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Conductive graphene polymer composites are considered promising functional materials in gas detection, strain detection, metal corrosion prevention, and electromagnetic wave absorption, owing to their good flexibility, lightweight, and adjustable conductivity. The internal defects or external damages of composite films will seriously affect the electrical and functional properties of the materials. Based on the conductive network inside the conductive polymer film and the self-inductance to ultrasonic wave, the defect self-monitoring system of the conductive polymer film is designed and optimized in this work. The self-damage detection system is composed of an electrode array, excitation source, resistance signal acquisition and processing circuit, and damage display. Aiming at different scenarios, the improved interdigital structure transducer for sensors and damage detection device for coating film with a large area are presented and optimized respectively. Meanwhile, the damage location algorithm based on time difference measurement and kernel density estimation algorithm is also optimized. The multiple damage detection is realized by a device with a 4 × 8 electrode array, and the relative error of damage area with 1 mm × 1 mm is less than 5%, and the lower detection limits of damage size are 0.3 mm × 0.3 mm. [ABSTRACT FROM AUTHOR]

The pH value plays a vital role in many biological and chemical reactions. In this work, the fiber-optic chemical pH sensors were fabricated based on carboxyl ZnCdSe/ZnS quantum dots (QDs) and tapered optical fiber. The photoluminescence (PL) intensity of QDs is pH-dependence because protonation and deprotonation can affect the process of electron-hole recombination. The evanescent wave of tapered optical fiber was used as excitation source in the process of PL. To obtain higher sensitivity, the end faces of fiber were optimized for cone region. By lengthening the cone region and shrinking the end diameter of optical fiber, evanescent wave was enhanced and the excitation times of QDs were increased, which improved the PL intensity and the sensitivity of the sensor. The sensitivity of sensor can reach as high as 0.139/pH in the range of pH 6.00–9.01. The surface functional modification was adopted to prepare sensing films. The carboxyl groups on the QDs ligands are chemically bonded to the fiber surface, which is good for response time (40 s) and stability (decreased 0.9 % for 5 min). These results demonstrated that ZnCdSe/ZnS QDs-based fiber-optic chemical pH sensors are promising approach in rapid and precise pH detection. [Display omitted] • The highly sensitive fiber-optic chemical pH sensors based on carboxyl ZnCdSe/ZnS quantum dots were studied. • Cone optimization can enhance evanescent wave intensity, depth of penetration, and frequency of generation. • The end faces of fiber were optimized for cone region to obtain higher sensitivity (0.139/pH, in the range of pH 6.00–9.01). • The sensing films were prepared by surface modification of cone region to reduce the response time (t 90 < 40 s). • The stability was verified in buffer with pH7.00 and standard seawater with different salinities (5 ‰, 20 ‰, 35 ‰). [ABSTRACT FROM AUTHOR]

Hole-edge crack quantification of bolt joints is critical for monitoring and estimating structural integrity of aircraft. The paper proposes a new triangle eddy current sensor array for the purpose of increasing the level of quantifying hole-edge crack parameters, especially, the crack angle. The new senor array consists of triangular coils instead of planar rectangular coils. The configuration of the novel sensor array, including the excitation current directions and the excitation winding shape, is optimized by simulation. The ability of the proposed sensing film to identify the crack parameters has been verified by finite element simulations and experiments. Results shows that triangular coils with same current directions in circumferentially adjacent coils and opposite current directions in axially adjacent coils achieve better performance in sensor linearity and resolution compared to rectangular coils. In addition, it has also been proved that the sensing film has a good potential to identify the crack depth and length.

Bolted joints are the primary structures for the load transfer of large-scale structures. It is vital to monitor the process of bolt cracking for enduring structural safety. In this paper, a structural health monitoring technique based on the embedding eddy current sensing film has been proposed to quantify the crack parameters of bolt cracking. Two configurations of the sensing film containing one-dimensional circumferential coil array and two-dimensional coil array are designed and verified to have the ability to identify three crack parameters: the crack angle, the crack depth, and the crack location in the axial direction of the bolt. The finite element method has been employed not only to verify the capacity of the sensing film, but also to investigate the interaction between the crack and the eddy current/magnetic field. It has been demonstrated that as the crack propagates, the variations of the induced voltage of the sensing coils are influenced by both eddy current effect and magnetic flux leakage, which play different roles in the different periods of the crack propagation. Experiments have been performed to verify the effectiveness and feasibility of the sensing film to quantify three crack parameters in the process of the bolt cracking.

Highlights • Up-to-date development of fiber-optic chemical sensors and biosensors are reviewed. • The role of sensing film in fiber-optic sensors are highlighted. • The fabrication of high-performance fiber-optic sensors are emphasized. • Combination of optical fibers with micro/nano-technologies are commented. Abstract The Internet-of-Things (IoT) has witnessed exponential growth over the past decade and will significantly reshape human life from every aspect, e.g., defense, environmental monitoring, energy, food safety, knowledge dissemination, healthcare and so on. Fiber-optic sensors, with both communication and sensing functions, have become a bridge to connect people and the whole world, so they are essential parts for accelerating the development of the IoT. Fiber-optic sensors possess the capability of translating a change of target analyte into optical signals and subsequently transmit an optical signal with target analyte information to people, machines or systems in real-time, even from a long distance. Therefore, exploration of high-performance fiber-optic chemical sensors and biosensors could significantly promote the development of the IoT. This review paper presents the foundations of fiber-optic chemical sensing or biosensing, including the sensing mechanisms of various fiber-optic sensors, sensing materials and the novel techniques for sensing materials deposition. Furthermore, recent developments on fiber-optic chemical sensors and biosensors are summarized, analyzed and discussed. Finally, the strategies and guidelines to further promote the development of fiber-optic sensors are also discussed. [ABSTRACT FROM AUTHOR]

In this work, a novel 3D graphene framework/Bi nanoparticle (GF/BiNP) film was fabricated with a facile preparation route. 3D graphene framework with porous structures was electrochemically reduced and in situ assembled on the electrode, and BiNPs with tunable morphologies were highly dispersed on the framework by a chemical reduction. Newly-designed 3D GF/BiNP film possessed a significantly large active area, fast electron transfer ability, high mass transfer efficiency, and excellent structure stability and binding strength on electrode. To demonstrate its superior ability, electrochemical sensors for the assay of heavy metal ions were constructed. As a result, a simultaneous assay of Pb 2+ and Cd 2+ with ultralow detection limits (0.02 μg L −1 of Pb 2+ and 0.05 μg L −1 of Cd 2+ , S/N = 3) and a wide linear range from 1 to 120 μg L −1 was achieved. Meanwhile, a separate analysis of Zn 2+ was performed to get optimum responses, in which a low detection limit of 4.0 μg L −1 (S/N = 3) with a linear range from 40 to 300 μg L −1 was observed, confirming the versatility of the GF/BiNP film in the detection of heavy metal ions. Moreover, excellent repeatability, reproducibility and stability, and reliable assays in real water samples were realized with constructed sensors. Due to its convenient preparation, favorable structures and excellent properties, prepared 3D GF/BiNP film will find great potential for advanced applications in environment, biomedicine and energy systems. [ABSTRACT FROM AUTHOR]

In the present study, temperature drift analysis of metal–oxide–semiconductor field‐effect transistor (MOSFET) is carried out using silicon nitride/SiO2 as dielectric film. An n‐channel depletion‐mode MOSFET was fabricated with silicon nitride ion‐sensitive field‐effect transistor (ISFET) on the same wafer. The study presents the fabrication, simulation and characterisation of MOSFET. The gate of the ISFET is stacked with silicon nitride/SiO2 sensing membrane that was deposited using low pressure chemical vapour deposition. Output and transfer characteristics of on‐chip fabricated Al gate MOSFET were obtained in order to study the fabricated ISFET behaviour to be used as pH sensor. Silicon nitride is preferred over SiO2 sensing film/dielectric (in case of MOSFET) which has better sensitivity and low drift. Process and device simulations were performed using Silvaco® TCAD tool. [ABSTRACT FROM AUTHOR]

A novel magnetic molecularly imprinted sensing film (MMISF) was fabricated for the determination of estradiol (E2) based on magnetic glassy carbon electrode (MGCE) and magnetic molecularly imprinted polymers (MMIPs). The MMIPs were synthesized by in situ polymerization of glutathione (GSH)-functionalized gold (Au)-coated Fe 3 O 4 (Fe 3 O 4 @Au-GSH) nanocomposites and aniline. The MMISF was constructed with MMIPs via a kind of “soft modification” where MMIPs were assembled and immobilized on the surface of MGCE or removed from it by freely installing a magnet into MGCE or not. The E2-MMIPs were obtained by MMIPs recognizing E2 from sample, and the electrochemical detection was carried out after forming the “soft modification” sensing film by putting MGCE into the E2-MMIPs suspension liquid. Afterwards, the “soft modification” MMISF was peeled off from the electrode by removing the magnet from MGCE. The interface of the electrode could be quickly refreshed through simple treatment for the next detection. The structures and morphologies of Fe 3 O 4 @Au-GSH, MMIPs and MMISF were investigated by Fourier transform infrared spectrometer, ultraviolet and visible spectrophotometer, scanning electron microscope and atomic force microscope. In addition, the MMISF was successfully used for detecting E2 in milk powder with good sensitivity, selectivity, reproducibility and efficiency. The linear range of the MMISF for E2 was 0.025–10.0 μmol L −1 with the limit of detection of 2.76 nmol L −1 ( S / N = 3). [ABSTRACT FROM AUTHOR]

Abstract: We report on improved ultrasonic atomizer method of depositing the sensing films on quartz crystal microbalance (QCM) sensors. The main objectives of the present work were minimizing the sensor-to-sensor response variation, improving the sensing film stability, and reducing amount of materials used during coating (reducing time of coating). In order to achieve the goals, we have redesigned and refabricated large parts of the atomizer system reported previously. The main principle of the operation—deposition of the fine mist generated by the ultrasonic device remained unchanged. The largest modifications encompass introduction of the new, sealed deposition chamber, considerable reduction of the flow resistance, and control over the flow rates of the mist and air streams in the system. The paper reports the new configuration of the ultrasonic atomizer method, optimization of the atomizer system performance (deposition parameters) and the results of improved quality of sensors fabricated using the new system. [Copyright &y& Elsevier]

Abstract: A novel fluorescent Cu(II) sensing film was developed by covalently attaching dansyl (5-dimethylamino-1-naphthalenesulfonyl) moieties onto glass slide surface based on self-assembled monolayer technique. Fluorescence measurements showed the emission of the dansyl-functionalized film was selectively quenched by Cu(II) ions and slightly influenced by the presence of other similar divalent metal ions (Pb(II), Zn(II), Ni(II), Co(II), etc.). In addition, the sensitivity of the film towards Cu(II) was increased as expected since more binding sites, the diethylenetriamine moieties, were incorporated into the spacer. It was also found that the presence of organic anions like acetate, citrate, and tartrate, etc. could enhance the quenching efficiency of Cu(II) compared with inorganic anions such as chloride, sulfate, and nitrate. This observation was explained by considering the spacer screening effect as discovered previously. Moreover, the response of the film toward Cu(II) is fully reversible which makes it attractive for sensing application. [Copyright &y& Elsevier]

A novel method for depositing gas sensing films on quartz crystal microbalance electrodes was developed. The method is based on the production of a fine mist of the solution with the sensing material by means of an ultrasonic atomizer. The mist is transported by a dry air flow to the quartz substrate allowing its deposition. The responses of the sensors are compared with those fabricated by spray coating method. It was found that even liquid films such as Apiezon L that were not stably deposited on polished gold electrodes by the spray method could be stably deposited using the atomizer, and an improvement of the reproducibility and sensitivity of the sensor response was achieved. [Copyright &y& Elsevier]

A new circular position sensor based on giant magnetoresistances has been developed. The sensing film is an AgCo nanogranular thin film patterned in a circular Wheatstone bridge configuration. This alloy shows a high magnetoresistance (8%) at room temperature within the field generated by an NdFeB permanent magnet that provides a sensitivity of 440 μV/V/(°). The operational temperature range of this sensor is -40°C/+120°C, although the magnetic film tolerates higher temperatures up to 200°C. These parameters and the contactless way of sensing make this device appropriate for automotive applications. The developed sensor presents excellent characteristics for life, since it is not sensitive to pollution; it is frictionless and does not present any type of electrical noise generated by contacts. [ABSTRACT FROM PUBLISHER]

Optical sensing films for ammonia have been investigated based on a fluorescent indicator aminofluorescein (AF). AF was immobilized in diverse organically modified silicates (ORMOSILSs) obtained by copolymerizing various proportions of methyltrimethoxysilane (Me–TriMOS), phenyltrimethoxysilane (Ph–TriMOS), dimethyldimethoxysilane (DiMe–DiMOS), and diphenyldimethoxysilane (DiPh–DiMOS) with tetramethoxysilane (TMOS). The effective polarities of ormosils were probed by using the solvatochromic dye ET (30) [2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)]phenolate. Compared with the fluorescent responses of fluorescein and fluorescein isothiocyanate, the fluorescent intensity enhancement of AF for ammonia was caused by the reaction between ammonia and the NH2 group on AF. The reaction may cause the reduction of the intermolecular self-quenching of AF to make a fluorescence enhancement of sensing film in NH3 solution. The ammonia sensing range and rate of response were found to highly depend on the type and content of organosilicon precursors employed. Films prepared with a 1:3, 1:1.5, 1:1.2, or 1:1 mole ratio (TMOS:Me–TriMOS, TMOS:Ph–TriMOS, TMOS:DiMe–DiMOS, or TMOS:DiPh–DiMOS) was found to be the best in terms of stability and response. Their detection limits for ammonia in water was 0.01, 0.5, 0.2, and 0.5 μg ml−1, respectively. [Copyright &y& Elsevier]

An organically modified silicate (ormosil) as a matrix for the fabrication of dissolved oxygen-sensing film was produced. The process included taking tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DMOS) as precursor and running a reaction at 60 °C in an open vial, which accelerates hydrolysis and condensation and results in the formation of emulsion. The film doped with tris-(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)3]2+) as an oxygen indicator exhibited a good linear relationship, fast response time, long-term stability and enhanced sensitivity to dissolved oxygen after optimizing the sol–gel processing parameters. The properties and the oxygen-sensing behavior of the film were investigated. The results presented here emphasized the significance of ormosil as a matrix for dissolved oxygen-sensing. [Copyright &y& Elsevier]

Hole-edge crack quantification of bolt joints is critical for monitoring and estimating structural integrity of aircraft. The paper proposes a new triangle eddy current sensor array for the purpose of increasing the level of quantifying hole-edge crack parameters, especially, the crack angle. The new senor array consists of triangular coils instead of planar rectangular coils. The configuration of the novel sensor array, including the excitation current directions and the excitation winding shape, is optimized by simulation. The ability of the proposed sensing film to identify the crack parameters has been verified by finite element simulations and experiments. Results shows that triangular coils with same current directions in circumferentially adjacent coils and opposite current directions in axially adjacent coils achieve better performance in sensor linearity and resolution compared to rectangular coils. In addition, it has also been proved that the sensing film has a good potential to identify the crack depth and length. [ABSTRACT FROM AUTHOR]

Bolted joints are the primary structures for the load transfer of large-scale structures. It is vital to monitor the process of bolt cracking for enduring structural safety. In this paper, a structural health monitoring technique based on the embedding eddy current sensing film has been proposed to quantify the crack parameters of bolt cracking. Two configurations of the sensing film containing one-dimensional circumferential coil array and two-dimensional coil array are designed and verified to have the ability to identify three crack parameters: the crack angle, the crack depth, and the crack location in the axial direction of the bolt. The finite element method has been employed not only to verify the capacity of the sensing film, but also to investigate the interaction between the crack and the eddy current/magnetic field. It has been demonstrated that as the crack propagates, the variations of the induced voltage of the sensing coils are influenced by both eddy current effect and magnetic flux leakage, which play different roles in the different periods of the crack propagation. Experiments have been performed to verify the effectiveness and feasibility of the sensing film to quantify three crack parameters in the process of the bolt cracking. [ABSTRACT FROM AUTHOR]