Carbon Nanotube Based Chemical Sensors

Carbon nanotubes CNTs)have been receiving enormous attention in the last decade due to their extraordinary mechanical properties and unique elec- tronic properties.This combination has produced an unprecedented range of applications for CNTs:elec- tronic,logic and memory chips,chemical and biosen- sots,composites,lithium batteries,gas storage,filters and membranes,etc.This presentation will focus on carbon nanotube based sensors and discuss fabrication, testing and performance.

Ubiquitous Sensor Network for Chemical Sensors

Wireless sensor networks have been identified as one of the most important technologies for the 21 st century.Recent advances in micro sensor fabrication technology and wireless communication technology enable the practical deployment of large-scale,low-power,inexpensive sensor networks.Such an approach offers an advantage over traditional sensing methods in many ways:large-scale,dense deployment not only extends spatial coverage and achieves higher resolution,but also increases the system's fault-tolerance and robustness.Moreover,the ad-hoc nature of wireless sensor networks makes them even more attractive for military and other risk-associated applications,such as environmental observation and habitat monitoring.

Recent developments in self-powered smart chemical sensors for wearable electronics

The next generation of electronics technology is purely going to be based on wearable sensing systems. Wearable electronic sensors that can operate in a continuous and sustainable manner without the need of an external power sources, are essential for portable and mobile electronic applications. In this review article, the recent progress and advantages of wearable self-powered smart chemical sensors systems for wearable electronics are presented. An overview of various modes of energy conversion and storage technologies for self-powered devices is provided. Self-powered chemical sensors (SPCS) systems with integrated energy units are then discussed, separated as solar cell-based SPCS, triboelectric nano-generators based SPCS, piezoelectric nano-generators based SPCS, energy storage device based SPCS, and thermal energy-based SPCS. Finally, the outlook on future prospects of wearable chemical sensors in self-powered sensing systems is addressed.

Roles of Chemical Gas Sensors in the Filed of Safety

1 Introduction Gas sensors have been used in a range of applications where they play a crucial role in ensuring that we live safely and comfortablely.Gas safety products,such as gas detectors/alarms,especially those equipped with combustible gas,toxic gas,or oxygen sensors,are one of the most important applications for gas sensors.The purpose of gas detector/alarm units is

Chemical Investigation of the NO_x Detection Mechanisms by Semiconductor Metal Oxide Nanoparticles

This work reports an FTIR study of the NO_x adsorption/desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150℃,in presence of O_2).The chemical reactions are monitored in situ and correlated with the variations of the SnO_2 electrical conductivity.On the basis of the FTIR spectra,two contributing mechanisms for the NO_x detection are suggested.The first one presents the formation of bridged nitrate groups bound to the SnO_2 surface via oxygen vacancies acting as electron donor sites.The second mechanism also involves surface oxygen vacancies in the coordination of NO_x,but this time the formation of NO_x anionic species is considered.Both mechanisms lead to the decrease of the electrical conductivity under NO_x adsorption.However,the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NO_x adsorption.On the contrary,the nitrosyl anionic species are reversible and,from the second NO_x adsorption/desorption cycle,ensure the reproducibility of the sensor response.

A Review on Surface Stress-Based Miniaturized Piezoresistive SU-8 Polymeric Cantilever Sensors

In the last decade, microelectromechanical systems(MEMS) SU-8 polymeric cantilevers with piezoresistive readout combined with the advances in molecular recognition techniques have found versatile applications,especially in the field of chemical and biological sensing.Compared to conventional solid-state semiconductor-based piezoresistive cantilever sensors, SU-8 polymeric cantilevers have advantages in terms of better sensitivity along with reduced material and fabrication cost. In recent times,numerous researchers have investigated their potential as a sensing platform due to high performance-to-cost ratio of SU-8 polymer-based cantilever sensors. In this article, we critically review the design, fabrication, and performance aspects of surface stress-based piezoresistive SU-8 polymeric cantilever sensors. The evolution of surface stress-based piezoresistive cantilever sensors from solid-state semiconductor materials to polymers, especially SU-8 polymer, is discussed in detail. Theoretical principles of surface stress generation and their application in cantilever sensing technology are also devised. Variants of SU-8 polymeric cantilevers with different composition of materials in cantilever stacks are explained. Furthermore, the interdependence of the material selection, geometrical design parameters, and fabrication process of piezoresistive SU-8 polymeric cantilever sensors and their cumulative impact on the sensor response are also explained in detail.In addition to the design-, fabrication-, and performancerelated factors, this article also describes various challenges in engineering SU-8 polymeric cantilevers as a universal sensing platform such as temperature and moisture vulnerability. This review article would serve as a guideline for researchers to understand specifics and functionality of surface stress-based piezoresistive SU-8 cantilever sensors.

A Novel Electrochemical Oxygen Sensor for Determination of Ultra-low Oxygen Contents in Molten Metal

A novel electrochemical oxygen sensor has been developed by using La beta -Al2O3 as solid electrolyte and Cr+Cr2O3 as reference electrode. The sensor not only can be used as normal oxygen sensor but also as an ultra-low oxygen sensor. Especially, it is very sensitive to measure ultra-low oxygen in molten metal. For estimating the accuracy of La beta -Al2O3 oxygen sensor, two series of oxygen activities in molten iron at different oxygen contents and different temperature were measured by both La beta -Al2O3 oxygen sensor and ZrO2 oxygen sensor. The theoretical values of oxygen activities in molten iron (3.30%C, in mass fraction) at 1723K and 1745K were also evaluated for comparing the measuring results of two sensors. At last, the error of measurement for La beta -Al2O3 oxygen sensor was discussed too.

Effect of Durian Peel Ash Added in Zinc Oxide/Reduced Graphene Oxide Composites Used as a Chemical Sensor for Hydrazine Detection

As the hydrazine is toxic, the methods to detect hydrazine at low concentrations are essential in scientific research. This preliminary study reported on how to increase the efficiency of ZnO/reduced graphene oxide (rGO) by adding durian peel ash (DPA) and using three-electrode method. The ZnO/rGO composites were prepared using chemical reaction of graphene oxide (GO) with zinc chloride. The rGO was prepared by the chemical reduction of GO using hydrazine. The properties of the samples were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and Potentiostat/Galvanostat. The results showed that the optimal condition for the composite material was 70%DPA:30%ZnO/rGO with the sensitivity of 222.92 mA/mM·cm2 and the current density up to 116.50 ± 0.95 A/g. The relationship between the current and the hydrazine concentration was I (μA) = 48.69 + 21.91C (mM) with R2 of 0.9870. The minimum concentration of hydrazine solution that the modified electrode can measure was 0.125 mM. The DPA powder can then be used to enhance the hydrazine detection efficiency at low concentrations.

The recent progress of laser-induced graphene based device applications

Laser writing is a fast and efficient technology that can produce graphene with a high surface area,whereas laser-induced graphene(LIG)has been widely used in both physics and chemical device application.It is necessary to update this important progress because it may provide a clue to consider the current challenges and possible future directions.In this review,the basic principles of LIG fabrication are first briefly described for a detailed understanding of the lasing process.Sub-sequently,we summarize the physical device applications of LIGs and describe their advantages,including flexible electronics and energy harvesting.Then,chemical device applications are categorized into chemical sensors,supercapacitors,batteries,and electrocatalysis,and a detailed interpretation is provided.Finally,we present our vision of future developments and challenges in this exciting research field.

Gas-sensing Properties of Sintered Bismuth Iron Tungstate

Gas sensor materials of bismuth tungstate and bismuth iron tungstate were prepared. Sintered bismuth iron tungstate gas sensors have a high sensitivity and selectivity to ethanol and acetone, show long-term stability of response under most operating conditions and insensitivity to atmospheric humidity and respond more quickly in relative case. The changes of the sensors in conductance are mediated by oxygen vacancy donors which caused by the direct reduction. Also, they are highly mobile and can quickly diffuse through the sample, thereby having a direct effect on the electronic carrier density. The phase composition and structure of these gas sensor materials were investigated by XRD technique.

Spatial distribution pattern of seafloor hydrothermal vents to the southeastern Kueishan Tao offshore Taiwan Island

Investigations of the diffusion activities both within and outside the seafloor hydrothermal vents, as well as related mineral genesis, have been one of the key focuses of ocean biogeochemistry studies. Many hy- drothermal vents are distributed close to the southern Okinawa Trough on the less-than-30-m deep shallow seafloor off Kueishan Tao, northeast of Taiwan Island. Investigations of temperature, pH and Eh at four depths of hydrothermal plume were carried out near Kueishan Tao at the white （24.83°N, 121.9°E） and yellow （24.83°N, 121.96°E） vents. An 87 h of temperature time series observation-undertaken near the white vent showed that tide is the main factor affecting the background environment. Based on the observed data, 3-dimensional sliced diffusion fields were obtained and analyzed. It was concluded that the plume diffused mainly from north to south due to ebb tide. The yellow vent＇s plume could effect as far as the white vent surface. From the temperature diffusion field, the vortices of the plume were observed. The Eh negative abnormality was a better indicator to search for hydrothermal plumes and locate hydrothermal vents than high temperature and low pH abnormalities.

Chemiluminescence Sensor for the Determination of Hydroxylamine by Electrostatically Immobilizing Luminol and Periodate

A novel chemiluminescence(CL) sensor, which can be used for hydroxylamine determination in combination with flow injection analysis, was developed by electrostatically immobilizing luminol and periodate on anion exchange resin respectively. Hydroxylamine was sensed by its enhancing effect on the weak CL reaction between luminol and periodate, which were eluted from the ion exchange column. The response of the sensor to hydroxylamine was linear in the concentration range of 8.0×10^(-8)-2.0×10^(-6)mol/L with a detection limit of 4.0×10^(-8)mol/L hydroxylamine(3σ).The relative standard deviation(RSD) was 2.0% for 9 repetitive determinations at a hydroxylamine concentration of 5.0×10^(-7) mol/L. The sensor could be reused for over 400 times with a good reproducibility and was used to determine hydroxylamine in wastewater.

Electrogenerated chemiluminescence sensor for the determination of metoclopramide using ordered mesoporous carbon for immobilizing tris(2,2'-bipyridyl)ruthenium

A novel electrogenerated chemiluminescence(ECL)sensor for the determination of metoclopramide was developed by employing ruthenium complex as an ECL signal producer and an ordered mesoporous carbon(OMC)material as modified material.The ECL sensor was fabricated by adsorption ruthenium complex into a mixture of OMC and Nafion,which showed good electrochemical and ECL behaviors.It was found that the ECL intensity of the sensor fabricated was greatly enhanced in the presence of metoclopramide.Based on this finding,a highly sensitive and reproducible ECL method was developed for the determination of metoclopramide.The result showed that the ECL intensity was linear with the concentration of metoclopramide in the range from 1.0×10-10 to 5.0×10-7M and the detection limit was 3×10-11M.The ECL sensor exhibited a long-term stability and a fine reproducibility with relative standard deviation of 1.0 % for 1.0×10-10M metoclopramide in 18 continuous determinations.The developed method has been applied to the determination of metoclopramide in tablet samples with satisfactory results.

Quartz Crystal Microbalance Sensor Deposited with LB Films of Functional Polymers for the Detection of Phenols in Vapour Phase

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Synthesis and Gas Sensing of TiO_2 Ultrafine Powders by Precipitating

We investigated the gas sensing characteristics of rutile and anatase TiO_2 nano-particle sensors for chemical warfare agents.TiO_2 nano-powders with rutile and anatase structure were fabricated by controlling pH value without heat treatment respectively.The mean particle size of TiO_2 powders were below 10 nm.As-prepared TiO_2 powders have several advantages of nano particle size and high surface area and could be a prominent candidate for nano-sensors.TiO_2 sensors were examined with DMMP for chemical warfare agents detection.

Advances and challenges of cellulose functional materials in sensors

As the most abundant natural polymer material on the earth,cellulose is a promising sustainable sensing material due to its high mechanical strength,excellent biocompatibility,good degrada-tion,and regeneration ability.Considering the inherent advantages of cellulose and the success of modern sensors,applying cellulose to sensors has always been the subject of considerable investigation,and significant progress has been made in recent decades.Herein,we reviewed the research progress of cellulose functional materials(CFMs)in recent years.According to the different sources of cellulose,the classification and preparation methods for the design and func-tionalization of cellulose were summarized with the emphasis on the relationship between their structure and properties.Besides,the applications of advanced sensors based on CFMs in recent years were also discussed.Finally,the potential challenges and prospects of the development of sensor based on CFMs were outlined.

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance （SPR） biosensors, novel highly sensitive SPR biosensors with Au nanopartieles and nanogratings enhancement have been proposed recently. But in practice, these structures have obvious disadvantages. In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parame- ters on the performance is investigated by using rigorous coupled wave analysis （RCWA）. Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters. The results indicate that significant sensitivity increase is associated with localized surface plasmons （LSPs） excitation mediated by nanoholes. Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves＇ width are obtained simultaneously under optimized structural parameters.

Electrochemically driven dynamic plasmonics

Dynamic plasmonics with the real-time active control capability of plasmonic resonances attracts much interest in the communities of physics,chemistry,and material science.Among versatile reconfigurable strategies for dynamic plasmonics,electrochemically driven strategies have garnered most of the attention.We summarize three primary strategies to enable electrochemically dynamic plasmonics,including structural transformation,carrier-density modulation,and electrochemically active surrounding-media manipulation.The reconfigurable microstructures,optical properties,and underlying physical mechanisms are discussed in detail.We also summarize the most promising applications of dynamic plasmonics,including smart windows,structural color displays,and chemical sensors.We suggest more research efforts toward the widespread applications of dynamic plasmonics.

A highly sensitive chemical gas detecting transistor based on highly crystalline CVD-grown MoSe2 films

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and rapid electrical responses to their surrounding environments. Here, we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor （FET） in a NO2 gas sensor. This sensor exhibited ultra-high sensitivity （S = ca. 1,907 for NO2 at 300 ppm）, real-time response, and rapid on-off switching. The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2, which leads to a significant increase in hole current in the off-state regime. Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor. This comprehensive study, which addresses material growth, device fabrication, characterization, and device simulations, not only indicates the utility of MoSe2 FETs for high-performance chemical sensors, but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.

Micro/Nanofiber Optical Sensors

As a low-dimensional optical fiber with diameter close to or below the wavelength of light,optical micro/nanofiber(MNF)offers a number of favorable properties for optical sensing,which have been exploited in a variety of sensing applications,including physical,chemical,and biological sensors.In this paper we review the principles and applications of silica,glass,and polymer optical micro/nanofibers for physical and chemical sensing.