Second Type Of Sensor Research Articles

(Invited) Epitaxial NiO-Graphene Gas Sensors

Integrated, highly sensitive and reversible sensor devices for toxic and hazardous gases in environmental pollution monitoring can be realized with graphene-based materials. Here we show that, single layer graphene grown on SiC can be utilized to implement sensor devices being extremely sensitive towards NO2 showing an n-type response. A second type of sensor with an added NiO layer on top of the single layer graphene changed its response to p-type but did not reduce its sensitivity. We show that the conduction switch from n-type to p-type was not a consequence of an alteration of the graphene layer but is found to be an effect of the NiO layer. We find that the NiO leads to lowering of the Fermi level to a point that a crossing of the Dirac Point in the graphene switched the conduction type. These sensors were tested in the 100 ppb NO2 regime, showing good response and a detection limit extrapolated to be below 1 ppb. This new NiO/graphene/SiC configuration can be an attractive p-type sub-ppb sensor platform for NO2 and related gases.

Conduction mechanisms in epitaxial NiO/Graphene gas sensors

Integrated, highly sensitive and reversible sensor devices for toxic and hazardous gases in environmental pollution monitoring can be realized with graphene-based materials. Here we show that, single layer graphene grown on SiC can be utilized to implement sensor devices being extremely sensitive towards NO2 showing an n-type response. A second type of sensor with an added NiO layer on top of the single layer graphene changed its response to p-type but did not reduce its sensitivity. We show that the conduction switch from n-type to p-type was not a consequence of an alteration of the graphene layer but is found to be an effect of the NiO layer. We find that the NiO leads to lowering of the Fermi level to a point that a crossing of the Dirac Point in the graphene switched the conduction type. These sensors were tested in the 100 ppb NO2 regime, showing good response and a detection limit extrapolated to be below 1 ppb. This new NiO/graphene/SiC configuration can be an attractive p-type sub-ppb sensor platform for NO2 and related gases.

Wideband Resistive Sensors for Double-Ridged Waveguides

Two types of resistive sensors with flat frequency response for WRD840 and WRD250 double-ridged waveguides were developed. The first type of sensors is optimized for microwave power measurements inside the waveguide. The second type of sensors is connected to the particular horn antenna and optimized for microwave pulse power density (or electric field strength) measurements in free space. The flat frequency response of the sensors was designed by changing the parameters of the sensing element. Proposed sensors can measure high-power microwave pulses covering frequency ranges 0.84-2.0 GHz and 2.6-7.8 GHz.

Hybrid Sensors Fabricated by Inkjet Printing and Holographic Patterning

Inkjet printing and patterning strategies have been developed for fabrication of hybrid holographic sensors using zeolite nanocrystals on glass-supported photopolymers. The flexibility of the proposed techniques was demonstrated by fabrication and characterization of two types of holographic sensors. The first type, which is a reversible sensor, is based on a transmission hologram recorded in a hydrophobic MFI-type zeolite doped layer with high sensitivity toward alcohols. In this type of sensor the patterning of the zeolite nanocrystals in the volume of the polymer layer is achieved by holographic recording; the pattern periodicity is in the submicrometer range. The second type of sensor is based on a reflection hologram, and it is produced by inkjet printing of zeolite nanocrystals on photopolymer layer before holographic recording. The resulting localized presence of zeolite nanocrystals in the layer is key for the performance of the sensor. Irreversible humidity sensors based on photopolymer layers do...

Recent Progress in Electrochemical HbA1c Sensors: A Review.

This article reviews recent progress made in the development of electrochemical glycated hemoglobin (HbA1c) sensors for the diagnosis and management of diabetes mellitus. Electrochemical HbA1c sensors are divided into two categories based on the detection protocol of the sensors. The first type of sensor directly detects HbA1c by binding HbA1c on the surface of an electrode through bio-affinity of antibody and boronic acids, followed by an appropriate mode of signal transduction. In the second type of sensor, HbA1c is indirectly determined by detecting a digestion product of HbA1c, fructosyl valine (FV). Thus, the former sensors rely on the selective binding of HbA1c to the surface of the electrodes followed by electrochemical signaling in amperometric, voltammetric, impedometric, or potentiometric mode. Redox active markers, such as ferrocene derivatives and ferricyanide/ferrocyanide ions, are often used for electrochemical signaling. For the latter sensors, HbA1c must be digested in advance by proteolytic enzymes to produce the FV fragment. FV is electrochemically detected through catalytic oxidation by fructosyl amine oxidase or by selective binding to imprinted polymers. The performance characteristics of HbA1c sensors are discussed in relation to their use in the diagnosis and control of diabetic mellitus.

Smart and Low Cost Technique for Forest Fire Detection using Wireless Sensor Network

line of sight and the early stage of the fire process problem could be solved with the second type of sensors. A new technology called Wireless Sensor Network (WSN) is nowadays receiving more attention and has started to be applied in forest fire detection. The Wireless nodes integrate on the same printed circuit board, the sensors, the data processing, the wireless transceiver and they all consume power from the same source- batteries. Unlike cell phones, WSN do not have the capability of periodic recharging. The sensors are devices capable of sensing their environment and computing data. The sensors sense physical parameters such as the temperature, pressure and humidity, as well as chemical parameters such as Carbon Monoxide, Carbon Dioxide and Nitrogen Dioxide. The sensors operate in a self-healing and self-organising wireless networking environment. One type of wireless technology is ZigBee which is a new industrial standard based on IEEE 802.15.4. This technology emphasises low cost battery powered application and small solar panels and is suited for low data rates and small range communications. Wireless Sensor Networks have seen rapid developments in a large number of applications. This kind of technology has the potential to be applied almost everywhere; this is why the research interest in sensor networks is becoming bigger and bigger every year. Forest fire detection and prevention is another real problem faced by a number of countries. Different methods for monitoring the emergence of fires have been proposed. The early methods were based on manned observation towers but this technique was inefficient and not entirely effective. Subsequently, camera surveillance systems and satellite imaging technologies were tried but this also proved ineffective at being able to efficiently monitor the initial start of the surface fire. For example, camera networks can be installed in different positions in the forests but these provide only line of sight pictures and may be affected by weather conditions and/or physical obstacles.

NOVEL STABLE HUMIDITY LAYERS PREPARED BY SURFACE GRAFT POLYMERIZATION OF ANIONIC MONOMERS MIXING WITH PHENOL-FORMALDEHYDE

In this study, humidity-sensitive polymer layer containing phenol-formaldehyde resin prepared by spinning coating on the comb-shape type electrode followed by UV-graft polymerization of soluble monomer was performed to improve the sensitivity. In this investigation, grafting of P-styrenesulfonic acid sodium salt (NaSS) treated with hexamethyldisilazan (HMDSZ) plasma and acrylic acid (AAc) followed by isopropanol (IPA) plasma were used as monomer for UV surface graft polymerization. Results show the first one adding different ratio of phenol-formaldehyde resin. This type of sensor has linear response with %RH, and high sensitivity (impedance from 106 to 103). The impedance of second type of sensor was linear response with %RH, impedance varies from 107 to 105.

Label-free optical biosensors based on Au 2S-coated gold nanorods

In this research, two new types of optical biosensors were explored from Au 2S-coated gold nanorods (Au 2S-coated GNRs) chemically attached with human IgG as recognizing probes. The first type of biosensors were suspended GNRs and exhibited sensitive shift of longitudinal plasmon wavelength in response to anti-human IgG, with the limit of detection down to 67 pM. The second type of sensors were on-chip-immobilized GNRs, able to be used repeatedly through measuring the change of plasmon absorption intensity at a fixed wavelength, with the limit of detection down to 33 pM. The latter sensors suited for dynamic measurements, having linear response over rang from 33 pM to 1.35 nM. Both the types of sensors not only preserved the desirable features of common GNR sensors but also easy for preparation and manipulation. The concept and methodology suggested in this study can serve as the basis to develop new methods for molecular binding events or other applications like in medical researches.

Solid-state microelectrode oxygen sensors

Two types of all-solid amperometric sensors, incorporating Nafion ® as the solid ionic conductor and exhibiting microelectrode behaviour, have been used as gaseous oxygen probes in the 1–25% (v/v) concentration range. The first one involved a Pt or Ag microdisc surrounded by a ring of the anode material, the two electrodes being in the same plane and covered by a solution-recast Nafion ® film. In a modified version of this type of sensor, a Au microband was used as the indicator electrode. Well-defined sigmoidal voltammograms for oxygen reduction from the gas phase were obtained and, when used in a constant potential mode, the sensing device showed good linearity ( r 2=0.9998–0.9988) with oxygen concentration in the gas stream and a satisfactory sensitivity of 8×10 −5 A cm −2 (%v/v) −1. The high detection limit of 2% (v/v), however, restricts the possible applications to crude monitoring in the higher oxygen concentration range. In the second type of sensor, Au electrodes were vacuum-deposited as thin layers on the same face of a Nafion ® membrane and a strip of uncovered ionic polymer between the two metal layers ensured completion of the electrical circuit. The gas samples were in contact with the electrode layers and oxygen reduction led to an exponential current rise over a wide potential range indicating very high mass transport rates. The sensitivity of the device was 20 nA (%v/v) −1 and it is suggested that with such a sensor configuration the electroactive gas reacts at the line formed by the gas/solid electrolyte/metal layer interface, i.e. at a virtual microband electrode.

Whole cell- and protein-based biosensors for the detection of bioavailable heavy metals in environmental samples

The principal goal of this work was to establish the feasibility of two biosensor technologies with enhanced specificity and selectivity for the detection of several bioavailable heavy metals in environmental samples. Two parallel strategies have been followed. The first approach was to construct whole cell bacterial biosensors that emit a bioluminescent or fluorescent signal in the presence of a biologically available heavy metal. The molecular basis of σ-54 promoters as sensing elements of environmental pollutants has been determined and a number of metal-induced promoter regions have been identified, sequenced and cloned as promoter cassettes. The specificity of the promoter cassettes has been determined using luxCDABE reporter systems. Whole cell-biosensors containing metal-induced lux reporter systems have been incorporated into different matrices for their later immobilisation on optic fibres and characterised in terms of their sensitivity and storage capacity. The second type of sensors was based on the direct interaction between metal-binding proteins and heavy metal ions. In this case, the capacitance changes of the proteins, such as synechoccocal metallothionein (as a GST-SmtA fusion protein) and the mercury regulatory protein, MerR, were detected in the presence of femtomolar to millimolar metal ion concentrations.

Using an Electro‐Optical Switch to Measure Soil Water Suction

AbstractA simple and inexpensive electro‐optical switch (infrared light‐emitting diode; IR LED) was used to show that soil water suctions can be measured accurately by employing nylon filter disks with different pore sizes. Nylon filter disks that become translucent when water is absorbed were shown to open or close an electro‐optical switch at specific soil water suctions associated with the air‐entry suction of a disk, thereby demonstrating the principle of a digital tensiometer. Sensors constructed by inserting a nylon filter disk in a switch were shown to operate across a suction range of 0.004 to 2.4 MPa and were tested in a silt loam soil under drying and wetting conditions. The switch‐sensor's performance was compared with a second type of sensor (CdS photoresistor with LED) made with a layered fritted‐glass disk instead of nylon. This second sensor was able to continuously detect changes of water content from air dry to saturated. We concluded, however, that the first type of sensor was superior for precisely measuring soil water suction.

A new straight pipe Coriolis mass flowmeter: the experimental characterisation

Motivated by the high industrial and metrological interest of Coriolis Mass Flowmeters (CMFs), and by the limitations of the existing CMFs, the authors have started a study of prototypes of new-concept CMFs, not subject to elastic deformation. The prototype described here belongs to a second type of sensor realised at the University of Naples, and it is called DIME-2 in order to distinguish it from the first type DIME-1 sensor. After the mathematical model, reported in a previous work, in this paper the experimental characterisation of the DIME-2 is presented and discussed.

Improved Tactile Sensors

Next generation robot grippers should be equipped with tactile sensors providing a sense of touch similar to the human hand by measuring the local distribution of forces on the surface.In this Paper two realized sensor types are presented. The first type of tactile sensors are capacitive sensors. Suitable materials for the electrodes and for the dielectric are carefully selected. To increase the sensitivity a multilayer technology and the embedding of conductive particles in the dielectric are performed.The second type of sensors uses a piezoelectric film of the polymer polyvinylidenefuoride (PVDF) as a sensor material. A tactile sensor with a spherical surface is constructed to measure the force distribution during rolling a workpiece on the finger tips. Using a special circuitry, quasistatic measurement can be achieved. Two steps to reduce the influence of temperature are realized. The measured characteristics of the realized sensor are presented.

Amperometric enzyme electrodes.

Three different types of amperometric enzyme electrode are described. The first type uses a conducting organic-salt electrode to oxidize NADH. Results for sensors for ethanol and for bile acids are presented. In the second type of sensor, flavoenzymes are directly oxidized on the surface of the conducting organic-salt electrode. Results for five different enzymes are described. The mechanism of the enzyme oxidation is discussed and the reaction is shown to take place by heterogeneous redox catalysis and not by homogeneous mediation. The enzymes are strongly adsorbed on the electrode; microelectrodes for in vivo studies can be constructed without a membrane. Results for in vivo studies of changing glucose levels in the brain of a freely moving rat are presented. The third type of sensor is designed to measure low levels of toxic gases such as H2S and HCN. This is done by monitoring the inhibition by the toxic gas of the activity of the respiratory enzyme cytochrome oxidase.