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A non-enzymatic electrochemical uric acid (UA) sensor based on heat-shrinkable polymer was fabricated via a simple and low-cost method without any complex electrode modification for the first time. We sputtered a gold electrode on the heat-shrinkable polymer with shadow masks, taking advantage of the heat shrinkage properties of the polymer to obtain a novel wrinkled gold electrode surface, then detected the UA concentration in aqueous conditions by square wave voltammetry. The performance of the shrink sensor, which was specific to the sensitivity and linearity, improved greatly compared with those non-shrinking ones. The accuracy and long-term stability of tests were also carried out, indicating a more accurate and stable sensor was achieved. Notably, a selectivity enhancement towards glucose interferent was experimentally observed. The selectivity coefficient decreased considerably after the heat shrink process, from −1.28 to −2.6. A new theoretical proposal related to reaction rate suppression was discussed, employing electrostatic shield effect between the wrinkled gold surface and biomolecules with different electrochemical reaction nature. It is a very simple but effective way to monitor UA concentration and the possible reaction control functions of the wrinkled surface can be rationally projected to tailor the electrode properties.

Compared to traditional continuous jets, synthetic jets (jets with oscillatory flow such that the time-average velocity is zero) have specific advantages, such as lower power requirement, simpler structure and the ability to produce an unsteady turbulent flow that is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a synthetic jet flow onto the tip region of a longitudinal fin used in an electronics cooling system. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-cooled-surface spacing, are recorded. The computational results show a good match with experimental results. In the experiments, an actual-scale (1 mm jet orifice) system is introduced and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up (44 mm jet orifice) is applied in a dynamically-similar way, then tested. Results of the experiments at the two scales, combined with the computational results, describe fin heat transfer coefficients on and near the jet impingement stagnation point. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m2K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how jet impingement cooling performance changes with orifice shape.

In this paper, we report an ion sensitive field effect transistor (IS-FET) sensor on anodic aluminum oxide (AAO) substrate, which can directly detect nitrate in water without a buffer solution. The free-standing AAO substrate has a highly ordered porous structure, which supports graphene and Au electrodes. The AAO substrate increases the exposed area of graphene in water. We describe the surface structure of the AAO substrate with scanning electron microscopy in each fabrication process. The device structure and mechanism are also explained in the paper. Graphene is used for the sensing material for its sensitivity in response to the surroundings. The nitrate selective membrane is synthesized and applied to the surface of graphene. The performance of the IS-FET sensors is characterized by a semiconductor analyzer. In the results, the performance of the device is significantly enhanced due to the porous structures of AAO. We successfully demonstrate the superior sensitivity and selectivity of the sensors. The detection limit is 0.05 ppm, and the response time is less than 3 seconds. [2020-0131]

Titanium dioxide (TiO2) is one of the most promising candidates for photoelectrochemistry applications. For a high photoelectrochemistry performance, the control of crystal structure and crystal facet is essential. The phase transformation of TiO2 is conventionally achieved by thermal annealing. Here, we report an approach for selective phase transformation of TiO2 containing exposed reactive facets with improved photoelectrochemistry performance. After femtosecond laser processing, TiO2 nanotubes with exposed reactive anatase {010} facets are prepared, and they have a maximum photocurrent density more than 5 times that of pure anatase. Additionally, this strategy can induce phase transformation in a selective area, which shows the advantages of patterning processing. Our method constructs a promising strategy for preparing functional nanomaterials with high performances and functionality.

In this work, reduced graphene oxide/titanium dioxide (rGO/TiO2) composite material was immobilized on shrink thermoplastic film using layer-by-layer (LBL) self-assembly to remove pollutants in water, and the results were compared with immobilized TiO2 on glass and shrink thermoplastic film. The structural and morphological properties of the immobilized photocatalysts were investigated using atomic force microscope and scanning electron microscope. The photocatalytic efficiency was measured by photodegradation of methylene blue under solar light illumination. The immobilized rGO/TiO2 on shrink thermoplastic film showed doubled photocatalytic efficiency than TiO2 on glass substrate, and no decrease of photocatalytic efficiency was shown after 5 h of operation. The use of shrink thermoplastic film and the introduction of graphene material contribute to an increase in catalytic efficiency of 63% and 28%, respectively. These results lead us to believe that the LBL self-assembled rGO/TiO2 composite on shrink thermoplastic film could be used in photocatalytic degradation of other water pollutants.

Numerous valuable studies on electron dynamics have focussed on the extraordinary properties of molybdenum disulfide (MoS2); however, most of them were confined to the level below the damage threshold. Here the electron dynamics of MoS2 under intense ultrafast laser irradiation was investigated by experiments and simulations. Two kinds of ablation mechanisms were revealed, which led to two distinct types of electron dynamics and final ablation morphology. At a higher fluence, the emergence of superheated liquid induced a dramatic change in the transient reflectivity and micro-honeycomb structures. At a lower fluence, the material was just removed by sublimation, and the ablation structure was relatively flat. X-ray photoelectron spectroscopic (XPS) measurements demonstrated that thermal decomposition only occurred at the higher fluence. Furthermore, a theoretical model was developed to deeply reveal the ultrafast dynamics of MoS2 ablation. The simulation results were in good agreement with the temporal and spatial reflectivity distribution obtained from the experiment. The electron and lattice temperature evolution was also obtained to prove the ablation mechanism. Our results revealed ultrafast dynamics of MoS2 above the damage threshold and are helpful for understanding the interaction mechanism between MoS2 and intense ultrafast lasers, as well as for MoS2 processing applications., Optoelectronics: Digging into molybdenum disulfide Ultrafast damage-causing laser pulses affect bulk molybdenum disulfide differently depending on their energy per area, revealing further insight into the ultrafast electron dynamics. The research group of Lan Jiang from Beijing Institute of Technology, in cooperation with Tianhong Cui of University of Minnesota, has predicted and examined what happened to molybdenum disulfide on electron and lattice level when intense femtosecond laser pulses irradiate. Lower damage-causing energies per area, known as fluences, removed material through inducing a solid-to-gas transition. Higher fluences caused superheating, liquidation, and the formation of nanocracks and nanoridges. Tests on electron dynamics obtained by the materials’ reflectivity with different fluences were followed by theoretical simulations, which further helped to reveal the electron and lattice temperature evolution. The findings further understandings for laser processing of molybdenum disulfide and for its use in optoelectronics.

Traditional lithography plays a significant role in the fabrication of micro- and nanostructures. Nevertheless, the fabrication process still suffers from the limitations of manufacturing devices with a high aspect ratio or three-dimensional structure. Recent findings have revealed that shrink polymers attain a certain potential in micro- and nanostructure manufacturing. This technique, denoted as heat-induced shrink lithography, exhibits inherent merits, including an improved fabrication resolution by shrinking, controllable shrinkage behavior, and surface wrinkles, and an efficient fabrication process. These merits unfold new avenues, compensating for the shortcomings of traditional technologies. Manufacturing using shrink polymers is investigated in regard to its mechanism and applications. This review classifies typical applications of shrink polymers in micro- and nanostructures into the size-contraction feature and surface wrinkles. Additionally, corresponding shrinkage mechanisms and models for shrinkage, and wrinkle parameter control are examined. Regarding the size-contraction feature, this paper summarizes the progress on high-aspect-ratio devices, microchannels, self-folding structures, optical antenna arrays, and nanowires. Regarding surface wrinkles, this paper evaluates the development of wearable sensors, electrochemical sensors, energy-conversion technology, cell-alignment structures, and antibacterial surfaces. Finally, the limitations and prospects of shrink lithography are analyzed.

The objective of this research is to develop a highly sensitive acoustic wave sensor using a tunneling current. The tunneling current device is fabricated with the hot embossing technology. Since polymethyl methacrylate (PMMA) is less expensive, has little stiffness, and is easier to work with micro-machining process compared to traditional silicon-based tunneling sensors, we fabricate the tip structure on the material using the hot embossing process. First, the frequency response of the tunneling device is measured by a piezoelectric transducer (PZT) and laser vibrometer to find the resonance frequency. Then the performance of the device is characterized by measuring the acoustic wave, which has the resonance frequency.

This paper presents a high-performance electrochemical sensor for dopamine detection based on graphene and gold nanoparticles. Experimental results show that the electroneutral gold nanoparticles are capable of enhancing the diffusion of ascorbic acid, improving the selectivity of graphene-based sensors. The optimal sensor with 5 layers of graphene and gold nanoparticles exhibits a low oxidation peak potential of 0.12 V, a high sensitivity of 1.32 µA/µM, a low detection limit of 10 nM, and favorable selectivity. The outstanding performance enables this sensor for possible monitoring the variation of neurotransmitters in vivo.

Femtosecond laser direct writing is widely exploited in surface periodic structures processing. However, this technique still faces challenges in obtaining high surface homogeneity and flexible morphology controllability. In this study, a flexible and efficient approach has been proposed to fabricate highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification. By precisely manipulating the laser-material interaction process, alternating amorphous-crystalline nanofringes are generated when employing femtosecond laser scanning over a Si sample, with almost no material removal. Following auxiliary chemical etching, highly homogeneous nanograting structures are obtained, and the morphology of the nanogratings can be flexibly managed through precisely controlling the duration of the etching process. Complex cross-scale patterns with remarkable structural colors that are visible under indoor light illumination are readily achieved on the sample surfaces exploiting our method. In addition, compared with traditional methods for laser-induced periodic surface structures, the fabrication efficiency is considerably improved. Our processing procedure offers potential applications in the fields of optics, nanoelectronics, and mechatronics.

An ultrasensitive microelectrode arrays (MEA) mercury sensor based on the heat-shrinkable polymer was fabricated by a very simple and low-cost method for the first time. We sputter a comb-finger gold electrode on the heat-shrinkable polymer, made use of the heat shrinkage and sticky characteristics of the polymer to construct MEA, and then detected the trace mercury ions (Hg2+) in the water by anodic stripping voltammetry. The characterization result indicated that the shrink polymer prepared by different heating temperature had controllable shrinkage ratios, and the electrode surface presented unique wrinkle structure by heating process. Due to the non-linear diffusion characteristic of the microelectrode and the microwrinkle structure, performance of the sensor had been improved greatly. The signal-to-noise ratio (Faraday current divide Background current) increased notably, and the sensor’s detection limit was achieved as 0.0874 ppb. This is a very effective way to detect ultra-low concentrations mercury ions and the heat-shrinkable film-based microelectrode arrays construction method can be applied to many fields.

Air-cooled heat sinks are widely used for electronics cooling. Active and passive cooling components can be added to enhance the performance of the air-cooled heat sinks. In this paper, piezoelectric translational agitators and synthetic jets are integrated as active cooling components while micro pin fins are adopted as a passive cooling scheme. The heat transfer performance of the active heat sink system that combines these active and passive cooling components along with a suction fan is experimentally investigated. The piezoelectric translational agitators installed within cooling channels are operating at 222 Hz ∼ 820 Hz with a peak-to-peak displacement of 1.0 mm ∼ 1.4 mm, depending on the attached carbon fiber blade type. The piezoelectric synthetic jet array provides impingement flow into the cooling channels with an inclined configuration, that has been successfully integrated into the system without interference with other components by using a wedge platform. The jet operates at 720 Hz with the jet velocity of up to 39 m/s. Micro pin fins are fabricated onto both surfaces of each heat sink channel walls by a double-sided microfabrication technique. They have diameter, height, and spacing of 500 μm, 250 μm, and 1500 μm, respectively. The experimental results indicate that the micro pin fins are most efficient among the employed active and passive cooling components, reducing thermal resistance up to 38%, compared to plain heat sink performance. The piezoelectric translational agitator reduces system thermal resistance by 22%, compared to the non-agitated condition, at the same through-flow rate. The synthetic jet shows weaker cooling capability in the setting tested, compared to enhancement by the agitator plates or pin fins. The active heat sink with the micro pin fins, agitators, and jets provides a thermal resistance of 0.064 °C/W at 70 CFM (33 L/sec) through-flow of air, about a 48% reduction from that of the non-agitated, plain heat sink under the same operating conditions. The results demonstrate how more effective the active heat sink system is compared to traditional air-cooled heat sinks.

Summary Dew water, mostly ignored until now, can provide clean freshwater resources, just by extracting the atmospheric vapor available in surrounding air. Inspired by silicon-based solar panels, the vapor can be harvested by a concept of water condensing panels. Efficient water harvesting requires not only a considerable yield but also a timely water removal from the surface since the very beginning of condensation to avoid the huge evaporation losses. This translates into strict surface properties, which are difficult to simultaneously realize. Herein, we study various functionalized silicon surfaces, including the so-called Black Silicon, which supports two droplet motion modes—out-of-plane jumping and in-plane sweeping, due to its unique surface morphology, synergistically leading to a pioneering combination of above two required characteristics. According to silicon material's scalability, the proposed silicon-based water panels would benefit from existing infrastructures toward dual functions of energy harvesting in daytime and water harvesting in nighttime., Graphical abstract, Highlights • Unusual condensation dynamics occur on the hierarchical Black Silicon metasurface • Near-zero water removal time and good water yield are simultaneously achieved • Great scalability and multifunctionality are accessible to the proposed water panel, Materials design; Materials property; Metamaterials; Surface

In this work, topology optimization was used to design a fixed-geometry fluidic diode of high diodicity, defined as the ratio of pressure drop of reverse flow to forward flow. Next, the fluidic diode was used in a valveless micropump. A three-dimensional and unsteady numerical analysis of fluid flow inside the micropump with the optimized diode was conducted by Computational Fluid Dynamics (CFD). Performance of a nozzle-diffuser type diode in the valveless micropump was also evaluated under the same conditions, for comparison. Both types of micropumps were fabricated and tested. The results show that the micropump with the designed fluidic diode can reach a flow rate of up to 33.5 ml/h, which is consistent with the simulation results and 2.2 times that of the nozzle-diffuser type micropump.

For the first time, we used a hybrid physical–chemical vapor deposition (HPCVD) method to fabricate perovskite solar cells (PSCs) based on perovskite films with both organic cations and halogen anions. A high power conversion efficiency (PCE) of 18.1% was achieved based on a mixed perovskite film of MAxFA1−xPb (IyBr1−y)3 and the efficiency of the PSCs with MAPbI3 and MAxFA1−xPbI3 films were 14.5% and 16.4%, respectively. Perovskite material components and bandgaps were precisely tuned to achieve high photoelectric conversion performance. Three different types of perovskite films employed include MAPbI3, MAxFA1−xPbI3, and MAxFA1−xPb (IyBr1−y)3 (which are also designated as MAPbI3, MA0.89FA0.11PbI3, and MA0.54FA0.46Pb (I0.94Br0.06)3 with the respective bandgaps of 1.60 eV, 1.58 eV, and 1.61 eV. The experimental results demonstrate the ability to fabricate both organic cation and halogen anion mixed perovskite films by the HPCVD method and achieve easily adjustable bandgaps. In addition, the perovskite films fabricated by HPCVD have superior surface morphology, large crystal size, and low surface roughness. Eventually, this vapor-based method will have great potential in the fabrication of large-area and flexible PSCs to promote commercial application and industrialization of future PSCs.

Titanium dioxide (TiO

The composition and crystallization process are essential for high-quality perovskite films. Cesium (Cs) and methylammonium chlorine (MACl) were found to affect the crystallization kinetics of perovskite, and the performance and stability of corresponding devices were greatly improved. We adopted an ion exchange method to remove MACl vapor and add Cs to form a multiple-cation-based perovskite film. With the increase of annealing time, Cl

This paper presents a two-dimensional (2D) transient numerical model for simulating the vapor deposition process for growing perovskite films. The diffusion process of methylammonium iodide (MAI) vapor through the processing chamber to react with the lead iodide (PbI2) substrate and grow the perovskite layer is analyzed with a diffusion coefficient that has been determined by measuring thicknesses of perovskite layers grown in a chemical vapor deposition (CVD) chamber. Innovations applied to the CVD chamber to improve the uniformity of layer thickness and offer control over the growth process are applied and computationally assessed. One is the addition of screens at various strategic locations in the chamber to improve flow uniformity. Another is changing the locations of MAI sublimation bowls and chamber outlet numbers and locations. The results show that adding screens makes the MAI vapor flow more uniform in the plenum while allowing a quicker purge of the N2 inert gas. This leads to a higher and more uniform growth rate of perovskite. The MAI vapor flow is influenced by the reaction plenum geometry, so the chamber is expected to allow good control of the process to achieve uniform surface deposition rate and controlled grain growth of the perovskite layer.

In common plasmonic configurations, energy loss and field enhancement are mutually restricted. In a vast majority of cases, high confinement goes together with high loss, which is a serious limitation for some applications. In an attempt of breaking this rule, which holds true for surface plasmon polariton (SPP) resonators, a multilayer trench grating microstructure with an asymmetric waveguide is considered. It supports both Fabry-Perot (FP) and cavity modes, whose hybridization exhibits unusual properties. The electric field enhancement was modulated by regulating the corresponding absorption and radiation quality factors. At the same time, energy loss was reduced, which is fundamentally ascribed to the mutual recycling of radiation energy between FP and cavity resonators. The maximum total quality factor and strongest field enhancement were both observed at the vicinity of quasi-static limit, thereby signifying that the structure exhibited simultaneous optimizations of field enhancement and loss inhibition, which is crucial to the design of high-quality SPP-based devices.

Blood-contacting medical devices that directly inhibit thrombosis and bacterial infection without using dangerous anticoagulant and antibacterial drugs can save countless lives but have proved extremely challenging. Here, a useful methodology is proposed that employs temporally shaped femtosecond laser ablation combined with fluorination to fabricate multifunctional three-dimensional (3D) micro-nanostructures with excellent hemocompatibility, zero cytotoxicity, outstanding biocompatibility, bacterial infection prevention, and long-term effectiveness on NiTi alloys. These multifunctional 3D micro-nanostructures present 0.1% hemolysis ratio and almost no platelet adhesion and activation, repel blood to inhibit blood coagulation in vitro, maintain 100% cell viability, and have exceptional stability over 6 months. Moreover, the multifunctional 3D micro-nanostructures simultaneously suppress bacterial colonization to form biofilm and kill 100% colonized Pseudomonas aeruginosa (P. aeruginosa) and 95.6% colonized Staphylococcus aureus (S. aureus) after 24 h of incubation, and bacterial residues can be easily removed. The fabrication method in this work has the advantages of simple processing, high efficiency, high quality, and high repeatability, and the new multifunctional 3D micro-nanostructures can effectively prevent thrombosis and bacterial infection, which can be widely applied to various clinical needs such as biomedical devices and implants.

Micro-supercapacitors are promising miniaturized energy storage devices that have attracted considerable research interest. However, their widespread use is limited by inefficient microfabrication technologies and their low energy density. Here, a flexible, designable micro-supercapacitor can be fabricated by a single pulse laser photonic-reduction stamping. A thousand spatially shaped laser pulses can be generated in one second, and over 30,000 micro-supercapacitors are produced within 10 minutes. The micro-supercapacitor and narrow gaps were dozens of microns and 500 nm, respectively. With the unique three-dimensional structure of laser-induced graphene based electrode, a single micro-supercapacitor exhibits an ultra-high energy density (0.23 Wh cm−3), an ultra-small time constant (0.01 ms), outstanding specific capacitance (128 mF cm−2 and 426.7 F cm−3) and a long-term cyclability. The unique technique is desirable for a broad range of applications, which surmounts current limitations of high-throughput fabrication and low energy density of micro-supercapacitors., Microfabrication for cost-effective miniaturized energy storage devices remains a challenge. Here, the authors propose a spatially shaped femtosecond laser method, which is ultrafast, one-step, high resolution and large-scale, for use in patterning flexible high-performance micro-supercapacitors.

This paper presents a photoelectrochemical (PEC) sensor using flexible polymer as the substrate for detection of hexavalent chromium (Cr(VI)) ions, showing a large sensing range from part per billion (ppb) level to part per million (ppm) level. This sensor utilizes layer-by-layer (LbL) self-assembled graphene intercalation to mediate the Schottky barrier formed between the metal electrodes (Au) and the photon-sensitive material (titanium dioxide, TiO 2 ), which enhances the photocurrent of the sensor more than three times. Additionally, graphene layer also improves the stability of the sensing signal (photocurrent) due to its role in facilitating the separation of photon-excited electrons and holes. Quercetin is used as the selective material in the sensing system, which can specifically interact with Cr(VI). The flexibility of metal electrode and nanomaterial films of the sensor allows the adoption of a flexible substrate, with great application potential in wearable or implantable sensors for animals and plants. The sensor shows a detection range from 14.9 to 3194.1 ppb in dissolved air, with a low detection limit of 9.5 ppb.

Early cancer diagnosis and treatment are crucial research fields of human health. One method that has proven efficient is biomarker detection which can provide real-time and accurate biological information for early diagnosis. This review presents several biomarker sensors based on electrochemistry, surface plasmon resonance (SPR), nanowires, other nanostructures, and, most recently, metamaterials which have also shown their mechanisms and prospects in application in recent years. Compared with previous reviews, electrochemistry-based biomarker sensors have been classified into three strategies according to their optimizing methods in this review. This makes it more convenient for researchers to find a specific fabrication method to improve the performance of their sensors. Besides that, as microfabrication technologies have improved and novel materials are explored, some novel biomarker sensors—such as nanowire-based and metamaterial-based biomarker sensors—have also been investigated and summarized in this review, which can exhibit ultrahigh resolution, sensitivity, and limit of detection (LoD) in a more complex detection environment. The purpose of this review is to understand the present by reviewing the past. Researchers can break through bottlenecks of existing biomarker sensors by reviewing previous works and finally meet the various complex detection needs for the early diagnosis of human cancer.

Trace heavy metal ions are probable carcinogens with concentrations at ppb levels. Ion selective electrode (ISE) technology is a conventional and widely used method to detect various ions with the advantages as rapid measurement, low power consumption and low cost. However, the detection limit of a conventional bulky ISE device is only able to reach ppm level so far, not sensitive enough for practically detecting heavy metal ions. A micro ion selective electrode (μISE) array which can realize multiplex detection of heavy metal ions on one chip is reported in this paper. Its detection limit for Pb2+, Cd2+, AsO2−, and Hg2+ can reach 1, 3, 10, and 1 ppb, respectively, within the permissible limits of drinking water. The micrometer scale device arrays from microfabrication processes demonstrated enhanced sensitivity, uniformity, and reduced response time (18 s) compared to conventional ISE. Our devices showed superb selectivity, and the performance dependence on temperature and pH values was investigated as well.

Mixed-potential type (MPT) NO2 sensors equipped with CeO2-B2O3 (B = Fe, Cr) sensing electrode (SE) and yttria-stabilized-zirconia (YSZ-8Y) electrolyte are fabricated. The new ceria-based nanocomposites synthesized by sol-gel method improve the NO2 gas sensing properties significantly. The highest response to NO2 is found for the sensor using CeO2-Cr2O3 binary oxides with 1:1 Ce/Cr sintered at 800 °C, resulting in 100 mV to 100 ppm with relatively fast response and recovery times at the working temperature of 450 °C. A linear relation is obtained for the sensor with configuration of Pt/YSZ/CeO2-B2O3 (B = Fe, Cr) between potential difference (ΔV) and the logarithm of the concentration of NO2 from 5 to 200 ppm, which the sensitivities are 40.5 and 74.0 mV/decade, respectively. Additionally, the sensor’s reproducibility, selectivity, cross-sensitivity and stability are investigated in details. Furthermore, the mixed potential sensing mechanism and catalytic activity to NO2 for ceria-based nanocomposites are also discussed.

The mixed-potential-type NO2 sensor based on a yttria-stabilized zirconia (YSZ) electrolyte with NiO sensing electrode and a three-phase boundary (TPB) was fabricated. The ion beam etching (IBE) technology with low energy was employed to etch the YSZ substrate for the first time. The characterization result indicates that the YSZ substrate prepared by argon ion (Ar+) beam with different incident angles (10° and 40°) obtains hollow and spike patterns on the surface, respectively. The sensing performance was improved by the self-organized nanostructures of TPB, which enhances the contact area obviously. The sensor using a YSZ substrate processed by 10° incident angle with 800 eV/60 mA energy demonstrates the largest response compared with other parameters to NO2 at 850 °C. Sensitivity of the sensors is achieved as 40.7 mV/decade, about 1.9 times as the initial YSZ substrate. In addition, the sensor also has good response-recovery transients, repeatability and selectivity.

This paper reports a highly sensitive micro sensor utilizing an ion selective membrane to determine trace arsenite with anodic stripping voltammetry in the presence of interferences. The sensor was fabricated by depositing an arsenite (As (III)) ion selective membrane on a gold electrode surface. Compared with the traditional sensor without an ionophore membrane, the proposed sensor achieved better voltammetric performance due to its superior selectivity to As (III). After applying the ionophore film, the sensor’s background current decreased from $1.375~\mu \text{A}$ to $0.320~\mu \text{A}$ , and its standard deviation decreased from $0.150~\mu \text{A}$ to $0.007~\mu \text{A}$ , leading to lower background noise and higher conformity. Meanwhile, the sensor demonstrated high selectivity with the existence of interference ions, such as Cd2+, Pb2+, and Hg2+. The detection and statistical analysis of As (III) were performed in the linear concentration range of 10–100 ppb ( $\text{R}^{2} = 0.993$ ) and a low limit of detection (LOD) of 1.10 ppb was obtained for 300s deposition. The sensor was successfully employed for the determination of As (III) in waste water and the results were in good agreement with those from a standard procedure. This highly sensitive and selective portable sensor holds great potential for on-line environmental monitoring.

Here we report an ultrasensitive trace mercury(II) micro sensor based on heat-shrinkable polymer (polyolefins, PO). The layer-by-layer self-assembly (LBL SA) method was employed to modify mixed gold nanoparticle (Au NPs) and graphene solution on a micro gold electrode with PO substrate. The unique wrinkle structure of the electrode surface and superior properties of modification film enhanced the performance of LBL SA graphene–Au NPs shrink sensor greatly in determination of Hg(II) using anodic stripping voltammetry (ASV): compared with a shrink gold electrode without surface modification, the sensitivity was improved for about 3.7 times from 0.197 to 0.721 μA/ppb; compared with a same-sized sensor without surface modification nor shrink, the sensitivity was improved for over 50 times. This sensor’s detection limit of Hg(II) was achieved as 0.931 ppb with a sensitivity of 0.721 μA/ppb. This simple but highly sensitive sensor can be widely used in applications of on-line environmental monitoring of Hg(II).

This paper reports a low-cost and highly sensitive flexible sensor for the determination of lead and cadmium in tap and lake water. This sensor achieved low detection limits and high performance by decorating cation-exchanging resin and in situ deposited bismuth on the working electrode. In situ deposited bismuth film was much easier to fabricate and formed a highly porous 3-dimensional structure, which provided more surface area for the reaction of the target ions. The cation-exchanging Nafion film can help reduce the interference caused by surface active compounds and enhance the pre-concentration of lead and cadmium at the same time. Flexible polypropylene film was chosen as the substrate to reduce the cost and expand the sensor's applications. Finally, the detection limits were 1.68 ppb for Pb and 1.24 ppb for Cd at the deposition time of 300 s. Particularly, this sensor revealed good linearity (R2ý=ý0.993) at a wide range of 10---500 ppb for cadmium in tap water environment. The proposed sensor was successfully applied to lead and cadmium determination in environmental water samples and the results were in good agreement with those from a standard procedure.

A new sensor based on decorated copper nanoparticles and self-assembled graphene was fabricated and exemplified with the determination of nitrate solutions. Traditionally, graphene is coated on the sensor by drop-casting, leading to poor adhesion between graphene and the sensor. The self-assembled graphene proposed in this paper not only have a firm connection with the substrate, but also provide a three-dimensional network structure for copper nanoparticles. Copper was found as an effective catalyst for nitrate reduction. The combination of copper nanoparticles and self-assembled graphene can greatly enhance the sensitivity. Thus, low detection limit of 7.89 µM is obtained for nitrate, which to our knowledge, is among the lowest reported in the literatures. This method was employed for the determination of nitrate in lake water and the results were in good agreement with those obtained from a standard analytical procedure.