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Estimation of pH is vital to assess the biochemical and biological processes in a wide variety of applications ranging from water to soil, health, and environment monitoring. This work reports a screen-printed flexible and disposable pH sensor using the impedimetric method. The pH sensor was fabricated by screen printing Graphene-Carbon modified Zinc Oxide based active layer on a paper substrate and shows nearly three orders of change in impedance magnitude in the pH range of 2 – 9. The sensor was carefully designed using COMSOL® Multiphysics software to understand the influence of electrode geometry and the electrical potential developed across the structure. The developed sensor was used for pH monitoring of soil and exhibited high sensitivity of 5.27 kΩ /pH (2-8) with a correlation coefficient (R 2 ) of 0.99. Finally, an IoT-enabled smart pH detection system was implemented for continuous pH monitoring for potential application in digital agriculture. The outcome demonstrates that the presented flexible and disposable pH sensor could open new opportunities for monitoring of water, product process, human health, and chemical (or bio) reactions even using small volumes of samples.

A miniaturized paper-based disposable pH sensor has been developed for the measurement of urine pH. The proposed sensor requires $2~\mu \text{l}$ of analyte solution for rapid detection of the analyte pH with a response time of 3.07 sec and 36.04 sec for acidic and basic pH, respectively. The sensor is fabricated via in situ deposition of polyaniline over the paper substrate by chemical oxidative synthesis. The sensitivity of the sensor is 1.6 $\text{k}\Omega $ /pH for acidic pH and 6.2 $\text{K}\Omega $ /pH for basic pH, at a frequency of 1kHz. The sensor has been characterized using scanning electron microscopy, Raman spectroscopy, and UV-vis spectroscopy to validate the formation of emeraldine salt and emeraldine base state of polyaniline. The varying optical band gap values of the in-situ deposited paper sensor in the acidic and basic region also validates the presence of polaron in acidic pH and formation of emeraldine base in basic pH. DC conductivity measurement reveals that the conductivity of the polyaniline coated paper substrate decreases at a higher pH value. For an in-depth understanding, a novel electrical equivalent model is proposed, and the electrical parameters extracted from the Bode impedance and phase plot. The fabricated sensor exhibits an average accuracy of 95.53% when tested with urine sample of healthy subjects and patients suffering from urinary tract infection (UTI).

Creatinine is a biochemical waste that is disseminated continually inside human blood. A synthetic polymer is developed in this study using Molecularly Imprinted Polymerization (MIP) technology with the precipitation polymerization method. The MIP polymer is used for finding the levels of creatinine from human serum samples with different creatinine concentrations. The MIP polymer is very selective to the specific adsorption of the molecules of creatinine. The produced MIP polymer is suitable for evaluating creatinine concentrations until 50 parts per million (ppm) that is thrice greater than the standard. The fabrication of chip-sized Micro-Electro-Mechanical-Systems (MEMS)-based interdigital (ID) sensors is described. The operation of the MEMS sensor is verified using the technique of Electrochemical Impedance Spectroscopy (EIS). The presented details of the development of MEMS ID sensor and creatinine specific MIP polymer are for detecting raised biotoxic waste levels, i.e. creatinine management is part of our research. The raised levels need monitoring by frequent pathological visits to those patients who have impaired kidney functioning. The complete system will be helpful for creatinine management at any time from home at a low cost. While early detection of an increase in creatinine and monitoring of kidney health to prevent further health-related complications are the goal of this research, results of up to 50 ppm are accessed. Until 50 ppm of MIP functionality is checked for confirming the MIP polymer adsorption of creatinine and the results are shown, which helps establish the sensing technology even if used for a patient with a high creatinine level.

A paper based chemiresistor has been fabricated to selectively sense ethanol in human breath. The chemiresistor was composed of a sensing mixture of multiwall-carbon-nano-tubes (MWCNTs), poly (diallyl-dimethyl-ammonium chloride) (PDDA), alcohol dehydrogenase (ADH), and coenzyme (NADH). The aluminum electrode was deposited on the paper surface, followed by drop-casting of the aforementioned sensing mixture. The resistance of the sensors was measured by exposing the same in gas-vapor mixture as well as the sample solution. The surface-modified MWCNTs specifically broke down ethanol present in the gas-vapor mixture or in a solution to generate a quantitative electronic response proportional to the ethanol concentration. Subsequently, the interference of other volatile organic materials was also tested to prove the selectivity and sensitivity of the sensor towards ethanol in the presence of different volatile organic compounds (VOCs). The variation of the resistance during the interaction between sensor and ethanol was also characterized by measuring the surface potential of the channel material under ethanol exposure using Kelvin probe force microscopy (KPFM). The sensor was integrated with a voltage divider circuit, a display, and a microcontroller unit to make a proof-of-concept prototype for the point-of-care (POC) detection of ethanol in human breath.

Wearable electrochemical sensors have attracted tremendous attention in recent years. Here, an integrated three-dimensional paper-based microfluidic electrochemical device (3D-PMED) with flexible wireless circuits is demonstrated for real-time monitoring of sweat potassium. The paper-based microfluidic pad is fabricated by printing wax patterns on cellulose paper and then folding the pre-patterned paper four times to form a five-layer stacked structure: sweat collector, vertical channel, transverse channel, electrode layer, and sweat evaporator. Also, we have discussed the different properties with three swear collector types. The sweat monitoring device is realized by integrating a screen-printed potassium ion-selective sensor on the PET substrate with the fabricated paper microfluidic pad. The sweat flow in 3D-PMED is modeled with red ink to generate the flow pathway of sweat and the capability of sweat storage. The detection range of the potassium ion-selective sensor is 1–32 mM, and the electrode response potential is 61.79 mV per decade of K+ concentration. The device has a small size that is suitable for everywhere on the body, and also have shown good selectivity for both anion and cation, and a stable performance within 1 week. This 3D-PMED has provided a simple, low-cost way for real-time dynamic sweat potassium monitoring when exercising.

The excellent characteristics of nanocellulose fiber-based papers have made them one of the most attractive and innovative materials for the development of electrochemical paper-based analytical devices (ePADs). Here, the authors describe a new ePAD based on cellulose nanofibers (CNs) for the determination of glucose concentration from whole blood samples. Cellulose acetate (CA) nanofibers were prepared by the electrospinning method. Then, the paper layer regenerated to cellulose by deacetylation in alkaline solution. To obtain a smooth and continuous CNs layer, it was treated with trimethyl chitosan (TMC). The formation of CA layer, its alkaline regeneration and TMC modification was confirmed by atomic force microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and energy dispersiveX-ray. Screen-printed three electrodes (SPEs) were fabricated by sputtering a thick layer of gold (Au) on the TMC/CNs substrate. Subsequently, reduced graphene oxide (rGO) was used to modify the surface of the working electrode. The fabrication steps of rGO-Au-SPE were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscop. The results showed that design, construction and modification process was well achieved. Next, glucose oxidase is successfully immobilized onto the regenerated CNs layer which has been previously located in the sensing area of the rGO-Au-SPEs. The ePAD glucose assay exhibited high sensitivity of $9.9\times 10^{-4}~\text{K}\Omega ^{-1} \cdot \text{mM} ^{-1}$ to glucose in the range 3.3 – 27.7 mM ( $\text{R}^{2} =0.99$ ) with a detection limit of 0.1 mM, high reproducibility (RSD = 0.57-1.59%) and outstanding selectivity as well as stability. This biosensing motif represents a general platform for the analysis of other biomarkers.

Pencil (graphite) on paper (PoP) electronics has gained significant attention due to its low cost and versatility in developing customizable disposable electronics. Despite the convenience of the PoP methodology in device fabrication its application in developing electronics is limited due to the absence of a bandgap in graphite. The present work is the first demonstration of the direct writing of 2D MoS2 trace on paper which was utilized as a pressure and strain sensor. Detailed characterization studies revealed the formation of rhombohedral and hexagonal phased MoS2 micro-flowers. XPS studies revealed the formation of mixed 1T (metallic) and 2H (semiconducting) phases of MoS2. With the increase in the number of traces of 2D MoS2 on paper, the resistance of the channel decreased owing to the increase in conducting channels. The as-fabricated pressure sensor displayed a sensitivity of 2.21 kPa−1 and strain sensor displayed a GF of 13. Also, the sensor displayed an excellent durability for 1600 cycles. The superior response of the sensor can be attributed to the synergistic properties of micro fibrous paper substrate and piezo-dependent electron transfer of 2D-MoS2. The presented technique enables “make it yourself” multifunctional device that have numerous potential applications in the field of consumer electronics and personal healthcare monitoring.

This report demonstrates the fabrication of SnS/paper based low-cost and flexible pressure sensor, employing a facile solvothermal synthesis followed by vacuum filtration, for artificial electronic skin and touchpad applications. The fabricated pressure sensor displayed a high sensitivity of 3.18 kPa $^{- {\sf 1}}$ and a response time $\sim 300$ msec. Inspired by the high value of sensitivity and an appreciable flexibility, a large-area pressure sensor array ( ${\sf 3} \times {\sf 3}$ ) was fabricated and integrated onto a human arm for demonstrating real-time applications. The fabricated sensor array was able to consistently detect and track random localized points of contact, the shape of an unknown object placed on top of it, and an index finger trajectory along the surface with high accuracy and precision. The fabricated device showed a negligible change in the performance over 500 bending cycles which indicates the highly robust nature of the device. Successful fabrication of such a cost-effective large-area pressure sensor array is a major step in flexible electronics, and holds immense potential in artificial electronic skin, security, personal healthcare applications.

Slow or non-healing wounds in chronic diabetic foot diseases are often associated with co-morbid circumstances, inevitably leading to lower limb amputations. The wound bed in chronic foot ulcers are prone to bacterial infections, with Staphylococcus aureus ( S. aureus ) acting as the major culprit in resisting the normal wound healing process. This study reports the development of a flexible screen-printed wound dressing based on a composite of Zeolitic Imidazolate Framework (ZIF 67) and carbon nitride (C3 N4) conjugated with S. aureus probe DNA for the detection of its corresponding target DNA. The nano-wound dressing was assessed using Electrochemical Impedance Spectroscopy (EIS) for the quantification of S. aureus target DNA within 1 fM to $10~\mu \text{M}$ . A direct proportionality between the charge transfer resistance ( $\text{R}_{\text {ct}}$ ) and S. aureus target DNA concentration. Circuit simulations detailing the quantifications of interfacial parameters, involved in the recognition event, were performed by curve fitting of Nyquist spectra in order to explain the variation of $\text{R}_{\text {ct}}$ with target DNA concentrations. The Limit of Detection (LoD), sensitivity and response time of the developed wound dressing-based sensor were found to be 0.46 fM, 0.25 $\text{k}\Omega $ /fM/mm2 and ~ 10 s respectively at 21.04 kHz, while being selective only towards S. aureus target DNA. The sensor was further validated in human serum samples and was shown to possess a shelf life of 35 days, thereby exhibiting tremendous potential to be implemented in connected health applications.

Conductivity is an important parameter which has definite correlation with the amount of moisture present within the transformer insulation. However, in existing methods conductivity is usually estimated from time domain (PDC) measurement, which is inadvertently noise prone and time consuming. Considering this issue, in this article presents a novel technique for conductivity estimation for moisture sensing of oil-paper insulation using frequency domain spectroscopy measurement (FDS). To this end, FDS measurement of oil-paper insulation was performed from 50mHz to 1kHz to obtain the imaginary complex permittivity $\varepsilon ''$ ( $\omega$ ), which is a function of conductivity ( $\sigma$ ) as well as imaginary complex susceptibility $\chi ''$ ( $\omega$ ). From the knowledge of frequency variation of both $\sigma $ and $\chi ''$ ( $\omega$ ), we developed an electrical equivalent model of the insulation. The equivalent model parameters were optimized until $\varepsilon ''$ ( $\omega$ ) computed from the proposed model and that obtained from original FDS measurement were almost identical. The conductivity values obtained from the equivalent model showed good agreement when compared with PDC measurement. To validate the practicability of the proposed method, experiments were conducted on various test samples and also on a few real life transformers. Most importantly, the measurement time was found to be reduced by 78.5%, enabling diagnosis of transformer insulation at a significantly reduced time.

The ratio of protein to creatinine (PCR) in urine is a measure of kidney health of a human body. We report the development of a point-of-care (POC) kidney function test (KFT) kit, which is composed of a paper-based PCR sensor, an opto-electrochemical measurement unit, a display, and a facility to transfer data to a smartphone. For the total protein sensor, the pieces of filter papers were coated with a mixture of alcoholic bromophenol blue and citric buffer leading to a chrome-yellow coloration. While for the creatinine sensor the papers were coated with alkaline picrate solution leading to a lemon-yellow coloration of the surface. Dispensing protein (creatinine) solution of known concentration on the respective sensors led to the conversion of chrome-yellow to bluish-green coloration (lemon-yellow to orange coloration) for the total protein (creatinine) sensor. The intensity of such colorations varied with the concentration of the analytes in the solutions. The variations in the intensities of colors with analyte concentration were quantified by integrating a light emitting diode (LED) at one side of each sensor and a light intensity sensor (LIS) on the other side. The intensity of the transmitted rays, passing through the sensors, was found to vary the electrical output of the LIS monotonically with the loading of the total protein or creatinine in the analyte. This helped in obtaining the calibration plots for the PCR sensors. Further, the sensors were employed for the on-spot detection of the unknown PCR in the real human urine samples.

Biological compounds like Dopamine (D), Xanthine (X), Ascorbic acid (AA) and Uric acid (UA) play a vital role in food, clinical and human metabolism. Since these compounds are present in biological fluids and have close standard potentials values, it is imperative to choose a method to sense these fluids without any electrochemical interference. Toray paper, with a porous gas diffusion layer imbibed with denser carbon fibers, is an excellent option that can be utilized as a working electrode for such sensing applications. Herein, the electroactivity of these compounds was tested using cyclic voltammetry and square wave voltammetry without any interference. The linear ranges for the compounds (D, X, AA, UA) are 10- $1000~\mu \text{M}$ , 7- $300~\mu \text{M}$ , 100- $1000~\mu \text{M}$ and 30- $1000~\mu \text{M}$ respectively, while the limits of detection are $9.67~\mu \text{M}$ , $6.54~\mu \text{M}$ , $97.12~\mu \text{M}$ and $28.74~\mu \text{M}$ respectively with S/N ratio of 1.5. Finally, the electrode was tested with human serum samples for the identification of D, X, AA and UA manifesting exceptional reproducibility.

Accurate measurement and monitoring of respiration is vital in patients affected by severe acute respiratory syndrome coronavirus - 2 (SARS-CoV-2). Patients with severe chronic diseases and pneumonia need continuous respiration monitoring and oxygenation support. Existing respiratory sensing techniques require direct contact with the human body along with expensive and heavy Holter monitors for continuous real-time monitoring. In this work, we propose a low-cost, non-invasive and reliable paper-based wearable screen printed sensor for human respiration monitoring as an effective alternative of existing sensing systems. The proposed sensor was fabricated using traditional screen printing of multi-walled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS) composite based interdigitated electrodes on paper substrate. The paper substrate was used as humidity sensing material of the sensor. The hygroscopic nature of paper during inhalation and exhalation causes a change in dielectric constant, which in turn changes the capacitance of the sensor. The composite interdigitated electrode configuration exhibited better response times with a rise time of 1.178s being recorded during exhalation and fall time of 0.88s during inhalation periods. The respiration rate of sensor was successfully examined under various breathing conditions such as normal breathing, deep breathing, workout, oral breathing, nasal breathing, fast breathing and slow breathing by employing it in a wearable mask, a mandatory wearable product during the current COVID-19 pandemic situation.Thus, the above proposed sensor may hold tremendous potential in wearable/flexible healthcare technology with good sensitivity, stability, biodegradability and flexibility at this time of need.

There is an increasing demand for measuring respiratory rate (RR) to monitor the progression of clinical events such as cardiac arrest or during the admission to the intensive care unit (ICU). Current methods of respiration monitoring are complex, invasive, expensive and therefore require alternative techniques. In this paper, we utilized wearable and flexible technology to develop humidity sensors for long-term continuous monitoring of respiration. Using manual drawing and printing techniques, the sensors were made based on graphite trace and silver nanoparticles as two different sensing materials. The surface morphologies of the devices were characterized by Scanning Electron Microscope (SEM) to show the construction of the sensors. Additionally, the material characterization was performed to obtain the Raman Spectra. Paper was chosen as a flexible substrate owing to its biodegradability, porosity, and disposability. The humidity sensing characteristics of the sensors indicated the best sensitivity of 0.0564% for Graphite on Paper (GOP) sensor. Furthermore, the hygroscopic nature of the paper enables converting the humidity changes during inhalation and exhalation into electrical signals. The electrical signals are transmitted via an interface to a computer using a simple data-logging set-up. A set of normal, deep and apnea breathing conditions could be easily differentiated from these signals along with information on respiration rate and pattern. The functionality of sensors was also tested after light and rigorous exercises. The proposed sensor combines the advantages of being low cost, non-invasive, highly sensitive, stable and holds tremendous potential for wearable/flexible healthcare technology.

Contamination of water bodies due to the disposal of natural and anthropogenic pollutants is one of the major global concerns in the recent times. Regular on-spot monitoring of water quality has become mandatory wherein diverse classes of materials such as organic, inorganic, heavy metals, or biological wastes are detected employing standard protocols. However, most of the existing laboratory techniques are either costly and/or time consuming owing to the process involving the expert driven sophisticated analysis techniques. Herein, we report the development of three paper based colorimetric sensors for the on-spot quantitative detection of the levels of fluoride (F−), lead (Pb2+), and pH in drinking water. The variations in the color-intensities of the paper sensors with the variation in the concentration of fluoride (F−), lead (Pb2+), and pH were converted into electronic signals to enable the development of a point-of-care-testing (POCT) device. For this purpose, initially, the sensors were characterized and calibrated with known concentrations of contaminates before successful validations with real samples. Thereafter, the sensors were illuminated with a light emitting diode from one side while the transmitted rays passing through the sensor was captured by a light dependent resistor (LDR) from the other side. The variation in the color intensity of the paper-sensor with the contaminant loading was found linearly varying with the resistance of the LDR. The sensor was then translated into a specific, stable and user friendly POCT device, which enabled inexpensive spot detection of pollutants in drinking water.

Monitoring blood coagulation in response to an anticoagulant (heparin) and its reversal agent (protamine) is essential during and after surgery, especially with cardiopulmonary bypass. A current clinical standard is the use of activated clotting time, where the mechanical movement of a plunger through a whole blood-filled channel is monitored to evaluate the endpoint time of coagulation. As a rapid, simple, low-volume, and cost-effective alternative, we have developed a paper microfluidic assay and Raspberry Pi-based device with the aim of quantifying the extent of blood coagulation in response to varying doses of heparin and protamine. The flow rate of blood through the paper microfluidic channel is automatically monitored using the Python-coded edge detection algorithm. For each set of the assay, 8- $ \mu \text{L}$ of fresh human whole blood (untreated and undiluted) from human subjects is loaded onto each of eight sample pads, which have been preloaded with varying amounts of heparin or protamine. The total assay time is 3–5 min including the time for sample loading and incubation.

Wireless, passive, and cost-efficient monitoring of moisture within packaged food and medicine is important to ensure their safety and freshness. This paper presents paper-based single spiral inductance–capacitance (LC) sensors and a distance-insensitive readout system. The parasitic capacitance of the single-spiral coil is used to form an LC resonant circuit with its inductance. The printing paper is utilized as a humidity sensing material. A model for the LC sensor is analyzed and compared with HFSS simulation, showing the relative error within 6.3%. Nano-silver paste for the single-spiral coil was screen printed on the printing paper. The LC sensors with 4, 6, and 8-turns coils were characterized at relative humidity levels of 15%-90%RH by a readout coil at a fixed position. Comparison shows that the 8-turn sensor has the best linearity with respect to humidity. The sensitivity and response time were measured to be 120 kHz/%RH and 60 minutes, respectively, with the hysteresis errors less than 0.9%. During the practical monitoring, the tested signal frequency will have a shift if the coil’s relative position alters. To weaken the influence of the coil’s position, a readout coil, working at the quasi-resonant with the LC sensor was utilized to enhance the readout, resulting in more stable signal. According to the experimental results, the improved readout system can restrain the frequency shift within 1.1% at a readout distance from 2–50 mm when the ambient humidity is 60%RH.

This paper describes a simple and low-cost test strip for on-site monitoring of methiocarb insecticide. Hydrophilic filter paper soaked in agarose solution was bounded by hydrophobic solid wax and then was coated with unmodified gold nanoparticles (AuNPs). AuNPs aggregation caused by methiocarb served as colorimetric response. We demonstrated detection capability of methiocarb both in solution- and substrate-based sensor. A good linear relationship was obtained between the colorimetric response and the concentration of methiocarb ranging from 20 to 80 ng mL $^{-1}$ with a limit of detection of 5 ng mL $^{-1}$ . Excellent selectivity toward methiocarb was observed among various pesticides and cationic and anionic ions. Furthermore, the proposed assay could successfully detect methiocarb in paddy and tap water with satisfactory results. It would be of interest for use as rapid, portable, and technically simple test strip in water quality monitoring.

Cardiac biomarker detection helps in early diagnosis of cardiac syndromes. However, a rapid, cost-effective, reliable, and easy-to-use sensor is still unavailable. Herein, we report a disposable, label free, impedance-based biosensor for the detection of two common cardiac biomarkers, Myoglobin (Myo), and Myeloperoxidase (MPO). The sensor is fabricated on Whatman filter paper coated with a conducting polymer, polyaniline (PAni). The PAni-coated paper is functionalized with glutaraldehyde, a homo-bi functional crosslinker, prior to the covalent attachment of antibodies specific to each biomarker protein. Non-specific active regions of the sensor are blocked by treatment with bovine serum albumin. Conductive silver paste is used to define electrodes for AC impedance measurement on the PAni coated filter paper. Binding of the target protein (Myo or MPO) to the specific antibody changes the impedance between the electrodes; this is detected using AC impedance spectroscopy. The impedance is measured using a frequency response analyzer with an AC excitation voltage of 100 mV in the frequency range of 100 Hz–100 kHz. We can successfully detect Myo and MPO in buffer solution within the concentration range of 100 ng/mL– $50~\mu \text{g}$ /mL. Detection limit obtained for these cardiac biomarkers spiked in human serum is $1~\mu \text{g}$ /mL. Further blocking using human serum improves the lower detection limit to 500 ng/mL. The developed biosensor uses inexpensive materials and fabrication techniques, detects cardiac biomarkers in clinically relevant concentrations rapidly (i.e., within 20 mins), and can be disposed in an environment friendly manner, thus making the sensor suitable for diagnostic applications.

This paper describes a humidity sensor fabricated by cross-linking poly(ionic liquid)s (PILs) in the cellulose fibers of printing paper via an in situ photoinitiated “thiol-ene” click reaction. The resultant sensors inherit the strong hydrophilicity and high ionic conductivity of the cellulose and PILs, respectively, which are the most important factors for a high-performance impedance-type humidity sensor. The introduction of PILs improved the sensitivity, hysteresis, response speed, and stability of the paper-based devices. The optimal paper-based device sensitivity increased by a factor of 1.4 after adding PILs, and the response time decreased to 25 s, which is comparable to that of the best reported paper-based humidity sensors.

Paper-based gas sensors represent an emerging important class of devices in flexible electronics. Colloidal nanocrystals unite large surface-to-volume ratio with excellent solution processability, offering avenues to high-performance paper-based gas sensors. One of the factors limiting the performance of paper-based gas sensors is the sphere-like morphology of semiconductor nanocrystals, making it difficult to construct a stable sensing network to ensure efficient carrier transport and mechanical robustness. Here we demonstrated sensitive and flexible gas sensor via the spray coating of PbS nanowires onto paper substrates at room temperature. The pencil-drawn graphite electrode was employed to simplify the sensor design and fabrication. Unlike the sphere-like PbS nanocrystals that usually assemble into compact thin-film solids, the PbS nanowires-on-paper sensor exhibits a porous network microstructure, which not only offers efficient pathway for gas adsorption and diffusion but also possesses inherent flexibility for superior mechanical bendability. The response of the PbS nanowires-on-paper sensor toward 50 ppm of NO2 at room temperature was 17.5, with the response and recovery time being 3 and 148 s, respectively. The sensor shows only a slight decrease in response (6% of the initial value) and identical temporal response when subject to 500 bending and unbending cycles. The competitive adsorption of NO2 with O2 on PbS surfaces is proposed as the sensing mechanism accounts for the high sensitivity and good reversibility at room temperature. Our results highlight the significance of the solution-processable nanowires as the ideal building blocks for the flexible paper-based gas sensors.

This paper focuses on fabricating cost effective and time-efficient bioelectrodes for enzymatic bio fuel cells by immobilizing the enzymes, glucose oxidase, and laccase on the surface of buckeye composite Bucky paper (BP) without any redox cofactors. Electrochemical studies including linear sweep voltammetry, cyclic voltammetry open circuit potential, and electrochemical impedance spectroscopy were carried out to evaluate the performance of the prepared electrodes. Maximum current density of 9.79 mA/cm2 at 0.4 V and 2 mA/cm2 at 0.3 V was observed for anode and cathode, respectively, at a scan rate of 10 mV/s at 40-mM glucose concentration. Morphological studies using scanning electron microscope revealed uniform dispersion of the enzymes on the surface of the BP electrodes facilitating the presence of enzyme active sites for catalytic reactions. The absence of redox cofactors in this approach dramatically reduces the cost and fabrication cycle time and also preserves their biocompatible nature. The fabricated BP-based bioelectrodes have shown excellent performance and further encourage toward future studies at the microfluidics level.

Millimeter-wave imaging may be used to assist in\ud the problem of wastepaper recognition during the sorting and\ud recycling process. Currently, there are a variety of techniques,\ud which are used within materials recovery facilities to sort waste\ud paper and card; however, improvements in sorting capability can\ud be realized using a multiple sensors to provide complementary\ud (orthogonal) data. This paper discusses the issues related to\ud the processes, which are currently used for sorting of recycled\ud wastepaper and the phenomenology for millimeter-wave imaging\ud of a wastepaper material. Experimental measurements and\ud images in the millimeter wave band are presented, which support\ud the proposed application.

Since its inception in 2002, the IEEE Sensors Conference has come a long way in establishing itself as a premier conference in the world on sensors and sensing technologies. With the entire world moving rapidly toward a ubiquitous intelligence society, the emphasis on deployment of trillions of sensors in the near future is driving the world of sensor technology like never before. It is reflected in the rapidly increasing research and development activities on sensors throughout the world today. The IEEE Sensors Council has done a remarkable job in promoting this area and providing a consistent platform for sharing and dissemination of knowledge related to all aspects of sensing and sensor development among researchers, manufacturers, and the users of sensors. The idea of holding the IEEE Sensors Conference in different parts of the world actively supports this promotion over different geographies. It could not have been more timely to hold SENSORS 2018, for the first time, in one of the largest and fastest developing economies of the world - India. The 2018 edition of the Sensors Conference was held on October 28–31 in New Delhi — the capital city of India that has been inhabited for six thousand years and has seen a great many upheavals in history.

This paper aims to develop a flexible and cost-effective dry electrode with low and stable contact impedance. With these benefits, the electrode can be practically used in ubiquitous bio-potential monitoring with similar signal-to-noise ratio as commercial wet electrode. A self-wetting electrode is developed by the aid of moisture naturally created by skin under the electrode. It consists of a layer of ethylcellulose fiber paper coated with PEDOT/PSS (PCwPEDOT) and a thin layer of parylene. PCwPEOT, which has a large contact area composed of micro-scale fibers, is a 30- $\mu \text{m}$ flexible membrane that acts as the electrode material. A 3- $\mu \text{m}$ parylene bonding at the backside of PCwPEOT, as a high-performance vacuum membrane, can collect moisture or sweat naturally evaporating from the skin and store it in the PCwPEDOT layer. This design increases the humidity of skin, especially the water content in the corneum, acting as electrolyte containing ions, increases effective contact area between electrode and skin, and decreases the impedance of the electrode. With an environmentally friendly and cost-effective fabrication process, the 33- $\mu \text{m}$ thickness of electrode is light and flexible. It can be tailored to proper size according to the application. It achieves lower contact impedance compared with dry electrodes with a similar structure. Its recording performance is comparable to commercial patch electrode. The proposed electrode provides high-quality signals, and comfortable user experience in bio-potential recording. It is feasible for developing a long-term wearable system for bio-potential monitoring.

This paper presents the design of a wideband Hilbert fractal antenna for the purpose of detecting and classifying different common partial discharge (PD) types in an oil-paper insulated system. Three common types of PDs are considered for the multi-class classification problem, namely, PD from a sharp point to ground plane, surface discharge, and PD from a void in the insulation. The different PD types showed variation in the detected frequency contents. The collected samples were processed using pattern recognition techniques to identify their corresponding PD types. A recognition rate of 95% was achieved when K-nearest neighbors was used as the classifier.

In this work we describe the Square Wave Anodic Stripping Voltammetry (SWASV) electrochemical technique for the determination of lead (Pb2+) and cadmium (Cd2+) metal ions at concentration of sub-part per billion (ppb) in aqueous solution. Moreover, simple and low-cost procedures for the fabrication of high performance working nano-electrode are reported. The electrode structure consists of a graphene paper (GP) $240~\mu \text{m}$ thick with the function of electrical conductor and substrate, a layer of nafion 0.5- $0.7~\mu \text{m}$ thick onto the graphene paper and bismuth nanoparticles embedded in the nafion thin layer. The bismuth nanoparticles were fabricated by electrodeposition starting from Bi(III) ions, employing a key step of hydrogen ions of nafion $\text{H}^{\mathbf {+}}$ exchange with bismuth ions Bi(III). This procedure is aimed to improve the bismuth nanoparticles concentration. The SWASV applied to the low-cost nanoelectrode allows detecting Pb2+ and Cd2+ at concentration as low as 0.1 ppb.

A course on the emerging topic “Smart Sensors and Internet of Things (IoT)” has been designed, developed, and delivered from 21st March 2016 to 31st March 2016 in the Department of Electrical Engineering, Jamia Millia Islamia (Central University), New Delhi-110025, India. This course was organized under a program initiated by the Government of India, entitled “Global Initiative of Academic Networks” for higher education. The basic objective is to bring the internationally and nationally acclaimed scientists on a single platform to motivate young minds of India so that India’s scientific and technological capacity reach global excellence. The course was designed to develop the technical skills for the students, the researchers, the engineers, and the faculties, who desire to address some of the issues faced by the people around the world in the fields of smart sensors and IoTs with applications in smart homes, smart cities, smart grids, smart environment, smart transport, and so on. The assessment of the course by the participants shows extreme usefulness of it.

A taxel device on flexible substrates based on the electrical contact resistance (ECR) variation mechanism is developed. The proposed taxel device consists of one top and one bottom substrates, which are coated with conductive polymer then face-to-face assembled. The device is tested with different substrate materials to show the viability of the ECR variation mechanism. It is found that when paper is used as the substrate material, because of its exclusive features of surface roughness and material compressibility, the ECR variation mechanism is greatly enhanced and the device exhibits higher sensitivity and larger working pressure range. Practical applications are investigated in elasticity measurement on phantom samples and biological tissues. The results are promising with our taxel device made on flexible substrates being capable of integration onto surgical tools and the potential to realize the psychical property of biological tissues.

Seamless integration of functional nanomaterials on paper can boost the functionality of paper-based flexible sensors and electronics. In this paper, we report the systematic study of a low-cost hydrothermal process for growing zinc oxide nanowires (ZnO NWs) on cellulose paper substrates. To control the competition between homogeneous and heterogeneous nucleation and obtain ZnO NWs with superior morphology and high growth efficiency, we tune the critical growth parameters including temperature, assistant chemicals, and seeding layer. We experimentally confirm the necessity of ammonium hydroxide as assistant chemical in the growth solution, and achieve a condition that generates the highest weight growth percentage of 40% in the tested range. We quantify the weight growth percentage of ZnO NWs over growth time, measure the electrical resistance of the ZnO-NW paper, and eventually establish an experimental guideline for preparing ZnO-NW paper with desired electrical property. To demonstrate potential applications of the ZnO-NW paper, we use the obtained ZnO-NW paper for sensing of ultraviolet light and mechanical touch. This paper provides experimental insights into hydrothermal growth of ZnO NWs on paper, and could further inspire novel utilization of ZnO-NW paper for flexible sensors and electronics.

Smartphone detection of Escherichia coli from field water samples is successfully demonstrated using paper microfluidics. A three-channel paper chip is designed and fabricated, with a negative control channel preloaded with bovine serum albumin (BSA)-conjugated beads and two E. coli detection channels preloaded with anti-E. coli-conjugated beads, for low- and high-concentration detection. Field water samples are introduced to the paper chip by dipping or pipetting, and the antigens from E. coli travel through the paper fibers by capillary action while the dust/soil or algae particles are effectively filtered. Antibody-conjugated beads, confined within the paper fibers, immunoagglutinate in the presence of E. coli antigens, while BSA-conjugated beads do not. The extent of immunoagglutination is quantified by evaluating Mie scatter intensity from the digital images taken at an optimized angle and distance using a smartphone. The assay results show excellent agreement with the MacConkey plate results, i.e., the count of viable E. coli. The scatter simulation procedure is introduced to substitute for experimental optimization, such that the proposed method can be easily adapted to the other types of samples. A smartphone application is developed, incorporating the internal gyroscope of a smartphone, to allow the user to position the smartphone at an optimized angle of scatter detection. The detection limit is single-cell-level and the total assay time is 90 s.

In this paper, we report the development of an oxygen sensor using a simple device made from a film of ZnO crystals dispersed over a paper surface. Due to the high porosity of this kind of device made from paper and ZnO, a large photoconductive effect is observed as result of the fast absorption and desorption of oxygen from the ZnO surface. To detect oxygen, we propose to use ultraviolet (UV) illumination over the photoconductive surface of the sensor, the applied UV light produces oxygen desorption causing current variations through the sensor that are proportional to the oxygen presence nearby the sensor surface. The sensor developed in this paper is attractive because it is remarkably easy to fabricate, employs only very low-cost materials for its construction, and shows a better sensitivity at low concentration of oxygen at partial vacuum environments.