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Herein, we report the development of a simple green methodology to fabricate N-doped carbon quantum dots (N-CQDs) with a high luminescence using R. graveolens leaves following the hydrothermal method. Optical, chemical, morphological, and electrochemical properties were thoroughly investigated employing a variety of analytical techniques. The fabricated N-CQDs have a spherical shape, with an average diameter of 4.5 nm. Excitation dependent emission behaviour, 18% QY and green fluorescence were all observed in the N-CQDs. They are particularly resistant to various impacts such as ionic strength, pH, continuous visible light irradiation, and storage time. Since Cr(VI) ions are highly carcinogenic and mutagenic, there is an urgent demand for sensitive, selective, and efficient sensors for monitoring and measuring the amount of Cr(VI) ion in water in the environment. Hence, we developed the prepared N-CQDs as a label-free fluorescence and electrochemical probe for detecting Cr(VI) ions selectively and sensitively in aqueous solutions. Relying on static quenching together with the inner filter effect, N-CQDs performed exceptionally well as fluorescence sensors for Cr(VI) ions. The N-CQDs exhibit a limit of detection of 300 and 5 nM in the photoluminescence and differential pulse voltammetry analysis, respectively. The detection of Cr(VI) ions in real water samples using the developed sensor through both methods presented high precision without any interference. In addition, we also developed paper sensing strips for field application by depositing N-CQD on filter paper, which has been satisfactorily evaluated for sensing Cr(VI) in solid-state and solution mediums. [Display omitted] • Facile and green synthesis of N-CQDs from Ruta graveolens leaves with a QY of 18%. • Behave as an effective fluorescent sensor for Cr(VI) ions with the LOD of 300 nM. • Acts as an electrochemical sensor for Cr(VI) ion with a LOD of 5 nM. • Fluorescent paper strips were fabricated to detect Cr(VI) ions easily and rapidly. • The dual sensor exhibits excellent detection ability in real sample analysis. [ABSTRACT FROM AUTHOR]

A paper-based colorimetric sensor system (PBCSS) was developed to detect the amount of bis(pinacolato)diboron (B2Pin2) and applied as a high-throughput screening protocol in Ir-catalyzed C−H borylation. First, 96 ligands were screened for the borylation of benzene, and then 12 of them were selected and tested for five substrates. These reaction mixtures were spotted in the PBCSS, showing a blue-violet color. The value of the gray scale of each reaction was obtained from these colored spots and converted to the extent of conversion of B2Pin2. The extents of conversion of B2Pin2 obtained from the PBCSS showed good correlation with those obtained from gas chromatography analysis. In addition, the modified conversion using blank data showed good correlation with the yield of products. [ABSTRACT FROM AUTHOR]

The wide range of pressure detection and the exceptional linearity are essential performance parameters for flexible pressure sensors, enabling them to adapt to diverse scenarios and acquire information accurately. However, currently available "ultra‐wide range" piezoresistive sensors lack an optimal solution that effectively balances sensing properties, device thickness, and process cost. This study proposes a distinctive approach by introducing a Janus conductive structure assembled with dual resistive sensitive layers. The design allows for a pressure‐induced staged transformation of the current transport path, effectively mitigating variations and saturation in sensor resistance over a wide pressure range. The resulting piezoresistive sensor demonstrates an unprecedented detection range of 0–3800 kPa, showcasing remarkable sensitivity of 4.11 kPa−1 and outstanding linearity of 99.9% within the range of 0–1000 kPa. Additionally, the sensor boasts a thickness of only ≈200 µm, made possible through the utilization of a cellulose nanofibers material matrix. These performance achievements stand at the forefront when compared to existing reports. This research explores the potential applications of these sensors and extended arrays in the domains of human health and motion monitoring. It investigates their utility in gait analysis for assisted posture correction, as well as in the assessment and rehabilitation of gait instability. [ABSTRACT FROM AUTHOR]

To address the challenges of missed detections in water surface target detection using solely visual algorithms in unmanned surface vehicle (USV) perception, this paper proposes a method based on the fusion of visual and LiDAR point-cloud projection for water surface target detection. Firstly, the visual recognition component employs an improved YOLOv7 algorithm based on a self-built dataset for the detection of water surface targets. This algorithm modifies the original YOLOv7 architecture to a Slim-Neck structure, addressing the problem of excessive redundant information during feature extraction in the original YOLOv7 network model. Simultaneously, this modification simplifies the computational burden of the detector, reduces inference time, and maintains accuracy. Secondly, to tackle the issue of sample imbalance in the self-built dataset, slide loss function is introduced. Finally, this paper replaces the original Complete Intersection over Union (CIoU) loss function with the Minimum Point Distance Intersection over Union (MPDIoU) loss function in the YOLOv7 algorithm, which accelerates model learning and enhances robustness. To mitigate the problem of missed recognitions caused by complex water surface conditions in purely visual algorithms, this paper further adopts the fusion of LiDAR and camera data, projecting the three-dimensional point-cloud data from LiDAR onto a two-dimensional pixel plane. This significantly reduces the rate of missed detections for water surface targets. [ABSTRACT FROM AUTHOR]

In complex environments a single visible image is not good enough to perceive the environment, this paper proposes a novel dual-stream real-time detector designed for target detection in extreme environments such as nighttime and fog, which is able to efficiently utilise both visible and infrared images to achieve Fast All-Weatherenvironment sensing (FAWDet). Firstly, in order to allow the network to process information from different modalities simultaneously, this paper expands the state-of-the-art end-to-end detector YOLOv8, the backbone is expanded in parallel as a dual stream. Then, for purpose of avoid information loss in the process of network deepening, a cross-modal feature enhancement module is designed in this study, which enhances each modal feature by cross-modal attention mechanisms, thus effectively avoiding information loss and improving the detection capability of small targets. In addition, for the significant differences between modal features, this paper proposes a three-stage fusion strategy to optimise the feature integration through the fusion of spatial, channel and overall dimensions. It is worth mentioning that the cross-modal feature fusion module adopts an end-to-end training approach. Extensive experiments on two datasets validate that the proposed method achieves state-of-the-art performance in detecting small targets. The cross-modal real-time detector in this study not only demonstrates excellent stability and robust detection performance, but also provides a new solution for target detection techniques in extreme environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel flexible gas sensor based on 2D WS 2 was reported for the first time. • The 2D WS 2 with S defects can enhance NH 3 gas sensitivity performance effectively. • Our devices can realize multifunctional sensing detection. For the important applications of gas identification related to specific diseases in healthcare, flexible gas sensors have attracted more attention. Among them, two-dimensional transition metal dichalcogenides (2D TMDs) have been known as good promising flexible gas-sensitive materials. While how to tightly attach 2D materials on flexible substrates is still challenging. Here, we propose an enhanced room-temperature flexible paper-substrate sensors based on 2D tungsten disulfide (WS 2) with S defects, which are facilely synthesized by chemical exfoliation and vacuum filtration method. Structure characterization shows that most of the as-prepared 2D WS 2 are within 3 layers. Spectroscopic characterization proves the existence of S defects on the surface of 2D WS 2 produced by chemical exfoliation. The room-temperature (25 °C) NH 3 gas sensitivity results show that the response intensity of 2D WS 2 with rich S defects is nearly three times higher than the highly crystalline 2D WS 2. The results of the flexible gas sensitivity indicate the fast response and high stability of our devices in breathing detection and bending experiments. Furthermore, the devices can effectively distinguish bending stress changes and gas-sensitive response signals at the same time, realizing multifunctional sensing detection. Our work will be a reference for fabricating flexible sensors based on 2D materials. [ABSTRACT FROM AUTHOR]

• A screen-printed sensor for direct measurement on concrete structures by filter paper. • The sensor is able to switch from corrosion probability evaluation to pH measurement. • The portable experimental setup was applied for on-site measurements in a museum. Reinforced concrete has been employed worldwide as a leading building material for public and private structures as well as in modern sculptural art. Although the unrivalled mechanical strength and modelling versatility of this material, several interrelated processes are responsible for its progressive degradation (e.g., carbonation, penetration of aging-promoting agents), decreasing its long-last durability and representing a risk for the public security or the cultural heritage. With the aim to tackle this issue, the present work reports a novel configuration of a screen-printed sensor, obtained by the combination of flexible and robust polyester support and wax-printed filter paper device for the direct application on the concrete surface. Our sensor consists of a polyester-printed three-electrochemical cell that allows dual measurements on reinforced concrete, namely (i) the evaluation of corrosion probability of the metallic reinforcements (which outperforms the half-cell potential standard method) and (ii) the employment of a pH-sensitive iridium oxide film for the measurement of the pH of concrete. The paper was used as a porous material capable of ensuring the electrochemical connection between the Ag/AgCl printed electrode and the concrete solid matrix, acting also as a protective envelope for the electrode. After the laboratory tests, which revealed the noteworthy performances of the sensors in distinguishing among different levels of corrosion as well as measuring the pH of concrete, the developed sensor was applied for on-site measurement at the Giacomo Manzù Museum (Ardea, Italy), demonstrating its suitability for the real application to cultural heritage conservation. Overall, this easy-to-handle and non-invasive diagnostic device provides an innovative analytical approach for the on-site and prompt multiparametric monitoring of the physico-chemical phenomena that endanger the long-lasting preservation of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Abstract: Electro-active papers (EAPap) made with cellulose have been known as a biomimetic actuator material according to their merits in terms of large bending deformation, low actuation voltage, ultra-lightweight, and biodegradability. This out-of-plane bending deformation is useful for achieving flapping wings, micro-insect robots, and smart wallpapers. On the other hand, in-plane strains, such as extension and contraction of EAPap materials are also promising for artificial muscle applications since the Young''s modulus of EAPap materials is large. This paper first reports the experimental investigation of the in-plane strain of EAPap materials in the presence of electric fields. The EAPap samples preparation and the in-plane strain measurement system are explained. The test results are shown in terms of electric field, frequency and the orientation of the samples. The power consumption and the strain energy of EAPap samples are discussed. Although there are still unknown facts in EAPap materials, this in-plane strain may be useful for artificial muscle applications. [Copyright &y& Elsevier]

A calix[4]arene based compound incorporating amide and morpholine moieties has been synthesized and its ion recognition property towards metal ions and application of its metal complex towards sensing of amino acids has been investigated. The synthesized compound interacts with Cu2+ with high selectivity and sensitivity (LOD, 0.1 ppb) in aqueous media with instant color change from colorless to yellow without interference from any other metal ions used in this study. The molecular structure of the calix compound (1) has been determined by single crystal X-ray study and the structure of its Cu2+ complex has been established by DFT calculation. The Cu2+ complex of 1 selectively detects tyrosine (LOD, 1.2 ppm) in water with distinct color change and without any interference from other 22 amino acids used in this study. The mechanism for detection of tyrosine with color change is also presented. For easy field application, paper based sensor strips have been prepared by coating compound 1 and its Cu2+ complex on filter paper, which have been used for semi-quantitative measurement of Cu2+ and tyrosine. Compound 1 and its Cu2+ complex have also been used for detection of Cu2+ and tyrosine, respectively in water and human saliva as real samples and satisfactory results are obtained. Calixarene based colorimetric sensor has been developed, which detects Cu2+ selectivity and its Cu2+ complex detects tyrosine selectively in water out of 22 amino acids tested. Paper based sensor strips are prepared for field application and it has been successfully tested in water. Unlabelled Image • Calixarene based colorimetric sensor is developed for detection of copper in water. • The copper complex of the sensor molecule selectively detects tyrosine in water. • Paper strips are developed for field application to detect copper and tyrosine in water. • This sensor is successfully applied for detection of copper and tyrosine in spiked sample. • Structure of the sensor is determined by X-ray and its copper complex by DFT calculation. [ABSTRACT FROM AUTHOR]

Humidity sensors are indispensable for various electronic systems and instrumentations. To develop a new humidity sensing mechanism is the key for the next generation of sensor technology. In this work, a novel flexible paper-based current humidity sensor is proposed. The developed alternating current electroluminescent devices (ACEL) consist of the electroless plating Ni on filter paper and silver nanowires (AgNWs) as the bottom and upper electrodes, and ZnS:Cu as the phosphor layer, respectively. The proposed humidity sensor is based on ACEL with the paper substrate and the ZnS:Cu phosphor layer as the humidity sensing element. The moisture effect on the optical properties of ACELs has been studied firstly. Then, the processing parameters of the paper-based ACELs such as electroless plated bottom electrode and spin-coated phosphor layer as a function of the humidity-sensitive characteristics are investigated. The sensing mechanism of the proposed sensor has been elucidated based on the Q ~ V analysis. The sensor exhibits an excellent linearity ( R 2 = 0.99965 ) within the humidity range from 20% to 90% relative humidity (RH) and shows excellent flexibility. We also demonstrate its potential application in postharvest preservation where the EL light is used for preservation and the humidity can be monitored simultaneously through the current. [ABSTRACT FROM AUTHOR]

On-site quantitative analysis of pesticides is important for food safety. Colorimetric gold nanobipyramids (AuNBPs) sensors are powerful methods for on-site detection. However, a single quantitative method and the instability of AuNBPs in solution limit the practicability of those sensors. Here, a paper-based multicolor AuNBPs sensor involved a colorimeter-assisted method for quantifying color was developed for quantitative detection of 2,4-dichlorophenoxyacetic acid (2,4-D), a common herbicide. The novelty of this study lies in developing a general paper-based quantitative on-site method (PQOM) for colorimetric AuNBPs sensors. Firstly, a paper-based analytical device (PAD) consisting of a nylon membrane, absorbent cotton layers, and two acrylic plates was fabricated to deposit AuNBPs. We demonstrated the PAD could improve the stability of AuNBPs and the detection sensitivity of AuNBPs sensors. Then, a handheld colorimeter was first used to quantify the color change of AuNBPs on the PAD based on the CIELab color space. Finally, as proof of concept, the PQOM was successfully employed to quantify 2,4-D by combining with an alkaline phosphatase-mediated AuNBPs growth method. In this method, 2,4-D specifically inhibited alkaline phosphatase activity to suppress the generation of l -ascorbic acid, thereby mediating AuNBPs growth. The developed sensor exhibited seven 2,4-D concentration-related colors and detected as low as 50 ng mL−1 2,4-D by naked-eye observation and 18 ng mL−1 2,4-D by a colorimeter. It was applied to detect 2,4-D in the spiked rice and apple samples with good recovery rates (91.8–112.0%) and a relative standard deviation (n = 5) < 5%. The success of this study provides a sensing platform for quantifying 2,4-D on site. [Display omitted] • A general on-site quantitative method was developed for gold nanobipyramids sensors. • A paper-based analytical device was fabricated for depositing gold nanobipyramids. • A colorimeter was first used to quantify gold nanobipyramids color change on paper. • 2,4-Dichlorophenoxyacetic acid in foods was tested by a paper-based multicolor sensor. • The sensor presented good color stability, detection sensitivity, and portability. [ABSTRACT FROM AUTHOR]

The graphene quantum dots (GQDs) was synthesized using potato starch and water by hydrothermal method and further used for reduction of tetracholoroauric acid to form graphene quantum dots-gold (GQDs@AuNPs) nanocomposite. The GQDs/GQDs@AuNPs were analyzed using FTIR, UV–Vis, Flourometry and HR-TEM. The synthesized GQDs@AuNPs were further used for fabrication of cost-effective screen-printed paper electrode (SPPE) based DNA sensor for the detection of O. tsutsugamushi using htrA gene specific 5′NH2 linked DNA probe. Modification of SPPE using GQDs@AuNPs nanocomposite and ssDNA probe was monitored using EIS, FTIR, FE-SEM and AFM. The sensor detection limit (LOD) was assessed as 0.002 ng/μl from the standard calibration curve with the correlation coefficient, R2 = 0.993. The sensitivity of the DNA sensor was calculated as 7700 μA/cm2/ng for ssGDNA of O. tsutsugamushi using cyclic voltammetry. The sensor validation was done using scrub typhus patient's blood DNA samples. The sensor showed good storage stability at 4 °C for six months with just a loss of 12% of the initial current values. The SPPE/DNA sensor developed is very specific, sensitive, stable and detects O. tsutsugamushi in less time. Scheme 1. Schematic of SPCE/GQDs A/ssDNA (probe) based Electrochemical DNA sensor for the detection of scrub typhus. [Display omitted] • The nanocomposite was synthesized using an ecofriendly approach used in the electrode fabrication process. • The disposable screen-printed paper electrodes were used as a sensing matrix to reduce the cost of the assay. • The synthesized nanocomposite enhanced the sensitivity of the paper electrode and provides a large surface area. • The DNA sensor is capable of selective and sensitive determination of O. tsutsugamushi GDNA in patient samples. • The developed sensor can detect the analyte up to picogram level (lower limit of detection was found 0.002 ng/μl of ssDNA). [ABSTRACT FROM AUTHOR]

• Smartphone-integrated printed-paper sensor for detection of dimethoate in foods. • Detection is based on the change of yellow color NPs to reddish-yellow. • Smartphone-color detector App and colorimetry used for analysis of dimethoate. • Advantages of the method are user-friendly, portable and low cost. Herein, a user-friendly and portable smartphone-integrated printed-paper sensor was designed with Cu@Ag nanoparticles (NPs) for on-site monitoring of dimethoate pesticide in food samples, and the results obtained are compared with those obtained by UV–vis spectrophotometry. The working principle for identification of dimethoate pesticide is the change of yellow color NPs to reddish-yellow with associated bathochromic shift of absorption peak when pesticide introduced onto the fabricated paper or glass vial containing the NPs. A smartphone-color detector App and colorimetry were used for quantitative analysis of dimethoate in food samples. Linearity range for analysis of dimethoate using paper sensor and colorimetry were 100–2000 µgL−1 and 50–2500 µgL−1 with detection limit of 30 and 16 µgL−1, respectively. The advantages of using smartphone-integrated paper devices are rapid, instrument-free detection and economic in terms of consumption of lower amounts of NPs solution compared to other NPs-based colorimetric methods. [ABSTRACT FROM AUTHOR]

This review shows the recent advances and state of the art in paper-based analytical devices (PADs) through the analysis of their integration with microfluidics and LOC micro- and nanotechnologies, electrochemical/optical detection and electronic devices as the convergence of various knowledge areas. The important role of the paper design/architecture in the improvement of the performance of sensor devices is discussed. The discussion is fundamentally based on μPADs as the new generation of paper-based (bio)sensors. Data about the scientific publication ranking of PADs, illustrating their increase as an experimental research topic in the past years, are supplied. In addition, an analysis of the simultaneous evolution of PADs in academic lab research and industrial commercialization highlighting the parallelism of the technological transfer from academia to industry is displayed. A general overview of the market behaviour, the leading industries in the sector and their commercialized devices is given. Finally, personal opinions of the authors about future perspectives and tendencies in the design and fabrication technology of PADs are disclosed. [ABSTRACT FROM AUTHOR]

The field of paper-based microfluidics has experienced rapid growth over the past decade. Microfluidic paper-based analytical devices (μPADs), originally developed for point-of-care medical diagnostics in resource-limited settings, are now being applied in new areas, such as environmental analyses. Low-cost paper sensors show great promise for on-site environmental analysis; the theme of ongoing research complements existing instrumental techniques by providing high spatial and temporal resolution for environmental monitoring. This review highlights recent applications of μPADs for environmental analysis along with technical advances that may enable μPADs to be more widely implemented in field testing. [ABSTRACT FROM AUTHOR]

Printed electrodes on a recyclable low-cost coated paper were used as a platform for constructing potentiometric ion sensors consisting of an ion-selective electrode (ISE) and a reference electrode (RE). The reference and working electrodes were printed by using a stable suspension of gold nanoparticles (AuNP) as the ink. Sintering turned the printed electrodes conductive. A poly(3,4-ethylenedioxythiophene) (PEDOT) layer, with poly(styrene sulfonate) (PSS) ions as counterions was deposited on the gold electrodes by electropolymerization, drop-casting or ink-jet printing. The reference electrode was prepared by further coating the PEDOT(PSS) layer with a poly(vinyl chloride) (PVC) membrane containing a lipophilic salt, tetrabutylammonium tetrabutylborate (TBA-TBB), thus resulting in a solid-contact reference electrode (SCRE). The working electrode was modified by coating the PEDOT(PSS) layer with a K + -selective membrane, to obtain a solid-contact K + -ISE. The electrochemical characteristics of the resulting electrode systems were studied by amperometric, potentiometric and electrochemical impedance spectroscopic (EIS) measurements. The potentiometric response toward K + ions was additionally studied. The surface structure of the PEDOT(PSS) layers deposited by the different methods was studied with atomic force microscopic (AFM) measurements. It was shown that a well-functioning planar electrode platform with good electrochemical characteristics could be prepared by ink-jet printing in a repeatable manner. The planar electrode platform presented here offers a user-friendly and ecological alternative to perform chemical analysis from small sample volumes. [ABSTRACT FROM AUTHOR]

Since OLED was first mass‐produced by Samsung Display, various researches related to OLEDs have been actively conducted and now days, People are using OLED displays every single day. As a next generation organic‐optoelectronic display, we suggest the All‐in‐one Sensor Display which can be used for fingerprint recognition, proximity sensor, illuminance sensing and photoplethysmogram which is an area of rapid interest in recent years. To demonstrate the All‐in‐one Sensor Display in entire display area, in this research, we successfully fabricated organic photodetectors (OPDs) in the OLED panels with our own materials, D‐01 and A‐01. Since designing a donor material and an acceptor material is key issue for high Signal to Noise ratio (SNR), we designed and synthesized the D‐01 and A‐01. With our own material based OPDs, All‐in‐one Sensor Display showed good characteristics and successfully recognized fingerprints. This research shows the possibility of the mass production of next organic diode and we believe that All‐in‐one Sensor Display will be the next display application beyond the OLEDs. [ABSTRACT FROM AUTHOR]

A solution for ambient light sensor (ALS) integration in a‐Si LCD with cost advantage and nearly the same performance as external ALS solution. In this work we provide practical solution for the most challenged smartphone [ABSTRACT FROM AUTHOR]

[Display omitted] • Printed foldable humidity sensor (PPHS) was fabricated from porous paper. • PPHS is highly senstitive, with the maximum 1480% change at 1 kHz. • PPHS is highly repeatable, with a 1.05% standard derivation for 3 runs. • PPHS rapidly responds (0.8 s) and recovers (0.78 s). • PPHS can be used for breath and proximity detections and non-touch switch. Paper based humidity sensors are low-cost, flexible, and biodegradable. However, the previously reported paper based humidity sensors exhibit poor repeatability, low sensitivity, high drift, and slow response. Here, we reported a new strategy to monolithically fabricate humidity sensor based on porous paper (PPHS) using robust and precise screen and gravure printings. PPHS is highly sensitive, with the maximum 1480% change at 1 kHz and the maximum 411.4% change at 10 kHz in capacitance, respectively. PPHS is highly repeatable (a 1.05% standard derivation in sensitivity for 3 continuous runs) and is stable and insensitive to a mild temperature change (15–30 °C). PPHS rapidly responds (0.8 s) and recovers (0.78 s). PPHS is also highly foldable and twistable. The high repeatability, high sensitivity, quick response/recovery, high foldability/twistability, and good stability of PPHS could be attributable to the combined effects of the high specific surface area of porous paper and the robust and precise printings. By comparison, PPHS is more sensitive than the previously reported paper-based humidity sensors and several humidity sensors fabricated using different substrates, materials, and printings. Due to these unique features, PPHS shows great potential applications in the humidity sensing, the breath detection, the proximity detection, and non-touch switch. [ABSTRACT FROM AUTHOR]

In this work, the electrical properties of graphene papers were investigated with the aim of developing pressure sensor prototypes for measuring pressures up to 2 kPa. In order to determine which graphene paper would be the most suitable, three different types of graphene papers, synthesized by different routes, were prepared and electrically characterized. The results of electrical characterizations, in terms of electrical conductivity and sheet resistance of graphene papers, are presented and discussed. Prototypes of pressure sensors are proposed, using graphene papers obtained by chemical oxidation (graphene oxide and reduced graphene oxide) and by electrochemical exfoliation. The prototypes were tested in static compression/decompression tests in the working range of 0 kPa to 1.998 kPa. The compression/decompression sensitivity values observed in these prototype sensors ranged from 20.8% ΔR/kPa for graphene sensors obtained by electrochemical exfoliation to 110.7% ΔR/kPa for those prepared from graphene oxide obtained by chemical oxidation. More expressive sensitivity values were observed for the sensors fabricated from GO, intermediate values for those made of rGO, while prototypes made of EG showed lower sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: The work presented in this paper addresses the issues of fault detection and isolation properties of the partial PCA method and the isolation-enhanced PCA method. In order to increase the sensitivity of the residuals with respect to various faults, the structured residuals generated from both partial PCA and isolation-enhanced PCA are optimized. For the residual evaluation, the bootstrap technique is combined with the CUSUM method to achieve fast and robust detection. Three sensor faults and three actuator faults were studied using simulations employing a rigorous, first principles based, paper machine simulator. All the faults were correctly detected and isolated with both studied methods, and the results are compared with the classical T 2 and SPE contribution plot methods. [Copyright &y& Elsevier]

With characters of low cost, portability, easy disposal, and high accuracy, as well as bulky reduced laboratory equipment, paper-based sensors are getting increasing attention for reliable indoor/outdoor onsite detection with nonexpert operation. They have become powerful analysis tools in trace detection with ultra-low detection limits and extremely high accuracy, resulting in their great popularity in medical detection, environmental inspection, and other applications. Herein, we summarize and generalize the recently reported paper-based sensors based on their application for mechanics, biomolecules, food safety, and environmental inspection. Based on the biological, physical, and chemical analytes-sensitive electrical or optical signals, extensive detections of a large number of factors such as humidity, pressure, nucleic acid, protein, sugar, biomarkers, metal ions, and organic/inorganic chemical substances have been reported via paper-based sensors. Challenges faced by the current paper-based sensors from the fundamental problems and practical applications are subsequently analyzed; thus, the future directions of paper-based sensors are specified for their rapid handheld testing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated. • The paper is used for the purpose of the humidity sensing material and the sensor substrate. • The as-fabricated paper-based humidity sensor is provided with outstanding humidity sensing properties and good stability. • The humidity sensor was applied to multifunctional applications including human breath rate, non-contact switch and skin humidity. It is of great significance to exploit a simple, cost-effective and environmentally friendly preparation method of multifunctional humidity sensors. However, most humidity sensors need complex manufacturing processes, high cost and narrow usage range. Herein, humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated, among which the paper is used for the purpose of the humidity sensing material and the sensor substrate. The sensitivity of the obtained sensor was improved by the modification of EPTAC, the response time was decreased to 25 s, which is equivalent to the first-rate paper-based humidity sensors. In addition, the paper-based humidity sensor is provided with well flexibility and biocompatibility, and it exhibits multifunctional applications in respiratory monitoring, non-contact switch and skin humidity monitoring. The low cost and facile preparation technique in this work could provide a useful strategy for developing multifunctional humidity sensor. [ABSTRACT FROM AUTHOR]

Paper electronics represents a newly raised concept that includes various types of electronic devices and circuits on paper. In this work, the authors report multigate oxide‐based homojunction electric‐double‐layer thin‐film transistors (TFTs) with cellulose nanofibers electrolyte film as the gate dielectrics on paper substrate. These flexible TFTs exhibit high performance with a high ON/OFF ratio of 107 and a high mobility of around 26 cm2 V−1 s−1. Resistor‐loaded inverters are demonstrated both in a bottom‐gate mode and an in‐plane‐gate mode. Logic AND operation is realized in a device with two in‐plane gates. Significantly, the universal logic NAND is experimentally demonstrated using a one transistor/one resistor structure by combining NOT and AND logics together. The paper‐based TFT devices are very interesting for emerging areas such as disposable paper electronics and sensors. [ABSTRACT FROM AUTHOR]

Systems using passive infrared sensors with a low resolution were recently proposed to answer the dilemma effectiveness–ethical considerations for human fall detection by Information and Communication Technologies (ICTs) in older adults. How effective is this type of system? We performed a systematic review to identify studies that investigated the metrological qualities of passive infrared sensors with a maximum resolution of 16× 16 pixels to identify falls. The search was conducted on PubMed, ScienceDirect, SpringerLink, IEEE Xplore Digital Library, and MDPI until November 26– 28, 2020. We focused on studies testing only these types of sensor. Thirteen articles were "conference papers", five were "original articles" and one was a found in arXiv.org (an open access repository of scientific research). Since four authors "duplicated" their study in two different journals, our review finally analyzed 15 studies. The studies were very heterogeneous with regard to experimental procedures and detection methods, which made it difficult to draw formal conclusions. All studies tested their systems in controlled conditions, mostly in empty rooms. Except for two studies, the overall performance reported for the detection of falls exceeded 85– 90% of accuracy, precision, sensitivity or specificity. Systems using two or more sensors and particular detection methods (eg, 3D CNN, CNN with 10-fold cross-validation, LSTM with CNN, LSTM and Voting algorithms) seemed to give the highest levels of performance (> 90%). Future studies should test more this type of system in real-life conditions. [ABSTRACT FROM AUTHOR]

We present a deep learning-based framework to design and quantify point-of-care sensors. As a use-case, we demonstrated a low-cost and rapid paper-based vertical flow assay (VFA) for high sensitivity C-Reactive Protein (hsCRP) testing, commonly used for assessing risk of cardio-vascular disease (CVD). A machine learning-based framework was developed to (1) determine an optimal configuration of immunoreaction spots and conditions, spatially-multiplexed on a sensing membrane, and (2) to accurately infer target analyte concentration. Using a custom-designed handheld VFA reader, a clinical study with 85 human samples showed a competitive coefficient-of-variation of 11.2% and linearity of R2 = 0.95 among blindly-tested VFAs in the hsCRP range (i.e., 0–10 mg/L). We also demonstrated a mitigation of the hook-effect due to the multiplexed immunoreactions on the sensing membrane. This paper-based computational VFA could expand access to CVD testing, and the presented framework can be broadly used to design cost-effective and mobile point-of-care sensors. [ABSTRACT FROM AUTHOR]

To ensure safe drinking water, it is necessary to have a simple method by which the probable pollutants are detected at the point of distribution. Nitrite contamination in water near agricultural locations could be an environmental concern due to its deleterious effects on the human population. The development of a frugal paper-based microfluidic sensor could be desirable to achieve the societal objective of providing safe drinking water. This work describes the development of a facile and cost-effective microfluidic paper-based sensor for quantitative estimation of nitrite in aquatic environments. A simple punching machine was used for fabrication and rapid prototyping of paper-based sensors without the need of any specialized equipment or patterning techniques. A reusable 3D printed platform served as the support for simultaneous testing of multiple samples. The nitrite estimation was carried out with smartphone-assisted digital image acquisition and colorimetric analysis. Under optimized experimental conditions, the variation in average grayscale intensity with concentration of nitrite was linear in the range from 0.1 to 10 ppm. The limits of detection and quantitation were 0.12 ppm and 0.35 ppm respectively. The reproducibility, expressed as relative standard deviation was 1.31%. The selectivity of nitrite detection method was determined by performing interference studies with commonly existing co-ions in water, such as bicarbonates, chloride and sulphate. The paper-based sensor was successfully applied for estimation of nitrite in actual water samples and showed high recoveries in the range of 83.5–109%. The results were in good agreement with those obtained using spectrophotometry. The developed paper-based sensor method, by virtue of its simplicity, ease of fabrication and use, could be readily extended for detection of multiple analytes in resource-limited settings. [ABSTRACT FROM AUTHOR]

A new approach to develop ultra low-cost, robust, rugged, and disposable potentiometric sensors is presented. A suspension of carbon nanotubes in a water-surfactant mixture (carbon nanotubes ink) is applied on conventional filter papers to turn them into conductive papers, which are then used as a substrate to build ion-selective electrodes. The electrodes are made by drop casting a membrane on a small circular area of the conductive paper. In this way, the carbon nanotubes act as both electric conductors and ion-to-electron transducers of the potentiometric signal. Electrodes for sensing K+, NH+, and pH were built and tested using this approach, and the results were compared with classical solid-state ion selective electrodes using carbon nanotubes as transducers and glassy carbon as a substrate. In all cases, the analytical performance (sensitivity, linear ranges, limits of detection, selectivity, etc.) of these disposable paper electrodes was similar to that obtained for the more conventional type of ion-selective-electrodes. This opens new avenues for very low-cost platforms for generation of chemical information. [ABSTRACT FROM AUTHOR]

In the last 10 years, paper-based electrochemical biosensors have gathered attention from the scientific community for their unique advantages and sustainability vision. The use of papers in the design the electrochemical biosensors confers to these analytical tools several interesting features such as the management of the solution flow without external equipment, the fabrication of reagent-free devices exploiting the porosity of the paper to store the reagents, and the unprecedented capability to detect the target analyte in gas phase without any sampling system. Furthermore, cost-effective fabrication using printing technologies, including wax and screen-printing, combined with the use of this eco-friendly substrate and the possibility of reducing waste management after measuring by the incineration of the sensor, designate these type of sensors as eco-designed analytical tools. Additionally, the foldability feature of the paper has been recently exploited to design and fabricate 3D multifarious biosensors, which are able to detect different target analytes by using enzymes, antibodies, DNA, molecularly imprinted polymers, and cells as biocomponents. Interestingly, the 3D structure has recently boosted the self-powered paper-based biosensors, opening new frontiers in origami devices. This review aims to give an overview of the current state origami paper-based biosensors, pointing out how the foldability of the paper allows for the development of sensitive, selective, and easy-to-use smart and sustainable analytical devices. [ABSTRACT FROM AUTHOR]

For the diabetes diagnosis, noninvasive methods are preferred to invasive methods; urine glucose measurement is an example of a noninvasive method. However, conventional noninvasive methods for urine glucose measurement are not intuitive. Furthermore, such methods exhibit low selectivity because they can detect interfering molecules in addition to glucose. Herein, we fabricate a noninvasive, intuitive, and highly selective paper sensor consisting of polyaniline nanoparticles (PAni-NPs) and red blood cell membranes (RBCMs). The PAni-NPs (adsorbed on the paper) are highly sensitive to hydrogen ions and change color from emeraldine blue to emeraldine green within a few seconds. The RBCM (coated on the PAni-NP-adsorbed paper) having the glucose transporter-1 protein plays the role of a smart filter that transports glucose but rejects other interfering molecules. In particular, the selectivity of the RBCM-coated PAni-NP-based paper sensor was approximately improved ∼85%, compared to the uncoated paper sensors. The paper sensor could detect urine glucose over the range of 0–10 mg/mL (0–56 mM), with a limit of detection of 0.54 mM. The proposed paper sensor will facilitate the development of a highly selective and colorimetric urine glucose monitoring system. [Display omitted] • A highly selective paper-based sensor was fabricated for noninvasive urine glucose detection. • PAni-NP-functionalized cellulose paper was coated with a cell membrane to enhance selectivity. • RBCM prevents interfering molecules from approaching GOx, whereas GLUT-1 in RBCM selectively transports glucose to GOx. • PAni and RPAni paper sensors can be a useful technique for early detection of diabetes and rapid screening of glucose. [ABSTRACT FROM AUTHOR]

Rapid, precise, and reproducible deposition of a broad variety of functional materials, including analytical assay reagents and biomolecules, has made inkjet printing an effective tool for the fabrication of microanalytical devices. A ubiquitous office device as simple as a standard desktop printer with its multiple ink cartridges can be used for this purpose. This Review discusses the combination of inkjet printing technology with paper as a printing substrate for the fabrication of microfluidic paper-based analytical devices (μPADs), which have developed into a fast-growing new field in analytical chemistry. After introducing the fundamentals of μPADs and inkjet printing, it touches on topics such as the microfluidic patterning of paper, tailored arrangement of materials, and functionalities achievable exclusively by the inkjet deposition of analytical assay components, before concluding with an outlook on future perspectives. [ABSTRACT FROM AUTHOR]

Energy prediction plays a significant role in energy-harvesting wireless sensors (EHWS), as it helps wireless sensors regulate their duty cycles, achieve energy neutrality, and extend their lifespan. To explore and analyze advanced technologies and methods regarding energy prediction for EHWS, this study identifies future research directions and addresses the challenges faced based on the current research status, assisting with future literature research. This scholarly inquiry delineates future research prospects and addresses prevailing challenges within the context of the extant research landscape, thereby facilitating prospective scholarly endeavors. This study employed the systematic mapping study (SMS) approach to screen and further investigate the relevant literature. After searching and screening for papers from the ACM, IEEE Xplore, and Web of Science (WOS) databases from January 2007 to December 2022, 98 papers met the requirements of this study. Subsequently, the SMS was conducted for five research questions. The results showed that the solution proposal type category had the largest proportion among all research types, accounting for 58% of the total number, indicating that the research focusing on this field is placed on improving the existing methods or proposing new ones. Additionally, based on the SMS analysis, this study provides a systematic review of the technical utilization and improvement approaches, as well as the strengths and limitations of the selected prediction methods. Furthermore, by considering the current research landscape, this paper identifies the existing challenges and suggests future research directions, thereby offering valuable insights to researchers for making informed decisions regarding their chosen paths. The significance of this study lies in its contribution to driving advancements in the field of energy-harvesting wireless sensor networks. The importance of this study is underscored by its contribution to advancing the domain of energy-harvesting wireless sensor networks, thereby serving as a touchstone for forthcoming researchers in this specialized field. [ABSTRACT FROM AUTHOR]

Quantum dots (QD) have seen a rapid uptake in display applications, especially as photoluminescent color conversion layers. In parallel, QD absorbers promise efficient photodetector components, with absorption peak tunability and monolithic integration. In this paper, we describe QD stack integration into infrared imagers, enabling accessible sensors for various display interfaces. [ABSTRACT FROM AUTHOR]

This paper presents a novel optical type in‐cell fingerprint sensor (iFP) technology, which can detect a user's fingerprint on display. By using low temperature polysilicon (LTPS) TFT process, new sensor material, and active pixel sensor circuit (APS), this sensor can detect a fingerprint image with good performance. The FPS/Touch/Display Driver IC (FTDI) is also implemented in this work, and successfully demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple diphenylimidazole-derived sensor was prepared for the detection of F-. • The deprotonated system showed an effective at the detection of trace water. • The deprotonated system was used to the trace water detect in chemical reagents. • The sensors-doped filter papers were applicable for the inkless writing. A simple diphenylimidazole-based colorimetric and fluorescent sensor (DIB) was successfully synthesized by one step reaction. DIB exhibited excellent selectivity and sensitivity for F- over various other anions with fluorescence enhancement effect. The limit of detection of DIB towards F- was evaluated to be 9.18 × 10-8 M. A plausible sensing mechanism of DIB towards F- had been proposed on the basis of spectral analysis and 1H NMR titration experiments, which the results suggested that the recognition process could be attributed to the deprotonation of imidazole group. Interestingly, the F- induced deprotonation system of DIB ·F could be employed as reversible sensor for trace water with high sensitivity and instant response. The color change easily recognized by the naked eye and low limit of detection (0.0022 %) improved the detection performance of DIB ·F for water. Importantly, the DIB ·F system had been successfully applied for the quantitative analysis of water content in experimental chemical reagents. In addition, sensor DIB and DIB ·F-incorporated filter papers could be utilized as inkless writing display device for F- and water detection, respectively, with reusability. [ABSTRACT FROM AUTHOR]

In this study, we have designed and synthesized novel betaine dyes with clear structural confirmation using 1H and 13C NMR spectroscopy, ESI-MS and UV–Vis analyses. For these betaines, we investigated their hydro-, iono-, thermo- and solvato-chromic sensor properties through UV–visible spectral changes and visual color changes. We observed hydrochromic properties in solution state by adding 3% water (V/V) and we checked solid state hydrochromic sensing property through betaine-embedded PEO film. For ionochromism, we used an equimolar concentration of salt to dye in solution. Thermochromic sensing studies were performed in a temperature range from 50 °C to −10 °C, and solvatochromism properties were investigated by increasing polarity using solvents from DCM to DMF. Finally, the experimental results were supported with theoretical studies. Image 1 • In the present study, six betaine dyes were synthesized and fully characterized. • Investigated multichromic properties with UV–visible and visual color changes. • The experimental results were supported with theoretical studies. • Hydrochromic result may be useful in water-jet rewritable paper applications. • First report for hydro-ionochromism for betaines for numerous visual color changes. [ABSTRACT FROM AUTHOR]

The fabrication, characterization, and applications of paper‐based screen‐printed carbon electrodes (SPCE) are discussed. In particular, microscopy images of the working electrode surface show a reproducible 3D pattern that enhances the performance of the device compared to that of a polyester‐based SPCE. Gold nanoparticles and CdSe@ZnS quantum dots are detected using different electrochemical techniques. [ABSTRACT FROM AUTHOR]

• Fabrication of an inkjet-printed paper-based SERS platform. • An effective AuSph Ink was developed with high stability over 1 year of storage. • Improvement of SERS capabilities by a hydrophobic modification of the paper. • Ultrasensitive quantification of thiram at 10−11 M with low sample volume (2 μL). • Reliable, robust and ultralow-cost SERS substrates (less than $ 0.01 per spot). We report the fabrication of a low-cost paper-based SERS platform with enhanced sensing capabilities. The sensor consists of a highly concentrated glycerol/ethanol dispersion of ca. 77 nm Au nanospheres (AuSph) inkjet-printed on hydrophobic chromatographic paper forming circular sensing spots of 1 mm in diameter. The AuSph ink exhibits high stability for 1 year. Interestingly, we demonstrate that the modification of the paper surface with hydrophobic ligands improve the sensing capabilities by confining the analyte solution in the AuSph sensing platform. It contributes to both concentrate the analyte, as well as, to decrease the sample volume to just a few μl. We also analyze the effect of the amount of the nanoparticles, tunable by the number of printing cycles, in the SERS performance of the plasmonic spots. The results show that 5 printing cycles give rise to sensing platforms with great SERS response in terms of intensity and uniformity. The spot-to-spot reproducibility is also analyzed observing good results even for AuSph spots from different printed papers. The paper-based SERS platform was tested towards the detection of crystal violet (CV) and the fungicide thiram. Additionally, applying a digital protocol for SERS analysis, a good linear correlation between the digital counts (or positive events) and the analyte concentration was obtained at the single-molecule SERS regime. In both cases, the quantification region threshold was 10−11 M. The great sensitivity performance of the inkjet-printed SERS substrate is reflected by the low sample volume needed (only 2 μL). The inkjet-printed SERS substrate and the fabrication method demonstrated to be efficient, reliable, reproducible and robust, with a cost less than $ 0.01 per spot. [ABSTRACT FROM AUTHOR]

Serious toxicity for organisms from pesticide glyphosate (Gly) residues to the ecosystem and human health has become a consensus. Rapid and selective detection of glyphosate, especially using a simple and portable instrument, is highly desired. In this work, we develop a novel enzyme-free rapid and visual ratiometric fluorescence sensor for selectively quantitative detecting glyphosate by integrating the designed blue carbon nanodots (CDs) and gold nanoclusters (Au NCs). The fluorescence of CDs can be quickly quenched via aggregation-caused quenching (ACQ) within 2 s after introducing glyphosate, resulting from the formation of CDs-Gly-CDs complex aggregation. While the Au NCs serve as the reference signal without any change, therefore leading to obvious and instant ratiometric fluorescence variation from blue to pink to orange. The broad linear range was obtained from 0 to 180 nM with a satisfactory detection limit of 4.19 nM. Furthermore, this approach was successfully applied to detect glyphosate in real samples and a portable smartphone platform integrated paper sensor was developed for in-site visual quantitative glyphosate detection, offering a promising strategy for the construction of enzyme-free trace hazard detection system. [Display omitted] • An enzyme-free ratiometric fluorescence sensor based on aggregation-caused quenching was designed. • The sensor was prepared by utilizing environmentally friendly nanomaterials. • The sensor exhibited visual and rapid detection to glyphosate residues. • Portable smartphone platform achieved on-site quantitative pesticides detection. [ABSTRACT FROM AUTHOR]

• Citrate functionalized AgNPs plated paper-based SERS sensor was synthesized. • An enhancement factor of 1.51 × 108 was obtained for the fabricated SERS sensor. • Paper-based SERS sensors were employed to fast quantify 2,4-D residue level in tea. • UVE-PLS ascertained optimum result with built sensor and RSD value of ≤4.56%. • Calculated LOD (1.0 × 10−4 µg/g) of built sensor was lower than the MRL of EC. Food safety is a growing concern in recent years. This work presents the design of a simple and sensitive method for predicting 2,4-D (2,4-dichlorophenoxyacetic acid) residue levels in green tea extract employing surface-enhanced Raman spectroscopy (SERS) coupled uninformative variable elimination-partial least squares (UVE-PLS). Herein, SERS active citrate functionalized silver nanoparticles (AgNPs) with enhancement factor 1.51 × 108 was used to prepare cellulose paper (common office) templated SERS sensor for acquiring SERS spectra of 2,4-D. The principle of the work was based on the interaction between 2,4-D and citrate group of AgNPs via chlorine atoms in the concentration range 1.0 × 10−4 to 1.0 × 103 µg/g. Three different wavenumber selection chemometric algorithms were studied comparatively to build an optimum calibration model, among them UVE-PLS showed enhanced performance as evident from the RPD value of 6.01 and Rp = 0.9864. Under optimized experimental condition proposed paper-based SERS sensor exhibited detection limit and RSD of 1.0 × 10−4 µg/g and <5%, respectively. In addition, the validation results by HPLC method were satisfactory (p > 0.05). [ABSTRACT FROM AUTHOR]

Green electronics is a trending and cost-effective method with potential application in health care monitoring and wearable electronics. We present a piezo resistive wearable pressure sensor using Polyaniline (PANI) incorporated with cellulose paper (CP) substrate. The ultralow-cost sensor is prepared by coating the sensing material on the paper using simple dip coating method. On stacking multiple PANI-CPs one upon another, the obtained flexible sensor demonstrates excellent sensitivity of 2.23 kPa−1, fast response of 70 ms and wide working range from 2 to 90 kPa. Furthermore, the sensor manifest excellent flexibility, outstanding stability up to 800 loading–unloading cycles and biodegradability. In addition, the pressure sensor can also be used for detecting rapid finger tapping. Apart from the other pressure sensors, this work mainly focusses on fabricating wearable piezo resistive sensors with low cost, facile fabricating process and shows potential for future applications in flexible wearable sensors. ga1 • Piezo resistive wearable pressure sensor was fabricate using PANI decorated on CP substrate. • The pressure sensor is prepared by coating the sensing material on to the paper using simple dip coating method. • The sensor demonstrates excellent sensitivity of 2.23 kPa−1, fast response of 70 ms and wide working range. • This work mainly focusses on fabricating wearable piezo resistive sensors with low cost, facile fabricating process. [ABSTRACT FROM AUTHOR]

Development of paper-based sensors that do not suffer with humidity interference is desirable for practical environmental applications. In this work, a laser processing method was reported to effectively modulate the cross-sensitivity to humidity of ZnO-based UV (Ultraviolet) sensors printed on paper substrate. The results reveal that the laser induced zinc oxide (ZnO) surface morphology contributes to the super-hydrophobicity of the printed ZnO nanoparticles, reducing humidity interference while enhancing UV sensitivity. Herein, this conducted research highlights for the first time that laser processing is an attractive choice that reduces the cross-sensitivity to water vapor in the UV sensing response of ZnO-based devices printed on paper, paving the way to low-cost and sophisticated paper-based sensors. [ABSTRACT FROM AUTHOR]

This study presents the design, simulation, implementation, and experimental characterization of a paperbased perforated disposable weight sensor system with a double piezoresistive layer. The demonstrated system is designed to achieve highly sensitive weight sensing operations with low-cost materials. For that purpose, the main fabrication material of the proposed disposable sensor is selected as a 289-µm-thick Strathmore 400 series Bristol paper. Approximately 48-µm-thick piezoresistive graphite paste is coated onto both sides of the paper-based cantilever beam with the aim of acquiring more sensitive weight-sensing capability. Additionally, the proposed paper-based structure has rows of closely spaced perforations at prespecified locations to facilitate the bending of the cantilever beam and to further increase the sensitivity of the system. A peripheral electronic read-out circuitry is developed and integrated into the system. It is experimentally demonstrated that the proposed weight-sensing system can measure miniature weights ranging to 2 g with a resolution of 20 mg. The implemented sensor has a sensitivity of 17.13 mV/mN or 168.01 mV/g. [ABSTRACT FROM AUTHOR]

Existing microfluidic technologies for blood tests have several limitations, including difficulties in integrating the sample preparation steps, such as blood dilution, and precise metering of tiny samples (microliter) for accurate downstream analyses on a chip. Digital microfluidics (DMF) is a liquid manipulation technique that can provide precise volume control of micro or nano-liter liquid droplets. Without using sensitive but complex detection methods for tiny droplets involving fluorescence, luminescence, and electrochemistry, this article presents a DMF device with embedded paper-based sensors to detect blood lithium-ion (Li+) concentration by colorimetry. Dielectrophoresis on the DMF device between two parallel planar electrodes separates plasma droplets (from tens to hundreds of nanoliters in volume) from undiluted whole blood (a few microliters) within 4 min with an efficiency exceeding 90%. The embedded paper sensors contain a detection reagent to absorb the DMF-transported plasma droplets. These droplets change the color of the paper sensors in accordance with the Li+ concentration. Subsequently, colorimetry is used to reveal the Li+ concentration via image analysis. The proposed method meets the detection-sensitivity requirement for clinical diagnosis of bipolar disorder, making the DMF device a potential therapeutic tool for rapid whole-blood Li+ detection. • Plasma droplets can be separated from whole blood via dielectrophoresis with DMF. • Paper sensor–embedded DMF devices can detect lithium ions via colorimetry. • Detection of lithium ions in whole blood can be completed within 4 min. [ABSTRACT FROM AUTHOR]

By using sensing technology, the individual component analysis at trace level in complex samples remains problematic simply because of various interfering species. For example, the determination of Cd2+ in rice is difficult due to the co-existing interfering metal cations at thousands or even millions of times higher concentrations. In this study, a heavy-metal ion sensitive BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based fluorometric paper sensor with assistance of solid phase extraction (SPE) was developed for the highly selective and sensitive determination of trace Cd2+ in rice. SPE column packed with prepared sulfonated PS–DVB microspheres was employed to enrich trace Cd2+ and meanwhile remove most interfering heavy-metal ions in simulated complex rice sample with oxalic acid as eluent, which was theoretically selected on the basis of f values. Mn2+, as a major coexistent heavy-metal ion, could not be easily removed by SPE, but showed little fluorescent response for BODIPY fluorometric paper sensor even in excess amounts. Combining the separation and enrichment capability of SPE column with the selectivity of BODIPY-based fluorometric paper sensor, we were able to detect trace Cd2+ in complex samples. The response of fluorometric paper sensor was linearly related with Cd2+ concentrations in the range of 0.5–4 μM, with a detection limit of 0.5 μM. Twelve real rice samples spiked with Cd2+ were analysed using this method and the results are in good agreement with ICP-MS measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report graphene-ink biosensor arrays on a microfluidic paper for metabolites. [•] The device is able to detect multiple metabolites sensitively and rapidly. [•] The device fabrication process is simple and inexpensive. [ABSTRACT FROM AUTHOR]