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In this study, we developed a cost-effective ion-sensing field-effect transistor (FET) with an extended gate (EG) fabricated on a separative paper substrate. The pH sensing characteristics of the paper EG was compared with those of other EGs fabricated on silicon, glass, or polyimide substrates. The fabricated paper-based EGFET exhibited excellent sensitivity close to the Nernst response limit as well as to that of the other substrate-based EGFETs. In addition, we found that all EGFETs, regardless of the substrate, have similar non-ideal behavior, i.e., drift phenomenon and hysteresis width. To investigate the degradation and durability of the paper EG after prolonged use, aging-effect tests were carried out in terms of the hysteresis width and sensitivity over a course of 30 days. As a result, the paper EG maintained stable pH sensing characteristics after 30 days. Therefore, we expect that paper EGFETs can provide a cost-effective sensor platform. [ABSTRACT FROM AUTHOR]

The integration of fully printed transistors on low cost paper substrates compatible with roll-to-roll processes is demonstrated here. Printed electronics promises to enable a range of technologies on paper including printed sensors, RF tags, and displays. However, progress has been slow due to the paper roughness and ink absorption. This is solved here by employing gravure printing to print local smoothing pads that also act as an absorption barrier. This innovative local smoothing process retains desirable paper properties such as foldability, breathability, and biodegradability outside of electronically active areas. Atomic force microscopy measurements show significant improvements in roughness. The polymer ink and printing parameters are optimized to minimize ink absorption and printing artifacts when printing the smoothing layer. Organic thin film transistors (OTFT) are fabricated on top of this locally smoothed paper. OTFTs exhibit performance on par with previously reported printed transistors on plastic utilizing the same materials system (pBTTT semiconductor, poly-4-vinylphenol dielectric). OTFTs deliver saturation mobility approaching 0.1 cm2V-1s-1 and on-off-ratio of 3.2 × 104. This attests to the quality of the local smoothing, and points to a promising path for realizing electronics on paper. [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile, Flexible, and Fast sensing of spike protein with SERS paper sensor. • Low-cost / Ecofriendly green assisted production of spherical silver nanoparticles. • Paper sensor detectability is 2.4 pg/ul of spike protein of SARS-CoV-2 virus. • Spike protein sensing in saliva is achieved with SERS paper sensor. • Lab on paper ensures environment sustainability by its safe disposal. Rapid investigation on the detection of spike protein with paper sensor is projected with Surface Enhanced Raman Spectroscopy (SERS). SERS sensor with lab on paper is preceded with facile, cost-effective strategy. Silver nanoparticles with average size of 20–30 nm were produced by green chemistry approaches, followed by loading the nanoparticles on hydrophobic paper surfaces. The very low %RSD (∼1.5) with mapping scan ensembles high reproducibility. Spike protein detection analysis derived the prominent finger print regions of amide bands as well abundant amnio acids (Phenylalanine-1003 cm−1, Tryptophan- 680 cm−1, Tyrosine-1473 cm−1) respectively. The detectability of sensor is gauged to be 2.4 pg / µL. Real time analysis on human saliva spiked with spike protein exhibited diagnosis within 2 min. Developed paper sensor provide us the scope of SERS technique to bring state of art in early detection of covid infections and safe disposal after its use. [ABSTRACT FROM AUTHOR]

Biosensors have emerged as a valuable tool with high specificity and sensitivity for fast and reliable detection of hazardous substances in drinking water. Numerous substances have been addressed using synthetic biology approaches. However, many proposed biosensors are based on living, genetically modified organisms and are therefore limited in shelf life, usability and biosafety. We addressed these issues by the construction of an extensible, cell-free biosensor. Storage is possible through freeze drying on paper. Following the addition of an aqueous sample, a highly efficient cell-free protein synthesis (CFPS) reaction is initiated. Specific allosteric transcription factors modulate the expression of ‘superfolder’ green fluorescent protein (sfGFP) depending on the presence of the substance of interest. The resulting fluorescence intensities are analyzed with a conventional smartphone accompanied by simple and cheap light filters. An ordinary differential equitation (ODE) model of the biosensors was developed, which enabled prediction and optimization of performance. With an optimized cell-free biosensor based on the Shigella flexneri MerR transcriptional activator, detection of 6 μg/L Hg(II) ions in water was achieved. Furthermore, a completely new biosensor for the detection of gamma-hydroxybutyrate (GHB), a substance used as date-rape drug, was established by employing the naturally occurring transcriptional repressor BlcR from Agrobacterium tumefaciens. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2 ), an important reactive oxygen species (ROS), is related to the oxidative stress in organisms, and plays important roles in a variety of cellular activities as well. So it is of crucial importance to develop sensitive and accurate sensing strategies to detect H 2 O 2 in biological systems. Herein, by taking advantage of the unique emission characteristics of aggregation induced emission (AIE) fluorogens, we proposed a non-enzymatic fluorescence platform for facile and sensitive detection of H 2 O 2 , both in solution state using fluorescence spectrometer and on paper-based sensor via visual inspection. Through the reaction between L -cysteine and H 2 O 2 , the fluorescence of TPE-M-L, an AIE fluorogen formed between maleimide-functionalized tetraphenylethene (TPE-M) and L -cysteine, is quenched, and highly sensitive non-enzymatic H 2 O 2 assay is readily carried out. The limit of detection (LOD) of 10 nM in solution state and 2.5 μM on paper-based sensor were obtained for H 2 O 2 detection, which were superior or comparable to those previously reported in literature. Moreover, by integrating glucose oxidase with the AIE fluorogen of TPE-M-L, highly sensitive and selective glucose detection was also conveniently achieved both in solution state and on paper-based sensor by the as-proposed strategy, with the LODs of 50 nM in solution state and 10 μM via visual observation, much better than those obtained by other fluorescence methods. The as-proposed sensing strategy was also successfully applied to assay glucose in human serum samples. Therefore, the paper-based fluorescence sensor exhibits the advantages of simple fabrication, high sensitivity and portability, and has great potential to be applied in on-site assay of H 2 O 2 and glucose in real samples. [ABSTRACT FROM AUTHOR]

Simple and selective paper-based colorimetric sensors using silver nanoprism (AgNPrs) were conveniently fabricated and developed for the determination of chloride ions (Cl − ) contaminated in the environment. Samples containing different concentrations of Cl − were analyzed. The analysis is based on the oxidative etching of the AgNPrs into smaller silver nanospheres (AgNPss) by Cl − . In the presence of Cl − , the distinctive color change of the AgNPrs from dark-violet to red was rapidly visualized by the naked eye in 5 min without the requirement of surface modification. For quantitative measurement using image processing, a good linear relationship (R 2 = 0.996) between logarithmic of Cl − concentration and the average mean color intensity was obtained in the range of 10–1000 mg L −1 with a detection limit of 1.3 mg L −1 . The developed sensors were investigated for precision, accuracy, and sensitivity and validated by the classical method. Statistical analysis proved that the developed sensors were precise, sensitive and accurate and can be used effectively for the analysis of Cl − in natural waters. [ABSTRACT FROM AUTHOR]

Today, diabetes mellitus is one of the most common diseases that affects the population on a worldwide scale. Patients suffering from this disease are required to control their blood-glucose levels several times a day through invasive methods such as piercing their fingers. Our NaGdF 4 : 5% Er3+, 3% Nd3+ nanoparticles demonstrate a remarkable ability to detect D-glucose levels by analysing alterations in their red-to-green ratio, since this sensitivity arises from the interaction between the nanoparticles and the OH groups present in the D-glucose molecules, resulting in discernible changes in the emission of the green and red bands. These luminescent sensors were implemented and tested on paper substrates, offering a portable, low-cost and enzyme-free solution for D-glucose detection in aqueous solutions with a limit of detection of 22 mg/dL. With this, our study contributes to the development of non-invasive D-glucose sensors, holding promising implications for managing diabetes and improving overall patient well-being with possible future applications in D-glucose sensing through tear fluid. [Display omitted] • The usual method for measuring glucose involves invasive finger or arm piercing. • We propose the use of NaGdF 4 : 5% Er3+, 3% Nd3+ as sensing probes for the non-invasive detection of D-glucose. • Detection of D-glucose relies on ErNd-NPs' luminescence, altering red-to-green ratio. • The ErNd-NPs were successfully implemented in paper substrates, providing a portable, low-cost sensor. • Achieved enzyme-free D-glucose detection with 22 mg/dL limit, advancing future non-invasive tear fluid sensing. [ABSTRACT FROM AUTHOR]

Flexible and thin-film humidity sensors are currently attracting the attention of the scientific community due to their portability and reduced size, which are highly useful traits for use in the Internet o Things (IoT) industry. Furthermore, in order to perform efficient and profitable mass production, it is necessary to develop a cost-effective and reproducible fabrication process and materials. Green fabrication methods and biodegradable materials would also minimize the environmental impact and create a sustainable IoT development. In this paper, flexible humidity sensors based on a common salt (NaCl) sensing layer are reported. Our sensors and the fabrication techniques employed, such as dip and spray coating, provide a biodegradable, low cost, and highly reproducible device. One of the sensors reported presents a typical resistive behaviour from 40% RH up to 85% RH with a sensitivity of 0.21 (Z/%RH). The performance of the sensors obtained with several fabrication techniques is studied and reported at multiple frequencies from 100 Hz to 10 MHz, showcasing its versatility and robustness. [ABSTRACT FROM AUTHOR]

• Fabrication of free standing CNT paper for the purpose of ubiquitous use. • Understandings of the detection mechanism and that enables to identify gas species from the transient behavior. • Correct reproducibility and following the mechanism show possibility for the realization of light and flexible gas sensor. In order to achieve light and flexible gas sensor, we fabricated a uniform carbon nanotube paper made by multi-walled carbon nanotube and employed it as a sensing part. Referring to the transient behavior, it was clarified that the sensor response followed Langmuir isotherm, similar to the previous results prepared on a glass substrate. A repetition characteristics was quite stable and sensitivity was higher than previous one. Thus, it opens prospects for application, but it is unclear why the sensitivity is high despite the increased thickness. [ABSTRACT FROM AUTHOR]

The development of paper-based sensors with the distance readout is particularly attractive for the point-of-care testing (POCT) of biomarkers. Herein, we report a paper-based sensor that can convert the viscosity change caused by the hydrogel degradation into the variance of water flow distance on the paper. The detection of alkaline phosphatase (ALP) and alpha-fetoprotein (AFP) is demonstrated as examples. Copper alginate (Cu-Alg) hydrogel can be formed when mixing the aqueous solutions of Cu2+ and alginate. The introduction of pyrophosphate ion (PPi) induces the gel-sol transition due to the high affinity between Cu2+ and PPi. However, in the presence of ALP, the gel-sol transition is prevented due to the hydrolysis of PPi by ALP. In these processes, the viscosity changes of the hydrogels are translated into the differences of the flow distances on the pH test papers. In addition, the tilt of the papers can increase the accuracy of detection. The detection of AFP is also fulfilled via the construction of the paper-based immunosensor using the ALP-linked AFP detection antibody. The developed paper-based sensors show excellent performance for the quantitative detection of biomarkers in real samples with remarkable selectivity. Overall, this convenient method has great potential in POCT applications. • A paper-based sensor is developed to detect ALP and AFP via distance readout. • It converts viscosity changes during the gel-sol transition into distance signals. • Copper alginate hydrogel can be degraded by PPi which is the substrate of ALP. • Paper-based immunosensor is built for the detection of AFP. • It shows excellent performance in the detection of ALP and AFP in human serum. [ABSTRACT FROM AUTHOR]

Accumulation of high concentrations of Al(III) in body has a direct impact on health and therefore, the trace detection of Al(III) has been a matter for substantial concern. An anionic metal organic framework ({[Me2NH2]0.5[Co(DATRz)0.5(NH2BDC)] ⋅ xG}n; 1; HDATRz=3,5‐diamino‐1,2,4‐triazole, H2NH2‐BDC=2‐amino‐1,4‐benzenedicarboxylic acid, G=guest molecule) composed of two types of secondary building units (SBU) and channels of varying sizes was synthesized by employing a rational design mixed ligand synthesis approach. Free −NH2 groups on both the ligands are immobilized onto the pore surface of the MOF which acts as a superior luminescent sensor for turn‐on Al(III) detection. Furthermore, the large channels could allow the counter‐ions to pass through and get exchanged to selectively detect Al(III) in presence of other seventeen metal ions with magnificent luminescence enhancement. The observed limit of detection is as low as 17.5 ppb, which is the lowest among the MOF‐based sensors achieved so far. To make this detection approach simple, portable and economic, we demonstrate MOF filter paper test for real time naked eye observation. [ABSTRACT FROM AUTHOR]

Research, design, fabrication and results of various screen printed capacitive humidity sensors is presented in this paper. Two types of capacitive humidity sensors have been designed and fabricated via screen printing on recycled paper and cardboard, obtained from the regional paper and cardboard industry. As printing ink, commercially available silver nanoparticle-based conductive ink was used. A considerable amount of work has been devoted to the humidity measurement methods using paper as a dielectric material. Performances of different structures have been tested in a humidity chamber. Relative humidity in the chamber was varied in the range of 35%-80% relative humidity (RH) at a constant temperature of 23 °C. Parameters of interest were capacitance and conductance of each sensor material, as well as long term behaviour. Process reversibility has also been considered. The results obtained show a mainly logarithmic response of the paper sensors, with the only exception being cardboard-based sensors. Recycled paper-based sensors exhibit a change in value of three orders of magnitude, whereas cardboard-based sensors have a change in value of few 10s over the entire scope of relative humidity range (RH 35%-90%). Two different types of capacitor sensors have been investigated: lateral (comb) type sensors and modified, perforated flat plate type sensors. The objective of the present work was to identify the most important factors affecting the material performances with humidity, and to contribute to the development of a sensor system supported with a Radio Frequency Identification (RFID) chip directly on the material, for use in smart packaging applications. Therefore, the authors built a passive and a battery-supported wireless module based on SL900A smart sensory tag's IC to achieve UHF-RFID functionality with data logging capability [ABSTRACT FROM AUTHOR]

The results of a voltage-current characteristics study of sensors made of graphite paper with multiwall nanotubes are presented. It has been found experimentally that these samples are usable as gas sensors for the detection of NH, H, and Cl in air. [ABSTRACT FROM AUTHOR]

An ionophore-based ion-selective optode platform on paper is described for the first time with a sodium optode as the example. Cellulose paper is shown to be an excellent substrate for adsorption of the required chromoionophore, ionophore, and ion-exchanger species. These adsorbed components form a hydrophobic phase that enables heterogeneous optical ion sensing in the absence of any plasticizer or organic polymer phase. [ABSTRACT FROM AUTHOR]

Highly sensitive and specific diagnostics for cannabis usage are essential for rapid on-site screening for illicit drug usage. To improve the sensitivity of THC immunoassays, a proper immobilization of the sensing elements on the sensor substrate is critical. In this work, we demonstrated the utilization of EDC/NHS coupling chemistry with nanocellulose to obtain efficient anchor layers for the immobilization of anti-immune complex antibodies on surfaces. In our approach, the high surface-to-volume ratio, OH-group-rich surface, and high hygroscopicity of TOCNF enable efficient surface functionalization and enhance water permeation inside the nanocellulose network structure, offering a hydrophilic spacer for the sensing antibodies. THC detection was shown in both SPR (surface plasmon resonance technique) and paper-based sensing systems. In SPR, antibody immobilization and the related interactions with the target molecule complex with 1–10 μg/mL THC were followed in-situ in aqueous environment, revealing robust attachment of the antibody to the nanocellulose layer and preserved bioactivity. Additionally, quantitative THC detection was enabled on paper substrate by colorimetric means by employing labeled anti-THC Fab antibody fragments as detection antibodies. THC detection efficiency of covalently linked biointerface was superior compared to the performance of physically linked biointerface. The chemical conjugation of anti-IC to nanocellulose allowed efficient binding, whereas supramolecular conjugation led to insufficient binding, highlighting the relevance of the developed nanocellulose-based anchor layer. Nanocellulose EDC/NHS coupling chemistry to obtain efficient immobilization of cannabis-specific antibodies on surfaces for solid sensors and paper-based immunoassays. [Display omitted] [ABSTRACT FROM AUTHOR]

Given the huge threat of Hg2+ to human health, it is always significant to develop Hg2+ monitoring tools. Utilizing its impacts on nanozyme catalysis is a promising strategy to realize Hg2+ detection. However, nearly all the assays fabricated based on the principle should be performed in solution and in laboratory and require bulky signal reading instruments, hindering their wider applications. It is highly desired to develop portable, efficient, and practical Hg2+ sensors. Herein, we proposed the in situ controllable growth of Ag nanoparticles (AgNPs) on paper to fabricate a smartphone optical nanosensor for highly sensitive Hg2+ detection based on enzyme-mimetic activity stimulation. The ultrasmall AgNPs were directly grown on paper wafers to obtain test strips, which further integrated a 3D-printed holder and an APP built-in smartphone to fabricate the sample-to-answer sensor. The AgNPs-based test strips exhibited a target-stimulated peroxidase-like activity to catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine, and the chromogenic information was captured and processed by the smartphone to rapidly report the level of Hg2+. With the portable nanosensor, highly sensitive and specific detection of Hg2+ was achieved, with a detection limit down to 0.44 nM. The sensor gathers the features of easy construction, simple operation, excellent capability, and robust performance together, promising great potential for rapid on-site analysis. [Display omitted] • In situ controllable growth of AgNPs on paper to fabricate test strips. • Hg2+-stimulated peroxidase-like activity to trigger chromogenic reactions. • Test strips, 3D-printed holder and APP built-in smartphone were integrated. • Smartphone-assisted paper-based optical nanosensor for sensitive Hg2+ detection. [ABSTRACT FROM AUTHOR]

In order to solve the problem of limited sensitivity of paper-based colorimetric sensors in the face of trace analyte, we verified the feasibility of improving the sensitivity by establishing a signal amplification method with high-abundance binding agent and confined nanopores/nanochannels through silica sol-gel treated paper fiber. The elevated abundance of agent serves to increase the absorption efficiency, and the silica nanopores/nanochannels generated on the fiber surface provide confined transport for molecules. By continuously flowing a large volume of sample vertically through the paper-based sensing membrane, the target could be enriched, increasing the signal accumulation, and realizing the sensitive paper-based sensing detection of target analyte. At the same time, we first proposed a novel pesticide detecting protocol based on nanozyme-catalyzed degradation. The chemical sensing of stable pesticides could be realized under the catalysis of nanozymes, and pesticides were degraded into easily detectable active small molecules. The limit of detection of imidacloprid was determined to be as low as 50 ppb with good selectivity. This novel paper-based pesticide sensor with high sensitivity holds great promise for future practical applications. [Display omitted] • A silica film-based paper signal amplification method was studied. • The nanochannels generated on the paper fiber could increase the abundance of captures and provide confined transport. • A brand new idea for pesticide detection based on nanozymes catalysis degradation was developed. [ABSTRACT FROM AUTHOR]

A novel paper-based colorimetric glucose sensor was proposed employing Prussian blue nanoparticles (PB NPs) as mimic peroxidase. The sensor was manufactured by spraying solution containing PB NPs, glucose oxidase and chromogenic agents into a paper, then coating the filter layer and spreading layer on the top. The layer-by-layer structure enabled the sensor detect glucose in whole blood, as well as elimination of the coffee-ring effect which ensure the performance. As a powerful alternative to natural peroxidase, PB NPs showed the mimic enzymatic activity well preserved in dry environment. The manufacture process of the sensor is easy to be industrialized. Under optimal conditions, the sensor exhibited a linear range from 2.5 mM to 25 mM for glucose in blood with satisfactory reproducibility (the coefficient of variant <4%), great storage stability (1 month at 45 °C) and excellent linearity compared with those commercial kits (R > 0.99). Coupled with a handhold device, the PB NPs-based test strip realized the goal of personal operation, user-friendly control, automatic readouts, and data storage, and able to link the Cloud, showing unique potential in clinical application, especially in community-level medical scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quantitation of urea by urease-mediated chitosan viscosity change on paper-based sensor. • Chitosan solution viscosity is converted to distance-readout on paper-based sensor. • Combination of paper-based sensor and distance-readout method for urea POCT. In this study, a paper-based sensor combined with visual distance-readout technique for point of-care testing (POCT) of urea was developed by urease-mediated chitosan viscosity change. A series of factors that affect the performance of the sensor were investigated, including the type of filter paper, chitosan concentration, acetic acid concentration and enzymatic reaction conditions. Under optimal conditions, the proposed method for urea determination has good linearity between 3.8–15.1 mM. The limit of quantitation is 3.8 mM. Finally, the paper-based sensor was successfully applied to the determination of urea in two diesel exhaust fluid (DEF) samples. The recoveries of urea were 91.4 % and 109.9 % in DEF-1 and DEF-2, respectively. The present study provides a novel approach, which integrates paper-based sensor and visual distance-readout technique, for monitoring urea in POCT application, especially in remote or resource-limited regions. [ABSTRACT FROM AUTHOR]

Environmental monitoring and biomedical diagnostics have attracted a lot of interest in the research community in recent years. Efforts are being made to develop technologies for sensors and diagnostic kits that provide a rapid and on-the-spot response. Microfluidics based lab-on-a-chip systems offer a promising solution in this direction. In the present study, we employ a simple method to fabricate labon- a-chip device or platform using commonly available materials, including cellulose paper and wax. Hydrophilic wells surrounded by hydrophobic boundaries are created by wax impregnation through the paper on heat treatment. We further demonstrate the application of these devices in the detection of iron contamination in water using colourimetric chemical reactions. Our results show that these devices can be used for obtaining qualitative as well as quantitative outcomes. We make use of image analysis tools to quantify the concentration of iron in the samples. The platform offers an affordable, accessible and versatile option for sensing applications in resource-limited settings. [ABSTRACT FROM AUTHOR]

Shortage of labor and increased work of young people are causing problems in terms of care and welfare of a growing proportion of elderly people. This is a looming social problem because people of advanced ages are increasing. Necessary in the fields of care and welfare, pneumatic artificial muscles in actuators of robots are being examined. Pneumatic artificial muscles have a high output per unit of weight, and they are soft, similarly to human muscles. However, in previous research of robots using pneumatic artificial muscles, rigid sensors were often installed at joints and other locations due to the robots' structures. Therefore, we developed a smart actuator that integrates a bending sensor that functions as a human muscle spindle; it can be externally attached to the pneumatic artificial muscle. This paper reports a smart artificial muscle actuator that can sense contraction, which can be applied to developed self-monitoring and robot posture control. [ABSTRACT FROM AUTHOR]

Paper-based devices are a leading alternative among the main analytical tools for point-of-care testing, due to their portability, low-cost, and ease-of-use. Colorimetric readouts are the most common method of detection in these microfluidic devices, enabling qualitative, semi-quantitative and fully quantitative analysis of multiple analytes. There is a multitude of ways to obtain a colorimetric output in such devices, including nanoparticles, dyes, redox and pH indicators, and each has unique drawbacks and benefits. There are also multiple variables that impact the analysis of colorimetric reactions in microfluidic paper-based systems, including color homogeneity, image capture methods, and the data handling itself. Here, we present a critical review of recent developments and challenges of colorimetric detection on microfluidic paper-based analytical devices (μPADs), and present thoughts and insights towards future perspectives in the area to improve the use of colorimetric readouts in conjunction with μPADs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile one-step solvothermal synthesis of FA-CDs using folic acid as raw materials. • FA-CDs and corresponding paper sensor can detect Hg2+ with LOD of 1.29 nM. • Both FA-CDs and paper sensor can be recovered by EDTA for detection of Hg2+. • FA-CDs exhibit excellent cellular imaging performance due to low cytotoxicity. In this work, the blue emission carbon dots (FA-CDs) are synthesized by one-pot solvothermal method by using folic acid as precursor. The FA-CDs emitted bright emission at 445 nm when excited at 360 nm with the QY of 31.2 %. The FA-CDs exhibit sensitive quenching response to Hg2+ with variable concentrations systematically, which determined FA-CDs can be employed as fluorescent probe, with a reliable linear relationship between fluorescence intensity and Hg2+ concentration, and a limit of detection (LOD) of 1.29 nM. Notably, the quenched FA-CDs can be recovered by using EDTA saturated solution with the emission comparable to initial in succession. The FA-CDs based paper sensor can be explored with similar detection performance, and it can also be restored by EDTA saturated solution. Both the restored CDs and paper sensor can be reused in the next turn for detecting Hg2+, which allowed the FA-CDs and their paper sensor can be serviced as sustainable probe for Hg2+ detection. The visual LOD of paper sensor can be determined at 0.1 μM, notably, the paper sensor can be reused at least 3 times with good performance, which is beneficial to environmental protection and saving resources. Possess excellent water solubility and non-toxic properties, the cellular imaging of FA-CDs was evaluated with excellent quality fluorescent image results. The FA-CDs provide a promising convenient fluorescent probe for multi-application in detection and imaging. [ABSTRACT FROM AUTHOR]

Antibiotic residues are a huge threat to food safety and ecological environment and florfenicol (FF) is one of the most wide-spread antibiotics entering the food chain. Hence, rapid and sensitive methods for the detection of FF in food are highly required. In this study, we present a facile method for the fabrication of three-dimensional (3D) ZnO@Ag nanoflowers (ZnO@Ag NFs) assembling on polyester fiber membrane (PFM), which can be used as an economic surface-enhanced Raman spectroscopy (SERS) paper sensor for sensitive determination of FF traces. 3D ZnO@Ag NFs that decorated on PFM provides sufficient "hot spots" and high chemical stability for the analytical platform. Without using any expensive materials and complicated methods, this flexible SERS substrate exhibits superior sensitivity, excellent uniformity, and well-reproducibility. The SERS response of the sensor toward FF shows excellent correlation during the range of 1 × 10−9 M to 1 × 10−3 M with the limit of detection (LOD) as low as 2.23 × 10−10 M. The recovery rate ranges from 97% to 101%, indicating that the SERS detection method provides a powerful tool for detecting toxic and harmful substances in food. • 3D ZnO@Ag nanoflowers were prepared by a simple wet chemical synthesis method. • 3D nanoflower structure is easier to adsorb more noble metal nanoparticles. • ZnO@Ag nanoflowers assembling on polyester fiber membrane as SERS paper sensor. • Aggregation-induced hot spots allow the LOD of FF at 2.23 × 10−10 M. • The paper sensor is easy to make, ultrasensitive, and satisfactory in real sample tests. [ABSTRACT FROM AUTHOR]

In this paper, the advances of distributed fusion estimation (DFE) algorithms for multi-sensor networked systems (NSs) are reviewed. First, several general DFE algorithms are reviewed. Then, some random phenomena in NSs are discussed, including data quantization, random transmission delays, packet dropouts, fading measurements and communication disturbances. Finally, the advances of DFE algorithms for NSs are summarized. [ABSTRACT FROM AUTHOR]

We evaluate and compare the performance of a 15.6‐inch mini‐LED backlit LCD (mLCD) with a commercial OLED panel. Results show that the mLCD exhibits advantages over the OLED panel in peak brightness, gamma curve, color volume, power consumption, and ambient contrast ratio. The LMK imaging photometer with a high‐resolution CMOS sensor is employed to characterize the halo effect and reconstruct the real luminance profiles based on the non‐ideal profile of the OLED display. We have also proposed a novel strategy to measure the backlight's point spread function. [ABSTRACT FROM AUTHOR]

A novel emissive Schiff‐base (3)has been synthesized through single‐step condensation of sulfanilamide and fluorogenic 3‐formylchromone. Compound (3) senses Fe3+ ion in semi‐aqueous media. Both fluorogenic and colorimetrical changes were observed in the presence of Fe3+ ions. Interestingly, on introduction of EDTA into the putative complex, [(3)+Fe3+], the spectroscopic changes were reversed. The ligand detects Fe3+ ions sensitively as the limit of detection for Fe3+ ion was 9.3×10−7 M. The probe performs molecular logic operation (INHIBIT) as well as function of a three‐input keypad lock. Further, the ligand (3)was successfully incorporated into Whatman filter paper as the test strips and aluminium coated silica gel plates, which showed a great selectivity for Fe3+ ions. [ABSTRACT FROM AUTHOR]

Current methods of monitoring breathing require cumbersome, inconvenient, and often expensive devices; this requirement sets practical limitations on the frequency and duration of measurements. This article describes a paper-based moisture sensor that uses the hygroscopic character of paper (i.e. the ability of paper to adsorb water reversibly from the surrounding environment) to measure patterns and rate of respiration by converting the changes in humidity caused by cycles of inhalation and exhalation to electrical signals. The changing level of humidity that occurs in a cycle causes a corresponding change in the ionic conductivity of the sensor, which can be measured electrically. By combining the paper sensor with conventional electronics, data concerning respiration can be transmitted to a nearby smartphone or tablet computer for post-processing, and subsequently to a cloud server. This means of sensing provides a new, practical method of recording and analyzing patterns of breathing. [ABSTRACT FROM AUTHOR]

Paper has been present in the world of analytical chemistry for centuries, but it seems that just a few years back it was rediscovered as a valuable substrate for sensors. We can easily list some of the countless advantages of this simple cellulosic substrate, including mechanical properties, three-dimensional fibrous structure, biocompatibility and biodegradability, easiness of production and modification, reasonable price, and availability all over the world. Those characteristics make paper a first-choice substrate for disposable sensors and integrated sensing platforms. Nowadays, numerous examples of paper-based sensors are being presented in the literature. This review describes some of the most prominent examples classifying them by type of detection: optical (colorimetric, fluorescence, surface-enhanced Raman spectroscopy, and transmittance methods) and electrochemical (voltammetric, potentiometric, and conductivity-based methods). We take a closer look at recent advances in immunoassays fabricated on paper, excluding simple lateral flow tests assembled on nitrocellulose. This review also summarizes the main advantages and disadvantages of the use of paper as a substrate for sensors, as well as its impact on their performance and application, presents a short history of paper in analytical chemistry, and discusses fabrication methods and available sources of paper. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors still face difficulties achieving a constantly adaptable micronanostructure of substrate materials. Interlinked microcone resistive sensors were fabricated by polydimethylsiloxane (PDMS) nanocone array. PDMS nanocone array was achieved by the second transferring tapered polymethyl methacrylate (PMMA) structure. In addition, self-assembly 2D carbon nanotubes (CNTs) networks as a conducting layer were prepared by a low-cost, dependable, and ultrafast Langmuir–Blodgett (LB) process. In addition, the self-assembled two-dimensional carbon nanotubes (CNTs) network as a conductive layer can change the internal resistance due to pressure. The results showed that the interlinked sensor with a nanocone structure can detect the external pressure by the change of resistivity and had a sensitive resistance change in the low pressure (<200 Pa), good stability through 2800 cycles, and a detection limit of 10 kPa. Based on these properties, the electric signals were tested, including swallowing throat, finger bending, finger pressing, and paper folding. The simulation model of the sensors with different structural parameters under external pressure was established. With the advantages of high sensitivity, stability, and wide detection range, this sensor shows great potential for monitoring human motion and can be used in wearable devices. [ABSTRACT FROM AUTHOR]

Tetrakis(4-sulfonatophenyl)porphyrin (TSPP) was immobilized on patterned paper and used as a sensor for heavy metal ions in an advanced organic chemistry course. The resulting sensor could detect Hg2+ and Cd2+ ions colorimetrically, while Cu2+ ion resulted in fluorescence quenching, thus demonstrating a multiplex capability of this paper-based sensor. From the synthesis of the porphyrin to the fabrication of the sensor, advanced undergraduate chemistry students gained first-hand experience with a classical organic synthesis, and also witnessed its application within 2-3 full-day laboratory sessions. This experiment is a good demonstration of how an easily synthesized compound can be exploited to tackle an important problem in real-world situations. [ABSTRACT FROM AUTHOR]

Ratiometric fluorescent sensors can suppress the interference of factors unrelated to analysis due to their built-in self-calibration characteristics, which exhibit higher sensitivity and more obvious visual detection in the process of qualitative and quantitative analysis. Herein, we constructed a ratiometric fluorescence probe based on fluorescent/colorimetric dual-mode method for the determination of arginine by encapsulating rhodamine B in-situ into UiO-66-NH 2 MOFs (UiO-66-NH 2 @RhB). The as-prepared probe showed dual-emission characteristics under a single excitation wavelength. The fluorescence intensity of UiO-66-NH 2 was increased significantly by arginine, while the emission peak intensity of rhodamine B remained stable, resulting in a single-signal response with fixed reference. Furthermore, the practicality of the presented sensor was successfully validated by quantitative detection of arginine in human serum. More significantly, paper-based sensors for arginine detection were devised by using carboxymethyl cellulose modified filter papers. Under the irradiation of ultraviolet light, the paper-based sensors would produce obvious color variation from lightpink to bluish violet. This work provided a convenient and efficient method for on-site detection of arginine. Schematic illustration of in-situ encapsulation strategy of ratiometric fluorescence probe UiO-66-NH 2 @RhB and paper-based sensor for visual detection of arginine. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Portable sensing platform integrated fluorescence sensor with smartphone-device. • Fluorescence of SiCDs quenched by Fe3+ through photoinduced electron transfer. • Fluorescence of SiCDs-Fe3+ recovered by AA owing to releasing –NH 2 /–OH. • " AA-Tester " App to analyze AA exhibits high sensitivity with LOD of 18.12 nmol/L. • SPOC sensor shows satisfactory accuracy with RSD of 0.79–2.31 % in AA detection. It is significant to develop low-cost, sensitive, and portable sensing platform for point-of-care testing of ascorbic acid (AA) in food quality evaluation. Herein, a smart point-of-care (SPOC) sensor, consisting of fluorescent paper chip, 3D printed-accessories and smartphone, was developed for ultrasensitive and visual quantitative detection of AA. Fluorescent paper chip was made through printing silicon doped carbon dots (SiCDs)-Fe3+ as "ink" onto filter paper, in which SiCDs emitting strong fluorescence signal quenched by Fe3+, and then recovered by AA owing to releasing –NH 2 /–OH and introducing defects on SiCDs. The smartphone with an application named " AA-Tester " was established to analyze AA and exhibited high sensitivity with low detection limits of 18.12 nmol/L. HPLC method was used to verify the SPOC sensor and obtained satisfactory accuracy with relative standard deviations of 0.79–2.31 %. The portable sensing platform integrated fluorescence sensor with smartphone-device will be favorable for ultrasensitive and on-the-spot detection of AA. [ABSTRACT FROM AUTHOR]

In this work, a novel analytical approach based on the photocatalytic decomposition of N -nitrosamines combined with headspace thin-film microextraction of the generated nitrogen oxides such as NO has been developed for the determination of the acyclic N -nitrosamine fraction in drinking water samples. A hydrophilic cellulose substrate modified with fluorescent silver nanoclusters (Ag NCs) was used both as extractant and sensing platform. A quenching effect of Ag NCs fluorescence occurs as the concentration of N -nitrosamines increases. Front-face fluorescence spectroscopy with a solid sample holder was employed for directly measuring the fluorescence quenching onto the cellulose substrate. In order to achieve an optimal analytical response, different parameters involved in the photocatalytic reaction as well as those concerning the microextraction step were fully investigated. It is demonstrated that the photodegradation rate of cyclic N -nitrosamines at acidic pH is much lower than that of acyclic ones, which can be the basis for the determination of the later fraction in waters. Under optimal conditions, a detection limit for the acyclic N -nitrosamine fraction around 0.08 μg L−1 using N -nitrosodimethylamine (NDMA) as model compound for calibration was obtained. Several drinking waters were spiked with acyclic N -nitrosamines showing recoveries in the range of 98–102% with a relative standard deviation of 3–4% (N = 3). N -nitrosamines generated as by-products during disinfection processes applied to water cause multiple adverse effects on human health being classified as potential human carcinogens. This study highlights the suitability of a fluorescent paper-based sensor for the rapid analysis of the acyclic N -nitrosamine fraction (i.e. the most abundant fraction) as a total index in drinking water, being useful as screening tool before exhaustive chromatographic analysis, which saves costs, time and reduces waste generation. [Display omitted] • In situ photocatalytic decomposition of N -nitrosamines to NO x species is performed. • Combination of microextraction with fluorescent paper-based sensing for NO x detection. • Ag NCs immobilized onto cellulose behave both as sorption and sensing platforms. • Front-face fluorescence spectroscopy as readout technique in the paper-based sensor. • A simple and rapid method for acyclic N -nitrosamines detection is accomplished. [ABSTRACT FROM AUTHOR]

2ʹ-(2-((4-(methylthio)phenyl)amino)-2-oxoethoxy)-[1,1ʹ-biphenyl]-2-yl 5(dimethyl amino)naphthalene-1-sulphonate (1) was synthesised and used as a F− ion sensor. The selectivity of sensor 1 with various anions (F−, Cl−, Br−, CH3COO−, C6H5COO− and H2PO4−) in DMSO was evaluated by 1H NMR, UV-visible and fluorescence study. For 1H NMR, an amide proton of sensor 1 disappeared due to the deprotonation reaction upon addition of F− ion. On the contrary, the proton signal of HF2− emerged at 16.11 ppm. Upon addition of F− ion, sensor 1 showed a new absorption band at 300 nm and the solution turned colourless. For fluorescence response, sensor 1 exhibited the enhancement of emission intensity at 434 nm with slight blue shift when titrated with F− ion. These results suggest that sensor 1 possessed high sensitivity and selectivity towards F− ion detection. In addition, the sensor 1 test strip coated on TLC plates and filter papers were demonstrated for specific detection F− ion. [ABSTRACT FROM AUTHOR]

A new, simple and easy-to-manufacture highly selective and sensitive dual-mode sensor A1, is used for CN− colorimetric and fluorescence detection. Interestingly, the solid powder of sensor A1 emits a strong green fluorescence, and has aggregation-induced emission properties. Single crystal diffraction analysis results prove that the generation of AIE properties is based on the J-aggregation mechanism. Simultaneously, A1 showed high selectivity and sensitivity to CN− in many interfering anions. The sensing mechanism of cyanide is carried out by deprotonation of the –OH group by the cyanide ion, and has been confirmed by spectroscopic studies, 1H NMR spectroscopy, Job's plot analyses and DFT calculation. The practicality of the sensor has been well proven by filter paper strips and small molecule smart fluorescent display materials. In addition, the sensor is used to detect cyanide in food materials (such as germinated potatoes, cassava and bitter almonds) with satisfactory results. The most important thing is considering the colorimetric and fluorescent dual modes, the ultra-fast response, excellent selectivity and recyclability that demonstrate its excellent value in practical applications. [ABSTRACT FROM AUTHOR]

This paper firstly introduces a flexible hybrid integration (FHI) architecture based on organic thin‐film transistors (OTFTs) for ubiquitous sensor systems, followed by description of the low power OTFT technologies. Then, progresses on sensor integration based on the OTFTs for FHI are discussed, proving the versatility of the technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acidification of paper substrates eliminate super-Nernstian response of Pb2+-ISEs. • 3D approximate (concentration-EMF-pH) analyses of the Pb2+-ISEs was introduced. • Pb2+-ISEs acceptable operational pH range of paper substrate with solution was 3–4. • Colour-coded graph was proposed to match paper substrates with unbuffered samples. • Pb2+ analysis in complex environmental samples was successfully performed. To address analysis of heavy metals in samples containing low volumes and/or high solid-to-liquid contents, microfluidic paper-based solution sampling coupled with Pb2+-ISEs was investigated. The acidification of paper substrates prior to their use was found effective at eliminating the otherwise observed super-Nernstian response of Pb2+-ISEs. Acidified paper substrates (at different pH) were evaluated and through 3D approximate (concentration-EMF-pH) analyses of the Pb2+-ISEs responses coupled with acidified paper substrates, the acceptable operational pH range (for paper substrate containing sample solution) of the potentiometric sensors was found to be between 3–4. Furthermore, to simplify the analytical protocol of heavy metal sensing using Pb2+-ISEs coupled with microfluidic paper-based solution sampling, a colour-coded matching graph was proposed to match the appropriate acidified paper substrate to the pH of the unbuffered sample solution. Such an approach was used for determination of Pb2+ in various complex environmental samples with small volumes of solution and/or high solid-to-liquid ratios, such as wet soil, street runoff, chemical spillage and plant dew. Although the samples were characterized with high ionic complexity, determinations by potentiometry and ICP-OES were found to be comparable, which validates the use of acidified paper substrates in reliable determination of lead(II) in complex sample matrices. [ABSTRACT FROM AUTHOR]

A paper-based chemiresistive sensor consisting of a single-walled carbon nanotubes network with electrodeposited gold nanoparticles (AuNPs-SWCNTs) was developed for the sensitive detection of As(III). A new sensing strategy was also proposed combined with a paper-based device for As(III) chemiresistive detection based on the electrochemical doping of As(0) on the AuNPs-SWCNTs channel. The proposed paper-based chemiresistive sensor was manufactured by wax printing and vacuum deposition using a water-based SWCNTs ink. The sensor sensitivity was enhanced by optimizing the volume of SWCNTs ink used in the formation of the sensing network in the paper and the sweep segment of cyclic voltammetry used for the electrochemical deposition of AuNPs. Additionally, the mechanism of the sensing strategy based on the electrochemical n-doping of As(0) to the AuNPs-SWCNTs sensing channel was investigated using a liquid-ion gated FET system. The As(III) concentration detected by the as-fabricated chemiresistive sensor is as low as 1.35 × 10−5 μM which is even lower than the maximum permissible concentration in drinking water defined by the WHO. In this paper, we provide a simple strategy for developing paper-based chemiresistive sensors with unique properties for practical As(III) determination. [Display omitted] • A paper-based chemiresistive sensor was developed for the detection of As(III). • The properties of the proposed semiconducting channel were characterized. • A sensing strategy was proposed without using any bio-recognition elements. • The key parameters for the sensor fabrication were optimized. • The concentration of As(III) can be detected as low as 0.001 ppb. [ABSTRACT FROM AUTHOR]

Regular monitoring of glucose and ketone contents in the body is vital for diabetic patients. Although estimation of the ketone content is necessary for proper healthcare monitoring, the research on the detection of ketone bodies is still nascent. Moreover, inaccurate eye-estimations and reliability are the key limitations of the widely used methodologies for estimating glucose in urine. Hence, simple procedures for fabricating reliable sensors are crucial for on-demand healthcare monitoring. Herein, we posit that a commercially available laser printer, without any added modifications, can be used to make paper-based sensors for colorimetric estimation of glucose and ketone in urine. We conducted a comprehensive experimental investigation to optimize the device designs for rapid estimation of the biomarkers. Also, for the first time, we present a detailed dynamic model of the flow-field in a variable cross-section paper device while considering the species transport and reaction kinetics within the porous media. Finally, we performed experiments with real urine samples to validate that our devices could detect results with zero false negatives. We believe that our present investigation and methodology can enable rapid and reliable fabrication of paper-based sensors for several fundamental studies and applications on affordable and non-invasive healthcare monitoring. [Display omitted] • A simple laser printer was used to make paper-based sensors for reliable estimation of glucose and ketone in urine. • A model was developed considering the variable channel area, the species transport and reaction kinetics in a paper device. • A desktop-based application was also developed for automatic estimation of the biomarkers in urine. • The methodology detected results with zero false negatives for complex real diseased samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A portable analytical device for performing reflectance measurements on paper-based supports is described. • It has been assembled using an electronic module consisting of six types of photodiodes (six channels). • The low-cost device allows to extend the potentiality with respect to usual RGB sensors. • A method based on the Kubelka-Munk theory for management of the output signals has been developed. • Performance was evaluated by using three different food dyes and a colorimetric assay for the determination of nitrites. A low-cost portable analytical device, suitable for performing reflectance measurements on paper supports is proposed. It consists of a simple module consisting of a matrix of six types of photodiodes (six channels) with maximum sensitivity at six different wavelengths in the visible region. The device was used in combination with paper-based analytical devices (PADs) suitably prepared by 3D printing using polycaprolactone, i.e. a biodegradable and biocompatible polymer. These PADs were used both as substrates for the imbibition of colored solutions and of reagents for colorimetric reactions. The constructive and electronic aspects are described and the instrumental noise, as well as the performance of this device were carefully evaluated in terms of repeatability and reproducibility by using three different food dyes and a colorimetric assay for the determination of nitrites with the Griess reagent. The development of this device also included the management of output signals that, once converted from raw signals into reflectance values, have been elaborated by the Kubelka-Munk theory. Finally, the application to real samples consisting of commercial aqueous solutions of Tartrazine yellow (E102), Ponceau red 4R (E124) and Patent blue V (E131), usually adopted for the coloration and/or decoration of homemade cakes and sugarcoated almonds, gave results in good agreement with values obtained by absorbance measurements performed by a benchtop spectrophotometer. This type of comparison pointed out that also the nitrite detection performed by reflectance measurements on synthetic samples allowed more than reliable results to be obtained. [ABSTRACT FROM AUTHOR]

The integration of smartphone with paper sensors recently has been gain increasing attentions because of the achievement of quantitative and rapid analysis. However, smartphone based upconversional paper sensors have been restricted by the lack of effective methods to acquire luminescence signals on test paper. Herein, by the virtue of 3D printing technology, we exploited an auxiliary reusable device, which orderly assembled a 980 nm mini-laser, optical filter and mini-cavity together, for digitally imaging the luminescence variations on test paper and quantitative analyzing pesticide thiram by smartphone. In detail, copper ions decorated NaYF 4 :Yb/Tm upconversion nanoparticles were fixed onto filter paper to form test paper, and the blue luminescence on it would be quenched after additions of thiram through luminescence resonance energy transfer mechanism. These variations could be monitored by the smartphone camera, and then the blue channel intensities of obtained colored images were calculated to quantify amounts of thiram through a self-written Android program installed on the smartphone, offering a reliable and accurate detection limit of 0.1 μM for the system. This work provides an initial demonstration of integrating upconversion nanosensors with smartphone digital imaging for point-of-care analysis on a paper-based platform. [ABSTRACT FROM AUTHOR]