Sensors

554 KiB

Open AccessArticle

Using Monoclonal Antibody to Determine Lead Ions with a Localized Surface Plasmon Resonance Fiber-optic Biosensor

by Tsao-Jen Lin and Mon-Fu Chung

Sensors 2008, 8(1), 582-593; https://doi.org/10.3390/s8010582 - 25 Jan 2008

Cited by 56 | Viewed by 11981

A novel reflection-based localized surface plasmon resonance (LSPR) fiber-optic probe has been developed to determine the heavy metal lead ion concentration. Monoclonal antibody as the detecting probe containing massive amino groups to capture Pb(II)-chelate complexes was immobilized onto gold nanoparticle-modified optical fiber (NMAuOF). [...] Read more.

A novel reflection-based localized surface plasmon resonance (LSPR) fiber-optic probe has been developed to determine the heavy metal lead ion concentration. Monoclonal antibody as the detecting probe containing massive amino groups to capture Pb(II)-chelate complexes was immobilized onto gold nanoparticle-modified optical fiber (NMAuOF). The optimal immobilizing conditions of monoclonal antibody on to the NMAuOF are 189 μg/mL in pH7.4 PBS for 2 h at 25°C. The absorbability of the functionalized NMAuOF sensor increases to 12.2 % upon changing the Pb(II)-EDTA level from 10 to 100 ppb with a detection limit of 0.27 ppb. The sensor retains 92.7 % of its original activity and gives reproducible results after storage in 5% D-( )-Trehalose dehydrate solution at 4°C for 35 days. In conclusion, the monoclonal antibody-functionalized NMAuOF sensor shows a promising result for determining the concentration of Pb(II) with high sensitivity. Full article

► Show Figures

776 KiB

Open AccessReview

Review on Hydrogel-based pH Sensors and Microsensors

by Andreas Richter, Georgi Paschew, Stephan Klatt, Jens Lienig, Karl-Friedrich Arndt and Hans-Jürgen P. Adler

Sensors 2008, 8(1), 561-581; https://doi.org/10.3390/s8010561 - 25 Jan 2008

Cited by 678 | Viewed by 40242

Abstract

Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background [...] Read more.

Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background of the special properties of stimuli-responsive hydrogels. Following, transducers are described which are able to convert the non-electrical changes of the physical properties of stimuli-responsive hydrogels into an electrical signal. Finally, the specific sensor properties, design rules and general conditions for sensor applications are discussed. Full article

(This article belongs to the Special Issue State-of-the-Art Polymer Based pH Sensors)

► Show Figures

3477 KiB

Open AccessArticle

Spatially Explicit Large Area Biomass Estimation: Three Approaches Using Forest Inventory and Remotely Sensed Imagery in a GIS

by Michael A. Wulder, Joanne C. White, Richard A. Fournier, Joan E. Luther and Steen Magnussen

Sensors 2008, 8(1), 529-560; https://doi.org/10.3390/s8010529 - 24 Jan 2008

Cited by 74 | Viewed by 19504

Abstract

Forest inventory data often provide the required base data to enable the largearea mapping of biomass over a range of scales. However, spatially explicit estimates ofabove-ground biomass (AGB) over large areas may be limited by the spatial extent of theforest inventory relative to [...] Read more.

Forest inventory data often provide the required base data to enable the largearea mapping of biomass over a range of scales. However, spatially explicit estimates ofabove-ground biomass (AGB) over large areas may be limited by the spatial extent of theforest inventory relative to the area of interest (i.e., inventories not spatially exhaustive), orby the omission of inventory attributes required for biomass estimation. These spatial andattributional gaps in the forest inventory may result in an underestimation of large areaAGB. The continuous nature and synoptic coverage of remotely sensed data have led totheir increased application for AGB estimation over large areas, although the use of thesedata remains challenging in complex forest environments. In this paper, we present anapproach to generating spatially explicit estimates of large area AGB by integrating AGBestimates from multiple data sources; 1. using a lookup table of conversion factors appliedto a non-spatially exhaustive forest inventory dataset (R² = 0.64; RMSE = 16.95 t/ha), 2.applying a lookup table to unique combinations of land cover and vegetation densityoutputs derived from remotely sensed data (R² = 0.52; RMSE = 19.97 t/ha), and 3. hybridmapping by augmenting forest inventory AGB estimates with remotely sensed AGB estimates where there are spatial or attributional gaps in the forest inventory data. Over our714,852 ha study area in central Saskatchewan, Canada, the AGB estimate generated fromthe forest inventory was approximately 40 Mega tonnes (Mt); however, the inventoryestimate represents only 51% of the total study area. The AGB estimate generated from theremotely sensed outputs that overlap those made from the forest inventory based approachdiffer by only 2 %; however in total, the remotely sensed estimate is 30 % greater (58 Mt)than the estimate generated from the forest inventory when the entire study area isaccounted for. Finally, using the hybrid approach, whereby the remotely sensed inputswere used to fill spatial gaps in the forest inventory, the total AGB for the study area wasestimated at 62 Mt. In the example presented, data integration facilitates comprehensiveand spatially explicit estimation of AGB for the entire study area. Full article

(This article belongs to the Special Issue Remote Sensing of Natural Resources and the Environment)

► Show Figures

1690 KiB

Open AccessArticle

The Tradeoff Analysis for Remote Sensing Image Fusion Using Expanded Spectral Angle Mapper

by Shaohui Chen, Hongbo Su, Renhua Zhang, Jing Tian and Lihu Yang

Sensors 2008, 8(1), 520-528; https://doi.org/10.3390/s8010520 - 24 Jan 2008

Cited by 15 | Viewed by 19891 | Correction

Abstract

Image fusion is a useful tool in integrating a high-resolution panchromaticimage (HRPI) with a low-resolution multispectral image (LRMI) to produce a highresolutionmultispectral image (HRMI). To date, many image fusion techniques have beendeveloped to try to improve the spatial resolution of the LRMI to [...] Read more.

Image fusion is a useful tool in integrating a high-resolution panchromaticimage (HRPI) with a low-resolution multispectral image (LRMI) to produce a highresolutionmultispectral image (HRMI). To date, many image fusion techniques have beendeveloped to try to improve the spatial resolution of the LRMI to that of the HRPI with itsspectral property reliably preserved. However, many studies have indicated that thereexists a trade- off between the spatial resolution improvement and the spectral propertypreservation of the LRMI, and it is difficult for the existing methods to do the best in bothaspects. Based on one minimization problem, this paper mathematically analyzes thetradeoff in fusing remote sensing images. In experiment, four fusion methods are evaluatedthrough expanded spectral angle mapper (ESAM). Results clearly prove that all the testedmethods have this property. Full article

► Show Figures

1930 KiB

Open AccessArticle

Thermal Degradation, Mechanical Properties and Morphology of Wheat Straw Flour Filled Recycled Thermoplastic Composites

by Fatih Mengeloglu and Kadir Karakus

Sensors 2008, 8(1), 500-519; https://doi.org/10.3390/s8010500 - 24 Jan 2008

Cited by 98 | Viewed by 40120

Abstract

Thermal behaviors of wheat straw flour (WF) filled thermoplastic compositeswere measured applying the thermogravimetric analysis and differential scanningcalorimetry. Morphology and mechanical properties were also studied using scanningelectron microscope and universal testing machine, respectively. Presence of WF inthermoplastic matrix reduced the degradation temperature of [...] Read more.

Thermal behaviors of wheat straw flour (WF) filled thermoplastic compositeswere measured applying the thermogravimetric analysis and differential scanningcalorimetry. Morphology and mechanical properties were also studied using scanningelectron microscope and universal testing machine, respectively. Presence of WF inthermoplastic matrix reduced the degradation temperature of the composites. One for WFand one for thermoplastics, two main decomposition peaks were observed. Morphologicalstudy showed that addition of coupling agent improved the compatibility between WFs andthermoplastic. WFs were embedded into the thermoplastic matrix indicating improvedadhesion. However, the bonding was not perfect because some debonding can also be seenon the interface of WFs and thermoplastic matrix. In the case of mechanical properties ofWF filled recycled thermoplastic, HDPE and PP based composites provided similar tensileand flexural properties. The addition of coupling agents improved the properties ofthermoplastic composites. MAPE coupling agents performed better in HDPE while MAPPcoupling agents were superior in PP based composites. The composites produced with thecombination of 50-percent mixture of recycled HDPE and PP performed similar with theuse of both coupling agents. All produced composites provided flexural properties requiredby the ASTM standard for polyolefin-based plastic lumber decking boards. Full article

► Show Figures

207 KiB

Open AccessArticle

Cytotoxicity Investigation on Cultured Human Blood Cells Treated with Single-Wall Carbon Nanotubes

by Olga Zeni, Rosanna Palumbo, Romeo Bernini, Luigi Zeni, Maurizio Sarti and Maria Rosaria Scarfì

Sensors 2008, 8(1), 488-499; https://doi.org/10.3390/s8010488 - 24 Jan 2008

Cited by 49 | Viewed by 20408

Abstract

The single-wall carbon nanotubes (SWCNTs) are one of the new materials ofemerging technologies. They are becoming increasingly studied for the possibleapplications in electronics, optics and biology. In particular, very promising fields ofapplication are the development of optical biosensors and the intracellular drug delivery.Nevertheless, [...] Read more.

The single-wall carbon nanotubes (SWCNTs) are one of the new materials ofemerging technologies. They are becoming increasingly studied for the possibleapplications in electronics, optics and biology. In particular, very promising fields ofapplication are the development of optical biosensors and the intracellular drug delivery.Nevertheless, there is a paucity of information on their toxicological properties and onpotential human health risk. In the present study the SWCNTs were investigated for thepossible induction of toxicity in human blood cells. Cell growth, viability, apoptosis andmetabolic activity were evaluated in proliferating human peripheral blood lymphocytes. Inun-stimulated human leukocytes primary DNA damage was also evaluated. SWCNTsconcentrations ranging from 1 to 50 μg/ml were tested, and treatment duration varied from6 to 72 h, in accordance with the biological target investigated. A statistically significantdecrease in cell growth was found in cells treated with the highest concentrations (25 and50 μg/ml). Such decrease was not associated to cell death or apoptosis, but it wasdemonstrated to be related to a decrease in metabolic activity, as assessed by resazurinassay. Moreover, treatments of 6 h with SWCNTs concentrations of 1, 5 and 10 μg/mlfailed to induce primary DNA damage on the entire human leukocytes population. Full article

(This article belongs to the Special Issue Optical Biosensors)

► Show Figures

592 KiB

Open AccessArticle

Lactoferrin Isolation Using Monolithic Column Coupled with Spectrometric or Micro-Amperometric Detector

by Vojtech Adam, Ondrej Zitka, Petr Dolezal, Ladislav Zeman, Ales Horna, Jaromir Hubalek, Jan Sileny, Sona Krizkova, Libuse Trnkova and Rene Kizek

Sensors 2008, 8(1), 464-487; https://doi.org/10.3390/s8010464 - 24 Jan 2008

Cited by 37 | Viewed by 48377

Abstract

Lactoferrin is a multifunctional protein with antimicrobial activity and others tohealth beneficial properties. The main aim of this work was to propose easy to usetechnique for lactoferrin isolation from cow colostrum samples. Primarily we utilizedsodium dodecyl sulphate – polyacrylamide gel electrophoresis for isolation [...] Read more.

Lactoferrin is a multifunctional protein with antimicrobial activity and others tohealth beneficial properties. The main aim of this work was to propose easy to usetechnique for lactoferrin isolation from cow colostrum samples. Primarily we utilizedsodium dodecyl sulphate – polyacrylamide gel electrophoresis for isolation of lactoferrinfrom the real samples. Moreover we tested automated microfluidic Experionelectrophoresis system to isolate lactoferrin from the collostrum sample. The welldeveloped signal of lactoferrin was determined with detection limit (3 S/N) of 20 ng/ml. Inspite of the fact that Experion is faster than SDS-PAGE both separation techniques cannotbe used in routine analysis. Therefore we have tested third separation technique, ionexchange chromatography, using monolithic column coupled with UV-VIS detector (LCUV-VIS). We optimized wave length (280 nm), ionic strength of the elution solution (1.5M NaCl) and flow rate of the retention and elution solutions (0.25 ml/min and 0.75 ml/min.respectively). Under the optimal conditions the detection limit was estimated as 0.1 μg/mlof lactoferrin measured. Using LC-UV-VIS we determined that lactoferrin concentrationvaried from 0.5 g/l to 1.1 g/l in cow colostrums collected in the certain time interval up to 72 hours after birth. Further we focused on miniaturization of detection device. We testedamperometric detection at carbon electrode. The results encouraged us to attempt tominiaturise whole detection system and to test it on analysis of real samples of humanfaeces, because lactoferrin level in faeces is closely associated with the inflammations ofintestine mucous membrane. For the purpose of miniaturization we employed thetechnology of printed electrodes. The detection limit of lactoferrin was estimated as 10μg/ml measured by the screen-printed electrodes fabricated by us. The fabricatedelectrodes were compared with commercially available ones. It follows from the obtainedresults that the responses measured by commercial electrodes are app. ten times highercompared with those measured by the electrodes fabricated by us. This phenomenonrelates with smaller working electrode surface area of the electrodes fabricated by us(about 50 %) compared to the commercial ones. The screen-printed electrodes fabricatedby us were utilized for determination of lactoferrin faeces. Regarding to fact that sample offaeces was obtained from young and healthy man the amount of lactoferrin in sample wasunder the limit of detection of this method. Full article

(This article belongs to the Special Issue Utilization of Electrochemical Sensors and Biosensors in Biochemistry and Molecular Biology)

► Show Figures

1301 KiB

Open AccessArticle

Multi-instrumental Analysis of Tissues of Sunflower Plants Treated with Silver(I) Ions – Plants as Bioindicators of Environmental Pollution

by Sona Krizkova, Pavel Ryant, Olga Krystofova, Vojtech Adam, Michaela Galiova, Miroslava Beklova, Petr Babula, Jozef Kaiser, Karel Novotny, Jan Novotny, Miroslav Liska, Radomir Malina, Josef Zehnalek, Jaromir Hubalek, Ladislav Havel and Rene Kizek

Sensors 2008, 8(1), 445-463; https://doi.org/10.3390/s8010445 - 24 Jan 2008

Cited by 83 | Viewed by 25390

Abstract

The aim of this work is to investigate sunflower plants response on stressinduced by silver(I) ions. The sunflower plants were exposed to silver(I) ions (0, 0.1, 0.5,and 1 mM) for 96 h. Primarily we aimed our attention to observation of basic physiologicalparameters. We [...] Read more.

The aim of this work is to investigate sunflower plants response on stressinduced by silver(I) ions. The sunflower plants were exposed to silver(I) ions (0, 0.1, 0.5,and 1 mM) for 96 h. Primarily we aimed our attention to observation of basic physiologicalparameters. We found that the treated plants embodied growth depression, coloured changes and lack root hairs. Using of autofluorescence of anatomical structures, such aslignified cell walls, it was possible to determine the changes of important shoot and rootstructures, mainly vascular bungles and development of secondary thickening. Thedifferences in vascular bundles organisation, parenchymatic pith development in the rootcentre and the reduction of phloem part of vascular bundles were well observable.Moreover with increasing silver(I) ions concentration the vitality of rhizodermal cellsdeclined; rhizodermal cells early necrosed and were replaced by the cells of exodermis.Further we employed laser induced breakdown spectroscopy for determination of spatialdistribution of silver(I) ions in tissues of the treated plants. The Ag is accumulated mainlyin near-root part of the sample. Moreover basic biochemical indicators of environmentalstress were investigated. The total content of proteins expressively decreased withincreasing silver(I) ions dose and the time of the treatment. As we compare the resultsobtained by protein analysis – the total protein contents in shoot as well as root parts – wecan assume on the transport of the proteins from the roots to shoots. This phenomenon canbe related with the cascade of processes connecting with photosynthesis. The secondbiochemical parameter, which we investigated, was urease activity. If we compared theactivity in treated plants with control, we found out that presence of silver(I) ions markedlyenhanced the activity of urease at all applied doses of this toxic metal. Finally we studiedthe effect of silver(I) ions on activity of urease in in vitro conditions. Full article

(This article belongs to the Special Issue Utilization of Electrochemical Sensors and Biosensors in Biochemistry and Molecular Biology)

► Show Figures

515 KiB

Open AccessArticle

Study of Copper and Purine-Copper Complexes on Modified Carbon Electrodes by Cyclic and Elimination Voltammetry

by Libuse Trnkova, Lenka Zerzankova, Filip Dycka, Radka Mikelova and Frantisek Jelen

Sensors 2008, 8(1), 429-444; https://doi.org/10.3390/s8010429 - 24 Jan 2008

Cited by 29 | Viewed by 11407

Abstract

Using a paraffin impregnated graphite electrode (PIGE) and mercury-modifiedpyrolytic graphite electrode with basal orientation (Hg-PGEb) copper(II) and Cu(II)-DNApurine base solutions have been studied by cyclic (CV) and linear sweep voltammetry(LSV) in connection with elimination voltammetry with linear scan (EVLS). In chlorideand bromide solutions [...] Read more.

Using a paraffin impregnated graphite electrode (PIGE) and mercury-modifiedpyrolytic graphite electrode with basal orientation (Hg-PGEb) copper(II) and Cu(II)-DNApurine base solutions have been studied by cyclic (CV) and linear sweep voltammetry(LSV) in connection with elimination voltammetry with linear scan (EVLS). In chlorideand bromide solutions (pH 6), the redox process of Cu(II) proceeded on PIGE with twocathodic and two anodic potentially separated signals. According to the eliminationfunction E4, the first cathodic peak corresponds to the reduction Cu(II) e^- → Cu(I) withthe possibility of fast disproportionation 2Cu(I) → Cu(II) Cu(0). The E4 of the secondcathodic peak signalized an electrode process controlled by a surface reaction. Theelectrode system of Cu(II) on Hg-PGEb in borate buffer (pH 9.2) was characterized by onecathodic and one anodic peak. Anodic stripping voltammetry (ASV) on PIGE and cathodicstripping voltammetry (CSV) on Hg-PGEb were carried out at potentials where thereduction of copper ions took place and Cu(I)-purine complexes were formed. By usingASV and CSV in combination with EVLS, the sensitivity of Cu(I)-purine complexdetection was enhanced relative to either ASV or CSV alone, resulting in higher peakcurrents of more than one order of magnitude. The statistical treatment of CE data wasused to determine the reproducibility of measurements. Our results show that EVLS inconnection with the stripping procedure is useful for both qualitative and quantitativemicroanalysis of purine derivatives and can also reveal details of studied electrodeprocesses. Full article

(This article belongs to the Special Issue Utilization of Electrochemical Sensors and Biosensors in Biochemistry and Molecular Biology)

► Show Figures

450 KiB

Open AccessArticle

Validating Evapotranspiraiton Equations Using Bowen Ratio in New Brunswick, Maritime, Canada

by Zisheng Xing, Lien Chow, Fan-Rui Meng, Herb W. Rees, Lionel Steve and John Monteith

Sensors 2008, 8(1), 412-428; https://doi.org/10.3390/s8010412 - 24 Jan 2008

Cited by 28 | Viewed by 10495

Abstract

Three methods including the Penman-Monteith (PM), Priestley-Taylor (PT), and 1963 Penman equation (PE) for calculating daily reference evapotranspiration (ETo) were evaluated in the Maritime region of Canada with the data collected from 2004 to 2007. An automatically operated meteorological station located on the [...] Read more.

Three methods including the Penman-Monteith (PM), Priestley-Taylor (PT), and 1963 Penman equation (PE) for calculating daily reference evapotranspiration (ETo) were evaluated in the Maritime region of Canada with the data collected from 2004 to 2007. An automatically operated meteorological station located on the Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, New Brunswick, Canada, was used to collect required meteorological data for evapotranspiration modeling. A Bowen Ratio system (BR) was setup near the Environment Canada grade one weather station to provide evapotranspiration observations for the validation research of reference evapotranspiration models. The results showed that the prediction from each of the tested models had a certain degree of offset in comparison with the observations obtained by the BR method. All of the tested models slightly overestimated evapotranspiration compared to the BR system by 5-14%, depending on the method. However, the PM generated a better fit to the pooled dataset while the PT produced the best prediction for the 2007 validation dataset. The PM generated the best estimation of evapotranspiration for year 2004 during a inter-annual comparison. The BR revealed that the average daytime ET for the site was around 2.5 mm day^-1(±0.1) averaged for Julian day 157-276 in 2004 to 2006 and possible condensation was 0.16 mm day^-1 for the same period. Crop coefficient (Kc) varied with different models, for example, 0.42 for the PM, 0.44 for the PT, and 0.67 for the PE with a slight yearly variation. With this set of Kc values, a validation with additional dataset collected in 2007 indicated that all three equations achieved a good fit with observations using the above Kc values. The PT performed slightly better than the other two models. A single factor analysis did not show any statistically significant difference between predicted and measured ET. With a consideration of simplicity and application for scaling up to landscape, this research suggested that the PT is the preferable method for estimating ET values in this region. Full article

► Show Figures

824 KiB

Open AccessReview

A Review of Interface Electronic Systems for AT-cut Quartz Crystal Microbalance Applications in Liquids

by Antonio Arnau

Sensors 2008, 8(1), 370-411; https://doi.org/10.3390/s8010370 - 21 Jan 2008

Cited by 156 | Viewed by 19587

Abstract

From the first applications of AT-cut quartz crystals as sensors in solutionsmore than 20 years ago, the so-called quartz crystal microbalance (QCM) sensor isbecoming into a good alternative analytical method in a great deal of applications such asbiosensors, analysis of biomolecular interactions, study [...] Read more.

From the first applications of AT-cut quartz crystals as sensors in solutionsmore than 20 years ago, the so-called quartz crystal microbalance (QCM) sensor isbecoming into a good alternative analytical method in a great deal of applications such asbiosensors, analysis of biomolecular interactions, study of bacterial adhesion at specificinterfaces, pathogen and microorganism detection, study of polymer film-biomolecule orcell-substrate interactions, immunosensors and an extensive use in fluids and polymercharacterization and electrochemical applications among others. The appropriateevaluation of this analytical method requires recognizing the different steps involved andto be conscious of their importance and limitations. The first step involved in a QCMsystem is the accurate and appropriate characterization of the sensor in relation to thespecific application. The use of the piezoelectric sensor in contact with solutions stronglyaffects its behavior and appropriate electronic interfaces must be used for an adequatesensor characterization. Systems based on different principles and techniques have beenimplemented during the last 25 years. The interface selection for the specific application isimportant and its limitations must be known to be conscious of its suitability, and foravoiding the possible error propagation in the interpretation of results. This article presentsa comprehensive overview of the different techniques used for AT-cut quartz crystalmicrobalance in in-solution applications, which are based on the following principles:network or impedance analyzers, decay methods, oscillators and lock-in techniques. Theelectronic interfaces based on oscillators and phase-locked techniques are treated in detail,with the description of different configurations, since these techniques are the most used inapplications for detection of analytes in solutions, and in those where a fast sensorresponse is necessary. Full article

(This article belongs to the Special Issue Piezoelectric Sensors for Determination of Analytes in Solutions)

► Show Figures

902 KiB

Open AccessReview

Biosensor Techniques Used for Determination of Telomerase Activity in Cancer Cells

by Eliona Kulla and Evgeny Katz

Sensors 2008, 8(1), 347-369; https://doi.org/10.3390/s8010347 - 21 Jan 2008

Cited by 12 | Viewed by 10441

Abstract

Measuring telomerase activity has proven successful for the determination of cancer in malignant somatic cells. Early conventional methods for the detection of telomerase activity include in vitro analysis via a primer extension assay, and the telomeric repeat amplification protocol (TRAP) assay. TRAP incorporates [...] Read more.

Measuring telomerase activity has proven successful for the determination of cancer in malignant somatic cells. Early conventional methods for the detection of telomerase activity include in vitro analysis via a primer extension assay, and the telomeric repeat amplification protocol (TRAP) assay. TRAP incorporates the polymerase chain reaction (PCR) step to increase the sensitivity of a given sample. However, research suggests that the TRAP technique suffers from false negative results, caused by failure of its PCR step. Other limitations of TRAP include the post-PCR steps involving polyacrylamide gel electrophoresis which are time inefficient. Thus, various efforts have been made to eliminate the PCR step of TRAP by using a variety of biosensor detection devices. This review mainly focuses on these alternatives including: optical, electrochemical, magnetic, and nanowire conductive signaling techniques to measure the telomerase activity produced via label free biosensor assay—via biocatalytic labels involving beacons, DNAzyme, ferrocenyl-naphthalene diimides, avidin-alkaline phosphatase and semiconductor quantum dots (QDs). These biosensor techniques are sensitive and provide precise and rapid results in the detection of telomerase activity. Full article

► Show Figures

900 KiB

Open AccessArticle

Sensitivity of PZT Impedance Sensors for Damage Detection of Concrete Structures

by Yaowen Yang, Yuhang Hu and Yong Lu

Sensors 2008, 8(1), 327-346; https://doi.org/10.3390/s8010327 - 21 Jan 2008

Cited by 202 | Viewed by 15922

Abstract

Piezoelectric ceramic Lead Zirconate Titanate (PZT) based electro-mechanicalimpedance (EMI) technique for structural health monitoring (SHM) has been successfullyapplied to various engineering systems. However, fundamental research work on thesensitivity of the PZT impedance sensors for damage detection is still in need. In thetraditional EMI [...] Read more.

Piezoelectric ceramic Lead Zirconate Titanate (PZT) based electro-mechanicalimpedance (EMI) technique for structural health monitoring (SHM) has been successfullyapplied to various engineering systems. However, fundamental research work on thesensitivity of the PZT impedance sensors for damage detection is still in need. In thetraditional EMI method, the PZT electro-mechanical (EM) admittance (inverse of theimpedance) is used as damage indicator, which is difficult to specify the effect of damage onstructural properties. This paper uses the structural mechanical impedance (SMI) extractedfrom the PZT EM admittance signature as the damage indicator. A comparison study on thesensitivity of the EM admittance and the structural mechanical impedance to the damages ina concrete structure is conducted. Results show that the SMI is more sensitive to the damagethan the EM admittance thus a better indicator for damage detection. Furthermore, this paperproposes a dynamic system consisting of a number of single-degree-of-freedom elementswith mass, spring and damper components to model the SMI. A genetic algorithm isemployed to search for the optimal value of the unknown parameters in the dynamic system.An experiment is carried out on a two-storey concrete frame subjected to base vibrations thatsimulate earthquake. A number of PZT sensors are regularly arrayed and bonded to the framestructure to acquire PZT EM admittance signatures. The relationship between the damageindex and the distance of the PZT sensor from the damage is studied. Consequently, thesensitivity of the PZT sensors is discussed and their sensing region in concrete is derived. Full article

(This article belongs to the Special Issue Sensors for Urban Environmental Monitoring)

► Show Figures

315 KiB

Open AccessArticle

Ad Hoc Modeling of Root Zone Soil Water with Landsat Imagery and Terrain and Soils Data

by Joel B. Sankey, Rick L. Lawrence and Jon M. Wraith

Sensors 2008, 8(1), 314-326; https://doi.org/10.3390/s8010314 - 21 Jan 2008

Cited by 3 | Viewed by 11754

Abstract

Agricultural producers require knowledge of soil water at plant rooting depths,while many remote sensing studies have focused on surface soil water or mechanisticmodels that are not easily parameterized. We developed site-specific empirical models topredict spring soil water content for two Montana ranches. Calibration [...] Read more.

Agricultural producers require knowledge of soil water at plant rooting depths,while many remote sensing studies have focused on surface soil water or mechanisticmodels that are not easily parameterized. We developed site-specific empirical models topredict spring soil water content for two Montana ranches. Calibration data sample sizeswere based on the estimated variability of soil water and the desired level of precision forthe soil water estimates. Models used Landsat imagery, a digital elevation model, and asoil survey as predictor variables. Our objectives were to see whether soil water could bepredicted accurately with easily obtainable calibration data and predictor variables and toconsider the relative influence of the three sources of predictor variables. Independentvalidation showed that multiple regression models predicted soil water with average error(RMSD) within 0.04 mass water content. This was similar to the accuracy expected basedon a statistical power test based on our sample size (n = 41 and n = 50). Improvedprediction precision could be achieved with additional calibration samples, and rangemanagers can readily balance the desired level of precision with the amount of effort tocollect calibration data. Spring soil water prediction effectively utilized a combination ofland surface imagery, terrain data, and subsurface soil characterization data. Rancherscould use accurate spring soil water content predictions to set stocking rates. Suchmanagement can help ensure that water, soil, and vegetation resources are usedconservatively in irrigated and non-irrigated rangeland systems. Full article

(This article belongs to the Special Issue Remote Sensing of Natural Resources and the Environment)

► Show Figures

745 KiB

Open AccessReview

A Review on the Electrochemical Sensors and Biosensors Composed of Nanowires as Sensing Material

by Umasankar Yogeswaran and Shen-Ming Chen

Sensors 2008, 8(1), 290-313; https://doi.org/10.3390/s8010290 - 21 Jan 2008

Cited by 439 | Viewed by 32003

Abstract

The development and application of nanowires for electrochemical sensors and biosensors are reviewed in this article. Next generation sensor platforms will require significant improvements in sensitivity, specificity and parallelism in order to meet the future needs in variety of fields. Sensors made of [...] Read more.

The development and application of nanowires for electrochemical sensors and biosensors are reviewed in this article. Next generation sensor platforms will require significant improvements in sensitivity, specificity and parallelism in order to meet the future needs in variety of fields. Sensors made of nanowires exploit some fundamental nanoscopic effect in order to meet these requirements. Nanowires are new materials, which have the characteristic of low weight with extraordinary mechanical, electrical, thermal and multifunctional properties. The advantages such as size scale, aspect ratio and other properties of nanowires are especially apparent in the use of electrical sensors such as electrochemical sensors and in the use of field-effect transistors. The preparation methods of nanowires and their properties are discussed along with their advantages towards electrochemical sensors and biosensors. Some key results from each article are summarized, relating the concept and mechanism behind each sensor, with experimental conditions as well as their behavior at different conditions. Full article

(This article belongs to the Special Issue Utilization of Electrochemical Sensors and Biosensors in Biochemistry and Molecular Biology)

► Show Figures

1122 KiB

Open AccessArticle

Application of Multiplexed FBG and PZT Impedance Sensors for Health Monitoring of Rocks

by Yaowen Yang, Venu Gopal Madhav Annamdas, Chao Wang and Yingxin Zhou

Sensors 2008, 8(1), 271-289; https://doi.org/10.3390/s8010271 - 21 Jan 2008

Cited by 83 | Viewed by 16135

Abstract

Reliable structural health monitoring (SHM) including nondestructiveevaluation (NDE) is essential for safe operation of infrastructure systems. Effectivemonitoring of the rock components of civil infrastructures such as tunnels and cavernsremains challenging. The feasibility of employing smart optical fibre sensor (OFS) andpiezoelectric impedance sensor made [...] Read more.

Reliable structural health monitoring (SHM) including nondestructiveevaluation (NDE) is essential for safe operation of infrastructure systems. Effectivemonitoring of the rock components of civil infrastructures such as tunnels and cavernsremains challenging. The feasibility of employing smart optical fibre sensor (OFS) andpiezoelectric impedance sensor made up of lead zirconate titanate (PZT) forcomprehensive health monitoring of rocks, covering load history monitoring/retrieval aswell as damage assessment is presented in this paper. The rock specimens are subjected tocyclic loading and their conditions are continuously monitored using OFS and PZTsensors. OFS based multiplexed fibre Bragg grating (FBG) sensors are surface bonded onthe rock specimens. Their strain sensing performance is compared with the conventionalelectric strain gauges (ESGs). In addition, PZT patches are also bonded on the specimensto study the damage pattern during different loading cycles. Unlike the FBGs or ESGs,PZT patches are used as bi-functional sensors and actuators, enabling them to be efficientdetectors of incipient damages using the principle of electromechanical impedance. Theexperimental study demonstrated superior performance of these smart FBG and PZTimpedance sensors. This work is expected to be useful for SHM based NDE application ofrock structures such as caverns and tunnels. Full article

(This article belongs to the Special Issue Sensors for Urban Environmental Monitoring)

► Show Figures

246 KiB

Open AccessArticle

Soil Moisture Profile Effect on Radar Signal Measurement

by Aurélie Le Morvan, Mehrez Zribi, Nicolas Baghdadi and André Chanzy

Sensors 2008, 8(1), 256-270; https://doi.org/10.3390/s8010256 - 21 Jan 2008

Cited by 60 | Viewed by 11297

Abstract

The objective of this paper is to analyze the behaviour of a backscattered signalaccording to soil moisture depth over bare soils. Analysis based on experimental verticalmoisture profiles and ASAR/ENVISAT measurements has been carried out. A modifiedIEM model with three permittivity layers (0-1cm, 1-2cm, [...] Read more.

The objective of this paper is to analyze the behaviour of a backscattered signalaccording to soil moisture depth over bare soils. Analysis based on experimental verticalmoisture profiles and ASAR/ENVISAT measurements has been carried out. A modifiedIEM model with three permittivity layers (0-1cm, 1-2cm, 2-5cm) has been developed andused in this study. Results show a small effect of moisture profile on the backscatteredsignal (less than 0.5dB). However, measurements and simulations have provided a moredetailed insight into the behaviour of the radar signal and have shown that it was importantto consistently use the same protocol when performing ground truth measurements of soilmoisture. Full article

► Show Figures

1015 KiB

Open AccessReview

Advances in Remote Sensing for Oil Spill Disaster Management: State-of-the-Art Sensors Technology for Oil Spill Surveillance

by Maya Nand Jha, Jason Levy and Yang Gao

Sensors 2008, 8(1), 236-255; https://doi.org/10.3390/s8010236 - 21 Jan 2008

Cited by 282 | Viewed by 33432

Abstract

Reducing the risk of oil spill disasters is essential for protecting the environmentand reducing economic losses. Oil spill surveillance constitutes an important component ofoil spill disaster management. Advances in remote sensing technologies can help to identifyparties potentially responsible for pollution and to identify [...] Read more.

Reducing the risk of oil spill disasters is essential for protecting the environmentand reducing economic losses. Oil spill surveillance constitutes an important component ofoil spill disaster management. Advances in remote sensing technologies can help to identifyparties potentially responsible for pollution and to identify minor spills before they causewidespread damage. Due to the large number of sensors currently available for oil spillsurveillance, there is a need for a comprehensive overview and comparison of existingsensors. Specifically, this paper examines the characteristics and applications of differentsensors. A better understanding of the strengths and weaknesses of oil spill surveillancesensors will improve the operational use of these sensors for oil spill response andcontingency planning. Laser fluorosensors were found to be the best available sensor for oilspill detection since they not only detect and classify oil on all surfaces but also operate ineither the day or night. For example, the Scanning Laser Environmental AirborneFluorosensor (SLEAF) sensor was identified to be a valuable tool for oil spill surveillance.However, no single sensor was able to provide all information required for oil spillcontingency planning. Hence, combinations of sensors are currently used for oil spillsurveillance. Specifically, satellite sensors are used for preliminary oil spill assessmentwhile airborne sensors are used for detailed oil spill analysis. While satellite remote sensingis not suitable for tactical oil spill planning it can provide a synoptic coverage of theaffected area. Full article

(This article belongs to the Special Issue Sensors for Disaster and Emergency Management Decision Making)

► Show Figures

2930 KiB

Open AccessArticle

Experimental Study on the Effects of Alumina Abrasive Particle Behavior in MR Polishing for MEMS Applications

by Dong-Woo Kim, Myeong-Woo Cho, Tae-Il Seo and Young-Jae Shin

Sensors 2008, 8(1), 222-235; https://doi.org/10.3390/s8010222 - 21 Jan 2008

Cited by 24 | Viewed by 12701

Abstract

Recently, the magnetorheological (MR) polishing process has been examined asa new ultra-precision polishing technology for micro parts in MEMS applications. In theMR polishing process, the magnetic force plays a dominant role. This method uses MRfluids which contains micro abrasives as a polishing media. [...] Read more.

Recently, the magnetorheological (MR) polishing process has been examined asa new ultra-precision polishing technology for micro parts in MEMS applications. In theMR polishing process, the magnetic force plays a dominant role. This method uses MRfluids which contains micro abrasives as a polishing media. The objective of the presentresearch is to shed light onto the material removal mechanism under various slurryconditions for polishing and to investigate surface characteristics, including shape analysisand surface roughness measurement, of spots obtained from the MR polishing process usingalumina abrasives. A series of basic experiments were first performed to determine theoptimum polishing conditions for BK7 glass using prepared slurries by changing the processparameters, such as wheel rotating speed and electric current. Using the obtained results,groove polishing was then performed and the results are investigated. Outstanding surfaceroughness of Ra=3.8nm was obtained on the BK7 glass specimen. The present resultshighlight the possibility of applying this polishing method to ultra-precision micro partsproduction, especially in MEMS applications. Full article

(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering)

► Show Figures

839 KiB

Open AccessArticle

Application of Design of Experiment Method for Thrust Force Minimization in Step-feed Micro Drilling

by Dong-Woo Kim, Myeong-Woo Cho, Tae-il Seo and Eung-Sug Lee

Sensors 2008, 8(1), 211-221; https://doi.org/10.3390/s8010211 - 21 Jan 2008

Cited by 25 | Viewed by 13801

Abstract

Micro drilled holes are utilized in many of today’s fabrication processes.Precision production processes in industries are trending toward the use of smaller holeswith higher aspect ratios, and higher speed operation for micro deep hole drilling. However,undesirable characteristics related to micro drilling such as [...] Read more.

Micro drilled holes are utilized in many of today’s fabrication processes.Precision production processes in industries are trending toward the use of smaller holeswith higher aspect ratios, and higher speed operation for micro deep hole drilling. However,undesirable characteristics related to micro drilling such as small signal-to-noise ratios,wandering drill motion, high aspect ratio, and excessive cutting forces can be observedwhen cutting depth increases. In this study, the authors attempt to minimize the thrustforces in the step-feed micro drilling process by application of the DOE (Design ofExperiment) method. Taking into account the drilling thrust, three cutting parameters,feedrate, step-feed, and cutting speed, are optimized based on the DOE method. Forexperimental studies, an orthogonal array L₂₇(3¹³) is generated and ANOVA (Analysis ofVariance) is carried out. Based on the results it is determined that the sequence of factorsaffecting drilling thrusts corresponds to feedrate, step-feed, and spindle rpm. Acombination of optimal drilling conditions is also identified. In particular, it is found in thisstudy that the feedrate is the most important factor for micro drilling thrust minimization. Full article

(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering)

► Show Figures

448 KiB

Open AccessArticle

Enzyme-Linked Electrochemical Detection of PCR-Amplified Nucleotide Sequences Using Disposable Screen-Printed Sensors. Applications in Gene Expression Monitoring

by Petra Horaková-Brazdilova, Miloslava Fojtova, Karel Vytras and Miroslav Fojta

Sensors 2008, 8(1), 193-210; https://doi.org/10.3390/s8010193 - 21 Jan 2008

Cited by 22 | Viewed by 10898

Abstract

Electrochemical enzyme-linked techniques for sequence-specific DNA sensingare presented. These techniques are based on attachment of streptavidin-alkalinephosphatase conjugate to biotin tags tethered to DNA immobilized at the surface ofdisposable screen-printed carbon electrodes (SPCE), followed by production andelectrochemical determination of an electroactive indicator, 1-naphthol. Via [...] Read more.

Electrochemical enzyme-linked techniques for sequence-specific DNA sensingare presented. These techniques are based on attachment of streptavidin-alkalinephosphatase conjugate to biotin tags tethered to DNA immobilized at the surface ofdisposable screen-printed carbon electrodes (SPCE), followed by production andelectrochemical determination of an electroactive indicator, 1-naphthol. Via hybridizationof SPCE surface-confined target DNAs with end-biotinylated probes, highly specificdiscrimination between complementary and non-complementary nucleotide sequences wasachieved. The enzyme-linked DNA hybridization assay has been successfully applied inanalysis of PCR-amplified real genomic DNA sequences, as well as in monitoring of planttissue-specific gene expression. In addition, we present an alternative approach involvingsequence-specific incorporation of biotin-labeled nucleotides into DNA by primerextension. Introduction of multiple biotin tags per probe primer resulted in considerableenhancement of the signal intensity and improvement of the specificity of detection. Full article

(This article belongs to the Special Issue Utilization of Electrochemical Sensors and Biosensors in Biochemistry and Molecular Biology)

► Show Figures

287 KiB

Open AccessArticle

Fabrication of a ZnO Pyroelectric Sensor

by Chun-Ching Hsiao, Kuo-Yi Huang and Yuh-Chung Hu

Sensors 2008, 8(1), 185-192; https://doi.org/10.3390/s8010185 - 21 Jan 2008

Cited by 34 | Viewed by 10117

Abstract

This paper proposes a two-step radio frequency (RF) sputtering process to forma ZnO film for pyroelectric sensors. It is shown that the two-step sputtering process with alower power step followed by a higher power step can significantly improve the voltageresponsivity of the ZnO [...] Read more.

This paper proposes a two-step radio frequency (RF) sputtering process to forma ZnO film for pyroelectric sensors. It is shown that the two-step sputtering process with alower power step followed by a higher power step can significantly improve the voltageresponsivity of the ZnO pyroelectric sensor. The improvement is attributed mainly to theformation of ZnO film with a strongly preferred orientation towards the c-axis.Furthermore, a nickel film deposited onto the uncovered parts of the ZnO film caneffectively improve the voltage responsivity at higher modulating frequencies since thenickel film can enhance the incident energy absorption of the ZnO layer. Full article

► Show Figures

358 KiB

Open AccessArticle

Chemical Sensing Sensitivity of Long-Period Grating Sensor Enhanced by Colloidal Gold Nanoparticles

by Jaw-Luen Tang and Jien-Neng Wang

Sensors 2008, 8(1), 171-184; https://doi.org/10.3390/s8010171 - 21 Jan 2008

Cited by 53 | Viewed by 10889

Abstract

A simple and effective method is proposed to improve spectral sensitivity anddetection limit of long period gratings for refractive index or chemical sensing, where thegrating surface is modified by a monolayer of colloidal gold nanoparticles. Thetransmission spectra and optical properties of gold nanospheres [...] Read more.

A simple and effective method is proposed to improve spectral sensitivity anddetection limit of long period gratings for refractive index or chemical sensing, where thegrating surface is modified by a monolayer of colloidal gold nanoparticles. Thetransmission spectra and optical properties of gold nanospheres vary with the differentrefractive index of the environment near the surface of gold nanospheres. The sensorresponse of gold colloids increases linearly with solvents of increasing refractive index.The results for the measurement of sucrose and sodium chloride solutions are reported,which show that this type of sensor can provide a limiting resolution of ~10^-3 to ~10^-4 forrefractive indices in the range of 1.34 to 1.39 and a noticeable increase in detection limit ofrefractive index to external medium. Full article

(This article belongs to the Special Issue Photonic Sensors for Chemical, Biological, and Nuclear Agent Detection)

► Show Figures

1311 KiB

Open AccessReview

Lightning Sensors for Observing, Tracking and Nowcasting Severe Weather

by Colin Price

Sensors 2008, 8(1), 157-170; https://doi.org/10.3390/s8010157 - 21 Jan 2008

Cited by 40 | Viewed by 16139

Abstract

Severe and extreme weather is a major natural hazard all over the world, oftenresulting in major natural disasters such as hail storms, tornados, wind storms, flash floods,forest fires and lightning damages. While precipitation, wind, hail, tornados, turbulence,etc. can only be observed at close [...] Read more.

Severe and extreme weather is a major natural hazard all over the world, oftenresulting in major natural disasters such as hail storms, tornados, wind storms, flash floods,forest fires and lightning damages. While precipitation, wind, hail, tornados, turbulence,etc. can only be observed at close distances, lightning activity in these damaging stormscan be monitored at all spatial scales, from local (using very high frequency [VHF]sensors), to regional (using very low frequency [VLF] sensors), and even global scales(using extremely low frequency [ELF] sensors). Using sensors that detect the radio wavesemitted by each lightning discharge, it is now possible to observe and track continuouslydistant thunderstorms using ground networks of sensors. In addition to the number oflightning discharges, these sensors can also provide information on lightningcharacteristics such as the ratio between intra-cloud and cloud-to-ground lightning, thepolarity of the lightning discharge, peak currents, charge removal, etc. It has been shownthat changes in some of these lightning characteristics during thunderstorms are oftenrelated to changes in the severity of the storms. In this paper different lightning observingsystems are described, and a few examples are provided showing how lightning may beused to monitor storm hazards around the globe, while also providing the possibility ofsupplying short term forecasts, called nowcasting. Full article

(This article belongs to the Special Issue Sensors for Disaster and Emergency Management Decision Making)

► Show Figures

328 KiB

Open AccessArticle

Electronic Nose Based on Metal Oxide Semiconductor Sensors as an Alternative Technique for the Spoilage Classification of Red Meat

by Noureddine El Barbri, Eduard Llobet, Nezha El Bari, Xavier Correig and Benachir Bouchikhi

Sensors 2008, 8(1), 142-156; https://doi.org/10.3390/s8010142 - 21 Jan 2008

Cited by 147 | Viewed by 16652

Abstract

The aim of the present study was to develop an electronic nose for the quality control of red meat. Electronic nose and bacteriological measurements are performed to analyse samples of beef and sheep meat stored at 4°C for up to 15 days. Principal [...] Read more.

The aim of the present study was to develop an electronic nose for the quality control of red meat. Electronic nose and bacteriological measurements are performed to analyse samples of beef and sheep meat stored at 4°C for up to 15 days. Principal component analysis (PCA) and support vector machine (SVM) based classification techniques are used to investigate the performance of the electronic nose system in the spoilage classification of red meats. The bacteriological method was selected as the reference method to consistently train the electronic nose system. The SVM models built classified meat samples based on the total microbial population into “unspoiled” (microbial counts < 6 log10 cfu/g) and “spoiled” (microbial counts ≥ 6 log10 cfu/g). The preliminary results obtained by the bacteria total viable counts (TVC) show that the shelf-life of beef and sheep meats stored at 4 °C are 7 and 5 days, respectively. The electronic nose system coupled to SVM could discriminate between unspoiled/ spoiled beef or sheep meats with a success rate of 98.81 or 96.43 %, respectively. To investigate whether the results of the electronic nose correlated well with the results of the bacteriological analysis, partial least squares (PLS) calibration models were built and validated. Good correlation coefficients between the electronic nose signals and bacteriological data were obtained, a clear indication that the electronic nose system can become a simple and rapid technique for the quality control of red meats. Full article

► Show Figures

407 KiB

Open AccessReview

Electrochemical Sensors Based on Organic Conjugated Polymers

by Md. Aminur Rahman, Pankaj Kumar, Deog-Su Park and Yoon-Bo Shim

Sensors 2008, 8(1), 118-141; https://doi.org/10.3390/s8010118 - 9 Jan 2008

Cited by 407 | Viewed by 26764

Abstract

Organic conjugated polymers (conducting polymers) have emerged as potentialcandidates for electrochemical sensors. Due to their straightforward preparation methods,unique properties, and stability in air, conducting polymers have been applied to energystorage, electrochemical devices, memory devices, chemical sensors, and electrocatalysts.Conducting polymers are also known to [...] Read more.

Organic conjugated polymers (conducting polymers) have emerged as potentialcandidates for electrochemical sensors. Due to their straightforward preparation methods,unique properties, and stability in air, conducting polymers have been applied to energystorage, electrochemical devices, memory devices, chemical sensors, and electrocatalysts.Conducting polymers are also known to be compatible with biological molecules in aneutral aqueous solution. Thus, these are extensively used in the fabrication of accurate,fast, and inexpensive devices, such as biosensors and chemical sensors in the medicaldiagnostic laboratories. Conducting polymer-based electrochemical sensors and biosensorsplay an important role in the improvement of public health and environment because rapiddetection, high sensitivity, small size, and specificity are achievable for environmentalmonitoring and clinical diagnostics. In this review, we summarized the recent advances inconducting polymer-based electrochemical sensors, which covers chemical sensors(potentiometric, voltammetric, amperometric) and biosensors (enzyme based biosensors,immunosensors, DNA sensors). Full article

(This article belongs to the Special Issue Electrochemical Sensors Based on Conductive Polymers)

► Show Figures

645 KiB

Open AccessReview

Assessment of Evapotranspiration and Soil Moisture Content Across Different Scales of Observation

by Willem W. Verstraeten, Frank Veroustraete and Jan Feyen

Sensors 2008, 8(1), 70-117; https://doi.org/10.3390/s8010070 - 9 Jan 2008

Cited by 300 | Viewed by 27722

Abstract

The proper assessment of evapotranspiration and soil moisture content arefundamental in food security research, land management, pollution detection, nutrient flows,(wild-) fire detection, (desert) locust, carbon balance as well as hydrological modelling; etc.This paper takes an extensive, though not exhaustive sample of international scientificliterature [...] Read more.

The proper assessment of evapotranspiration and soil moisture content arefundamental in food security research, land management, pollution detection, nutrient flows,(wild-) fire detection, (desert) locust, carbon balance as well as hydrological modelling; etc.This paper takes an extensive, though not exhaustive sample of international scientificliterature to discuss different approaches to estimate land surface and ecosystem relatedevapotranspiration and soil moisture content. This review presents:(i) a summary of the generally accepted cohesion theory of plant water uptake andtransport including a shortlist of meteorological and plant factors influencing planttranspiration;(ii) a summary on evapotranspiration assessment at different scales of observation (sapflow,porometer, lysimeter, field and catchment water balance, Bowen ratio,scintillometer, eddy correlation, Penman-Monteith and related approaches);(iii) a summary on data assimilation schemes conceived to estimate evapotranspirationusing optical and thermal remote sensing; and(iv) for soil moisture content, a summary on soil moisture retrieval techniques atdifferent spatial and temporal scales is presented.Concluding remarks on the best available approaches to assess evapotranspiration and soilmoisture content with and emphasis on remote sensing data assimilation, are provided. Full article

(This article belongs to the Special Issue Remote Sensing of Natural Resources and the Environment)

► Show Figures

615 KiB

Open AccessArticle

Changes in Spectral Properties, Chlorophyll Content and Internal Mesophyll Structure of Senescing Populus balsamifera and Populus tremuloides Leaves

by Karen L. Castro and G. Arturo Sanchez-Azofeifa

Sensors 2008, 8(1), 51-69; https://doi.org/10.3390/s8010051 - 9 Jan 2008

Cited by 61 | Viewed by 14467

Abstract

In this paper we compare leaf traits and spectral reflectance for sunlit andshaded leaves of Populus tremuloides and Populus balsamifera during autumnsenescence using information derived from an Analytical Spectral Devise (ASD) FullRange spectrometer. The modified simple ratio (mSR₇₀₅) and modified normalizeddifference [...] Read more.

In this paper we compare leaf traits and spectral reflectance for sunlit andshaded leaves of Populus tremuloides and Populus balsamifera during autumnsenescence using information derived from an Analytical Spectral Devise (ASD) FullRange spectrometer. The modified simple ratio (mSR₇₀₅) and modified normalizeddifference index (mND₇₀₅) were effective in describing changes in chlorophyll contentover this period. Highly significant (P less than 0.01) correlation coefficients were found betweenthe chlorophyll indices (mSR₇₀₅, mND₇₀₅)) and chlorophyll a, b, total chlorophyll andchlorophyll a/b. Changes in mesophyll structure were better described by the plantsenescence reflectance index (PSRI) than by near-infrared wavebands. Overall, P.balsamifera exhibited lower total chlorophyll and earlier senescence than P. tremuloides.Leaves of P. balsamifera were also thicker, had a higher proportion of intercellular spacein the spongy mesophyll, and higher reflectance at 800 nm. Further research, using largersample sizes over a broader range of sites will extend our understanding of the spectraland temporal dynamics of senescence in P. tremuloides and P. balsamifera and will beparticularly useful if species differences are detectable at the crown level using remotelysensed imagery. Full article

(This article belongs to the Special Issue Remote Sensing of Natural Resources and the Environment)

► Show Figures

342 KiB

Open AccessArticle

Input-output Transfer Function Analysis of a Photometer Circuit Based on an Operational Amplifier

by Wilmar Hernandez

Sensors 2008, 8(1), 35-50; https://doi.org/10.3390/s8010035 - 9 Jan 2008

Cited by 11 | Viewed by 15605

Abstract

In this paper an input-output transfer function analysis based on the frequencyresponse of a photometer circuit based on operational amplifier (op amp) is carried out. Opamps are universally used in monitoring photodetectors and there are a variety of amplifierconnections for this purpose. However, [...] Read more.

In this paper an input-output transfer function analysis based on the frequencyresponse of a photometer circuit based on operational amplifier (op amp) is carried out. Opamps are universally used in monitoring photodetectors and there are a variety of amplifierconnections for this purpose. However, the electronic circuits that are usually used to carryout the signal treatment in photometer circuits introduce some limitations in theperformance of the photometers that influence the selection of the op amps and otherelectronic devices. For example, the bandwidth, slew-rate, noise, input impedance and gain,among other characteristics of the op amp, are often the performance limiting factors ofphotometer circuits. For this reason, in this paper a comparative analysis between twophotodiode amplifier circuits is carried out. One circuit is based on a conventional currentto-voltage converter connection and the other circuit is based on a robust current-to-voltageconverter connection. The results are satisfactory and show that the photodiode amplifierperformance can be improved by using robust control techniques. Full article

(This article belongs to the Special Issue Intelligent Sensors)

► Show Figures

239 KiB

Open AccessArticle

Wavelength Dependence of Photoinduced Microcantilever Bending in the UV-VIS Range

by Lorenz J. Steinbock and Mark Helm

Sensors 2008, 8(1), 23-34; https://doi.org/10.3390/s8010023 - 9 Jan 2008

Cited by 10 | Viewed by 9710

Abstract

Micromechanical devices such as microcantilevers (MC) respond to irradiationwith light by at least two different, photon-mediated processes, which induce MC bendingas a consequence of differential surface stress. The first and slow bending is due to theabsorption of photons, whose energy is transformed into [...] Read more.

Micromechanical devices such as microcantilevers (MC) respond to irradiationwith light by at least two different, photon-mediated processes, which induce MC bendingas a consequence of differential surface stress. The first and slow bending is due to theabsorption of photons, whose energy is transformed into heat and causes bending ofbimetallic microcantilevers due to thermal expansion. The second type of deflection is fastand caused by photons of sufficient energy to promote electrons across the Schottky barrierand thus create charge carriers, resulting in photoinduced stress that causes MC bending. Inthis study, the MC bending response to irradiation with light of wavelengths ranging from250 to 700 nm was investigated. Measurements of the immediate mechanical response tophotoinduced stress as a function of the wavelength of incident light provide an avenue tothe determination of the cut-off wavelength/energy of the Schottky barrier in the MCdevices under investigation. For a gold coated Si3Ni4 microcantilever we measured a cutoffwavelength of 1206 nm, which lies in the range of the literature value of 1100 nm. Full article

(This article belongs to the Special Issue Cantilever, Microcantilevers and Nanocantilever Sensors and Biosensors)

► Show Figures

Journal Menu

Journal Browser

Sensors, Volume 8, Issue 1 (January 2008) – 32 articles , Pages 1-593

Further Information

Guidelines

MDPI Initiatives

Follow MDPI