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Sensors, Volume 8, Issue 11 (November 2008), Pages 6791-7563

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Open AccessArticle An Electrochemical DNA Biosensor Developed on a Nanocomposite Platform of Gold and Poly(propyleneimine) Dendrimer
Sensors 2008, 8(11), 6791-6809; doi:10.3390/s8116791
Received: 29 September 2008 / Revised: 22 October 2008 / Accepted: 27 October 2008 / Published: 1 November 2008
Cited by 28 | PDF Full-text (846 KB) | HTML Full-text | XML Full-text
Abstract
An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed [...] Read more.
An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the codeposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°′ = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (Rct) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)63-/4-) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)63-/4-) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)63-/4- redox probe. Full article
(This article belongs to the Special Issue Dendritic Sensors: From Dendrimer Molecules to Dendritic Cells)
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Open AccessArticle Dielectric Constant Modelling with Soil–Air Composition and Its Effect on Sar Radar Signal Backscattered over Soil Surface
Sensors 2008, 8(11), 6810-6824; doi:10.3390/s8116810
Received: 16 July 2008 / Revised: 27 August 2008 / Accepted: 29 October 2008 / Published: 1 November 2008
Cited by 3 | PDF Full-text (196 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this paper is to present the contribution of a new dielectric constant characterisation for the modelling of radar backscattering behaviour. Our analysis is based on a large number of radar measurements acquired during different experimental campaigns (Orgeval’94, Pays de [...] Read more.
The objective of this paper is to present the contribution of a new dielectric constant characterisation for the modelling of radar backscattering behaviour. Our analysis is based on a large number of radar measurements acquired during different experimental campaigns (Orgeval’94, Pays de Caux’98, 99). We propose a dielectric constant model, based on the combination of contributions from both soil and air fractions. This modelling clearly reveals the joint influence of the air and soil phases, in backscattering measurements over rough surfaces with large clods. A relationship is established between the soil fraction and soil roughness, using the Integral Equation Model (IEM), fitted to real radar data. Finally, the influence of the air fraction on the linear relationship between moisture and the backscattered radar signal is discussed. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
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Open AccessArticle An All Fiber White Light Interferometric Absolute Temperature Measurement System
Sensors 2008, 8(11), 6825-6845; doi:10.3390/s8116825
Received: 9 August 2008 / Revised: 4 October 2008 / Accepted: 27 October 2008 / Published: 1 November 2008
Cited by 5 | PDF Full-text (354 KB) | HTML Full-text | XML Full-text
Abstract
Recently the author of this article proposed a new signal processing algorithm for an all fiber white light interferometer. In this article, an all fiber white light interferometric absolute temperature measurement system is presented using the previously proposed signal processing algorithm. Stability [...] Read more.
Recently the author of this article proposed a new signal processing algorithm for an all fiber white light interferometer. In this article, an all fiber white light interferometric absolute temperature measurement system is presented using the previously proposed signal processing algorithm. Stability and absolute temperature measurement were demonstrated. These two tests demonstrated the feasibility of absolute temperature measurement with an accuracy of 0.015 fringe and 0.0005 fringe, respectively. A hysteresis test from 373K to 873K was also presented. Finally, robustness of the sensor system towards laser diode temperature drift, AFMZI temperature drift and PZT non-linearity was demonstrated. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Effect of External Vibration on PZT Impedance Signature
Sensors 2008, 8(11), 6846-6859; doi:10.3390/s8116846
Received: 8 August 2008 / Revised: 24 October 2008 / Accepted: 31 October 2008 / Published: 1 November 2008
Cited by 6 | PDF Full-text (549 KB) | HTML Full-text | XML Full-text
Abstract
Piezoelectric ceramic Lead Zirconate Titanate (PZT) transducers, working on the principle of electromechanical impedance (EMI), are increasingly applied for structural health monitoring (SHM) in aerospace, civil and mechanical engineering. The PZT transducers are usually surface bonded to or embedded in a structure [...] Read more.
Piezoelectric ceramic Lead Zirconate Titanate (PZT) transducers, working on the principle of electromechanical impedance (EMI), are increasingly applied for structural health monitoring (SHM) in aerospace, civil and mechanical engineering. The PZT transducers are usually surface bonded to or embedded in a structure and subjected to actuation so as to interrogate the structure at the desired frequency range. The interrogation results in the electromechanical admittance (inverse of EMI) signatures which can be used to estimate the structural health or integrity according to the changes of the signatures. In the existing EMI method, the monitored structure is only excited by the PZT transducers for the interrogating of EMI signature, while the vibration of the structure caused by the external excitations other than the PZT actuation is not considered. However, many structures work under vibrations in practice. To monitor such structures, issues related to the effects of vibration on the EMI signature need to be addressed because these effects may lead to misinterpretation of the structural health. This paper develops an EMI model for beam structures, which takes into account the effect of beam vibration caused by the external excitations. An experimental study is carried out to verify the theoretical model. A lab size specimen with different external excitations is tested and the effect of vibration on EMI signature is discussed. Full article
(This article belongs to the Special Issue Sensor Algorithms)
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Open AccessArticle A Solid Trap and Thermal Desorption System with Application to a Medical Electronic Nose
Sensors 2008, 8(11), 6885-6898; doi:10.3390/s8116885
Received: 9 September 2008 / Revised: 19 October 2008 / Accepted: 30 October 2008 / Published: 4 November 2008
Cited by 5 | PDF Full-text (219 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a solid trap/thermal desorption-based odorant gas condensation system has been designed and implemented for measuring low concentration odorant gas. The technique was successfully applied to a medical electronic nose system. The developed system consists of a flow control unit, [...] Read more.
In this paper, a solid trap/thermal desorption-based odorant gas condensation system has been designed and implemented for measuring low concentration odorant gas. The technique was successfully applied to a medical electronic nose system. The developed system consists of a flow control unit, a temperature control unit and a sorbent tube. The theoretical analysis and experimental results indicate that gas condensation, together with the medical electronic nose system can significantly reduce the detection limit of the nose system and increase the system’s ability to distinguish low concentration gas samples. In addition, the integrated system can remove the influence of background components and fluctuation of operational environment. Even with strong disturbances such as water vapour and ethanol gas, the developed system can classify the test samples accurately. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Bioavailability of Cd, Zn and Hg in Soil to Nine Recombinant Luminescent Metal Sensor Bacteria
Sensors 2008, 8(11), 6899-6923; doi:10.3390/s8116899
Received: 17 September 2008 / Revised: 8 October 2008 / Accepted: 31 October 2008 / Published: 4 November 2008
Cited by 24 | PDF Full-text (277 KB) | HTML Full-text | XML Full-text
Abstract
A set of nine recombinant heavy metal-specific luminescent bacterial sensors belonging to Gram-negative (Escherichia and Pseudomonas) and Gram-positive (Staphylococcus and Bacillus) genera and containing various types of recombinant metalresponse genetic elements was characterized for heavy metal bioavailability studies. All [...] Read more.
A set of nine recombinant heavy metal-specific luminescent bacterial sensors belonging to Gram-negative (Escherichia and Pseudomonas) and Gram-positive (Staphylococcus and Bacillus) genera and containing various types of recombinant metalresponse genetic elements was characterized for heavy metal bioavailability studies. All nine strains were induced by Hg and Cd and five strains also by Zn. As a lowest limit, the sensors were detecting 0.03 μg·L-1 of Hg, 2 μg·L-1 of Cd and 400 μg·L-1 of Zn. Limit of determination of the sensors depended mostly on metal-response element, whereas the toxicity of those metals towards the sensor bacteria was mostly dependent on the type of the host bacterium, with Gram-positive strains being more sensitive than Gram-negative ones. The set of sensors was used to evaluate bioavailability of Hg, Cd and Zn in spiked soils. The bioavailable fraction of Cd and Zn in soil suspension assay (2.6 – 5.1% and 0.32 – 0.61%, of the total Cd and Zn, respectively) was almost comparable for all the sensors, whereas the bioavailability of Hg was about 10-fold higher for Gram-negative sensor cells (30.5% of total Hg), compared to Gram-positive ones (3.2% of the total Hg). For Zn, the bioavailable fraction in soil-water suspensions and respective extracts was comparable (0.37 versus 0.33% of the total Zn). However, in the case of Cd, for all the sensors used and for Hg concerning only Gram-negative sensor strains, the bioavailable fraction in soilwater suspensions exceeded the water-extracted fraction about 14-fold, indicating that upon direct contact, an additional fraction of Cd and Hg was mobilized by those sensor bacteria. Thus, for robust bioavailability studies of heavy metals in soils any type of genetic metal-response elements could be used for the construction of the sensor strains. However, Gram-positive and Gram-negative senor strains should be used in parallel as the bioavailability of heavy metals to those bacterial groups may be different. Full article
(This article belongs to the Section Biosensors)
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Open AccessArticle Determination of Dopamine in the Presence of Ascorbic Acid by Nafion and Single-Walled Carbon Nanotube Film Modified on Carbon Fiber Microelectrode
Sensors 2008, 8(11), 6924-6935; doi:10.3390/s8116924
Received: 2 June 2008 / Revised: 23 October 2008 / Accepted: 30 October 2008 / Published: 4 November 2008
Cited by 25 | PDF Full-text (369 KB) | HTML Full-text | XML Full-text | Correction
Abstract
Carbon fiber microelectrode (CFME) modified by Nafion and single-walled carbon nanotubes (SWNTs) was studied by voltammetric methods in phosphate buffer saline (PBS) solution at pH 7.4. The Nafion-SWNTs/CFME modified microelectrode exhibited strongly enhanced voltammetric sensitivity and selectivity towards dopamine (DA) determination in [...] Read more.
Carbon fiber microelectrode (CFME) modified by Nafion and single-walled carbon nanotubes (SWNTs) was studied by voltammetric methods in phosphate buffer saline (PBS) solution at pH 7.4. The Nafion-SWNTs/CFME modified microelectrode exhibited strongly enhanced voltammetric sensitivity and selectivity towards dopamine (DA) determination in the presence of ascorbic acid (AA). Nafion-SWNTs film accelerated the electron transfer reaction of DA, but Nafion film as a negatively charged polymer restrained the electrochemical response of AA. Voltammetric techniques separated the anodic peaks of DA and AA, and the interference from AA was effectively excluded from DA determination. Linear calibration plots were obtained in the DA concentration range of 10 nM - 10 μM and the detection limit of the anodic current was determined to be 5 nM at a signal-to-noise ratio of 3. The study results demonstrate that DA can be determined without any interference from AA at the modified microelectrode, thereby increasing the sensitivity, selectivity, and reproducibility and stability. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Selective D3 Receptor Antagonist SB-277011-A Potentiates the Effect of Cocaine on Extracellular Dopamine in the Nucleus Accumbens: a Dual Core-Shell Voltammetry Study in Anesthetized Rats
Sensors 2008, 8(11), 6936-6951; doi:10.3390/s8116936
Received: 8 August 2008 / Revised: 8 October 2008 / Accepted: 3 November 2008 / Published: 4 November 2008
Cited by 5 | PDF Full-text (107 KB) | HTML Full-text | XML Full-text
Abstract
Dopamine (DA) D3 receptors have been associated with drug intake and abuse and selectively distribute in the brain circuits responding to drug administration. Here we examined the effects of an acute systemic administration of cocaine (15 mg/kg) alone or preceded by treatment [...] Read more.
Dopamine (DA) D3 receptors have been associated with drug intake and abuse and selectively distribute in the brain circuits responding to drug administration. Here we examined the effects of an acute systemic administration of cocaine (15 mg/kg) alone or preceded by treatment with the selective D3 receptor antagonist SB-277011-A (10 mg/kg) on DA levels concurrently in the rat nucleus accumbens shell and core sub-regions (NAcshell and NAccore, respectively). It is shown that cocaine increases extracellular DA in both compartments and that blocking D3 receptors with SB-277011-A, although the latter is devoid of dopaminergic effects per se, potentiates these effects. No differences in the amplitude of the response were observed between NAcshell and NAccore compartments, though the dopaminergic response in the NAcshell was transient whereas that in the NAccore rose slowly to reach a plateau. These results demonstrate the feasibility to use multiprobe voltammetry to measure discrete monoaminergic responses in discrete areas of the brain and confirm the effect of D3 receptors antagonist at modifying the neurochemical effects of cocaine. Full article
(This article belongs to the Special Issue Amperometric Sensors and Techniques for Neurochemical Monitoring)
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Open AccessArticle A Novel Vehicle Classification Using Embedded Strain Gauge Sensors
Sensors 2008, 8(11), 6952-6971; doi:10.3390/s8116952
Received: 21 July 2008 / Revised: 19 September 2008 / Accepted: 30 October 2008 / Published: 5 November 2008
Cited by 8 | PDF Full-text (542 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new vehicle classification and develops a traffic monitoring detector to provide reliable vehicle classification to aid traffic management systems. The basic principle of this approach is based on measuring the dynamic strain caused by vehicles across pavement to [...] Read more.
This paper presents a new vehicle classification and develops a traffic monitoring detector to provide reliable vehicle classification to aid traffic management systems. The basic principle of this approach is based on measuring the dynamic strain caused by vehicles across pavement to obtain the corresponding vehicle parameters – wheelbase and number of axles – to then accurately classify the vehicle. A system prototype with five embedded strain sensors was developed to validate the accuracy and effectiveness of the classification method. According to the special arrangement of the sensors and the different time a vehicle arrived at the sensors one can estimate the vehicle’s speed accurately, corresponding to the estimated vehicle wheelbase and number of axles. Because of measurement errors and vehicle characteristics, there is a lot of overlap between vehicle wheelbase patterns. Therefore, directly setting up a fixed threshold for vehicle classification often leads to low-accuracy results. Using the machine learning pattern recognition method to deal with this problem is believed as one of the most effective tools. In this study, support vector machines (SVMs) were used to integrate the classification features extracted from the strain sensors to automatically classify vehicles into five types, ranging from small vehicles to combination trucks, along the lines of the Federal Highway Administration vehicle classification guide. Test bench and field experiments will be introduced in this paper. Two support vector machines classification algorithms (one-against-all, one-against-one) are used to classify single sensor data and multiple sensor combination data. Comparison of the two classification method results shows that the classification accuracy is very close using single data or multiple data. Our results indicate that using multiclass SVM-based fusion multiple sensor data significantly improves the results of a single sensor data, which is trained on the whole multisensor data set. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Usage of Underground Space for 3D Cadastre Purposes and Related Problems in Turkey
Sensors 2008, 8(11), 6972-6983; doi:10.3390/s8116972
Received: 16 October 2008 / Revised: 30 October 2008 / Accepted: 3 November 2008 / Published: 5 November 2008
Cited by 7 | PDF Full-text (521 KB) | HTML Full-text | XML Full-text
Abstract
Modern cities have been trying to meet their needs for space by using not only surface structures but also by considering subsurface space use. It is also anticipated that without planning of underground spaces for supporting surface city life in the years [...] Read more.
Modern cities have been trying to meet their needs for space by using not only surface structures but also by considering subsurface space use. It is also anticipated that without planning of underground spaces for supporting surface city life in the years and generations to come, there will be serious and unavoidable problems with growing populations. The current Turkish cadastral system, including land right registrations, has been trying to meet users’ needs in all aspects since 1924. Today Turkey’s national cadastre services are carried out by the General Directorate of Land Titles and Cadastre (TKGM). The Cadastre Law, Number 3402, was approved in 1985 to eliminate problems by gathering all existing cadastral regulations under one law and also to produce 3D cadastral bases to include underground spaces and determine their legal status in Turkey. Although the mandate for 3D cadastre works is described and explained by the laws, until now the bases have been created in 2D and the reality is that legal gaps and deficiencies presently exist in them. In this study, the usage of underground spaces for the current cadastral system in Turkey was briefly evaluated, the concept of 3D cadastral data is examined and the need for using subsurface and 3D cadastre in addition to the traditional 2D register system, related problems and registration are mentioned with specific examples, but without focusing on a specific model. Full article
(This article belongs to the Section Remote Sensors)
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Open AccessArticle Quantifying Cutting and Wearing Behaviors of TiN- and CrNCoated AISI 1070 Steel
Sensors 2008, 8(11), 6984-6998; doi:10.3390/s8116984
Received: 18 September 2008 / Revised: 6 October 2008 / Accepted: 31 October 2008 / Published: 5 November 2008
Cited by 7 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
Hard coatings such as titanium nitride (TiN) and chromium nitride (CrN) are widely used in cutting and forming tools against wear and corrosion. In the present study, hard coating films were deposited onto AISI 1070 steels by a cathodic arc evaporation plating [...] Read more.
Hard coatings such as titanium nitride (TiN) and chromium nitride (CrN) are widely used in cutting and forming tools against wear and corrosion. In the present study, hard coating films were deposited onto AISI 1070 steels by a cathodic arc evaporation plating (CAVP) technique. These samples were subjected to wear in a conventional lathe for investigating the tribological behaviour of coating structure, and prenitrided subsurface composition was characterized using scanning electron microscopy (SEM), line scan analyses and X-ray diffraction (XRD). The wear properties of TiN- and CrNcoated samples were determined using an on-line monitoring system. The results show that TiN-coated samples demonstrate higher wear resistance than CrN-coated samples. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Classification Metrics for Improved Atmospheric Correction of Multispectral VNIR Imagery
Sensors 2008, 8(11), 6999-7011; doi:10.3390/s8116999
Received: 18 August 2008 / Revised: 29 September 2008 / Accepted: 30 October 2008 / Published: 5 November 2008
Cited by 4 | PDF Full-text (771 KB) | HTML Full-text | XML Full-text
Abstract
Multispectral visible/near-infrared (VNIR) earth observation satellites, e.g., Ikonos, Quickbird, ALOS AVNIR-2, and DMC, usually acquire imagery in a few (3 – 5) spectral bands. Atmospheric correction is a challenging task for these images because the standard methods require at least one shortwave [...] Read more.
Multispectral visible/near-infrared (VNIR) earth observation satellites, e.g., Ikonos, Quickbird, ALOS AVNIR-2, and DMC, usually acquire imagery in a few (3 – 5) spectral bands. Atmospheric correction is a challenging task for these images because the standard methods require at least one shortwave infrared band (around 1.6 or 2.2 µm) or hyperspectral instruments to derive the aerosol optical thickness. New classification metrics for defining cloud, cloud over water, haze, water, and saturation are presented to achieve improvements for an automatic processing system. The background is an ESA contract for the development of a prototype atmospheric processor for the optical payload AVNIR-2 on the ALOS platform. Full article
(This article belongs to the Special Issue Remote Sensing of Land Surface Properties, Patterns and Processes)
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Open AccessArticle Mesoscale Near-Surface Wind Speed Variability Mapping with Synthetic Aperture Radar
Sensors 2008, 8(11), 7012-7034; doi:10.3390/s8117012
Received: 8 October 2008 / Revised: 31 October 2008 / Accepted: 3 November 2008 / Published: 5 November 2008
Cited by 7 | PDF Full-text (1497 KB) | HTML Full-text | XML Full-text
Abstract
Operationally-significant wind speed variability is often observed within synthetic aperture radar-derived wind speed (SDWS) images of the sea surface. This paper is meant as a first step towards automated distinguishing of meteorological phenomena responsible for such variability. In doing so, the research [...] Read more.
Operationally-significant wind speed variability is often observed within synthetic aperture radar-derived wind speed (SDWS) images of the sea surface. This paper is meant as a first step towards automated distinguishing of meteorological phenomena responsible for such variability. In doing so, the research presented in this paper tests feature extraction and pixel aggregation techniques focused on mesoscale variability of SDWS. A sample of twenty eight SDWS images possessing varying degrees of near-surface wind speed variability were selected to serve as case studies. Gaussian high- and low-pass, local entropy, and local standard deviation filters performed well for the feature extraction portion of the research while principle component analysis of the filtered data performed well for the pixel aggregation. The findings suggest recommendations for future research. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
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Open AccessArticle Remote Sensing Monitoring of Changes in Soil Salinity: A Case Study in Inner Mongolia, China
Sensors 2008, 8(11), 7035-7049; doi:10.3390/s8117035
Received: 18 September 2008 / Revised: 29 October 2008 / Accepted: 4 November 2008 / Published: 7 November 2008
Cited by 15 | PDF Full-text (953 KB) | HTML Full-text | XML Full-text
Abstract
This study used archived remote sensing images to depict the history of changes in soil salinity in the Hetao Irrigation District in Inner Mongolia, China, with the purpose of linking these changes with land and water management practices and to draw lessons [...] Read more.
This study used archived remote sensing images to depict the history of changes in soil salinity in the Hetao Irrigation District in Inner Mongolia, China, with the purpose of linking these changes with land and water management practices and to draw lessons for salinity control. Most data came from LANDSAT satellite images taken in 1973, 1977, 1988, 1991, 1996, 2001, and 2006. In these years salt-affected areas were detected using a normal supervised classification method. Corresponding cropped areas were detected from NVDI (Normalized Difference Vegetation Index) values using an unsupervised method. Field samples and agricultural statistics were used to estimate the accuracy of the classification. Historical data concerning irrigation/drainage and the groundwater table were used to analyze the relation between changes in soil salinity and land and water management practices. Results showed that: (1) the overall accuracy of remote sensing in detecting soil salinity was 90.2%, and in detecting cropped area, 98%; (2) the installation/innovation of the drainage system did help to control salinity; and (3) a low ratio of cropped land helped control salinity in the Hetao Irrigation District. These findings suggest that remote sensing is a useful tool to detect soil salinity and has potential in evaluating and improving land and water management practices. Full article
(This article belongs to the Special Issue Remote Sensing of Natural Resources and the Environment)
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Open AccessArticle Electrochemical Performance of a Carbon Nanotube/La-Doped TiO2 Nanocomposite and its Use for Preparation of an Electrochemical Nicotinic Acid Sensor
Sensors 2008, 8(11), 7085-7096; doi:10.3390/s8117085
Received: 1 September 2008 / Revised: 22 September 2008 / Accepted: 27 September 2008 / Published: 7 November 2008
Cited by 4 | PDF Full-text (482 KB) | HTML Full-text | XML Full-text
Abstract
A carbon nanotube/La-doped TiO2 (La-TiO2) nanocomposite (CLTN) was prepared by a procedure similar to a complex/adsorption process. Scanning electron microscopy (SEM) images show that the La-TiO2 distributes on the carbon nanotube walls. The CLTN was mixed with paraffin [...] Read more.
A carbon nanotube/La-doped TiO2 (La-TiO2) nanocomposite (CLTN) was prepared by a procedure similar to a complex/adsorption process. Scanning electron microscopy (SEM) images show that the La-TiO2 distributes on the carbon nanotube walls. The CLTN was mixed with paraffin to form a CLTN paste for the CLTN paste electrode (CLTNPE). The electrochemical characteristics of CLTNPE were compared with that of conventional carbon electrodes such as the carbon paste electrode (CPE) and glass carbon electrode (GC). The CLTNPE exhibits electrochemical activity and was used to investigate the electrochemistry of nicotinic acid (NA). The modified electrode has a strong electrocatalytic effect on the redox of NA. The cyclic voltammetry (CV) redox potential of NA at the CLTNPE is 320 mV. The oxidation process of NA on the CLTNPE is pH dependent. A sensitive chronoamperometric response for NA was obtained covering a linear range from 1.0×10-6 mol·L-1 to 1.2×10-4 mol·L-1, with a detection limit of 2.7×10-7 mol·L-1. The NA sensor displays a remarkable sensitivity and stability. The mean recovery of NA in the human urine is 101.8%, with a mean variation coefficient (RSD) of 2.6%. Full article
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Open AccessArticle Determination of Vitamin C (Ascorbic Acid) Using High Performance Liquid Chromatography Coupled with Electrochemical Detection
Sensors 2008, 8(11), 7097-7112; doi:10.3390/s8117097
Received: 4 August 2008 / Revised: 4 November 2008 / Accepted: 6 November 2008 / Published: 7 November 2008
Cited by 25 | PDF Full-text (517 KB) | HTML Full-text | XML Full-text
Abstract
Vitamin C (ascorbic acid, ascorbate, AA) is a water soluble organic compound that participates in many biological processes. The main aim of this paper was to utilize two electrochemical detectors (amperometric – Coulouchem III and coulometric – CoulArray) coupled with flow injection [...] Read more.
Vitamin C (ascorbic acid, ascorbate, AA) is a water soluble organic compound that participates in many biological processes. The main aim of this paper was to utilize two electrochemical detectors (amperometric – Coulouchem III and coulometric – CoulArray) coupled with flow injection analysis for the detection of ascorbic acid. Primarily, we optimized the experimental conditions. The optimized conditions were as follows: detector potential 100 mV, temperature 25 °C, mobile phase 0.09% TFA:ACN, 3:97 (v/v) and flow rate 0.13 mL·min-1. The tangents of the calibration curves were 0.3788 for the coulometric method and 0.0136 for the amperometric one. The tangent of the calibration curve measured by the coulometric detector was almost 30 times higher than the tangent measured by the amperometric detector. Consequently, we coupled a CoulArray electrochemical detector with high performance liquid chromatography and estimated the detection limit for AA as 90 nM (450 fmol per 5 μL injection). The method was used for the determination of vitamin C in a pharmaceutical preparations (98 ± 2 mg per tablet), in oranges (Citrus aurantium) (varied from 30 to 56 mg/100 g fresh weight), in apples (Malus sp.) (varied from 11 to 19 mg/100 g fresh weight), and in human blood serum (varied from 38 to 78 μM). The recoveries were also determined. Full article
(This article belongs to the Section Biosensors)
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Open AccessArticle Integrated Optic Surface Plasmon Resonance Measurements in a Borosilicate Glass Substrate
Sensors 2008, 8(11), 7113-7124; doi:10.3390/s8117113
Received: 9 August 2008 / Revised: 3 November 2008 / Accepted: 7 November 2008 / Published: 11 November 2008
Cited by 18 | PDF Full-text (806 KB) | HTML Full-text | XML Full-text
Abstract
The surface plasmon resonance (SPR) technique is a well-known optical method that can be used to measure the refractive index of organic nano-layers adsorbed on a thin metal film. Although there are many configurations for measuring biomolecular interactions, SPR-based techniques play a [...] Read more.
The surface plasmon resonance (SPR) technique is a well-known optical method that can be used to measure the refractive index of organic nano-layers adsorbed on a thin metal film. Although there are many configurations for measuring biomolecular interactions, SPR-based techniques play a central role in many current biosensing experiments, since they are the most suited for sensitive and quantitative kinetic measurements. Here we give some results from the analysis and numerical elaboration of SPR data from integrated optics experiments in a particular borosilicate glass, chosen for its composition offering the rather low refractive index of 1.4701 at 633 nm wavelength. These data regard the flow over the sensing region (metal window) of different solutions with refractive indexes in the range of interest (1.3÷1.5) for the detection of contaminants in aqueous solutions. After a discussion of the principles of SPR, of the metal window design optimization by means of optical interaction numerical modeling, and of waveguide fabrication techniques, we give a description of system setup and experimental results. Optimum gold film window thickness and width in this guided-wave configuration has been for the first time derived and implemented on an integrated optic prototype device. Its characterization is given by means of the real time waveguide output intensity measurements, which correspond to the interaction between the sensing gold thin film window and the flowing analyte. The SPR curve was subsequently inferred. Finally, a modified version of the device is reported, with channel waveguides arranged in a Y-junction optical circuit, so that laser source stability requirements are lowered by a factor of 85 dB, making possible the use of low cost sources in practical applications. Full article
(This article belongs to the Section Biosensors)
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Open AccessArticle Rapid Urban Mapping Using SAR/Optical Imagery Synergy
Sensors 2008, 8(11), 7125-7143; doi:10.3390/s8117125
Received: 11 September 2008 / Revised: 7 November 2008 / Accepted: 10 November 2008 / Published: 12 November 2008
Cited by 15 | PDF Full-text (1083 KB) | HTML Full-text | XML Full-text
Abstract
This paper highlights the potential of combining Synthetic Aperture Radar (SAR) and optical data for operational rapid urban mapping. An algorithm consisting of a completely unsupervised procedure for processing pairs of co-registered SAR/optical images is proposed. In a first stage, a texture [...] Read more.
This paper highlights the potential of combining Synthetic Aperture Radar (SAR) and optical data for operational rapid urban mapping. An algorithm consisting of a completely unsupervised procedure for processing pairs of co-registered SAR/optical images is proposed. In a first stage, a texture analysis is conducted independently on the two images using eight different chain-based Gaussian models. In a second stage, the resulting texture images are partitioned by an unsupervised fuzzy K-means approach. Finally, a fuzzy decision rule is used to aggregate the results provided by the classification of texture images obtained from the pair of SAR and optical images. The method was tested and validated on images of Bucharest (Romania) and Cayenne (French Guiana). These two study areas are of different terrain relief, urban settlement structure and land cover complexity. The data set included Radarsat-1/ENVISAT and SPOT-4/5 images. The developed SAR/optical information fusion scheme improved the capabilities of urban areas extraction when compared with the separate use of SAR and optical sensors. It also proved to be suitable for monitoring urbanization development. The encouraging results thus confirm the potential of combining information from SAR and optical sensors for timely urban area analysis, as required in cases of disaster management and planning in urban sprawl areas. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
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Open AccessArticle NO2 Detection Using Microcantilever Based Potentiometry
Sensors 2008, 8(11), 7144-7156; doi:10.3390/s8117144
Received: 1 July 2008 / Revised: 1 October 2008 / Accepted: 10 October 2008 / Published: 12 November 2008
Cited by 19 | PDF Full-text (1057 KB) | HTML Full-text | XML Full-text
Abstract
A highly sensitive and novel sensor platform for gases and volatile chemicals using microcantilever based potentiometry is reported. A resonant cantilever is used to detect the changes in surface work functions of functionalized substrates caused by adsorption of target gas molecules. Surface [...] Read more.
A highly sensitive and novel sensor platform for gases and volatile chemicals using microcantilever based potentiometry is reported. A resonant cantilever is used to detect the changes in surface work functions of functionalized substrates caused by adsorption of target gas molecules. Surface work function (SWF) changes were measured for different functionalization layers made of transition metal oxide thin films with the flow of NO2. The rate of change in SWF for In2O3 and SnO2 were found to be ~80 and ~100 μV/sec, respectively, for 70 ppm NO2. A sensitivity of 64 μV/sec for SWF change was also found for 70 ppm NO2 concentration for isolated clusters of ZnO nanowires, indicating that this technique is applicable even for nano-clusters of sensing materials where amperometric detection is impossible due to material discontinuity. NO2 detection as low as 400 ppb was possible using highly insulating In2O3 and SnO2 thin films (resistivity > 1 TΩ/⎕). Two different forms of nano scale graphite were compared with the transition oxide based functionalization layer for sensing sub-ppm NO2 sensing. It was observed that nanostructured graphite (NG) shows much higher sensitivity and lower response time than transition metal oxides. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Mercury Determination in Fish Samples by Chronopotentiometric Stripping Analysis Using Gold Electrodes Prepared from Recordable CDs
Sensors 2008, 8(11), 7157-7171; doi:10.3390/s8117157
Received: 7 August 2008 / Revised: 5 November 2008 / Accepted: 7 November 2008 / Published: 12 November 2008
Cited by 13 | PDF Full-text (439 KB) | HTML Full-text | XML Full-text
Abstract
A simple method for manufacturing gold working electrodes for chronopotentiometric stripping measurements from recordable CD-R’s is described. These gold electrodes are much cheaper than commercially available ones. The electrochemical behavior of such an electrode and the working parameters for mercury determination by [...] Read more.
A simple method for manufacturing gold working electrodes for chronopotentiometric stripping measurements from recordable CD-R’s is described. These gold electrodes are much cheaper than commercially available ones. The electrochemical behavior of such an electrode and the working parameters for mercury determination by chronopotentiometric stripping analysis were studied. Detection limit was 0.30 μg Hg/L and determination limit was 1.0 μg Hg/L for a deposition time of 600 s. Using the developed working electrodes it was possible to determine the total mercury in fish samples. A method for fish sample digestion was developed by using a mixture of fuming nitric acid and both concentrated sulfuric and hydrochloric acids. The recovery degree for a known amount of mercury introduced in the sample before digestion was 95.3% (n=4). Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Interferometric Phase Improvement Based on Polarimetric Data Fusion
Sensors 2008, 8(11), 7172-7190; doi:10.3390/s8117172
Received: 2 June 2008 / Revised: 7 September 2008 / Accepted: 7 November 2008 / Published: 13 November 2008
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Abstract
In this paper, a method is proposed to improve the interferometric phase quality, based on fusing data from different polarimetric channels. Since lower amplitude implies less reliable phase in general, the phase quality of polarimetric interferometric data can be improved by seeking [...] Read more.
In this paper, a method is proposed to improve the interferometric phase quality, based on fusing data from different polarimetric channels. Since lower amplitude implies less reliable phase in general, the phase quality of polarimetric interferometric data can be improved by seeking optimal fusion of data from different polarizations to maximize the resulting amplitude. In the proposed approach, for each pixel, two coherent polarimetric scattering vectors are synchronously projected onto a same optimum direction, maximizing the lower amplitude of the two projections. In the single-look case, the fused phase is equivalent to the weighted average of phases in all polarimetric channels. It provides a good physical explanation of the proposed approach. Without any filtering, the phase noise and the number of residue points are significantly reduced, and the interferometric phase quality is greatly improved. It is a useful tool to preprocess the phase ahead of phase unwrapping. The Cloude’s coherence optimization method is used for a comparison. Using the data collected by SIR-C/X-SAR, the authors demonstrate the effectiveness and the robustness of the proposed approach. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
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Open AccessArticle Analysis of Land Use Change and Urbanization in the Kucukcekmece Water Basin (Istanbul, Turkey) with Temporal Satellite Data using Remote Sensing and GIS
Sensors 2008, 8(11), 7213-7223; doi:10.3390/s8117213
Received: 27 September 2008 / Revised: 15 October 2008 / Accepted: 11 November 2008 / Published: 13 November 2008
Cited by 11 | PDF Full-text (817 KB) | HTML Full-text | XML Full-text
Abstract
Accurate and timely information about land use and land cover (LULC) and its changes in urban areas are crucial for urban land management decision-making, ecosystem monitoring and urban planning. Also, monitoring and representation of urban sprawl and its effects on the LULC [...] Read more.
Accurate and timely information about land use and land cover (LULC) and its changes in urban areas are crucial for urban land management decision-making, ecosystem monitoring and urban planning. Also, monitoring and representation of urban sprawl and its effects on the LULC patterns and hydrological processes of an urbanized watershed is an essential part of water resource planning and management. This paper presents an image analysis study using multi temporal digital satellite imagery of LULC and changes in the Kucukcekmece Watershed (Metropolitan Istanbul, Turkey) from 1992 to 2006. The Kucukcekmece Basin includes portions of the Kucukcekmece District within the municipality of Istanbul so it faces a dramatic urbanization. An urban monitoring analysis approach was first used to implement a land cover classification. A change detection method controlled with ground truth information was then used to determine changes in land cover. During the study period, the variability and magnitude of hydrological components based on land-use patterns were cumulatively influenced by urban sprawl in the watershed. The proposed approach, which uses a combination of Remote Sensing (RS) and Geographical Information System (GIS) techniques, is an effective tool that enhances land-use monitoring, planning, and management of urbanized watersheds. Full article
(This article belongs to the Special Issue Sensors for Urban Environmental Monitoring)
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Open AccessArticle Multifunctional Polypeptide EQCN Sensors: Probing the Cysteamine-Glutathione Film Permeability with Hg(II) Ions
Sensors 2008, 8(11), 7224-7240; doi:10.3390/s8117224
Received: 16 October 2008 / Revised: 10 November 2008 / Accepted: 13 November 2008 / Published: 14 November 2008
Cited by 6 | PDF Full-text (1756 KB) | HTML Full-text | XML Full-text
Abstract
Multifunctional films are the basis of biosensors and play an important role in the emerging field of nanobioelectronics. In this work, films of a tripeptide glutathione (GSH) immobilized on a self-assembled monolayer of cysteamine (CA-SAM) on a quartz crystal Au piezosensor have [...] Read more.
Multifunctional films are the basis of biosensors and play an important role in the emerging field of nanobioelectronics. In this work, films of a tripeptide glutathione (GSH) immobilized on a self-assembled monolayer of cysteamine (CA-SAM) on a quartz crystal Au piezosensor have been synthesized and characterized using electrochemical quartz crystal nanogravimetry (EQCN) with a Hg(II) ion probe. It has been found that in contrast to previously studied Au/GSH films, the Au/CA-GSH films strongly hinder the formation of Hg0 with bulk properties while still allowing for relatively easy permeation by Hg(II) ions. This results in complete disappearance of the sharp Hg0 electrodissolution peak which is observed on bare Au and Au/GSH piezosensors. The multiple-peak anodic behavior of Au/CA and bare Au is replaced by a single high-field anodic peak of mercury reoxidation in the case of Au/CA-GSH sensors. The mass-to-charge plots indicate predominant ingress/egress of Hg(II) to/from the film. The strong hindrance of CA-SAM to bulk-Hg0 formation is attributed to film-stabilizing formation of surface (CA)2Hg2+ complexes with conformation evaluated by ab initio quantum mechanical calculations of electronic structure using Hartree-Fock methods. The associates CA-GSH provide an additional functionality of the side sulfhydryl group which is free for interactions, e.g. with heavy metals. It is proposed that in the film, the CA-GSH molecules can assume open (extended) conformation or bent hydrogen-bonded conformation with up to four possible internal hydrogen bonds. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle Microwave Imaging of Cotton Bales
Sensors 2008, 8(11), 7241-7258; doi:10.3390/s8117241
Received: 22 August 2008 / Revised: 6 November 2008 / Accepted: 13 November 2008 / Published: 14 November 2008
Cited by 2 | PDF Full-text (323 KB) | HTML Full-text | XML Full-text
Abstract
Modern moisture restoration systems are increasingly capable of adding water to cotton bales. However, research has identified large variations in internal moisture within bales that are not readily monitored by current systems. While microwave moisture sensing systems can measure average bale moisture, this can be deceptive where water is unevenly distributed. In some cases, localized internal moisture levels exceed 7.5%, the upper safe limit for cotton bale storage, as determined by the USDA, as above this level, bales degrade and lose value. A high proportion of stored bales containing excess moisture have been discovered throughout the US in increasing numbers over the past several seasons, making the detection and prevention of this occurrence a critical goal. Previous research by the authors resulted in the development of microwave moisture-sensing technology. The current study examines an extension to this technology to allow for detailed cotton bale moisture imaging. The new technique incorporates a narrow beam imaging antenna coupled to a tomographic imaging algorithm. The imaging technique was able to resolve small (< 1 cm) high-permittivity structures against a low permittivity background. Moreover, the system was able to identify structures of known permittivity with high accuracy (coefficient of determination (r2) > 0.99). In preliminary testing on a wet commercial UD bale, the technique was able to accurately image and resolve the location of the pre-placed internal wet layer. Full article
(This article belongs to the Special Issue Sensor Algorithms)
Open AccessArticle A Mobile Sensor Network System for Monitoring of Unfriendly Environments
Sensors 2008, 8(11), 7259-7274; doi:10.3390/s8117259
Received: 15 October 2008 / Revised: 7 November 2008 / Accepted: 13 November 2008 / Published: 14 November 2008
Cited by 31 | PDF Full-text (1374 KB) | HTML Full-text | XML Full-text
Abstract
Observing microclimate changes is one of the most popular applications of wireless sensor networks. However, some target environments are often too dangerous or inaccessible to humans or large robots and there are many challenges for deploying and maintaining wireless sensor networks in [...] Read more.
Observing microclimate changes is one of the most popular applications of wireless sensor networks. However, some target environments are often too dangerous or inaccessible to humans or large robots and there are many challenges for deploying and maintaining wireless sensor networks in those unfriendly environments. This paper presents a mobile sensor network system for solving this problem. The system architecture, the mobile node design, the basic behaviors and advanced network capabilities have been investigated respectively. A wheel-based robotic node architecture is proposed here that can add controlled mobility to wireless sensor networks. A testbed including some prototype nodes has also been created for validating the basic functions of the proposed mobile sensor network system. Motion performance tests have been done to get the positioning errors and power consumption model of the mobile nodes. Results of the autonomous deployment experiment show that the mobile nodes can be distributed evenly into the previously unknown environments. It provides powerful support for network deployment and maintenance and can ensure that the sensor network will work properly in unfriendly environments. Full article
(This article belongs to the Special Issue Wireless Sensor Technologies and Applications)
Open AccessArticle Use of Reflectance Measurements for the Detection of N, P, K, ADF and NDF Contents in Sainfoin Pasture
Sensors 2008, 8(11), 7275-7286; doi:10.3390/s8117275
Received: 16 October 2008 / Revised: 4 November 2008 / Accepted: 11 November 2008 / Published: 14 November 2008
Cited by 8 | PDF Full-text (137 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this study was to determine the relationships between nitrogen (N), phosphorus (P), potassium (P), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of sainfoin (Onobrychis sativa Lam.) pasture and canopy reflectance. Canopy reflectance measurements were made [...] Read more.
The objective of this study was to determine the relationships between nitrogen (N), phosphorus (P), potassium (P), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of sainfoin (Onobrychis sativa Lam.) pasture and canopy reflectance. Canopy reflectance measurements were made by using a portable spectroradiometer. An experiment was conducted in the Turkey in May and June in 2007 and 2008. Sainfoin pasture N, P, K, ADF and NDF contents correlated linearly with the reflectance ratios R780/650 (0.61≤ r² ≤0.80) and first derivatives of the reflectance ratios 760/630 (0.70≤ r² ≤0.84). Linear equations between each forage variable and reflectance or first derivatives reflectance had high r² (0.68≤ r² ≤0.83 and 0.79≤ r² ≤0.90, respectively) in R780 and R760 wavelengths. In stepwise regression of the reflectance (in 460, 550, 650 and 780 nm wavelengths), the r2 of predicted and measured N, P, K, ADF and NDF contents of sainfoin pasture were (0.85, 0.85, 0.78, 0.81 and 0.74, respectively), in stepwise regression of the first derivatives of reflectance (in 440, 530, 630 and 760 nm wavelengths), the r2 of predicted and measured N, P, K, ADF and NDF contents of sainfoin pasture were (0.87, 0.91, 0.83, 0.93 and 0.86, respectively). Our results suggest that canopy reflectance in blue, green, red and near infrared wavebands with NIR/Red and NDVI ratios can be used for nondestructive prediction of forage quality variables in sainfoin pasture. Full article
(This article belongs to the Section Remote Sensors)
Open AccessArticle Minimal-Drift Heading Measurement using a MEMS Gyro for Indoor Mobile Robots
Sensors 2008, 8(11), 7287-7299; doi:10.3390/s8117287
Received: 10 October 2008 / Revised: 12 November 2008 / Accepted: 14 November 2008 / Published: 17 November 2008
Cited by 10 | PDF Full-text (484 KB) | HTML Full-text | XML Full-text
Abstract
To meet the challenges of making low-cost MEMS yaw rate gyros for the precise self-localization of indoor mobile robots, this paper examines a practical and effective method of minimizing drift on the heading angle that relies solely on integration of rate signals [...] Read more.
To meet the challenges of making low-cost MEMS yaw rate gyros for the precise self-localization of indoor mobile robots, this paper examines a practical and effective method of minimizing drift on the heading angle that relies solely on integration of rate signals from a gyro. The main idea of the proposed approach is consists of two parts; 1) self-identification of calibration coefficients that affects long-term performance, and 2) threshold filter to reject the broadband noise component that affects short-term performance. Experimental results with the proposed phased method applied to Epson XV3500 gyro demonstrate that it effectively yields minimal drift heading angle measurements getting over major error sources in the MEMS gyro output. Full article
(This article belongs to the Special Issue Aerospace Sensor Systems)
Open AccessArticle Can Commercial Digital Cameras Be Used as Multispectral Sensors? A Crop Monitoring Test
Sensors 2008, 8(11), 7300-7322; doi:10.3390/s8117300
Received: 7 October 2008 / Revised: 30 October 2008 / Accepted: 14 November 2008 / Published: 17 November 2008
Cited by 26 | PDF Full-text (2321 KB) | HTML Full-text | XML Full-text
Abstract
The use of consumer digital cameras or webcams to characterize and monitor different features has become prevalent in various domains, especially in environmental applications. Despite some promising results, such digital camera systems generally suffer from signal aberrations due to the on-board image [...] Read more.
The use of consumer digital cameras or webcams to characterize and monitor different features has become prevalent in various domains, especially in environmental applications. Despite some promising results, such digital camera systems generally suffer from signal aberrations due to the on-board image processing systems and thus offer limited quantitative data acquisition capability. The objective of this study was to test a series of radiometric corrections having the potential to reduce radiometric distortions linked to camera optics and environmental conditions, and to quantify the effects of these corrections on our ability to monitor crop variables. In 2007, we conducted a five-month experiment on sugarcane trial plots using original RGB and modified RGB (Red-Edge and NIR) cameras fitted onto a light aircraft. The camera settings were kept unchanged throughout the acquisition period and the images were recorded in JPEG and RAW formats. These images were corrected to eliminate the vignetting effect, and normalized between acquisition dates. Our results suggest that 1) the use of unprocessed image data did not improve the results of image analyses; 2) vignetting had a significant effect, especially for the modified camera, and 3) normalized vegetation indices calculated with vignetting-corrected images were sufficient to correct for scene illumination conditions. These results are discussed in the light of the experimental protocol and recommendations are made for the use of these versatile systems for quantitative remote sensing of terrestrial surfaces. Full article
(This article belongs to the Special Issue Aerospace Sensor Systems)
Open AccessArticle A Comprehensive Automated 3D Approach for Building Extraction, Reconstruction, and Regularization from Airborne Laser Scanning Point Clouds
Sensors 2008, 8(11), 7323-7343; doi:10.3390/s8117323
Received: 15 September 2008 / Revised: 21 October 2008 / Accepted: 7 November 2008 / Published: 17 November 2008
Cited by 108 | PDF Full-text (2488 KB) | HTML Full-text | XML Full-text
Abstract
Three dimensional city models are necessary for supporting numerous management applications. For the determination of city models for visualization purposes, several standardized workflows do exist. They are either based on photogrammetry or on LiDAR or on a combination of both data acquisition [...] Read more.
Three dimensional city models are necessary for supporting numerous management applications. For the determination of city models for visualization purposes, several standardized workflows do exist. They are either based on photogrammetry or on LiDAR or on a combination of both data acquisition techniques. However, the automated determination of reliable and highly accurate city models is still a challenging task, requiring a workflow comprising several processing steps. The most relevant are building detection, building outline generation, building modeling, and finally, building quality analysis. Commercial software tools for building modeling require, generally, a high degree of human interaction and most automated approaches described in literature stress the steps of such a workflow individually. In this article, we propose a comprehensive approach for automated determination of 3D city models from airborne acquired point cloud data. It is based on the assumption that individual buildings can be modeled properly by a composition of a set of planar faces. Hence, it is based on a reliable 3D segmentation algorithm, detecting planar faces in a point cloud. This segmentation is of crucial importance for the outline detection and for the modeling approach. We describe the theoretical background, the segmentation algorithm, the outline detection, and the modeling approach, and we present and discuss several actual projects. Full article
(This article belongs to the Special Issue LiDAR for 3D City Modeling)
Open AccessArticle Evaluation of Different Outlier Detection Methods for GPS Networks
Sensors 2008, 8(11), 7344-7358; doi:10.3390/s8117344
Received: 4 November 2008 / Revised: 14 November 2008 / Accepted: 17 November 2008 / Published: 17 November 2008
Cited by 8 | PDF Full-text (262 KB) | HTML Full-text | XML Full-text
Abstract
GPS (Global Positioning System) devices can be used in many applications which require accurate point positioning in geosciences. Accuracy of GPS decreases due to outliers resulted from the errors inherent in GPS observations. Several approaches have been developed to detect outliers in [...] Read more.
GPS (Global Positioning System) devices can be used in many applications which require accurate point positioning in geosciences. Accuracy of GPS decreases due to outliers resulted from the errors inherent in GPS observations. Several approaches have been developed to detect outliers in geodetic observations. It is important to determine which method is most effective at distinguishing outliers from normal observations. This paper investigates the behavior of conventional statistical test methods (Data Snooping (DS), Tau and t tests), some robust methods (Andrews’s M-Estimation, Huber’s MEstimation, Tukey’s M-Estimation, Danish Method, Yang-I M-Estimation, Yang-II MEstimation, and fuzzy logic method in detection of outliers for three GPS networks having different characteristics. Test results are evaluated and the performances of different methods are presented quantitatively. Full article
(This article belongs to the Section Remote Sensors)
Open AccessArticle Nano-Scale Characterization of a Piezoelectric Polymer (Polyvinylidene Difluoride, PVDF)
Sensors 2008, 8(11), 7359-7368; doi:10.3390/s8117359
Received: 9 October 2008 / Revised: 6 November 2008 / Accepted: 12 November 2008 / Published: 18 November 2008
Cited by 15 | PDF Full-text (551 KB) | HTML Full-text | XML Full-text
Abstract
The polymer polyvinylidene difluoride (PVDF) has unique piezoelectric properties favorable for Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS) applications. In the present research, we conducted nanometer-length scale characterization of this material using several high-resolution techniques. Specifically, we used an atomic force microscope [...] Read more.
The polymer polyvinylidene difluoride (PVDF) has unique piezoelectric properties favorable for Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS) applications. In the present research, we conducted nanometer-length scale characterization of this material using several high-resolution techniques. Specifically, we used an atomic force microscope (AFM) to study the nanoand microstructures of the PVDF under stress and to measure their nanoscale conductivity and piezoelectricity. We found that the surface morphology, electronic structure, and microstructure are profoundly affected under electrical potential. Such a behavior is important for the properties and performance of MEMS and NEMS. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering)
Open AccessArticle Selectivity Enhancement in Multisensor Systems Using Flow Modulation Techniques
Sensors 2008, 8(11), 7369-7379; doi:10.3390/s8117369
Received: 22 May 2008 / Revised: 11 November 2008 / Accepted: 11 November 2008 / Published: 19 November 2008
Cited by 5 | PDF Full-text (121 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the use of a new technique to obtain transient sensor information is introduced and its usefulness to improve the selectivity of metal oxide gas sensors is discussed. The method is based on modulating the flow of the carrier gas [...] Read more.
In this paper, the use of a new technique to obtain transient sensor information is introduced and its usefulness to improve the selectivity of metal oxide gas sensors is discussed. The method is based on modulating the flow of the carrier gas that brings the species to be measured into the sensor chamber. In such a way, the analytes’ concentration at the surface of the sensors is altered. As a result, reproducible patterns in the sensor response develop, which carry important information for helping the sensor system, not only to discriminate among the volatiles considered but also to semi-quantify them. This has been proved by extracting features from sensor dynamics using the discrete wavelet transform (DWT) and by building and validating support vector machine (SVM) classification models. The good results obtained (100% correct identification among 5 volatile compounds and nearly a 89% correct simultaneous identification and quantification of these volatiles), which clearly outperform those obtained when the steady-state response is used, prove the concept behind flow modulation. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle From Maxwell’s Equations to Polarimetric SAR Images: A Simulation Approach
Sensors 2008, 8(11), 7380-7409; doi:10.3390/s8117380
Received: 2 June 2008 / Revised: 26 September 2008 / Accepted: 15 November 2008 / Published: 19 November 2008
Cited by 6 | PDF Full-text (1960 KB) | HTML Full-text | XML Full-text
Abstract
A new electromagnetic approach for the simulation of polarimetric SAR images is proposed. It starts from Maxwell’s equations, employs the spectral domain full-wave technique, the moment method, and the stationary phase method to compute the far electromagnetic fields scattered by multilayer structures. [...] Read more.
A new electromagnetic approach for the simulation of polarimetric SAR images is proposed. It starts from Maxwell’s equations, employs the spectral domain full-wave technique, the moment method, and the stationary phase method to compute the far electromagnetic fields scattered by multilayer structures. A multilayer structure is located at each selected position of a regular rectangular grid of coordinates, which defines the scene area under imaging. The grid is determined taking into account the elementary scatter size and SAR operational parameters, such as spatial resolution, pixel spacing, look angle and platform altitude. A two-dimensional separable “sinc” function to represent the SAR spread point function is also considered. Multifrequency sets of single-look polarimetric SAR images are generated, in L-, C- and X-bands and the images are evaluated using several measurements commonly employed in SAR data analysis. The evaluation shows that the proposed simulation process is working properly, since the obtained results are in accordance with those presented in the literature. Therefore, this new approach becomes suitable for carrying out theoretical and practical studies using polarimetric SAR images. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
Open AccessArticle Improved Progressive Polynomial Algorithm for Self-Adjustment and Optimal Response in Intelligent Sensors
Sensors 2008, 8(11), 7410-7427; doi:10.3390/s8117410
Received: 28 August 2008 / Revised: 21 October 2008 / Accepted: 17 November 2008 / Published: 19 November 2008
Cited by 28 | PDF Full-text (248 KB) | HTML Full-text | XML Full-text
Abstract
The development of intelligent sensors involves the design of reconfigurable systems capable of working with different input sensors signals. Reconfigurable systems should expend the least possible amount of time readjusting. A self-adjustment algorithm for intelligent sensors should be able to fix major [...] Read more.
The development of intelligent sensors involves the design of reconfigurable systems capable of working with different input sensors signals. Reconfigurable systems should expend the least possible amount of time readjusting. A self-adjustment algorithm for intelligent sensors should be able to fix major problems such as offset, variation of gain and lack of linearity with good accuracy. This paper shows the performance of a progressive polynomial algorithm utilizing different grades of relative nonlinearity of an output sensor signal. It also presents an improvement to this algorithm which obtains an optimal response with minimum nonlinearity error, based on the number and selection sequence of the readjust points. In order to verify the potential of this proposed criterion, a temperature measurement system was designed. The system is based on a thermistor which presents one of the worst nonlinearity behaviors. The application of the proposed improved method in this system showed that an adequate sequence of the adjustment points yields to the minimum nonlinearity error. In realistic applications, by knowing the grade of relative nonlinearity of a sensor, the number of readjustment points can be determined using the proposed method in order to obtain the desired nonlinearity error. This will impact on readjustment methodologies and their associated factors like time and cost. Full article
(This article belongs to the Special Issue Intelligent Sensors)
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Open AccessArticle Intracerebroventricular Administration of Amyloid β-protein Oligomers Selectively Increases Dorsal Hippocampal Dialysate Glutamate Levels in the Awake Rat
Sensors 2008, 8(11), 7428-7437; doi:10.3390/s8117428
Received: 9 July 2008 / Revised: 10 November 2008 / Accepted: 11 November 2008 / Published: 19 November 2008
Cited by 13 | PDF Full-text (291 KB) | HTML Full-text | XML Full-text
Abstract
Extensive evidence supports an important role for soluble oligomers of the amyloid β-protein (Aβ) in Alzheimer’s Disease pathogenesis. In the present study we combined intracerebroventricular (icv) injections with brain microdialysis technology in the fully conscious rat to assess the effects of icv administered SDS-stable low-n Aβ oligomers (principally dimers and trimers) on excitatory and inhibitory amino acid transmission in the ipsilateral dorsal hippocampus. Microdialysis was employed to assess the effect of icv administration of Aβ monomers and Aβ oligomers on dialysate glutamate, aspartate and GABA levels in the dorsal hippocampus. Administration of Aβ oligomers was associated with a +183% increase (p<0.0001 vs. Aβ monomer-injected control) in dorsal hippocampal glutamate levels which was still increasing at the end of the experiment (260 min), whereas aspartate and GABA levels were unaffected throughout. These findings demonstrate that icv administration and microdialysis technology can be successfully combined in the awake rat and suggests that altered dorsal hippocampal glutamate transmission may be a useful target for pharmacological intervention in Alzheimer’s Disease. Full article
(This article belongs to the Special Issue Amperometric Sensors and Techniques for Neurochemical Monitoring)
Open AccessArticle Sputtered Encapsulation as Wafer Level Packaging for Isolatable MEMS Devices: A Technique Demonstrated on a Capacitive Accelerometer
Sensors 2008, 8(11), 7438-7452; doi:10.3390/s8117438
Received: 11 October 2008 / Revised: 11 November 2008 / Accepted: 14 November 2008 / Published: 19 November 2008
Cited by 3 | PDF Full-text (1192 KB) | HTML Full-text | XML Full-text
Abstract
This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the [...] Read more.
This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the wafer level after fabrication. A MEMSTech 50g capacitive accelerometer was used to demonstrate a sputtered encapsulation technique. Encapsulation with a very uniform surface profile was achieved using spin-on glass (SOG) as a sacrificial layer, SU-8 as base layer, RF sputtered silicon as main structural layer, eutectic gold-silicon as seal layer, and liquid crystal polymer (LCP) as outer encapsulant layer. SEM inspection and capacitance test indicated that the movable elements were released after encapsulation. Nanoindentation test confirmed that the encapsulated device is sufficiently robust to withstand a transfer molding process. Thus, an encapsulation technique that is robust, CMOS compatible, and economical has been successfully developed for packaging isolatable MEMS devices at the wafer level. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering)
Open AccessArticle Study of the Relationships between the Spatial Extent of Surface Urban Heat Islands and Urban Characteristic Factors Based on Landsat ETM+ Data
Sensors 2008, 8(11), 7453-7468; doi:10.3390/s8117453
Received: 25 July 2008 / Revised: 11 November 2008 / Accepted: 12 November 2008 / Published: 20 November 2008
Cited by 21 | PDF Full-text (404 KB) | HTML Full-text | XML Full-text
Abstract
Ten cities with different population and urban sizes located in the Pearl River Delta, Guangdong Province, P.R. China were selected to study the relationships between the spatial extent of surface urban heat islands (SUHI) and five urban characteristic factors such as urban [...] Read more.
Ten cities with different population and urban sizes located in the Pearl River Delta, Guangdong Province, P.R. China were selected to study the relationships between the spatial extent of surface urban heat islands (SUHI) and five urban characteristic factors such as urban size, development area, water proportion, mean NDVI (Normalized Vegetation Index) and population density, etc. The spatial extent of SUHI was quantified by using the hot island area (HIA). All the cities are almost at the same latitude, showing similar climate and solar radiation, the influence of which could thus be eliminated during our computation and comparative study. The land surface temperatures (LST) were retrieved from the data of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) band 6 using a mono-window algorithm. A variance-segmenting method was proposed to compute HIA for each city from the retrieved LST. Factors like urban size, development area and water proportion were extracted directly from the classification images of the same ETM+ data and the population density factor is from the official census. Correlation and regression analyses were performed to study the relationships between the HIA and the related factors, and the results show that HIA is highly correlated to urban size (r=0.95), population density (r=0.97) and development area (r=0.83) in this area. It was also proved that a weak negative correlation existed between HIA and both mean NDVI and water proportion for each city. Linear functions between HIA and its related factors were established, respectively. The HIA can reflect the spatial extent and magnitude of the surface urban heat island effect, and can be used as reference in the urban planning. Full article
(This article belongs to the Section Remote Sensors)
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Open AccessArticle Geological Interpretation of PSInSAR Data at Regional Scale
Sensors 2008, 8(11), 7469-7492; doi:10.3390/s8117469
Received: 16 July 2008 / Revised: 12 September 2008 / Accepted: 20 October 2008 / Published: 24 November 2008
Cited by 38 | PDF Full-text (3369 KB) | HTML Full-text | XML Full-text
Abstract
Results of a PSInSAR™ project carried out by the Regional Agency for Environmental Protection (ARPA) in Piemonte Region (Northern Italy) are presented and discussed. A methodology is proposed for the interpretation of the PSInSARTM data at the regional scale, easy to [...] Read more.
Results of a PSInSAR™ project carried out by the Regional Agency for Environmental Protection (ARPA) in Piemonte Region (Northern Italy) are presented and discussed. A methodology is proposed for the interpretation of the PSInSARTM data at the regional scale, easy to use by the public administrations and by civil protection authorities. Potential and limitations of the PSInSARTM technique for ground movement detection on a regional scale and monitoring are then estimated in relationship with different geological processes and various geological environments. Full article
(This article belongs to the Special Issue Synthetic Aperture Radar (SAR))
Open AccessArticle Large Scale Environmental Monitoring through Integration of Sensor and Mesh Networks
Sensors 2008, 8(11), 7493-7517; doi:10.3390/s8117493
Received: 9 October 2008 / Accepted: 14 November 2008 / Published: 24 November 2008
Cited by 12 | PDF Full-text (792 KB) | HTML Full-text | XML Full-text
Abstract
Monitoring outdoor environments through networks of wireless sensors has received interest for collecting physical and chemical samples at high spatial and temporal scales. A central challenge to environmental monitoring applications of sensor networks is the short communication range of the sensor nodes, [...] Read more.
Monitoring outdoor environments through networks of wireless sensors has received interest for collecting physical and chemical samples at high spatial and temporal scales. A central challenge to environmental monitoring applications of sensor networks is the short communication range of the sensor nodes, which increases the complexity and cost of monitoring commodities that are located in geographically spread areas. To address this issue, we propose a new communication architecture that integrates sensor networks with medium range wireless mesh networks, and provides users with an advanced web portal for managing sensed information in an integrated manner. Our architecture adopts a holistic approach targeted at improving the user experience by optimizing the system performance for handling data that originates at the sensors, traverses the mesh network, and resides at the server for user consumption. This holistic approach enables users to set high level policies that can adapt the resolution of information collected at the sensors, set the preferred performance targets for their application, and run a wide range of queries and analysis on both real-time and historical data. All system components and processes will be described in this paper. Full article
(This article belongs to the Special Issue Wireless Sensor Technologies and Applications)
Open AccessArticle Pattern Recognition via PCNN and Tsallis Entropy
Sensors 2008, 8(11), 7518-7529; doi:10.3390/s8117518
Received: 5 September 2008 / Revised: 7 November 2008 / Accepted: 17 November 2008 / Published: 25 November 2008
Cited by 17 | PDF Full-text (331 KB) | HTML Full-text | XML Full-text
Abstract
In this paper a novel feature extraction method for image processing via PCNN and Tsallis entropy is presented. We describe the mathematical model of the PCNN and the basic concept of Tsallis entropy in order to find a recognition method for isolated [...] Read more.
In this paper a novel feature extraction method for image processing via PCNN and Tsallis entropy is presented. We describe the mathematical model of the PCNN and the basic concept of Tsallis entropy in order to find a recognition method for isolated objects. Experiments show that the novel feature is translation and scale independent, while rotation independence is a bit weak at diagonal angles of 45° and 135°. Parameters of the application on face recognition are acquired by bacterial chemotaxis optimization (BCO), and the highest classification rate is 72.5%, which demonstrates its acceptable performance and potential value. Full article
(This article belongs to the Special Issue Image Sensors)
Open AccessArticle A Study on Increasing Sensitivity of Rectangular Microcantilevers Used in Biosensors
Sensors 2008, 8(11), 7530-7544; doi:10.3390/s8117530
Received: 27 October 2008 / Revised: 10 November 2008 / Accepted: 10 November 2008 / Published: 25 November 2008
Cited by 15 | PDF Full-text (628 KB) | HTML Full-text | XML Full-text
Abstract
This study proposes a new microcantilever design with a rectangular hole at the fixed end of the cantilever that is more sensitive than conventional ones. A commercial finite element analysis software ANSYS is used to analyze it. The Stoney equation is first [...] Read more.
This study proposes a new microcantilever design with a rectangular hole at the fixed end of the cantilever that is more sensitive than conventional ones. A commercial finite element analysis software ANSYS is used to analyze it. The Stoney equation is first used to calculate the surface stress induced moment, and then applied to the microcantilever free end to produce deflection. The stress analysis of the proposed and conventional designs is performed, followed by dynamic analysis of the proposed design. We found that the Sader equation is more accurate than Stoney in predicting cantilever deflections, and that for increasing the sensitivity of a microcantilever biosensor increasing the cantilever thickness is more practical. Full article
(This article belongs to the Special Issue BioMEMS)
Open AccessArticle An Open Localization and Local Communication Embodied Sensor
Sensors 2008, 8(11), 7545-7563; doi:10.3390/s8117545
Received: 9 October 2008 / Accepted: 12 November 2008 / Published: 25 November 2008
Cited by 32 | PDF Full-text (907 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we describe a localization and local communication system which allows situated agents to communicate locally, obtaining at the same time both the range and the bearing of the emitter without the need of any centralized control or any external [...] Read more.
In this paper we describe a localization and local communication system which allows situated agents to communicate locally, obtaining at the same time both the range and the bearing of the emitter without the need of any centralized control or any external reference. The system relies on infrared communications with frequency modulation and is composed of two interconnected modules for data and power measurement. Thanks to the open hardware license under which it is released, the research community can easily replicate the system at a low cost and/or adapt it for applications in sensor networks and in robotics. Full article
(This article belongs to the Section Chemical Sensors)
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Review

Jump to: Research

Open AccessReview Microsensors for in vivo Measurement of Glutamate in Brain Tissue
Sensors 2008, 8(11), 6860-6884; doi:10.3390/s8116860
Received: 8 August 2008 / Revised: 24 October 2008 / Accepted: 3 November 2008 / Published: 4 November 2008
Cited by 26 | PDF Full-text (323 KB) | HTML Full-text | XML Full-text
Abstract
Several immobilized enzyme-based electrochemical biosensors for glutamate detection have been developed over the last decade. In this review, we compare first and second generation sensors. Structures, working mechanisms, interference prevention, in vitro detection characteristics and in vivo performance are summarized here for [...] Read more.
Several immobilized enzyme-based electrochemical biosensors for glutamate detection have been developed over the last decade. In this review, we compare first and second generation sensors. Structures, working mechanisms, interference prevention, in vitro detection characteristics and in vivo performance are summarized here for those sensors that have successfully detected brain glutamate in vivo. In brief, first generation sensors have a simpler structure and are faster in glutamate detection. They also show a better sensitivity to glutamate during calibration in vitro. For second generation sensors, besides their less precise detection, their fabrication is difficult to reproduce, even with a semi-automatic dip-coater. Both generations of sensors can detect glutamate levels in vivo, but the reported basal levels are different. In general, second generation sensors detect higher basal levels of glutamate compared with the results obtained from first generation sensors. However, whether the detected glutamate is indeed from synaptic sources is an issue that needs further attention. Full article
(This article belongs to the Section Biosensors)
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Open AccessReview Recent Progress in Nucleic Acid Aptamer-Based Biosensors and Bioassays
Sensors 2008, 8(11), 7050-7084; doi:10.3390/s8117050
Received: 4 September 2008 / Revised: 25 October 2008 / Accepted: 30 October 2008 / Published: 7 November 2008
Cited by 69 | PDF Full-text (944 KB) | HTML Full-text | XML Full-text
Abstract
As the key constituents of the genetic code, the importance of nucleic acids to life has long been appreciated. Despite being composed of only four structurally similar nucleotides, single-stranded nucleic acids, as in single-stranded DNAs and RNAs, can fold into distinct three-dimensional [...] Read more.
As the key constituents of the genetic code, the importance of nucleic acids to life has long been appreciated. Despite being composed of only four structurally similar nucleotides, single-stranded nucleic acids, as in single-stranded DNAs and RNAs, can fold into distinct three-dimensional shapes due to specific intramolecular interactions and carry out functions beyond serving as templates for protein synthesis. These functional nucleic acids (FNAs) can catalyze chemical reactions, regulate gene expression, and recognize target molecules. Aptamers, whose name is derived from the Latin word aptus meaning “to fit”, are oligonucleotides that can bind their target ligands with high affinity and specificity. Since aptamers exist in nature but can also be artificially isolated from pools of random nucleic acids through a process called in vitro selection, they can potentially bind a diverse array of compounds. In this review, we will discuss the research that is being done to develop aptamers against various biomolecules, the progress in engineering biosensors by coupling aptamers to signal transducers, and the prospect of employing these sensors for a range of chemical and biological applications. Advances in aptamer technology emphasizes that nucleic acids are not only the fundamental molecules of life, they can also serve as research tools to enhance our understanding of life. The possibility of using aptamer-based tools in drug discovery and the identification of infectious agents can ultimately augment our quality of life. Full article
(This article belongs to the Special Issue Molecular Recognition and Sensors, Including Molecular Imprinting)
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Open AccessReview Recent Updates of DNA Incorporated in Carbon Nanotubes and Nanoparticles for Electrochemical Sensors and Biosensors
Sensors 2008, 8(11), 7191-7212; doi:10.3390/s8117191
Received: 3 July 2008 / Revised: 12 October 2008 / Accepted: 10 November 2008 / Published: 13 November 2008
Cited by 22 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
Innovations in the field of electrochemical sensors and biosensors are of much importance nowadays. These devices are designed with probes and micro electrodes. The miniaturized designs of these sensors allow analyses of materials without damaging the samples. Some of these sensors are [...] Read more.
Innovations in the field of electrochemical sensors and biosensors are of much importance nowadays. These devices are designed with probes and micro electrodes. The miniaturized designs of these sensors allow analyses of materials without damaging the samples. Some of these sensors are also useful for real time analysis within the host system, so these sensors are considered to be more advantageous than other types of sensors. The active sensing materials used in these types of sensors can be any material that acts as a catalyst for the oxidation or reduction of particular analyte or set of analytes. Among various kinds of sensing materials, deoxyribonucleic acid (DNA), carbon nanotubes (CNTs) and nanoparticles have received considerable attraction in recent years. DNA is one of the classes of natural polymers, which can interact with CNTs and nanoparticles to form new types of composite materials. These composite materials have also been used as sensing materials for sensor applications. They have advantages in characteristics such as extraordinary low weight and multifunctional properties. In this article, advantages of DNA incorporated in CNT and nanoparticle hybrids for electrochemical sensors and biosensors are presented in detail, along with some key results noted from the literature. Full article
(This article belongs to the Section Biosensors)
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