C allowed the printed toner to reflow, and the spreading of the hydrophobic polymer through the filter paper was characterized. Using the developed μPADs, we conducted model colorimetric assays for glucose and bovine serum albumin (BSA). We found that heating of filter paper at 200 °C for 60 min caused the pyrolysis of cellulose in the paper. The pyrolysis resulted in the formation of aldehydes that could interfere with molecular assays involving redox reactions. To overcome this problem, we confirmed that the removal of the aldehyde could be readily achieved by washing the μPADs with aqueous bleach. Overall, the developed fabrication method should be compatible with most toner laser printers and will make μPADs accessible in resource-limited circumstances.

Herein, we report a KBr-impregnated paper substrate as a sample probe to enhance the attenuated total reflection-Fourier transform infrared (ATR-FTIR) signal strength of anionic surfactants (AS) and non-ionic surfactants (NS) in an aqueous solution. The mechanism for the sensing of AS and NS is based on the strong interaction of surfactants with the silicate groups (SiO44−) of the KBr-impregnated paper substrate. The role of SiO44− on the surface of the paper is to enhance the adsorption of AS and NS, resulting in improved IR signal intensities for the target analytes. The improved signal intensity at 1253 cm−1 (SO42−, symmetric stretching) for AS and 1114 cm−1 (C–O–C, stretching vibration) for NS were selected for quantification. SEM-EDX was employed to determine the elemental compositions of pre- and post-adsorbed AS and NS on glass fibre filter paper (GFF). The linear range for the determination of AS and NS was 10–100 μg L−1 with a method detection limit (MDL) of 4 μg L−1 and method quantification limit (MQL) of 12 μg L−1. The good relative recovery of 71.4–109.7% and the interference studies showed the selectivity of the method for the determination of AS and NS in environmental water and commodity samples. The advantages of this method include its cost-effectiveness, enhanced sensitivity, disposability and accessibility of the paper substrate.

Due to the modern pursuit of the quality of life, science and technology have rapidly developed, resulting in higher requirements for various detection methods based on analytical technology. Herein, the development, fabrication, detection and application of paper-based microfluidic chips (μPAD) are summarized. We aim to provide a comprehensive understanding of paper chips, and then discuss challenges and future prospects in this field.

In this work, we developed a cost-effective and environmentally friendly anthocyanin-based paper sensor with high sensitivity and optical visibility for the rapid detection of ammonia in aqueous solutions. The detection principle is based on a color change upon ammonia exposure to an anthocyanin-containing paper, which can be recorded simply via a smartphone. The paper sensors were fabricated by extracting anthocyanin from different sources (i.e., red cabbage, blueberry, and blackberry) and immersing pre-cut paper in anthocyanin extracts. Anthocyanin was extracted from different sources into water and aqueous ethanolic solution (80%) using solid–liquid extraction (SLE) and sonication assisted extraction (SAE) methods. The sensor sensitivity and optical visibility were improved by selecting a suitable combination of anthocyanin source, extraction technique, and solvent and controlling the ammonia release from the samples via alkalinization using a suitable base. Sensors fabricated with anthocyanin extracted from red cabbage (Red-C) into water using the SLE method and samples alkalinized with NaOH showed higher sensor sensitivity and better optical visibility. The Red-C anthocyanin sensors also exhibited a visible color change from dark to light blue for ammonia samples with concentrations as low as 2 mg NH3–N/L. Moreover, the spike recovery results of the sensors (101.9–109.4%) were in good agreement with those of the standard spectrophotometry method (105.4–112.2%), which suggest that these biosensors are a promising analytical tool as a replacement for time-consuming and environmentally unfriendly standard spectrophotometry methods for the on-site screening of ammonia.

Imprecise control of fluid flows in paper-based devices is a major challenge in pushing the innovations in this area towards societal implementation. Assays on paper tend to have low reaction yield and reproducibility issues that lead to poor sensitivity and detection limits. Understanding and addressing these issues is key to improving the performance of paper-based devices. In this work, we use colorimetric analysis to observe the mixing behaviour of molecules from two parallel flow streams in unobstructed (on unpatterned paper) and constricted flow (through the gap of a patterned hourglass structure). The model system used for characterization of mixing involved the reaction of Fe3+ with SCN− to form the coloured, soluble complex Fe(SCN)2+. At all tested concentrations (equal concentrations of 50.0 mM, 25.0 mM or 12.5 mM for KSCN and FeCl3 in each experiment), the reaction yield increases (higher colorimetric signal) and better mixing is obtained (lower relative standard deviation) as the gap of the flow constriction becomes smaller (4.69–0.32 mm). This indicates enhanced passive mixing of reagents. A transition window of gap widths exhibiting no mixing enhancement (about 2 mm) to gap widths exhibiting complete mixing (0.5 mm) is defined. The implementation of gap sizes that are smaller than 0.5 mm (below the transition window) for passive mixing is suggested as a good strategy to obtain complete mixing and reproducible reaction yields on paper. In addition, the hourglass structure was used to define the ratio of reagents to be mixed (2 : 1, 1 : 1 and 1 : 2 HCl–NaOH) by simply varying the width ratio of the input channels of the paper. This allows easy adaptation of the device to reaction stoichiometry., Efficient passive mixing can be achieved by contricting the reagent flow using structures having narrow gaps.

In this research, we demonstrate a facile approach for the synthesis of a graphite-analogous layer-by-layer heterostructured CuO/ZnO/carbon paper using a graphene oxide paper as a sacrificial template. Cu2+ and Zn2+ were inserted into the interlayer of graphene oxide papers via physical absorption and electrostatic effects and then, the Mn+-graphene oxide paper was annealed in air to generate 2D nanoporous CuO/ZnO nanosheets. Due to the graphene oxide template, the structure of the obtained CuO/ZnO nanosheets with an average size of ∼50 nm was duplicated from the graphene oxide paper, which displayed a layer-by-layer structure on the microscale. The papers composed of nanosheets had an average pore size of ∼10 nm. Moreover, the as-prepared CuO-ZnO papers displayed high hybridization on the nanoscale. More importantly, the thickness of the single-layer CuO/ZnO nanosheet was about 2 nm (3-4 layer atom thickness). The as-synthesized nano-hybrid material with a high specific surface area and conjunct bimodal pores could play key roles for providing a shorter diffusion path and rapid electrolyte transport, which could further facilitate electrochemical reactions by providing more active sites. As an electrode material, it displayed high performances as a non-enzymatic sensor for the detection of glucose with a low potential (0.3 V vs. SCE), high sensitivity (3.85 mA mM-1 cm-2), wide linear range (5 μM to 3.325 mM), and low detection limit of 0.5 μM.

Nowadays quantitative chemical analysis is usually costly, instrument-dependent, and time-consuming, which limits its implementation for remote locations and resource-limited regions. Inspired by the ancient papercutting art (kirigami), we herein introduce a novel cut-and-paste protocol to fabricate 3D microfluidic paper-based analytical devices (μPADs) that are suitable for on-site quantitative assay applications. The preparation of the device is fast, simple, and independent of any lithographic devices or masks. Particularly designed reaction “channels” were pre-cut from a piece of filter paper, then assembled back to the silanized, superhydrophobic paper pads. The different layers of the device were assembled using a chemically-inert adhesive spray. The fabricated device has high efficiency of liquid handling (up to 60 times faster than conventional methods) and it is particularly inexpensive. Beyond the benchtop fabrication advantage, in conjunction with a custom mobile app developed for colorimetric analysis, we were able to quantify representative environmental contaminants (i.e., the amount of Cr(VI) and nitrite ions) in various water samples with the cut-and-paste μPADs (namely kPADs). Their detection limits (0.7 μg mL−1 for Cr(VI) and 0.4 μg mL−1 for nitrite ions, respectively) are comparable with conventional spectrophotometric methods, which confirm the potential of kPADs for on-site environmental/sanitary monitoring and food toxin pre-screening.

Free-standing graphene-based composite paper electrodes with various active materials have attracted tremendous interest for next-generation lithium-ion batteries (LIBs) due to advantages such as their light weight, excellent mechanical flexibility, and superior electrochemical performance. However, despite its high theoretical energy density, SnS2 is rather difficult to composite with the graphene paper, because conventional reduction procedures for graphene oxide (GO) induce either decomposition or oxidation of SnS2. Herein, a novel solid/gas two-phase interface hydrothermal process is reported to fabricate flexible free-standing SnS2/graphene nanocomposite papers (SGP) assisted by a reducing and stabilizing agent thioacetamide aqueous solution. Such hydrothermal process not only successfully reduces SnS2/graphene oxide paper (SGOP) to SGP, but more importantly, keeps intact the paper configuration as well as the phase stability of SnS2. The as-prepared SGP electrode exhibits high reversible discharge capacity, outstanding cyclic stability and rate capability, which can be attributed to the synergistic effect of the conductive and flexible graphene matrix for accommodation of the volumetric changes of SnS2 upon cycling and the planar SnS2 nanospacers between the graphene layers introducing nanopores for penetration of electrolyte and inhibition of graphene nanosheets restacking. This report demonstrates a new strategy for more active materials with promising lithium storage properties joining the flexible graphene-based paper electrode family.

Wearable electrochemical sensors have attracted tremendous attention in recent years. Here, a three-dimensional paper-based microfluidic electrochemical integrated device (3D-PMED) was demonstrated for real-time monitoring of sweat metabolites. The 3D-PMED was fabricated by wax screen-printing patterns on cellulose paper and then folding the pre-patterned paper four times to form five stacked layers: the sweat collector, vertical channel, transverse channel, electrode layer and sweat evaporator. A sweat monitoring device was realized by integrating a screen-printed glucose sensor on polyethylene terephthalate (PET) substrate with the fabricated 3D-PMED. The sweat flow process in 3D-PMED was modelled with red ink to demonstrate the capability of collecting, analyzing and evaporating sweat, due to the capillary action of filter paper and hydrophobicity of wax. The glucose sensor was designed with a high sensitivity (35.7 μA mM−1 cm−2) and low detection limit (5 μM), considering the low concentration of glucose in sweat. An on-body experiment was carried out to validate the practicability of the three-dimensional sweat monitoring device. Such a 3D-PMED can be readily expanded for the simultaneous monitoring of alternative sweat electrolytes and metabolites.

Free-standing graphene (FSG) paper plays a vital role in a wide variety of applications as an electrode material. Specifically, the electrical properties of FSG are the most important factor affecting its use as an electrode material. Herein, the vacuum filtration technique is utilized to fabricate GO paper, which is then reductively treated with HI. Initially, the electrical conductivity is measured for GO papers with different thicknesses by varying the concentration of GO precursor as well as the reduction time. The FSG paper with a thickness of 3 microns exhibits the lowest sheet resistance and further characterization is carried out to reveal the origin of this enhancement of electrical properties. The low resistance is attributed to its crystalline nature, stacking height (Lc), in-plane crystallite size (La) and defect density (nD). Meanwhile, iodide ions intercalated into the graphene layers act as hole-carriers, and their intercalation is favoured over adsorption at the surface.

In this study, optical microfluidic paper analytical devices (μPADs) for glucose detection from whole blood samples with a small sample volume (2 μL) have been developed on a single paper. In the proposed method, a mushroom-shaped analytical device contains a sample inlet zone and a detection zone. When blood is dripped onto the inlet region of a μPAD, the plasma diffuses to the detection region. The detection region is implanted with a metallic three-dimensional (3D) polymer hydrogel vehicle. The gel vehicle consists of a copper complex that responds to oxygen changes and glucose oxidase (GOx) immobilized inside the gel as a bioactivity preservative. The phosphorescence of the copper complex is enhanced by oxygen consumed by detection of glucose with a limit of detection (S/N = 3) of 0.44 mM, and the total analysis of the sample is completed within 1 min. The validity of the proposed research is demonstrated using control samples and real-world whole blood samples of glucose concentrations ranging from 3 to 200 mM, and the detection results are shown to be in agreement with those obtained using a glucometer. Attaining a simple device for analysing glucose in human whole blood without any pretreatment procedures and having a broad sensing range while consuming a small sample volume remain challenging; thus, our new analytical device is of great interest.

Herein, a new colorimetric paper sensor based on the layer-by-layer assembled multilayers of a cationic surfactant, tetrabutylammonium bromide (TBABr), and an anionic surfactant, sodium dodecyl sulfate (SDS), modified on filter paper was developed for the determination of total antioxidant capacity (TAC). In this study, gallic acid (GA) was used as the antioxidant standard. The fabricated (TBABr/SDS)3/PAD was loaded with Fe3+ ions to obtain Fe3+/(TBABr/SDS)3/PAD, exhibiting high selectivity for the detection of GA when compared with the case of other metal ions. The interaction between GA and the Fe3+/(TBABr/SDS)3/PAD sensor occurred rapidly, and the colorimetric paper sensor changed from yellow to purple immediately. The quantitative detection of GA was enabled by taking an image using an ordinary smartphone and applying the ImageJ software based on the change in color. Under optimum conditions, a linear response was obtained between the change in the color of the sensor and the TAC value expressed in terms of gallic acid equivalents. The linear range was from 0.50 μM to 6.50 mM with the detection limit of 0.35 μM. The colorimetric paper sensor was applied to detect the TAC in three kinds of green tea and vegetable samples, which provided the good recoveries of 86.0–109.9%. The proposed sensor is simple, cheap, equipment-free, rapid and environmentally friendly. In addition, the colorimetric sensor Fe3+/(TBABr/SDS)3/PAD has potential applicability for TAC detection in real food samples.

With more and more applications, the mechanical strength of graphene paper (GP) has attracted significant attention in recent years. In this report, GPs were prepared by flow-induced filtration of electrochemical exfoliated graphene sheets. By adjusting the concentration of solution, we found graphene sheets fabricated in 0.1 M K2SO4 have the thinnest average thickness. And by uniaxial in-plane tensile tests operated on a self-developed in situ scanning electron microscopy (SEM) tensile stage, the corresponding GP has the best fracture strength of 192 MPa. This is due to that the thickness decrease of exfoliated graphene will increase the quantity of interlayer crosslinks, thus improving the mechanical properties of GPs. This research may open a new way to obtain high-strength GPs for applications.

The conversion of CO2 into useful chemicals can lead to the production of carbon neutral fuels and reduce greenhouse gas emissions. A key technological challenge necessary to enable such a process is the development of substrates that are active, cost effective, and selective for this reaction. In this regard, the reduction of CO2 via electrochemical means is one of the most attractive alternatives but still requires rather unique electrodes. Considering the potential of this approach, this report describes a one-step methodology for the synthesis of carbon electrodes derived from simple paper and modified with various metallic nanoparticles. Upon a preliminary selection based on the catalytic activity towards CO2 reduction, the electrodes containing CuNPs were further characterized by Raman spectroscopy, and electrical/electrochemical techniques. These electrodes were then applied for the electrochemical reduction of CO2, leading to the formation of compounds with one carbon atom (formic acid), two carbon atoms (ethenone), three carbon atoms (propanoic acid) and four carbon atoms (butanol and butanoic acid). Fil: Gomez, Federico Jose Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Biología Agrícola de Mendoza. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Instituto de Biología Agrícola de Mendoza; Argentina Fil: Chumanov, George. Clemson University; Estados Unidos Fil: Silva, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Biología Agrícola de Mendoza. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Instituto de Biología Agrícola de Mendoza; Argentina. Clemson University; Estados Unidos Fil: Garcia, Carlos D.. Clemson University; Estados Unidos

Foodborne pathogens are responsible for hundreds of thousands of deaths around the world each year. Rapid screening of agricultural products for these pathogens is essential to reduce and/or prevent outbreaks and pinpoint contamination sources. Unfortunately, current detection methods are laborious, expensive, time-consuming and require a central laboratory. Therefore, a rapid, sensitive, and field-deployable pathogen-detection assay is needed. We previously developed a colorimetric sandwich immunoassay utilizing immuno-magnetic separation (IMS) and chlorophenol red-β-D-galactopyranoside for Salmonella detection on a paper-based analytical device (μPAD); however, the assay required many sample preparation steps prior to the μPAD as well as laboratory equipment, which decreased user-friendliness for future end-users. As a step towards overcoming these limitations in resource-limited settings, we demonstrate a reusable 3D-printed rotational manifold that couples with disposable μPAD layers for semi-automated reagent delivery, washing, and detection in 65 minutes. After IMS to clean the sample, the manifold performs pipette-free reagent delivery and washing steps in a sequential order with controlled volumes, followed by enzymatic amplification and colorimetric detection using automated image processing to quantify color change. Salmonella was used as the target pathogen in this project and was detected with the manifold in growth media and milk with detection limits of 4.4 × 102 and 6.4 × 102 CFU mL−1 respectively. The manifold increases user friendliness and simplifies immunoassays resulting in a practical product for in-field use and commercialization.

A graphene oxide paper (GOP) was irradiated with 500 keV proton for total fluence of 2 × 1013 cm−2 to 2 × 1015 cm−2 in a ground-based irradiation simulator. The spacing of layer, surface chemical composition, structural defects, thermal conductivity and electrical property of the GOP before and after irradiation was measured. The results indicated that the spacing of layer decreased after irradiation. The ratio of total carbon atom and total oxygen atom increased from 2.40 to 4.31 as well as the sp2 hybridized carbons obviously increased after 2 × 1015 cm−2 irradiation. The XPS analysis suggested the occurrence of reduction, and the Raman spectra indicated that the defects were produced after proton irradiation. Furthermore, the thermal conductivity of GOP decreased, and then increased smoothly as the irradiation fluences were increased, and the electrical property showed the similar trend. The change in the thermal and electrical properties for GOP could be attributed to the defects and the removal of oxygen-containing functional groups, which lead to the phonon conduct path and scattering centers changed under proton irradiation. This study could promote the application of GOP in future space expeditions.

Herein, an ease-of-use and highly sensitive origami-based “book” shaped three-dimensional electrochemical paper microdevice based on nucleic acid testing (NAT) methodology was developed for sample-to-answer detection of pathogens from whole blood and food samples. The whole steps of NAT, including sample preparation, amplification and detection, were performed by alternately folding the panels of the microdevice, just like flipping a book. The screen-printing electrodes were combined with wax-printing technology to construct a paper-based electrochemical unit to monitor Loop-mediated isothermal amplification (LAMP) reaction with an electrochemical strategy. After nucleic acid extraction and purification with the glass fiber, the LAMP reaction was performed for 45 min to amplify the extracted nucleic acid sequence, followed by the execution of the electrochemical interrogation reaction based on methylene blue (MB) and double-stranded LAMP amplicons. Starting with whole blood and food samples spiked with Salmonella typhimurium, this microdevice was successfully applied to identify pathogens from biological samples with satisfactory sensitivity and specificity. Therefore, the proposed origami-based “book” shaped three-dimensional paper microdevice has great potential for disease diagnosis, food safety analysis applications in the future.

Children's shoes are potential sources of toxic heavy metals, especially for younger children. Electrochemical detection could be applied for effective stripping analysis of heavy metals (such as Cd and Pb). However, the substrates of working electrodes are still limited and it is not well known which property is critical. Herein ITO glass was used as the substrate and the working electrode was modified with carbon cement for stripping analysis of Cd and Pb. The electrochemical impedance spectra of the ITO modified electrodes suggested the connection between the resistance and the electrochemical responses of heavy metals in stripping analysis, depending on the dilution ratio of the carbon cement. After optimization, the ITO modified electrodes in paper-based analytical devices could be used to sensitively quantify Cd and Pb with the concentration ranging from 10 to 1000 ppb. The detection limit of Pb2+ could reach less than 1 ppb while that of Cd2+ could reach 5 ppb, depending on the pH value of the sample solution. The paper-based electroanalytical devices could be used to quantify the concentration of Cd and Pb in children's shoes. This study implied the impact of the electric conductivity of the electrode substrates on stripping analysis, which might help to find more materials for the fabrication of the working electrodes.

Contamination of milk by mycotoxins is a serious problem worldwide. Herein, we focused on the detection of aflatoxin B1 (AflB1) using a paper microfluidic device fabricated with specific aptamers as biorecognition elements. The fabrication process resulted in the generation of a leak proof microfluidic device where two zones were designed: control and test. Detection is achieved by color change when aflatoxin reacts with an aptamer followed by salt induced aggregation of gold nanoparticles. Specific aptamers for aflatoxin B1 were immobilized successfully onto the surface of gold nanoparticles. Biophysical characterization of the conjugated AuNPs-aptamer was done by UV-vis spectroscopy, DLS (dynamic light scattering), TEM (transmission electron microscopy). Under optimal conditions, the microfluidic device showed an excellent response for aflatoxin B1 detection in the range of 1 pM to 1 μM with a detection limit of up to 10 nM in spiked samples. Disadvantages associated with conventional techniques of ELISA were overcome by this one step detection technique with low operation cost, simple instrumentation, and user-friendly format with no interference due to chromatographic separation. The developed microfluidic paper-based analytical device (μPAD) can provide a tool for on-site detection of food toxins in less than a minute which is the main requirement for both qualitative and quantitative analysis in food safety and environmental monitoring.

Efficient and low-cost oil/water separation remains a great challenge for industries. Natural cellulose-based filter paper, because of its abundance, low cost, biodegradability and excellent chemical stability, has been developed as an oil/water separator in recent years. In the present study, a superhydrophilic and underwater superoleophobic filter paper is successfully prepared by an aldol condensation reaction to crosslink glucose molecules with filter paper. The prepared filter paper is characterized by IR-spectroscopy, SEM spectroscopy and wettability measurements, and it has high underwater oil contact angles of over 162° for hexane, toluene and petroleum ether. It is shown that the modified filter paper has high water recovery from various oil/water mixtures, not only in a gentle environment but also in acidic, alkaline, and salty environments and at different temperatures. Moreover, the glucose modified filter paper shows excellent oil/water emulsion separation efficiency (>99%) and good recycling performance. The preparation is economic and could be easily scaled up, suggesting its great potential for large-scale industrial applications.

Designing and controlling spontaneous imbibition is becoming a key requirement for advanced devices, presenting a substantial scientific and engineering challenge. Here we describe an approach that allows directional imbibition into designed geometries. A set of custom domains based on paper microfluidics mold nano-imbibition in user-Defined shapes such as curvatures, corners, and vertices into mesoporous thin films; enabling localized chemical reactions with programmable designs. The method also achieves nano-size filtration, allows the generation and delivery of reagent gradients in a nanofluidic fashion, and it can be used as a reactor for the synthesis of patterned metallic nanoparticle arrays. By using this easyto-build hybrid platform, users can create functional nanofluidic domains in custom geometries and perform spatially shaped chemistry. The ability to integrate mesoporous nanofluidic generation and paper-based microfluidics has made the hybrid system an exciting candidate for versatile nanoflow applications. Fil: Mercuri, Magalí. Comisión Nacional de Energía Atómica; Argentina Fil: Gimenez, Rocio Aldana. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Berli, Claudio Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Bellino, Martin Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina

This paper demonstrates a facile strategy for the development of nanosilver decorated polyaniline coated (PAg) paper-based electrodes for the fabrication of solid-state symmetrical supercapacitors. PAg based printing paper was developed through a two-step process involving initial silver nucleation and growth on the paper followed by aniline polymerization. The developed electrically conductive paper exhibited a highly porous structure and excellent mechanical stability. Further symmetrical supercapacitors having the configuration PAg/electrolyte/PAg were fabricated and evaluated for electrochemical performance such as specific capacitance (483 F g−1 and 613 F g−1 in aqueous 1 M H2SO4 and PVA–H2SO4 gel electrolytes respectively), energy density (69.56 and 85.13 W h kg−1), and power density (243.44 and 405.375 W kg−1) and cycling stability (90% of its capacitance retention even after 2000 cycles), exhibiting excellent performance under various bending conditions. All these exciting results suggest that the developed paper-based flexible solid-state energy device can serve as an efficient, sustainable, and low-cost energy storage system for portable microelectronic devices which are expected to revolutionize the perception of energy-storage devices in the electronics industry.

Textile-based microfluidic analytical devices have demonstrated significant potentials in biomolecular detection; however, to date, they have not been integrated with a shape memory polymer to prepare a thermoresponsive device for human sweat analysis. Herein, a thermoresponsive textile/paper-based microfluidic analysis system was constructed by combining biocompatible polyurethane (PU), cotton fabric and a paper-based colorimetric sensor. The coating of PU endowed the textile with temperature-dependent shape memory capability and patterned the channels to guide the liquid transport. A paper-based colorimetric sensor was prepared via a layer-by-layer deposition method and coupled with a smartphone for the quantitative analysis of glucose concentration. The as-prepared thermoresponsive textile/paper-based microfluidic analysis system had the dynamic range of 50–600 μM and the detection limit of 13.49 μM. After being fixed in the inner collar of a shirt, the system demonstrated great capabilities for the thermal-triggered sweat transport and in situ detection of glucose in human sweat under a high-temperature condition (59 °C). This study not only provides a low-cost and easy-to-wear sweat analysis tool for the health monitoring of people working at high temperatures, but also expands the applications of shape memory polymers and textile-based microfluidic devices in point-of-care testing.

Robust, reliable and cost-effective paper-based analytical device for potentiometric pholcodine (opiate derivative drug) ion sensing has been prepared and characterized. A printed pholcodinium (PHL)2+/5-nitrobarbiturate (NB)− ion-association complex as a sensory material-based all-solid-state ion-selective electrode (ISE) on a chemically reduced graphene oxide (CRGO) solid-contact, and a printed all-solid-state Ag/AgCl reference electrode, has been combined on a hydrophobic paper substrate coated with fluorinated alkyl silane (CF3(CF2)7CH2CH2SiCl3, CF10). The sensors revealed a potentiometric slope of 28.7 ± 0.3 mV dec−1 (R2 = 0.9998) over a linear range starting from 2.0 × 10−7 M to 1.0 × 10−2 M and a detection limit of 0.04 μg mL−1. The repeatability and stability of the pholcodine paper-based sensor was found to be 2.32%. The RSD% (n = 6) was found to be 2.67% when using five different paper-based sensors. The sensor revealed an excellent selectivity towards PHL over dextromethorphan, codeine, ephedrine, carbinoxamine, caffeine, ketamine, and K+, Na+ and Ca2+ ions. It showed a good recovery (94–104%) for the determination of PHL in different artificial serum samples. The presented paper-based analytical device was successfully introduced for PHL determination in different pharmaceutical formulations (i.e. syrups and suspensions) containing pholcodine. The current work can be considered as a promising possible analytical tool to obtain cost-effective and disposable paper-based potentiometric sensing devices. These devices can be potentially manufacturable at large scales in pharmaceutical, clinical and forensic applications for opiate drug assessment.

Electrochemical Paper-based Analytical Devices (ePADs) are an alternative to traditional portable analytical techniques due to features such as low-cost, easy surface modification with different materials, and high sensitivity. A fast and simple method to fabricate enhanced ePADs using pencil-drawing which involves the CO2 laser treatment of the carbon surface deposited on paper is described. The electrochemical performances of the devices were evaluated using cyclic voltammetry (CV) with different redox probes and electrochemical impedance spectroscopy (EIS). The electrochemical results show that a treated surface presents a lower resistance to charge transfer and changes the approach of the probe and the overlap of its orbitals with the electrode. To investigate the effects of the laser treatment process, chemical and structural characteristics were evaluated using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results indicated that laser treatment promoted the restoration of carbon–carbon double bonds and removed a thin layer of nanodebris present in commercial pencils, resulting in an improvement of the electrochemical kinetics. As a proof-of-concept, the Pencil-Drawing Electrode (PDE) was used for the detection and quantification of furosemide (FUR) in a sample of synthetic urine, exhibiting a limit of detection (LOD) of 2.4 × 10−7 mol L−1. The percentages of recovery of the FUR added to the samples A and B were 95% and 110%, respectively. The analysis using CO2 laser-treated PDE resulted in a fast, simple, and reliable method for this doping agent.

© The Royal Society of Chemistry. In this work, new protic ionic liquids (PILs) with 1-ammonium-2-propanol cation and nine different anions: formate (For), acetate (Ac), lactate (Lac), trifluoroacetate (TFA), chloroacetate (ClA), trichloroacetate (TClA), 3-chloropropionate (3-ClP), 4-chlorobutyrate (4-ClB) and mandelate (Man) were prepared in order to study their antimicrobial activity and possible application for fungi and bacteria removal from deteriorated paper heritage. Ten filamentous fungal strains isolated from specific pigmented area of the damaged books: Trichoderma sp., Cladosporium sp., Penicillium sp.(1-3), Penicillium citrinum, Aspergillus sp.(1,2), Aspergillus flavus, Fusarium graminearum, eight Gram positive and Gram negative ATCC bacterial strains: B. subtilis(6633), S. aureus(6538), E. faecalis(19433), K. rhizophila(9341), E. coli(11229), S. enteritidis(13076), P. mirabilis(12453), P. aeruginosa(15692) and two yeast Candida strains: Candida albicans(ATCC 10231) and Candida albicans(L) were used in this study. The results indicated that antimicrobial activity of selected ionic liquids is significantly affected by the size and specific functional groups in the anion structure. These facts opened the possibility for molecular design of new ionic liquids with strong inhibition properties against the specific bacterial, mould and yeast strains. The significant antimicrobial properties observed in this research suggest that studied PILs may have potential applications in the paper art and artefact cleaning and conservation replacing thus, conventional solvents and organic substances that are toxic for humans and environment.

Semiconductor heterostructures are regarded as an efficient way to improve the photocurrent in photoelectrochemical cell-type (PEC) photodetectors. To better utilize solar energy, TiO2@Sn3O4 arrays vertically aligned on carbon fiber papers were synthesized via a hydrothermal route with a two-step method and used as photoanodes in a self-powered photoelectrochemical cell-type (PEC) photodetector under visible light. TiO2@Sn3O4 heterostructures exhibit a stable photocurrent of 180 μA, which is a 4-fold increase with respect to that of the Sn3O4 nanoflakes on carbon paper, and a two-order increase with respect to that of the TiO2 NRs arrays. The evolution of hydrogen according to the photo-catalytic water-splitting process showed that Sn3O4/TiO2 heterostructures have a good photocatalytic hydrogen evolution activity with the rate of 5.23 μmol h−1, which is significantly larger than that of Sn3O4 nanoflakes (0.40 μmol h−1) and TiO2 nanorods (1.13 μmol h−1). Furthermore, the mechanism behind this was discussed. The detector has reproducible and flexible properties, as well as an enhanced photosensitive performance.

This report describes the systematic combination of structurally diverse plasmonic metal nanoparticles (AgNPs, AuNPs, Ag core–Au shell NPs, and anisotropic AuNPs) on flexible paper-based materials to induce signal-enhancing environments for surface enhanced Raman spectroscopy (SERS) applications. The anisotropic AuNP-modified paper exhibits the highest SERS response due to the surface area and the nature of the broad surface plasmon resonance (SPR) neighboring the Raman excitation wavelength. The subsequent addition of a second layer with these four NPs (e.g., sandwich arrangement) leads to the notable increase of the SERS signals by inducing a high probability of electromagnetic field environments associated with the interparticle SPR coupling and hot spots. After examining sixteen total combinations, the highest SERS response is obtained from the second layer with AgNPs on the anisotropic AuNP paper substrate, which allows for a higher calibration sensitivity and wider dynamic range than those of typical AuNP–AuNP arrangement. The variation of the SERS signals is also found to be below 20% based on multiple measurements (both intra-sample and inter-sample). Furthermore, the degree of SERS signal reductions for the sandwiched analytes is notably slow, indicating their increased long-term stability. The optimized combination is then employed in the detection of let-7f microRNA to demonstrate their practicability as SERS substrates. Precisely introducing interparticle coupling and hot spots with readily available plasmonic NPs still allows for the design of inexpensive and practical signal enhancing substrates that are capable of increasing the calibration sensitivity, extending the dynamic range, and lowering the detection limit of various organic and biological molecules.

PEDOT:PSS organic printed electronics chemical interactions with the ink-receiving layer (IRL) of monopolar inkjet paper substrates and coating color composition were evaluated through Raman spectroscopy mapping in Z (depth) and (XY) direction, Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDS). Other evaluated properties of the IRLs were pore size distribution (PSD), surface roughness, ink de-wetting, surface energy and the impact of such characteristics on the electronics performance of the printed layers. Resin-coated inkjet papers were compared to a multilayer coated paper substrate that also contained an IRL but did not contain the plastic polyethylene (PE) resin layer. This substrate showed better electronic performance (i.e., lower sheet resistance), which we attributed to the inert coating composition, higher surface roughness and higher polarity of the surface which influenced the de-wetting of the ink. The novelty is that this substrate was rougher and with somewhat lower printing quality but with better electronic performance and the advantage of not having PE in their composite structure, which favors recycling. © 2019 The Royal Society of Chemistry., Knowledge Foundation; AForsk Foundation [18-281]; J. Gust. Richert Foundation [2018-00459]; Knut and Alice Wallenberg Foundation through the Wallenberg Wood Science Center; Swedish Graphic Companies Federation; Treesearch.se

In the history of civilization, Xuan paper with its superior texture, durability and suitable characteristics for writing and painting, has played an important role in the dissemination of culture and art. Xuan paper has won the reputation of "the king of paper that lasts for 1000 years" and was inscribed on the Representative List of the Intangible Cultural Heritage of Humanity by the Educational, Scientific and Cultural Organization of the United Nations in 2009. However, the surface of the commercial unprocessed Xuan paper has a large number of large-sized pores with a poor resistance to water, allowing ink droplets to easily spread during the writing and painting process. In this study, we report a new kind of nanocomposite Xuan (HNXP) paper comprising ultralong hydroxyapatite (HAP) nanowires and plant cellulose fibers with unique ink wetting performance, high whiteness and excellent durability. The as-prepared HNXP paper sheets with various weight ratios of ultralong HAP nanowires ranging from 10% to 100% are all superhydrophilic with a water contact angle of zero. In contrast, the ink contact angle of the HNXP paper can be well controlled by adjusting the weight ratio of ultralong HAP nanowires, and the ink contact angle of the HNXP paper increases with increasing weight ratio of ultralong HAP nanowires. The experimental results show the unique ink wetting behavior of the as-prepared HNXP paper, which is absent in the traditional Xuan paper. This new kind of nanocomposite Xuan paper comprising ultralong hydroxyapatite nanowires and plant cellulose fibers is promising for applications in calligraphy and painting arts.

This paper demonstrates a new and simplified configuration for capillary electrophoresis-amperometric detection (CE-AD) using a paper microfluidic chip incorporating inexpensive wax printing and screen printing based methods and then used for electrophoretic separation and simultaneous in-channel amperometric detection of three clinically relevant neurochemicals in a single run without using any decouplers. Detection of neurochemicals e.g., dopamine, epinephrine and serotonin is crucial for early prediction of neurological disorders including Parkinson's, Alzheimer's, dementia, as well as progressive neuro-psychiatric conditions such as depression, anxiety, as well as certain cardiovascular diseases. The plasma concentrations of such neurochemicals are as important as those present in cerebrospinal fluid (CSF) and can be useful for rapid and convenient biosensing. However, simultaneous detection of such neurochemicals in a complex mixture such as human serum requires their separation prior to detection. With the developed microchip, separation and detection of the neurochemicals were exhibited within 650 seconds without pre-treatment and the procedure was validated with spiked fetal bovine serum samples. Beside this, the developed paper microfluidic chip has potential to be integrated in point-of-care diagnosis with onsite detection ability. Moreover, the use of a straight channel capillary, a screen-printed carbon electrode without decoupler, in-channel amperometric detection and low sample volume requirements (2 μL) are shown as additional advantages.

A graphene/silicon composite paper is considered as a promising anode material for flexible batteries. Herein, a highly conductive, flexible, self-supporting, and binder-free graphene/Si composite paper has been prepared via in situ iodine doping and simultaneous reduction of a graphene oxide/silicon composite slice with a solution of hydrohalic (HI) acid as a reducing agent. The in situ iodine doping not only increases the electrical conductivity of the graphene/silicon composite paper, but also improves the strength of the graphene matrix; this results in high capacity and enhanced cycling stability. The in situ iodine-doped composite paper is used as a flexible, self-supporting, and binder-free electrode. The composite paper exhibits a stable capacity retention of 805 mA h g−1 after 100 cycles and an enhanced rate capability, which shows superior performance as compared to the common thermally reduced rGO/Si composites. The high flexibility and high conductivity as well as improved electrochemical performance of this binder-free self-supporting paper anode make it attractive for LIB applications in flexible storage devices.

In the present study, the performance of catalytic wet oxidation (CWO) was investigated for the treatment of two simulated pulping effluents (with chemical oxygen demand (COD) = 15 000 and 17 000 mg L-1, respectively) from large and small scale pulp and paper mills. CWO was performed in a 0.7 L capacity high pressure reactor at 190 degrees C temperature and 0.9 MPa oxygen partial pressure for 3 h duration with activated carbon (AC) supported Cu-Ce catalyst. More than 70% reduction in chemical oxygen demand (COD) and 90% color removal from the wastewaters were achieved during CWO. The biodegradability ratio of wastewater samples was improved to 0.52 from the initial values of 0.26 and 0.31, respectively. The conversion of lignin after CWO was confirmed by nuclear magnetic resonance analysis. Homo-catalytic oxidation equally contributed to organics degradation during the hetero-catalytic reaction. The detailed results on metal leaching, hydrothermal treatment without oxygen and catalyst reuse are also presented.

Paper is a permeable porous material composed of a solid network of fibers. It is cheap, abundant, disposable and recyclable and has self-powered fluid wicking properties that are useful in building analytical devices. Paper-based cell assays are still in their infancy compared with enzyme- and protein-based analyses. For the first time, we show the potential of rice paper (an organic paper specifically used in Chinese calligraphy) for building cell analysis platforms. Rice paper's solution wicking and surface characterizations prove that it has a similar chemical configuration as that of a standard Whatman filter paper. Moreover, lactate dehydrogenase (LDH) release assay and WST-1 cell growth assay show that rice paper has better cell-compatibility features and improved cell distribution. The cell anchors and spreads along the cellulose fiber of the rice paper, whereas the porous rice paper matrix provides a sufficient surface area for cell growth. Cell-based immunohistochemistry was conducted to measure the expression of O-linked N-acetylglucosamine (O-GlcNAc) protein on prostate cancer cell DU145. An enhanced colorimetric signal was observed from cells grown on rice paper-based cell culture platform than those grown on 2D culture dish. The feasibility of fabricating rice paper with both direct crafting and wax printing—as well as on-paper cell immunoassays for on-demand applications—confirms the potential of rice paper as a new substrate for building paper devices for cell biology studies.

A much simpler and broadly applicable dip-coating method using silica nanoparticles and a silane coupler for preparing hydrophobic paper is presented. Both producing surface hydrophobization without additional surface treatment and increasing the adhesive force between the paper and the coated material can be realized by an almost one-step procedure. The modified filter paper could not only selectively permeate oil from a mixture, but also exhibits superior recyclability, indicating its great potential application in the oil–water separation area.

Here, a ratiometric fluorescent test paper for the visual and on-site determination of environmental fluoride ions was fabricated by inkjet-printing of the as-prepared “ink” onto a filter paper. The “ink” was prepared by mixing the fluoride-sensitive organic probe (C-TIPS) with red CdTe quantum dots (QDs) in an optimal proportion. The designed fluorescent fluoride probe shows a turn-on effect in the presence of fluoride ions. With the aid of thee red fluorescence of CdTe QDs, the test paper exhibited a distinguishable fluorescence color change from red to purple to blue under a UV lamp. The as-prepared ratiometric-fluorescent test paper displayed a superior sensitivity and visual effectiveness to quantify fluoride ions, with a detection limit of 0.285 μM which is lower than the World Health Organization (WHO) defined limit (79 μM). Moreover, the test paper is highly applicable for the detection of fluoride ions in natural waters in a very simple, cost efficient and on-site way.

Graphene/Co3O4 nanowire composite films were successfully synthesized using a simple, three-step treatment, and the effect of the Co3O4 nanowire content on the electrochemical properties of the composite films was studied. The one-dimensional Co3O4 nanowires were homogeneously embedded and dispersed between prepared graphene papers, forming a layered graphene/Co3O4 nanowire hybrid structure. These composite films exhibited better electrochemical properties than previously reported ones, such as graphene/CNT, where carbon spheres existed in the graphene composites, which were fabricated using the same method but without the Co3O4 nanowires. The addition of a small amount of Co3O4—typically 8 : 1 by weight (reduced graphene oxide (RGO) : Co3O4)—to form thick RGO/Co3O4 sandwiches in the form of papers resulted in an excellent specific charge capacity of 278.936 C g−1 at a scan rate of 5 mV s−1. These results indicate the potential of the composite for the development of highly capacitive energy storage devices for practical applications.

While surface-enhanced Raman scattering (SERS) is a useful technique for the rapid and sensitive detection of biochemical compounds, conventional SERS chips suffer from high cost, complicated fabrication, inefficient sample collection processes and being not biocompatible. Here, we developed a facile, low-cost and highly sensitive gold nanostar (AuNS) immobilized paper-based SERS substrate that can be easily prepared in any laboratory. We performed studies on the paper materials, immobilization strategies, and SERS acquisition conditions to optimize the SERS enhancement and demonstrated that an optimized SERS signal was obtained from a dry substrate and wet analyte configuration suitable for rapid point-of-care detection. Using crystal violet (CV) as the Raman probe molecule, the optimized SERS substrate was prepared by having multiple drops of ∼100 pM of sodium citrate-treated colloidal AuNS on common laboratory filter paper before acquiring SERS spectra of CV freshly dripped onto the pre-dried AuNS-filter paper substrate. The optimized AuNS-filter paper substrate exhibited a SERS enhancement factor higher than that of two commercial Au/Ag-based SERS chips, with a detection limit of 1 nM CV and a SERS enhancement factor of up to 1.2 × 107. Such an optimized dry substrate and wet analyte configuration meant that the paper-based SERS substrate could be stored before use and Raman acquisition could be performed immediately without the need for the sample to dry. This makes the AuNS-filter paper substrate a simple and low-cost tool for trace level detection of biochemical species in a rapid, sensitive and non-destructive manner.

This contribution reports a novel “Magnetic Paper – Based ELISA” using core–shell magnetite@polydopamine nanoparticles supported on a Whatman paper-like new solid immunoassay platform specifically for IgM-dengue antibodies recognition as the proof-of-concept target for antibodies isotype IgM detection. Affordable procedures to deposit magnetite nanoparticles on cellulose paper sheets (Whatman type-1 and ss903) and to conjugate such nanoparticles with anti human-IgM antibodies using polydopamine as linker are reported. Structural features, magnetic behavior, coating homogeneity, and the nanoparticles/linked antibodies ratio were determined. Additionally, “Magnetic Paper – Based ELISA” for IgM-dengue antibodies detection provides a system with improved analytical response (two orders more sensitive with a 700 times lower limit of detection (LOD) than traditional ELISA or using magnetic beads without depositing), appropriate accuracy for real sample detection, low cost, easy manufacturing, and effortless and easy handling.

We have prepared a microfluidic paper-based analytical device (μPAD) for the determination of cysteine and homocysteine based on 1,5-diphenylcarbazide-capped silver nanoparticles. The μPAD was developed to identify and quantify the levels of cysteine and homocysteine. The proposed μPAD enabled the detection of cysteine and homocysteine using a colorimetric reaction based on modified silver nanoparticles. The color of the modified AgNPs in the test zone immediately changed after the addition of cysteine and homocysteine. Based on this change, the quantification of these two amino acids was achieved using an RGB color model and ImageJ software. Under optimized conditions, the proposed device enabled the determination of cysteine in the 0.20–20.0 μM concentration range with a limit of detection (LOD) of 0.16 μM. In addition, the LOD of homocysteine was calculated to be 0.25 μM with a linear range of 0.50–20.0 μM. In this work, we focused on the use of the μPAD for the analysis of a series of human urine samples.

A novel and flexible oxygen sensing patch was successfully developed for wearable, industrial, food packaging, pharmaceutical and biomedical applications using a cost-efficient and rapid prototypable additive inkjet print manufacturing process. An oxygen sensitive ink was formulated by dissolving ruthenium dye and ethyl cellulose polymer in ethanol in a 1 : 1 : 98 (w/w/w) ratio. The patch was fabricated by depositing the oxygen sensitive ink on a flexible parchment paper substrate using an inkjet printing process. A maximum absorbance from 430 nm to 480 nm and a fluorescence of 600 nm was observed for the oxygen sensitive ink. The capability of the oxygen sensitive patch was investigated by measuring the fluorescence quenching lifetime of the printed dye for varying oxygen concentration levels. A fluorescence lifetime decay (τ) from ≈4 μs to ≈1.9 μs was calculated for the printed oxygen sensor patch, for oxygen concentrations varying from ≈5 mg L−1 to ≈25 mg L−1. A sensitivity of 0.11 μs mg L−1 and a correlation coefficient of 0.9315 was measured for the printed patches. The results demonstrated the feasibility of employing an inkjet printing process for the rapid prototyping of flexible and moisture resistant oxygen sensitive patches which facilitates a non-invasive method for monitoring oxygen and its concentration levels.

Here we describe an aqueous asymmetric supercapacitor assembled using Co(OH)F nanorods on Ni foam (Co(OH)F@NF) as the positive electrode and layered Ti3C2Tx paper on Ni foam (Ti3C2Tx@NF) as the negative electrode. The Co(OH)F@NF was fabricated by a facile hydrothermal process. The nanorods were constructed as three-dimensional networks with stable structures and good durability in electrochemical reactions. As expected, the Co(OH)F@NF exhibited excellent capacitance (1265 mF cm−2 at 1 mA cm−2) and wonderful rate performance (90% from 1 to 10 mA cm−2). The Co(OH)F@NF//Ti3C2Tx@NF asymmetric supercapacitor devices showed high capacitance of 376 mF cm−2 and excellent rate capacity of 91% retention. When the two Co(OH)F@NF//Ti3C2Tx@NF devices were combined in series, a red led bulb could be lit for 12 minutes, further corroborating the possibility of the devices being used for practical applications.

4-Nitrophenol (4-NP) is a promulgated priority pollutant, which can cause a negative impact on human health. The development of a direct and effective technique for the rapid detection and screening of 4-NP is, therefore, of urgent need. In this study, the blue luminescent sulfur-doped graphene quantum dots (S-GQDs) with a size of 1-5 nm are fabricated using a one-step pyrolysis procedure in the presence of citric acid and 3-mercaptosuccinic acid. The S-GQDs exhibit a strong emission band at 450 nm under the excitation of 330 nm UV light. 4-NP can serve as the fluorescence quencher by the π-π interaction with S-GQD, resulting in the linear decrease in fluorescence intensity after the addition of various 4-NP concentrations ranging from 10 nM to 200 μM. The S-GQDs serve as the sensing probe to enhance the analytical performance on 4-NP detection with the limit of detection values of 0.7 and 3.5 nM in deionized water and wastewater, respectively. The S-GQD based sensing platform can be used to detect 4-NP in different matrices of water and wastewater. In addition, the detected percentages of spiked 4-NP concentrations in the presence of different matrices and interferences are in the range of (98 ± 5)-(108 ± 2)%. Moreover, the S-GQD based paper sensor can rapidly screen 4-NP in wastewater within 1 min. Results obtained in this study clearly demonstrate the superiority of S-GQDs as a promising fluorescence probe for highly sensitive and selective detection of a wide concentration range of 4-NP in deionized water and wastewater.

The addition of G- and V-series organophosphorus chemical warfare agents and simulants to a paper-based assay of a dual-luminescent Ir(iii)/Eu(iii) dyad generated different emissive responses between the classes and compound types. The emission responses are complex and based not only on altering the balance between red Eu(iii)-based and blue Ir(iii)-based luminescent components, but also incorporate other factors such as analyte volatility, concentration and UV absorption. The extent of this emission colour change was analysed colorimetrically and related to the change in RGB output over time.

Solvent-free electrically conductive composites have been applied to flexible electronics to obtain high electrical conductivity. However, some of the proposed composites have low electrical conductivities and are unable to meet the requirements of commercial printable electronics. In this study, solvent-free electrically conductive Ag/EVA (ethylene vinyl acetate) composites for paper-based printable electronics were prepared by a thermal melting method. The properties of these electrically conductive Ag/EVA composites, including particle sizes, morphologies and phase purities of the flake silver flake powders, were investigated using a particle size analyzer, scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results showed that nanometer-thick flake silver flake powders with smooth and flat surfaces were made by the nanofilm transition technique. These obtained powders were able to form smooth face-to-face contacts, which facilitated the formation of an excellent conductive network in the conductive system. Dynamic mechanical analysis (DMA) was conducted to investigate the mechanical properties of EVA and Ag/EVA composites. A Fourier transformation infra-red (FTIR) spectrometer, laser micro-Raman spectrometer and thermogravimetric analyzer were used to analyze the organic functional groups, glass transition temperatures and thermal weight losses of the EVA resin and solvent-free electrically conductive composites. The solvent-free electrically conductive Ag/EVA composite, which contained 55 wt% of the as-prepared flake silver flake powders, was found to have an extremely low volume resistivity of 1.23 × 10−4 Ω cm as well as excellent bending performance and adhesion. These features indicate the great potential of these composites for application in printed electronics.

This study proposes a novel method for the fabrication of paper-based microfluidic devices using laser-induced selective thermal reflow for wax penetration. A layer of wax was evenly deposited on the front side of a filter paper; then a low-cost diode laser was used to scan the designed area from the back side of the filter paper. At the laser irradiated spot, the wax was heated, melted down and penetrated through the whole thickness of the filter paper, and formed hydrophobic barriers on the hydrophilic cellulose fibers. The patterned hydrophobic wax barriers on the filter paper defined the flow path of the fluid for the paper-based microfluidic device. Compared with conventional two-step (deposit and reflow) approaches for paper-based microfluidics using wax barriers, e.g. wax printing, stamping or photolithography, the proposed fabrication protocol achieved wax patterning and reflow simultaneously, conducted during the laser scan process, and without the requirement for any sophisticated instruments or a cleanroom environment. A series of tests were also conducted for the characterization of the proposed paper-based microfluidic device fabrication technique. The fabrication technique used in this approach could have broad application potential in point-of-care diagnosis and testing, especially for applications in the developing world.

Printing of electronic devices on a paper substrate using 2D graphene-based ink is an opening gate to innovative applications, where devices would be biodegradable, eco-friendly and can be disposed of with negligible impact on the environment. A resistor is a key element of electronic devices and their application area depends upon its power rating and temperature coefficient of resistance (TCR). In this work, in house developed graphene ink is successfully utilized to fabricate a paper-based resistor using a bar coating technique. Dimensional patterning with precise known values of resistance is achieved using a laser with freedom of shape and size which has been explored for the first time on a paper substrate. The resistor has potential to handle ∼7 W power at room temperature with capacity to withstand up to 200 V which is the highest among reported printed resistors. A dual, low and high TCR is observed, correspondingly in cold (173 K to 300 K) and hot (300 K to 373 K) temperature regions with an activation energy Ea of ∼8 meV for the cold region which is 375 percent lower than the hot region (∼30 meV). The dual TCR behaviour is of great importance for application as a stable resistor up to room temperature, and as a thermistor above room temperature.

A flexible free-standing nitrogen-doped graphene paper (N-GP) is fabricated via a facile hydrothermal approach with doping reaction occurring at the solid/gas interface of graphene oxide and ammonia vapor. Ammonia not only facilitates the doping of oxidized graphene paper efficiently with a nitrogen doping level of ca. 6.81%, but also promotes its reduction. The electrochemical properties of N-GP as an anode of lithium ion batteries (LIB) are evaluated and N-GP delivers almost doubled reversible discharge capacity compared to the undoped graphene paper (GP) as well as a good cyclic stability and rate performance. The proposed strategy to realize simultaneous reduction and nitrogen doping of graphene oxide via hydrothermal approach at the solid/gas interface offers a green and facile solution to modify graphene paper with desired electrochemical performances for LIB application.