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Metal halide perovskite quantum dots (QDs) with unique physicochemical properties are promising candidates for next-generation optoelectronics, but they often suffer from stability issues that severely limit their potential for practical applications. In this work, we adopt an oleic acid/oleylamine-free approach to synthesize MAPbBr3 quantum dot (MQD) papers by incorporating MQDs into cellulose nanofiber frameworks. The abundant long-chain binding ligands containing sulfate terminal groups within the cellulose nanofiber remarkably stabilize the MQD structure, enabling the fabrication of self-power and flexible MQD paper photodetectors with a responsivity of ∼0.19 mA W−1, detectivity of 1.58 × 108 cm Hz1/2 W−1, and excellent bendability and reliability after 500 bending cycles. More importantly, these MQD/cellulose-based self-powered photodetectors demonstrate extraordinarily high environmental stability, maintaining more than 90% of the initial responsivity after 60 days. The simple disposability of the paper-based device is also illustrated by burning within one second, suggesting the ease of device elimination. Our work provides a unique approach to designing ultra-stable perovskite QD-based electronics with unprecedented functionalities. [ABSTRACT FROM AUTHOR]

Hygroscopic cellulose office papers possess the ability to absorb water or moisture, resulting in enhanced electrical conductivity. This study demonstrates the utilization of humidified office papers as versatile, disposable, and renewable broadband photodetectors for diverse applications. The developed paper-photodetectors (P-PDs) allow simultaneous detection of broadband light and temperature. By effectively controlling and managing the water content, sealed office papers offer reliable detection of both visible and UV light, along with temperature measurements. Notably, they are characterized by flexibility, scalability, eco-friendliness, and cost-effectiveness. [ABSTRACT FROM AUTHOR]

The creation of MFC-active smart molecules by tuning functionality has received considerable attention owing to its versatile applicability. Pyrene-based twisted donor–acceptor (D–A) dyes (PySS and PySP) have been synthesized and characterized. Here, the pyrene is directly connected with thiophene, and this unit is further linked terminally to photoactive species (thiophene/pyridine) via a four-carbon unit conjugated spacer. These molecules show excellent solvatochromic properties, with a substantial shifting of the emission wavelength (PySS- 147 nm and PySP- 130 nm). The lowest transition state contains a significant contribution from ICT characteristics, as evidenced by spectral analysis and computational calculations. Moreover, these are identified as 'aggregation-induced enhanced emission' (AIEE) active compounds and exhibit mechanofluorochromism (MFC). By grinding, PySS and PySP display MFC features with 50 nm and 54 nm red shifting, respectively. Interestingly, PySS shows a gradual emission change from green (510 nm) to orange emission (578 nm) by gradually changing the pressure with a hydraulic press (0 to 12.5 tons). The single crystal structure of both compounds was investigated to understand the structure–property relationship for MFC. The crystal packing shows that the twisted molecules (dihedral angle between pyrene and thiophene is 59.36° and 56.93° for PySS and PySP, respectively) are loosely bound with several weak interactions (C–H⋯π, C–π⋯H, H⋯H, C–H⋯O). Interestingly, it was observed that two molecules in a unit cell are arranged in an antiparallel fashion; these molecular pairs are linearly connected to another pair axially, forming a long one-dimensional chain-type arrangement. On applying pressure, these twisted molecular pairs may slowly planarize, leading the molecules to come closer, thus changing the molecular interaction and the emission properties. A feasibility study of the potentiality of using these compounds in data encryption–decryption and security ink has also been demonstrated. [ABSTRACT FROM AUTHOR]

Inkless photonic paper has shown great potential as an alternative to traditional paper due to its unique structural color, which is dye-free and non-photobleaching. However, it is still highly challenging to produce large-area photonic crystal paper, and its angle dependence, complicated printing procedure, and difficulty of high-resolution printing have greatly limited its applications. To address these challenges, we developed a new UV printing strategy using amorphous structured inverse opal PEGDA photonic paper. The photonic paper is prepared using an amorphous assembly of colloidal SiO2 particles as templates, which are fabricated by spray coating dispersions of SiO2 particles with the addition of carbon black. The photonic paper possesses structural color with low angle independency when the observation angle varies from 0° to 40°, and the unvivid structural color can be tuned in the whole visible region by exposure to UV radiation for different amounts of time, providing a fast, convenient and high-resolution printing technique. Through a chromatic-printing-like method using a series of different masks, multi-color printing is also realized. The printed images can be further protected from UV irradiation using a layer of PET film, which provides a method to store the printings for a longer time in a harsh environment. [ABSTRACT FROM AUTHOR]

In this work, paper-based flexible X-ray detectors were developed. Outstanding detection performance and high stability were realized by combining the intrinsic flexibility of the PbI2 nanocrystal, and the bendability of cellulose fiber paper. The devices were prepared using a scalable solution infiltration method and a screen-printing method. The PbI2 nanocrystal was coating onto the fiber instead of filling the micropore between the fibers. This special microstructure suppresses the effect of the carrier lateral diffusion by restricting the transport of the photoexcited carriers along the longitudinal direction of fibers, which promotes carrier transport, and improves photodetection performance. All of the pixels showed a high consistency of sensitivity, and a high signal-to-noise ratio, which ranged from 76.7 to 78.3 mC Gy-1 cm-2, and 296.4 to 327.3, respectively. In addition, benefitting from the unfilled micropores which serve as a stress buffer zone, the devices reveal high flexibility when the composite structure is in tension or compression. After 1000 bending cycles, no cracks were found in the nanocrystalline layer on the fibers, and the photocurrent was maintained at over 87%. In addition, a linear array X-ray imager was successfully implemented using the as-fabricated devices. [ABSTRACT FROM AUTHOR]

The design of the three-dimensional (3D) porous and defective molecular structure of nanocarbons can potentially enhance their functionalities for advanced electronic applications by providing a large working volume, rapid transport of electrolytes and reactants, and active sites for electrochemical reactions. Here, we report successful fabrication of 3D porous and defective nanocarbons by direct pyrolysis of crab shell-derived chitin nanofiber paper. The pyrolyzed chitin nanofiber paper has tunable electrical resistivity (1013 to 10−2 Ω cm), 3D porous structures with layered nanofiber networks, and defective nitrogen-doped carbon molecular structures. The pyrolyzed chitin nanofiber paper shows good performance as a photosensor and an energy-storage supercapacitor electrode, proving that the tailored 3D porous and defective carbon structures play key roles in the drastic improvement of the performance. This pioneering approach can be used for fabrication of chitin nanofiber-derived nanocarbons with excellent multiple functions for future sustainable electronics. [ABSTRACT FROM AUTHOR]

The pressing priority for flexible photo-responsive systems is scalability and simplistic fabrication routes at low production costs. The extraordinary properties seen in 2D materials, paired with solution-processing advantages, assert their employability for superior photoresponsive systems. Herein, we demonstrate versatile and flexible photodetectors and photo-thermal actuators by integrating 2D materials onto paper substrates. All-solution processed flexible photodetectors have been fabricated by spray coating dispersions of MoS2 nanosheets onto screen printed carbon electrodes. By employing MoSe2 as a photothermal conversion layer, actuators with paper-tape bilayers have also been demonstrated. For both photoresponsive applications, the process of calendering investigated in detail results in remarkable augmentation of the performances. Real-world thermally stimulated soft robotic applications like jacks, grippers and crawlers are realized by leveraging a configuration dependent response to illumination. Thus, a well-structured and feasible implementation of a chain of protocols that includes screen printing, spray coating, lamination and calendering with paper as the substrate led us to fabricate flexible photoresponsive systems with significantly enhanced performances. [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]

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]

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]

Organic long-persistent luminescence (OLPL) materials present significant promise in anti-counterfeiting and information encryption due to their straightforward preparation process and adjustable luminescence properties. In this study, we present a novel approach to the growth regulation of OLPL systems, focusing on an easily crystallizable doping system for in situ anti-counterfeiting applications. Utilizing p-TPD as the guest molecule and various host molecules, we synthesized doped crystals with uniform particle size and afterglow durations ranging from 2.0 s to 4.5 s. Furthermore, leveraging the unique host–guest pairing relationship and facile crystallization characteristics, we developed a "paper-ink" encryption strategy with in situ anti-counterfeiting capabilities. This innovative approach allows encrypted paper and paired ink to fully display encrypted information, while ordinary paper treated with the ink remains blank unless further processed with an information display reagent. Notably, the encrypted paper maintains its encryption effectiveness even when exposed to water. These advancements underscore the potential of organic-doped long afterglow materials in enhancing information security for secure communication and data protection. [ABSTRACT FROM AUTHOR]

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

A newly proposed idea for the fabrication of white magnetic paper is presented. These papers are fabricated from a layered composite of bacterial cellulose (BC) sheets. Magnetic BC sheets are prepared by the incorporation of CoFe2O4 nanoparticles (NPs) in the BC structure (MBC). White BC sheets were formed by the impregnation of ZnO NPs in the BC nanofibrils (ZBC), and then forming a ZBC/MBC/ZBC sandwich structure. This structure was then hot-pressed to obtain white magnetic paper. The fabricated magnetic BC paper exhibits a ‘whiteness’ of over 80%, with a high reflectance of over 70% in the visible spectral range. XRD and SEM analysis confirmed the presence of the BC, CoFe2O4 and ZnO phases in the white magnetic paper. The whiteness of the paper is improved further with a higher concentration of ZnO NPs, but at the cost of a reduction in the mechanical properties. Magnetic hysteresis was observed in the fabricated white magnetic paper with a saturation magnetization of ∼20 emu g−1, comparable to the literature values for black magnetic papers. The white magnetic paper was demonstrated to exhibit flexibility and foldability just like regular paper sheets but can also be distinguished by subjecting it to an external magnetic field. This gives potential for its use as security paper or in anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

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

Paper-based sensing technology has attracted much attention due to its light weight, low cost, ease of fabrication, and many other advantages. Here we combine paper-based sensing technology with a direct laser writing method to design and fabricate a simple and wearable healthcare sensor based on polyimide (PI)/paper bilayer structure. With assistance of infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, scanning electron microscopy and coupled electrical–mechanical testing, the effect of material processing temperature on the sensing characteristics of the PI/paper bilayer film was studied. The PI/paper bilayer film-based sensors have been successfully demonstrated for their use in monitoring pulsing and respiration activities, and in working as dual sensors for simultaneously detecting force and humidity stimuli. The differential response of PI and paper to different chemical and physical stimuli would make the PI/paper bilayer film a versatile platform for developing multi-functional and multi-modal sensors. [ABSTRACT FROM AUTHOR]

Transportation and storage of primary agricultural products, processed foods, and special items should be carried out in accordance with the requirements of cold chain transport to ensure that they are maintained within the appropriate low temperature range. Time-temperature indicators (TTIs) have proven to be an effective tool for monitoring food temperature history during the cold chain transport. Herein, a disposable paper nano-temperature sensor for color-changing temperature indicators was developed based on the strong linear photoluminescence dependence of cesium–lead–bromide perovskite nanocrystals (CsPbBr3 NCs), where the anion-exchange reaction between Br− and I− can be influenced by the melting temperature from different compositions of n-hexane/1-octadecene (ODE) mixtures. The actual temperature of a mixed solvent exceeds the specified threshold temperature (Tt), causing the mixed solvent containing iodide ions to melt, flow and impregnate the film, and thus resulting in an irreversible change in the fluorescence (FL) emission wavelength of the CsPbBr3 NCs. The FL emission wavelength is red-shifted from the original 517 nm to 650 nm, showing a large Stokes shift of more than 130 nm, which can be directly observed under a UV lamp from green to yellow, orange, and red. Accordingly, this disposable paper nano-temperature sensor with multiple color change patterns and multiple threshold temperatures of −68 °C to +4 °C is effective, portable, and stable, which provides new insights into efficient temperature monitoring for cold chain transport. [ABSTRACT FROM AUTHOR]

The development of viologen-based photochromic composite materials with a fast response to ultraviolet light has become a major research focus. In this paper, we fabricated viologen-based composite films with excellent durability and rapid photochromic performance by the solution casting method. The films changed color within one second when exposed to ultraviolet light (3 W, 365 nm). This was because ZnO NPs photogenerated electrons that enhanced the photoreduction of viologens with matched energy bands. The decoloration process of the films could be regulated by different moisture levels while keeping their photochromic properties unaffected. Moreover, the films exhibited less than 15% change in absorbance over 20 repeated coloring and fading cycles. Therefore, the excellent photoresponsiveness, repeatability and environmental friendliness of the films provide them potential for applications in areas such as rewritable paper, solar UV detection, smart windows and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Organic transistors are being developed for a variety of flexible electronics applications. They are usually fabricated on polymeric substrates, but considering the significant negative impact of plastic waste on the global environment and taking into account the many desirable properties of paper, there have also been efforts to use paper as a substrate for organic transistors. In this review we provide a brief overview of these efforts. [ABSTRACT FROM AUTHOR]

Organophosphorous pesticides pose a significant threat to public health, making its detection critical. Herein, a new fluorescent metal–organic framework, Eu-NDC, was synthesized, which possessed a 3D supramolecular structure assembled through π⋯π interactions between the naphthalene rings in its adjacent coordination-bonded layers. Then, four different products of the Eu-NDC MOF (Eu-NDC-1/2/3/4) with different morphologies were further obtained by altering the ratio of the raw materials. Among them, the fluorescence properties and BET surface area of the micro-nanoscale Eu-NDC-3 were significantly enhanced, making it the most favorable for detection. Eu-NDC-3 as a turn-off fluorescence probe for methyl paraoxon (DMNP) exhibited excellent sensitivity and selectivity, anti-interference and durability. Thus, considering these features, an intelligent logic gate was designed, showing great promise for application in smart sensing. Furthermore, an Eu-NDC-3-loaded electrospun fibrous strip was fabricated as a portable and in situ platform for visual DMNP assay. [ABSTRACT FROM AUTHOR]

Flexible wearable electromagnetic interference (EMI) shielding materials have attracted great attention with the development of portable electronic devices, and paper based EMI shielding materials turn to be ideal candidates due to their flexibility, biodegradability and low cost. In this study, conductive MXene nanosheet decorated paper was developed through a simple dip-coating technique, where the MXene nanosheets can be strongly adhered onto the surface of cellulose fiber to construct an effective conductive network. Meanwhile, a low surface energy and micro-nano-structured 1H, 1H, 2H, 2H perfluorodecanethiol (PFDT)/carbon black (CB) layer was further introduced onto the surface to construct a superhydrophobic surface, avoiding the hygroexpansion of paper in water or moisture environments effectively. As a result, the prepared PFDT/CB/MXene@Paper exhibits reflection dominant EMI shielding performance, and a specific SE value of up to 3339.6 dB cm-2 g-1 was achieved. Importantly, the EMI shielding performance can be well maintained towards cyclic bending and in various acid, alkali, salt, and UV environments, which enhance the applicability of paper based functional materials significantly. Finally, its high conductivity also endows it with good Joule heating performance, improving the wearing comfort when used as a wearable EMI shielding material. This study will undoubtedly provide a high-efficiency design strategy for fabricating high-performance paper based EMI shielding materials. [ABSTRACT FROM AUTHOR]

Self-powered pressure sensors based on triboelectric and piezoelectric principles have been widely reported in the field of flexible electronics, but they can't achieve static pressure detection. Herein, we propose a facilely fabricated electrochemical self-powered pressure sensor for static and dynamic pressure detection. Specifically, it mainly consists of Cu/Al electrodes, LiCl and filter paper. Among them, the Cu/Al electrodes are used for electrochemical reactions, LiCl provides sufficient conductive ions in the electrochemical reaction, and the rough surface microstructure of the filter paper determines the good pressure sensing performance of the sensor. The results show that the sensor can spontaneously output current in the pressure range of 1–30 kPa, with a maximal output current of 29.4 μA at 30 kPa, exhibiting characteristics of power generation and pressure detection. The pressure sensing mechanism of the sensor is revealed by analyzing the current response and the morphology characterization. similar to many electrochemical self-powered pressure sensors based on complex technology and high cost, the proposed pressure sensor has also been successfully used in multifunctional applications, such as finger joint detection, Morse code transmission and abdominal respiration detection. In addition, the different respiratory states can be recognized using the proposed sensor and machine learning. This work provides a reference for the development of simple and low-cost electrochemical self-powered pressure sensors. [ABSTRACT FROM AUTHOR]

In recent years, paper-based bending strain (PBS) sensors for bending deformation and angle detections have attracted much attention in flexible electronics. However, PBS sensors based on a surface microcrack sensing mechanism have drawbacks of small response and poor water resistance. Herein, we construct a cross-section interface between two conductive papers to form a PBS sensor that can be encapsulated using adhesive tape. Benefiting from the cross-section interface response mechanism of the PBS sensor, it can be directly encapsulated with polyimide tape without worrying about the destruction of the paper surface microstructure. Therefore, the PBS sensor shows excellent water resistance. Meanwhile, the proposed PBS sensor has good bending strain properties. Taking the bending angle of 35.7° as an example, the PBS sensor has a very high response (36.5, relative current ratio after and before bending), good repeatability (2000 times) and acceptable response/recovery times (0.34/0.35 s). In addition, the potential applications of the PBS sensor in the human body and security doors are confirmed. This work not only proposes a novel, high-response, waterproof, and low-cost PBS sensor, but also provides new strategies for the development of bending strain sensors from cross-section interfaces with surface encapsulation. [ABSTRACT FROM AUTHOR]