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Rapid detection of pesticides in fruits is an ongoing challenge. The objective of the present study was to develop novel fluorescent microfluidic paper chips for specific recognition and sensitive detection of the pesticide 2,4-D through the electron-transfer-induced fluorescence quenching mechanism. CdTe quantum dots (QDs) were deposited onto cellulose paper (base material) to yield imprinted paper chips (paper@QDs@MIPs). This method allows the transferability of the molecularly imprinted fluorescence sensor from the liquid phase to the solid phase (paper base) for rapid and portable analysis. The resultant imprinted paper chips were effectively characterized, and they exhibited ideal ordered spatial network structure, chemical stability, and fluorescence property. The paper@QDs@MIPs showed that 2,4-D binding significantly reduced the fluorescence intensity within less than 18 min, and it achieved satisfactory linearity in the range of 0.83–100 μM and high detectability of 90 nM. The recognition specificity for 2,4-D relative to its analogues was shown, and the imprinting factor was 2.13. In addition, the recoveries of the spiked bean sprouts at three concentration levels ranged within 94.2–107.0%, with a relative standard deviation of less than 5.9%. Collectively, the device provided an effective platform for rapid recognition, convenience, and detection of trace food pollutants in complex matrices, thereby ensuring food safety and further promoting surface imprinting studies. [ABSTRACT FROM AUTHOR]

Herein, Cu-doped Co-ZIF nanoplate arrays are uniformly grown on a commercial paper towel substrate first. After a subsequent annealing treatment, well-defined Cu-doped Co/CoO nanoparticles embedded in N-doped carbon hybrid nanoplate arrays supported on the carbon paper substrate (denoted as Cu-doped Co/CoO/NC NPAs@CP) are obtained, which exhibit excellent performance as a low-cost, lightweight and binder-free anode for lithium ion storage. [ABSTRACT FROM AUTHOR]

Commercial paper as an indispensable material in our daily life is extremely easily destroyed by water and fire. And obtaining paper with the writable, non-flammable and superhydrophobic properties is still a challenging issue. Inspired from nature, biomimetic nanowires made from hydroxyapatite (HAP) can be used as raw materials to fabricate functional paper. In this study, we present a superior, fire-resistant and repairable superhydrophobic PFDS-paper@ZnO exhibiting remarkable oil absorption–combustion performance. In particular, the layered structure of the paper might be the reason of its excellent superhydrophobicity even after 20 abrasion cycles with sandpaper (400 cW). In contrast, the common paper was destroyed after 5 abrasion cycles with sandpaper under identical conditions. It was observed that the intrinsic fire-resistant nature of the paper was expected to reduce the risk of fire and might be used as an absorbent for flammable oil. On the one hand, such burnt paper can recover its original superhydrophobicity by facile modification after multiple cycles, achieving the repairable performance of its superhydrophobic surface. On the other hand, the burnt paper without subsequent modification exhibits superhydrophilicity in air and also underwater superoleophobicity, which can be used for efficient surfactant-stabilized oil-in-water emulsion separation. This study expands the potential applications of functional paper, which might be a breakthrough for traditional papermaking industries. [ABSTRACT FROM AUTHOR]

Cellular viability measurements quantify decreased proliferation or increased cytotoxicity caused by drug candidates or potential environmental toxins. Direct viability measures count each cell to provide an accurate readout. This approach can prove analytically challenging and time-consuming when cells are maintained in 3D structures akin to tissues or solid tumors. While less labor-intensive, indirect viability measures can be less accurate due to the heterogeneous structural and chemical microenvironment that arises when cells are maintained in tissue-like architectures and in contact with extracellular matrices. Here we determine the analytical figures of merit of five indirect viability assays in the paper-based cell culture platform we continue to develop in our laboratory: calcein-AM staining, the CellTiter-Glo assay, imaging fluorescent protein expression, propidium iodide staining, and the resazurin assay. We also determined the compatibility of each indirect assay with hypoxic conditions, intra-experimental repeatability, inter-experimental reproducibility, and ability to predict a potency value for a known antineoplastic drug. Our results show that each assay has benefits and drawbacks to consider when choosing the appropriate readout to answer a particular research question. We also highlight that only one indirect readout is unaffected by hypoxia, a commonly overlooked variable in cell culture that likely yields inaccurate viability measures. [ABSTRACT FROM AUTHOR]

Solar-driven evaporators (SDEs) have attracted increasing attention in producing potable freshwater. Developing a multitasking SDE with stable self-floating performance, long-term salt resistance, effective heat management, pollutant degradation capability and good scalability for industrial production is significant but challenging. This work demonstrates the fabrication of a cellulose paper-based SDE with rough photothermal coating, controlled Janus wettability and a hierarchical Fenton catalyst for advanced solar desalination. Through the surface deposition of an urchin-like nanocatalyst and polypyrrole coating, a rough photothermal top layer for enhanced light trapping (98.6%) and a Fenton catalytic bottom layer for in situ pollutant degradation (98.1%) are constructed. Benzophenone-terminated polydimethylsiloxane is designed to realize facile asymmetric photo-grafting on porous paper, which further endows the evaporator with controlled Janus wettability, stable self-floating performance, long-term salt resistance, efficient heat management and rapid water transfer. Benefiting from such advantages, high solar-to-vapor efficiency (95.3%) and evaporation rate (1.88 kg m−2 h−1) are obtained. This cellulose paper-based evaporator also exhibits mechanical flexibility, portability and cost-effectiveness. Furthermore, the preparation process, including simple deposition and cleaner photo-grafting, is feasible and scalable for industrial production. This work provides innovative concepts for developing advanced paper evaporators to realize multitasking solar desalination. [ABSTRACT FROM AUTHOR]

A new fluorescent probe (T2) containing pyrene-hydrazone furan moieties was developed and synthesized through a two-step process and then coated onto filter paper to form a paper-based sensor for TNT detection. The T2 sensor uses photoinduced electron transfer (PET) induced fluorescence quenching to detect TNT. The sensor properties were studied using fluorescence spectra, 1H-NMR titration and density functional theory (DFT) calculations. The reaction time of the T2 paper-based sensor for TNT detection was only five minutes. A smartphone was used as an alternative instrument to detect fluorescence signals and a typical image J-processing application was employed to evaluate the grayscale values of the smartphone-captured photographs. The sensor showed a linear concentration range for TNT detection of between 30–500 μM and a detection limit of 30 μM. The T2 paper-based sensor was found to have high selectivity and sensitivity, and it can successfully detect and image TNT in actual samples. This research demonstrates that a T2 paper-based sensor is a promising alternative for TNT detection owing to its short reaction time, high selectivity, sensitivity, and easy applicability. [ABSTRACT FROM AUTHOR]

Bioelectrochemical technologies have attracted significant scientific interest because the effective bacterial electron exchange with external electrodes can provide a sustainable solution that joins environmental remediation and energy recovery. Multispecies electroactive bacterial biofilms are catalysts that will drive the operation of bioelectrochemical devices. Unfortunately, there is a lack of understanding of key mechanisms determining their electron-generating capabilities and syntrophic relations within microbial communities in biofilms. This is because there are no universally standardized models for simple, rapid, reliable, and cost-effective fabrication and characterization of electroactive multispecies biofilms. The heterogeneous and long-term nature of biofilm formation has hampered the development of those models. This work develops novel biofabrication and analysis platforms by creating innovative, paper-based 3-D systems that accurately recapitulate the structure, function, and physiology of living multispecies biofilms. Multiple layers of paper containing bacterial cells were stacked to simulate different layered 3-D biofilm models with defined cellular compositions and microenvironments. Overall bacterial electrogenic capabilities through the biofilm structures were characterized by thoroughly monitoring collective electron flows through different external resistors. Changes in the type of species and order of stacking created biofilm modeling which allowed for the study of their electrogenic performance via variation in electron flow rate output. Furthermore, multi-laminate structures allowed for straightforward de-stacking and layer-by-layer separation for analyses of pH distribution and cellular viability. Our multi-laminate structures provide a new strategy for (i) controlling the biofilm geometry of 3-D bacterial cultures, (ii) monitoring the microbial electoral properties, and (iii) constructing an artificial biofilm layer by layer. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) tumor models have gained increased attention in life-science applications as they better represent physiological conditions of in vivo tumor microenvironments, and thus, possess big potential for guiding drug screening studies. Although various techniques proved effective in growing cancer cells in 3D, their procedures are typically complex, time consuming, and expensive. Here, we present a versatile, robust, and cost-effective method that utilizes a paper platform to create cryopreservable high throughput arrays of 3D tumor models. In the approach, we use custom 3D printed masks along with simple chemistry modifications to engineer highly localized hydrophilic 'virtual microwells', or microspots, on paper for 3D cell aggregation, surrounded by hydrophobic barriers that prevent inter-microspot mixing. The method supports the formation and cryopreservation of 3D tumor arrays for extended periods of storage time. Using MCF-7 and MDA-MB-231 breast cancer cell lines, we show that the cryopreservable arrays of paper-based 3D models are effective in studying tumor response to cisplatin drug treatment, while replicating key characteristics of the in vivo tumors that are absent in conventional 2D cultures. This technology offers a low cost, easy, and fast experimental procedure, and allows for 3D tumor arrays to be cryopreserved and thawed for on-demand use. This could potentially provide unparalleled advantages to the fields of tissue engineering and personalized medicine. [ABSTRACT FROM AUTHOR]

From HIV and influenza to emerging pathogens like COVID-19, each new infectious disease outbreak has highlighted the need for massively-scalable testing that can be performed outside centralized laboratory settings at the point-of-care (POC) in order to prevent, track, and monitor endemic and pandemic threats. Nucleic acid amplification tests (NAATs) are highly sensitive and can be developed and scaled within weeks while protein-based rapid tests require months for production. Combining NAATs with paper-based detection platforms are promising due to the manufacturability, scalability, and simplicity of each of these components. Typically, paper-based NAATs consist of three sequential steps: sample collection and preparation, amplification of DNA or RNA from pathogens of interest, and detection. However, these exist within a larger ecosystem of sample collection and interpretation workflow, usability, and manufacturability which can be vastly perturbed during a pandemic emergence. This review aims to explore the challenges of paper-based NAATs covering sample-to-answer procedures along with three main types of clinical samples; blood, urine, and saliva, as well as broader operational, scale up, and regulatory aspects of device development and implementation. To fill the technological gaps in paper-based NAATs, a sample-in-result-out system that incorporates the integrated sample collection, sample preparation, and integrated internal amplification control while also balancing needs of users and manufacturability upfront in the early design process is required. [ABSTRACT FROM AUTHOR]

The integration of SERS-active enhanced agents with the functional supporting substrate of paper to expand the application of SERS technology has attracted much attention. However, it is still highly desired to improve the detection ability of paper-based SERS substrates for complex mixtures to extend the application of SERS further in real-word scenarios. Herein, we assemble raspberry-like bimetallic Au@AgNP nanostructures with multiple hotspots on an arrow-shaped paper strip to detect complex samples sensitively. Raspberry-like bimetallic nanoparticles show more sensitive and stable SERS performance than spherical AgNPs, which improves the practicability of SERS-based paper substrates in realistic situations. The intervention of charge gradients as well as designing of arrow-shaped non-interference tips yields the substrate-integrated shunt and preconcentration abilities for mixture samples. Thus, this SERS-based paper substrate may provide a promising way for the determination of complex samples in food security and environmental protection. Our work will have a positive impact in pushing forward the application process of SERS technology in real-word scenarios. [ABSTRACT FROM AUTHOR]

A novel method of coupling electrochemistry (EC) with mass spectrometry (MS) is illustrated with a paper-based electrochemical cell supported by carbon nanotubes (CNTs). The electrochemically formed ions, created at appropriate electrochemical potentials, are ejected into the gas phase from the modified paper, without the application of additional potential. The electrochemical cell was fabricated by using a rectangular CNT-coated Whatman 42 filter paper with printed electrodes, using silver paste. This was used for studying the electrochemical conversion of thiols to disulfides, and the functionalization of polycyclic aromatic hydrocarbons (PAHs), which involve S–S and C–C bond formations, respectively. We also demonstrate the versatility of the set-up by utilizing it for the detection of radical cations of metallocenes, monitoring the oxidation of sulfides through the detection of reactive intermediates, and the detection of radical cations of PAHs, all of which occur at specific applied potentials. Finally, the applicability of this technique for qualitative and quantitative analyses of environmentally relevant molecules has been demonstrated by studying the electrochemical oxidation of glucose (Glu) to gluconic acid (GlcA) and saccharic acid (SacA). [ABSTRACT FROM AUTHOR]

Even in the age of electronic information, paper has always played an important role in most fields. Conventional cellulose-based paper is highly porous, rough, hydrophilic and possesses a single function. In this review, the development and challenges of cellulose-based paper are illustrated. In this case, inorganic paper can be regarded as the candidate material for the paper-making field. This review aims to summarize the most recent progress on inorganic paper. Significantly, different kinds of inorganic raw materials for designing inorganic paper will be presented, followed by a summary of their emerging applications. The raw materials can be divided into four parts: hydroxyapatite-based, silicon-based, carbon-based, as well as metal–organic framework-based materials. The inorganic paper produced by these raw materials has many applications, such as fire-resistance, pollutant treatment, actuator, flexible electronics and energy storage. The development of inorganic paper may provide new inspiration for the paper-making field. [ABSTRACT FROM AUTHOR]

Recently, paper has gained traction in the biotechnology research field due to its ability to be a substrate for 3D cell culture. In this work, we demonstrate the application of paper-based 3D cell culture for rapid and easy screening of the effect of natural compounds on melanin production. Whatman No. 1 filter paper was used as the substrate for B16F10 melanoma cell culture. The use of paper is beneficial for supporting the 3D structure of cells, which makes the result more reliable due to the similarity to in vivo conditions. Furthermore, paper is beneficial for melanin observation due to melanin's black color, which is easily in situ visualized after it is cultured on white paper. Matrigel was used to encapsulate cells before being pipetted onto the paper to prevent the passing of cells through paper pores. The intensity of melanin can then be observed with the naked eye and analyzed by scanning the paper. The analysis process took only 20 minutes, which is faster than that of the conventional absorbance spectroscopy, owing to the elimination of centrifugation, melanin solubilization, and the absorbance measurement step. The color intensity on the paper showed a direct proportion with increased α-MSH concentrations, confirming that the color on the paper was melanin. The 3D structure of cells was confirmed by using a scanning electron microscope. To demonstrate the application of the paper-based scaffold, paper-based 3D cell culture was used for screening the effects of Kojic acid and Arbutin on melanin production, which showed increased anti-melanogenesis effects with increased concentrations of natural compounds. High cell viability was observed over 120 hours. In conclusion, the developed paper-based scaffold can be used for screening the effect of natural compounds on melanin production, as a rapid and simple method with low cost. [ABSTRACT FROM AUTHOR]

A luminescent trimethylamine (TMA) sensor, PTMA-Ir, has been designed and synthesized through immobilizing a phosphorescent iridium(III) complex on a TMA-imprinted polymer. Detailed study shows that the quenching of phosphorescence of PTMA-Ir can serve as a reporter for the binding of TMA on the imprinting sites, thus providing a sensitive, selective, and rapid detection of TMA in both aqueous solutions and gaseous states. Loading PTMA-Ir on filter paper produced a deposition T-Ir, the phosphorescence of which is quenched within 5 s upon exposure to TMA vapor with detection limits of 9.0 ± 0.1 ppm under argon and 15.0 ± 0.1 ppm in an air atmosphere. This work provided an effective method for establishing an imprinting polymer-immobilized luminescent amine sensor. [ABSTRACT FROM AUTHOR]

Polymers and surfactants are used in many technological and industrial applications such as the manufacture of functional materials and coatings, personal care and pharmaceutical products, food science, paints, anti-icing fluids, tertiary oil recovery and the paper industry. Polymer–surfactant mixtures are particularly important in shampoos and conditioners. However, as in almost every other industry over the past five or more decades, the performance of hair care formulations has been significantly improved by the use of petrochemical-derived ingredients. As a result, cosmetic formulations, and hair care formulations in particular, have been based primarily on polymers and surfactants that are neither renewable, nor derived from environmentally friendly processes, nor have a positive environmental impact. This contrasts with the extensive use of natural and renewable products, mainly plant extracts, in cosmetics in ancient times. Therefore, the substitution of currently used ingredients with others of natural origin has been a top priority for the cosmetic industry over the last two decades, and in order to achieve greater consumer acceptance, it is crucial to maintain and, where possible, improve the technical performance of such products. This paper describes the complexities and challenges of developing greener shampoo and conditioner ingredients and formulations to meet current and future needs, and outlines a methodological approach based on model hair surfaces and a selection of appropriate experimental and numerical techniques to achieve our goals. Some encouraging technical routes using biosurfactants, biopolymers and bio-based polymers are presented, along with the significant opportunity to obtain a wide range of green ingredients through molecular design and well-controlled biotechnological processes. Similar concerns apply to other cosmetic products such as waxes, fragrances, bleaching agents, etc. [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 remarkable properties of layered semiconductor nanosheets (LSNs), such as scalable production, bandgap tunability and mechanical flexibility, have promoted them as promising building blocks for nanoelectronics and bioelectronics. However, it is still a challenge to efficiently control the charge transport in LSNs. Here, we demonstrate a novel LSN field-effect transistor (FET) using ionic paper (i-paper) as a solid-like gate dielectric, achieving a highly efficient ionic control of hole and electron transport in MoS2 and WSe2 LSNs, respectively. The i-paper contains a three-dimensional (3D) nanopore structure that allows ionic liquids (ILs) to infiltrate the LSN surface, providing a very large ion/carrier interfacial region as well as an efficient ion transport channel. We achieve an ultra-high current on–off ratio of over 105 for both p-type and n-type i-paper gated LSN FETs. By directly attaching one common i-paper to both n-type and p-type LSN layers, a flexible LSN-based inverter circuit with a gain of ∼3 is realized. Moreover, high-performance i-paper gated LSN FETs are capable of detecting a temperature change as low as 0.02 K. Our results can hold great implications for wide applications of i-paper gated LSN FETs in the future. [ABSTRACT FROM AUTHOR]

Bacterial meningitis, an infection of the membranes (meninges) and cerebrospinal fluid (CSF) surrounding the brain and spinal cord, is one of the major causes of death and disability worldwide. Higher case-fatality rates and short survival times have been reported in developing countries. Hence, a quick, straightforward, and low-cost approach is in great demand for the diagnosis of meningitis. In this research, a microfluidic fully paper-based analytical device (μFPAD) integrated with loop-mediated isothermal amplification (LAMP) and ssDNA-functionalized graphene oxide (GO) nano-biosensors was developed for the first time for a simple, rapid, low-cost, and quantitative detection of the main meningitis-causing bacteria, Neisseria meningitidis (N. meningitidis). The results can be successfully read within 1 hour with the limit of detection (LOD) of 6 DNA copies per detection zone. This paper device also offers versatile functions by providing a qualitative diagnostic analysis (i.e., a yes or no answer), confirmatory testing, and quantitative analysis. These features make the presented μFPAD capable of a simple, highly sensitive, and specific diagnosis of N. meningitis. Furthermore, this microfluidic approach has great potential in the rapid detection of a wide variety of different other pathogens in low-resource settings. [ABSTRACT FROM AUTHOR]

A novel miniaturized and sustainable platform exploiting two merged paper-based substrates has been applied for the programmable pre-concentration of analytes of interest and electrochemical detection of mercury traces in drinking water using printable sensor strips. This strategy represents a novel versatile possibility in merging humble materials maximizing their impacts on analytical and remediation challenges. [ABSTRACT FROM AUTHOR]

Fluorescence detection of pesticide contamination enables timely control of food safety. This study aims to construct novel and facile microfluidic paper-based analytical devices for the ratiometric fluorescence determination of pesticides. Through fluorescence resonance energy transfer (FRET) of nitrobenzoxadiazole (NBD) and CdTe quantum dots (QDs), the new microfluidic paper chips allowed the rapid and selective visual detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The performance changes of the fluorescent material on solid matrix material were studied in detail. The sensor products exhibited visual observability and fluorescence characteristics. Under optimized conditions, the sensors showed satisfactory linearity in the range of 0.56–80 μM, and achieved detection limits as low as 90 nM. The sensors were successfully applied for soybean sprouts and lake water samples. Four levels of spiked-in 2,4-D concentrations were obtained with high recovery rates ranging from 86.2% to 109.5% and the RSD less than 4.19%. Thus, the present work described the integration of surface imprinted grafts on cellulose paper and ratiometric fluorescence techniques for highly sensitive separation and detection of pesticides in real food and environmental samples. Ultimately, this study paved the way for the development of novel ratiometric fluorescence detection to address food safety and environmental issues. [ABSTRACT FROM AUTHOR]

In this work, zinc-doped carbon dots (Zn-CDs) were anchored on a three-dimensional wheel type paper-based microfluidic chip, and were decorated with 6-mercaptonicotinic acid (MNA) and L -cysteine (L -Cys) for highly sensitive and rapid fluorescence detection of Cu2+. Zn-CDs were first anchored on paper through the amide bonds between the carboxyl groups of the Zn-CDs and the amino groups of the paper. Afterwards, Zn-CDs were decorated with MNA and L -Cys, effectively preventing the Zn-CDs from aggregation. The nitrogen atom on the pyridine ring and the carboxylic acid groups in MNA and L -Cys coordinated with Cu2+ to form a nonfluorescent ground-state complex, causing the fluorescence quenching of the Zn-CDs. The three-dimensional rotary design could simplify the operation process and achieve simultaneous analysis of multiple samples with different concentrations. Under optimal conditions, the fluorescent sensor exhibits linear response for the determination of Cu2+ in the range from 0.1 to 60 μg L−1 with the detection limit (LOD) of 0.018 μg L−1. The proposed strategy provides a novel way for the highly sensitive detection of Cu2+ in a complex water environment. [ABSTRACT FROM AUTHOR]

Fluid manipulation in microfluidic systems is often controlled by active pumps that are relatively large in size and require external power sources which limit their portability and use in limited-resource settings. In this work, portable, detachable, low-cost, and power-free paper pumps with engineered capillary tubes (referred to as "grooves") that can passively drive viscous fluids based on capillary action are presented. The proposed grooved paper pumps are capable of generating a controllable flow of complex biofluids within microfluidic devices with minimal user intervention and no external power sources. The pumping performance of grooved paper pumps in this study is tested with undiluted, unseparated whole blood samples – demonstrating successful transport of approximately 150 μL of blood within an average time of 5 minutes to 50 minutes, depending on their design parameters. Results for the flow rate of grooved paper pumps indicate that the number of grooves created within the porous paper determines the profile of the generated flow rate. The experimental data also show that as the number of grooves in the pumps is increased, the flow rate approaches a constant value for the entire duration of pumping before the pump becomes saturated. The promising performance of grooved paper pumps with whole blood offers potential applications of these small, disposable pumps in point-of-care diagnostics in which time is crucial and access to external power is limited. [ABSTRACT FROM AUTHOR]

Sodium thiocyanate (NaSCN) is a naturally antibacterial component in milk, but excessive consumption of thiocyanate may cause potential risks to human health. Currently available methods for the detection of thiocyanate have some disadvantages such as poor sensitivity and high price. Here, we report a robust and cost-effective method to detect NaSCN based on paper substrates deposited with in situ reduced Ag nanoparticles by surface-enhanced Raman spectroscopy (SERS). Densely packed multilayer AgNPs provide uniform narrow nanogaps, which exponentially enhance the Raman signals. Moreover, these homogeneous narrow hotspots ensure that this method has high sensitivity (the limit of detection is 10−12 mol L−1), a wide linear range (from 10−9 mol L−1 to 10−4 mol L−1), and remarkable reproducibility (the coefficient of variation within a SERS sensor is 6.5%). Spiked milk samples were detected and the recovery rates of NaSCN were in the range of 95.1%–108.0%. This paper-based SERS sensor offers great potential for sensitive NaSCN detection and milk analysis. [ABSTRACT FROM AUTHOR]

Amino acids are closely related to human health, and their rapid determination is important for the rapid diagnosis, timely treatment, and assessment of serious diseases. In this work, we propose a novel paper-based sample-processing device combined with isotope-dilution MS for the fast analysis of 11 amino acids from blood samples. By using an isoelectric focusing electrokinetic separation method, without the aid of carrier ampholytes and the addition of inhibitors, this approach uses only the characteristic of the isoelectric point of the target amino acids to achieve separation and purification from other coexisting components in the medium; it can meet the requirements for mass spectrometry detection. Driven by a DC voltage, a stable and sharp pH gradient (pH 3–10.5 over 5 mm) can be established in a glass-fiber paper-based fluidic channel with a MS-friendly electrolyte. Amphoteric species can be well separated from the complex blood matrix and concentrated into a narrow band in the channel within 2 min, which is 20 times faster than a commercial kit method. The method can be applied to both liquid and dry spot samples, and the cleaned sample band can be simply dissolved for direct IDMS detection in ESI MRM mode. This method is a promising strategy for the rapid MS-based detection of amino acids from serum without pre-separation via liquid chromatography. [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]

Photonic paper with dynamically tunable color has been widely investigated due to its excellent ability to change its optical patterns under external variation. Herein, a UV-responsive metal–insulator–metal (MIM) Fabry-Perot cavity is proposed to prepare dynamic photonic paper through introducing disulfide bonds containing polyurethane as an insulating layer. The as-prepared MIM cavity based photonic paper shows dynamically tunable color variation in almost the whole visible gamut under different UV-irradiation durations. In addition, by simply adjusting the UV-irradiation duration at each point with the aid of a photomask, multicolor patterns could be "written" onto the as-prepared MIM photonic paper. What's more, thanks to the dynamic feature of the disulfide bond, the color patterns on the photonic paper could also be "erased" by thermal treatment, making the photonic paper "rewritable". Together with all these features, the proposed UV-responsive MIM photonic paper would exhibit great potential for application in information anticounterfeiting, dynamic color display devices and environment-friendly inkless color printing. [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-based sensors offer an affordable yet powerful platform for field and point-of-care (POC) testing due to their self-pumping ability and utility for many different analytical measurements. When combined with electrochemical detection using small and portable electronics, sensitivity and selectivity of the paper devices can be improved over naked eye detection without sacrificing portability. Herein, we review how the field of electrochemical paper-based analytical devices (ePADs) has grown since it was introduced a decade ago. We start by reviewing fabrication methods relevant to ePADs with more focus given to the electrode fabrication, which is fundamental for electrochemical sensing. Multiple sensing approaches applicable to ePADs are then discussed and evaluated to present applicability, advantages and challenges associated with each approach. Recent applications of ePADs in the fields of clinical diagnostics, environmental testing, and food analysis are also presented. Finally, we discuss how the current ePAD technologies have progressed to meet the analytical and practical specifications required for field and/or POC applications, as well as challenges and outlook. [ABSTRACT FROM AUTHOR]

With the rapid development of wearable electronic devices, multifunctional ultrarobust, thermoconductive, nonflammable, and electromagnetic interference (EMI) shielding films which are widely utilized to efficiently dissipate heat generated from electronic components are in high demand. The poor scalability and mechanical flexibility of multifunctional papers usually hinder their practical application. In this study, mass-scalable ultrarobust graphene nanoplatelet (GnP) cross-linked aramid nanofiber (ANF) papers with a nacre-bioinspired structure are fabricated via an evaporation-induced self-assembly approach. By chemical cross-linking between two-dimensional GnPs and one-dimensional ANFs in the nacre-bioinspired structure by a phosphorus agent, the excellent toughness and folding endurance of the GnP based ANF papers have been successfully achieved with simultaneous integration of high-level multifunctional properties. Specifically, the ultrarobust GnP based ANF paper with 50 wt% GnP loading exhibits exceptional ultimate tensile strength (437 MPa), Young's modulus (19.7 GPa) and toughness (23.9 MJ m−3) as well as superb folding endurance after 10 000 bending cycles. Moreover, the highly ordered alignment of GnP induced an unprecedented thermal/electrical conductivity, and the GnP (50 wt%) based ANF papers with an ultrathin thickness of 21 μm show a superb in-plane thermal conductivity (up to 68.2 W m−1 K−1) and outstanding absolute effectiveness EMI shielding (up to 11 060 dB cm2 g−1) and are comparable with some commercial metals/alloys. These outstanding mechanical flexibility integrated superb thermal/EMI properties along with mass-scale production pave the way for practical applications of GnP based ANF papers in the development of advanced thermal management materials in autonomous cars, air vehicles and wearable devices. [ABSTRACT FROM AUTHOR]