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Sensors, Volume 12, Issue 1 (January 2012) , Pages 1-1129

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Open AccessEditorial Sensors Best Paper Award 2012
Sensors 2012, 12(1), 1127-1129; https://doi.org/10.3390/s120101127
Received: 20 January 2012 / Accepted: 23 January 2012 / Published: 23 January 2012
Cited by 3 | PDF Full-text (131 KB) | HTML Full-text | XML Full-text
Abstract
Since 2011, Sensors has been instituting an annual award to recognize outstanding papers that are related to sensing technologies and applications and meet the aims, scope and high standards of this journal [1]. To improve the timeliness of the award, we have decided [...] Read more.
Since 2011, Sensors has been instituting an annual award to recognize outstanding papers that are related to sensing technologies and applications and meet the aims, scope and high standards of this journal [1]. To improve the timeliness of the award, we have decided that starting from next year, only papers published in the preceding three years will be eligible for the competition. [...] Full article
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Open AccessArticle Pre-Processing of Point-Data from Contact and Optical 3D Digitization Sensors
Sensors 2012, 12(1), 1100-1126; https://doi.org/10.3390/s120101100
Received: 9 December 2011 / Revised: 5 January 2012 / Accepted: 17 January 2012 / Published: 20 January 2012
Cited by 13 | Viewed by 3514 | PDF Full-text (3687 KB) | HTML Full-text | XML Full-text
Abstract
Contemporary 3D digitization systems employed by reverse engineering (RE) feature ever-growing scanning speeds with the ability to generate large quantity of points in a unit of time. Although advantageous for the quality and efficiency of RE modelling, the huge number of point datas [...] Read more.
Contemporary 3D digitization systems employed by reverse engineering (RE) feature ever-growing scanning speeds with the ability to generate large quantity of points in a unit of time. Although advantageous for the quality and efficiency of RE modelling, the huge number of point datas can turn into a serious practical problem, later on, when the CAD model is generated. In addition, 3D digitization processes are very often plagued by measuring errors, which can be attributed to the very nature of measuring systems, various characteristics of the digitized objects and subjective errors by the operator, which also contribute to problems in the CAD model generation process. This paper presents an integral system for the pre-processing of point data, i.e., filtering, smoothing and reduction, based on a cross-sectional RE approach. In the course of the proposed system development, major emphasis was placed on the module for point data reduction, which was designed according to a novel approach with integrated deviation analysis and fuzzy logic reasoning. The developed system was verified through its application on three case studies, on point data from objects of versatile geometries obtained by contact and laser 3D digitization systems. The obtained results demonstrate the effectiveness of the system. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle Activity Inference for Ambient Intelligence Through Handling Artifacts in a Healthcare Environment
Sensors 2012, 12(1), 1072-1099; https://doi.org/10.3390/s120101072
Received: 29 November 2011 / Revised: 10 January 2012 / Accepted: 16 January 2012 / Published: 20 January 2012
Cited by 25 | Viewed by 3697 | PDF Full-text (2406 KB) | HTML Full-text | XML Full-text
Abstract
Human activity inference is not a simple process due to distinct ways of performing it. Our proposal presents the SCAN framework for activity inference. SCAN is divided into three modules: (1) artifact recognition, (2) activity inference, and (3) activity representation, integrating three important [...] Read more.
Human activity inference is not a simple process due to distinct ways of performing it. Our proposal presents the SCAN framework for activity inference. SCAN is divided into three modules: (1) artifact recognition, (2) activity inference, and (3) activity representation, integrating three important elements of Ambient Intelligence (AmI) (artifact-behavior modeling, event interpretation and context extraction). The framework extends the roaming beat (RB) concept by obtaining the representation using three kinds of technologies for activity inference. The RB is based on both analysis and recognition from artifact behavior for activity inference. A practical case is shown in a nursing home where a system affording 91.35% effectiveness was implemented in situ. Three examples are shown using RB representation for activity representation. Framework description, RB description and CALog system overcome distinct problems such as the feasibility to implement AmI systems, and to show the feasibility for accomplishing the challenges related to activity recognition based on artifact recognition. We discuss how the use of RBs might positively impact the problems faced by designers and developers for recovering information in an easier manner and thus they can develop tools focused on the user. Full article
(This article belongs to the Special Issue Smart Spaces and Ubiquitous Solutions)
Open AccessArticle Computer Reconstruction of Plant Growth and Chlorophyll Fluorescence Emission in Three Spatial Dimensions
Sensors 2012, 12(1), 1052-1071; https://doi.org/10.3390/s120101052
Received: 4 January 2012 / Revised: 13 January 2012 / Accepted: 16 January 2012 / Published: 18 January 2012
Cited by 29 | Viewed by 4120 | PDF Full-text (923 KB) | HTML Full-text | XML Full-text
Abstract
Plant leaves grow and change their orientation as well their emission of chlorophyll fluorescence in time. All these dynamic plant properties can be semi-automatically monitored by a 3D imaging system that generates plant models by the method of coded light illumination, fluorescence imaging [...] Read more.
Plant leaves grow and change their orientation as well their emission of chlorophyll fluorescence in time. All these dynamic plant properties can be semi-automatically monitored by a 3D imaging system that generates plant models by the method of coded light illumination, fluorescence imaging and computer 3D reconstruction. Here, we describe the essentials of the method, as well as the system hardware. We show that the technique can reconstruct, with a high fidelity, the leaf size, the leaf angle and the plant height. The method fails with wilted plants when leaves overlap obscuring their true area. This effect, naturally, also interferes when the method is applied to measure plant growth under water stress. The method is, however, very potent in capturing the plant dynamics under mild stress and without stress. The 3D reconstruction is also highly effective in correcting geometrical factors that distort measurements of chlorophyll fluorescence emission of naturally positioned plant leaves. Full article
(This article belongs to the Section Remote Sensors)
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Open AccessArticle Electronic Voltage and Current Transformers Testing Device
Sensors 2012, 12(1), 1042-1051; https://doi.org/10.3390/s120101042
Received: 2 December 2011 / Revised: 7 January 2012 / Accepted: 10 January 2012 / Published: 18 January 2012
Cited by 5 | Viewed by 3356 | PDF Full-text (307 KB) | HTML Full-text | XML Full-text
Abstract
A method for testing electronic instrument transformers is described, including electronic voltage and current transformers (EVTs, ECTs) with both analog and digital outputs. A testing device prototype is developed. It is based on digital signal processing of the signals that are measured at [...] Read more.
A method for testing electronic instrument transformers is described, including electronic voltage and current transformers (EVTs, ECTs) with both analog and digital outputs. A testing device prototype is developed. It is based on digital signal processing of the signals that are measured at the secondary outputs of the tested transformer and the reference transformer when the same excitation signal is fed to their primaries. The test that estimates the performance of the prototype has been carried out at the National Centre for High Voltage Measurement and the prototype is approved for testing transformers with precision class up to 0.2 at the industrial frequency (50 Hz or 60 Hz). The device is suitable for on-site testing due to its high accuracy, simple structure and low-cost hardware. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle Post-Synapse Model Cell for Synaptic Glutamate Receptor (GluR)-Based Biosensing: Strategy and Engineering to Maximize Ligand-Gated Ion-Flux Achieving High Signal-to-Noise Ratio
Sensors 2012, 12(1), 1035-1041; https://doi.org/10.3390/s120101035
Received: 21 December 2011 / Revised: 13 January 2012 / Accepted: 13 January 2012 / Published: 18 January 2012
Viewed by 3935 | PDF Full-text (186 KB) | HTML Full-text | XML Full-text
Abstract
Cell-based biosensing is a “smart” way to obtain efficacy-information on the effect of applied chemical on cellular biological cascade. We have proposed an engineered post-synapse model cell-based biosensors to investigate the effects of chemicals on ionotropic glutamate receptor (GluR), which is a focus [...] Read more.
Cell-based biosensing is a “smart” way to obtain efficacy-information on the effect of applied chemical on cellular biological cascade. We have proposed an engineered post-synapse model cell-based biosensors to investigate the effects of chemicals on ionotropic glutamate receptor (GluR), which is a focus of attention as a molecular target for clinical neural drug discovery. The engineered model cell has several advantages over native cells, including improved ease of handling and better reproducibility in the application of cell-based biosensors. However, in general, cell-based biosensors often have low signal-to-noise (S/N) ratios due to the low level of cellular responses. In order to obtain a higher S/N ratio in model cells, we have attempted to design a tactic model cell with elevated cellular response. We have revealed that the increase GluR expression level is not directly connected to the amplification of cellular responses because the saturation of surface expression of GluR, leading to a limit on the total ion influx. Furthermore, coexpression of GluR with a voltage-gated potassium channel increased Ca2+ ion influx beyond levels obtained with saturating amounts of GluR alone. The construction of model cells based on strategy of amplifying ion flux per individual receptors can be used to perform smart cell-based biosensing with an improved S/N ratio. Full article
(This article belongs to the Special Issue Live Cell-Based Sensors)
Open AccessArticle Optimal Methods of RTK-GPS/Accelerometer Integration to Monitor the Displacement of Structures
Sensors 2012, 12(1), 1014-1034; https://doi.org/10.3390/s120101014
Received: 24 November 2011 / Revised: 6 January 2012 / Accepted: 9 January 2012 / Published: 17 January 2012
Cited by 25 | Viewed by 4641 | PDF Full-text (1508 KB) | HTML Full-text | XML Full-text
Abstract
The accurate measurement of diverse displacements of structures is an important index for the evaluation of a structure’s safety. In this study, a comparative analysis was conducted to determine the integrated RTK-GPS/accelerometer method that can provide the most precise structure displacement measurements. For [...] Read more.
The accurate measurement of diverse displacements of structures is an important index for the evaluation of a structure’s safety. In this study, a comparative analysis was conducted to determine the integrated RTK-GPS/accelerometer method that can provide the most precise structure displacement measurements. For this purpose, three methods of calculating the dynamic displacements from the acceleration data were comparatively analyzed. In addition, two methods of determining dynamic, static, and quasi-static displacements by integrating the displacements measured from the RTK-GPS system and the accelerometer were also comparatively analyzed. To ensure precise comparison results, a cantilever beam was manufactured onto which diverse types of displacements were generated to evaluate the measurement accuracy by method. Linear variable differential transformer (LVDT) measurements were used as references for the evaluation to ensure accuracy. The study results showed that the most suitable method of measuring the dynamic displacement with the accelerometer was to calculate the displacement by filtering and double-integrating the acceleration data using the FIR band-pass filter. The integration method that uses frequency-based displacement extraction was most appropriate for the integrated RTK-GPS/accelerometer method of comprehensively measuring the dynamic, static, and quasi-static displacements. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle FBG Sensor for Contact Level Monitoring and Prediction of Perforation in Cardiac Ablation
Sensors 2012, 12(1), 1002-1013; https://doi.org/10.3390/s120101002
Received: 25 November 2011 / Revised: 3 January 2012 / Accepted: 14 January 2012 / Published: 17 January 2012
Cited by 16 | Viewed by 3970 | PDF Full-text (696 KB) | HTML Full-text | XML Full-text
Abstract
Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, [...] Read more.
Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, the catheter is accidently pushed through the heart wall due to the application of excessive force. Despite the various capabilities of currently available technology, there has yet to be any data establishing how cardiac perforation can be reliably predicted. Thus, two new FBG based sensor prototypes were developed to monitor contact levels and predict perforation. Two live sheep were utilized during the study. It was observed during operation that peaks appeared in rhythm with the heart rate whenever firm contact was made between the sensor and the endocardial wall. The magnitude of these peaks varied with pressure applied by the operator. Lastly, transmural perforation of the left atrial wall was characterized by a visible loading phase and a rapid signal drop-off correlating to perforation. A possible pre-perforation signal was observed for the epoxy-based sensor in the form of a slight signal reversal (12–26% of loading phase magnitude) prior to perforation (occurring over 8 s). Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2012)
Open AccessArticle Transformation of Hand-Shape Features for a Biometric Identification Approach
Sensors 2012, 12(1), 987-1001; https://doi.org/10.3390/s120100987
Received: 28 November 2011 / Revised: 5 January 2012 / Accepted: 6 January 2012 / Published: 16 January 2012
Cited by 3 | Viewed by 3500 | PDF Full-text (390 KB) | HTML Full-text | XML Full-text
Abstract
The present work presents a biometric identification system for hand shape identification. The different contours have been coded based on angular descriptions forming a Markov chain descriptor. Discrete Hidden Markov Models (DHMM), each representing a target identification class, have been trained with such [...] Read more.
The present work presents a biometric identification system for hand shape identification. The different contours have been coded based on angular descriptions forming a Markov chain descriptor. Discrete Hidden Markov Models (DHMM), each representing a target identification class, have been trained with such chains. Features have been calculated from a kernel based on the HMM parameter descriptors. Finally, supervised Support Vector Machines were used to classify parameters from the DHMM kernel. First, the system was modelled using 60 users to tune the DHMM and DHMM_kernel+SVM configuration parameters and finally, the system was checked with the whole database (GPDS database, 144 users with 10 samples per class). Our experiments have obtained similar results in both cases, demonstrating a scalable, stable and robust system. Our experiments have achieved an upper success rate of 99.87% for the GPDS database using three hand samples per class in training mode, and seven hand samples in test mode. Secondly, the authors have verified their algorithms using another independent and public database (the UST database). Our approach has reached 100% and 99.92% success for right and left hand, respectively; showing the robustness and independence of our algorithms. This success was found using as features the transformation of 100 points hand shape with our DHMM kernel, and as classifier Support Vector Machines with linear separating functions, with similar success. Full article
(This article belongs to the Special Issue Hand-Based Biometrics Sensors and Systems)
Open AccessArticle Prediction of BOD, COD, and Total Nitrogen Concentrations in a Typical Urban River Using a Fluorescence Excitation-Emission Matrix with PARAFAC and UV Absorption Indices
Sensors 2012, 12(1), 972-986; https://doi.org/10.3390/s120100972
Received: 6 December 2011 / Revised: 6 January 2012 / Accepted: 13 January 2012 / Published: 16 January 2012
Cited by 82 | Viewed by 4636 | PDF Full-text (1881 KB) | HTML Full-text | XML Full-text
Abstract
The development of a real-time monitoring tool for the estimation of water quality is essential for efficient management of river pollution in urban areas. The Gap River in Korea is a typical urban river, which is affected by the effluent of a wastewater [...] Read more.
The development of a real-time monitoring tool for the estimation of water quality is essential for efficient management of river pollution in urban areas. The Gap River in Korea is a typical urban river, which is affected by the effluent of a wastewater treatment plant (WWTP) and various anthropogenic activities. In this study, fluorescence excitation-emission matrices (EEM) with parallel factor analysis (PARAFAC) and UV absorption values at 220 nm and 254 nm were applied to evaluate the estimation capabilities for biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total nitrogen (TN) concentrations of the river samples. Three components were successfully identified by the PARAFAC modeling from the fluorescence EEM data, in which each fluorophore group represents microbial humic-like (C1), terrestrial humic-like organic substances (C2), and protein-like organic substances (C3), and UV absorption indices (UV220 and UV254), and the score values of the three PARAFAC components were selected as the estimation parameters for the nitrogen and the organic pollution of the river samples. Among the selected indices, UV220, C3 and C1 exhibited the highest correlation coefficients with BOD, COD, and TN concentrations, respectively. Multiple regression analysis using UV220 and C3 demonstrated the enhancement of the prediction capability for TN. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Sap Flow Sensors: Construction, Quality Control and Comparison
Sensors 2012, 12(1), 954-971; https://doi.org/10.3390/s120100954
Received: 1 December 2011 / Revised: 11 January 2012 / Accepted: 12 January 2012 / Published: 16 January 2012
Cited by 20 | Viewed by 5331 | PDF Full-text (498 KB) | HTML Full-text | XML Full-text
Abstract
This work provides a design for two types of sensors, based on the thermal dissipation and heat ratio methods of sap flow calculation, for moderate to large scale deployments for the purpose of monitoring tree transpiration. These designs include a procedure for making [...] Read more.
This work provides a design for two types of sensors, based on the thermal dissipation and heat ratio methods of sap flow calculation, for moderate to large scale deployments for the purpose of monitoring tree transpiration. These designs include a procedure for making these sensors, a quality control method for the final products, and a complete list of components with vendors and pricing information. Both sensor designs were field tested alongside a commercial sap flow sensor to assess their performance and show the importance for quality controlling the sensor outputs. Results show that for roughly 2% of the cost of commercial sensors, self-made sap flow sensors can provide acceptable estimates of the sap flow measurements compared to the commercial sensors. Full article
(This article belongs to the Section Physical Sensors)
Open AccessReview Recent Advances in Polymeric Materials Used as Electron Mediators and Immobilizing Matrices in Developing Enzyme Electrodes
Sensors 2012, 12(1), 923-953; https://doi.org/10.3390/s120100923
Received: 14 December 2011 / Revised: 15 January 2012 / Accepted: 16 January 2012 / Published: 16 January 2012
Cited by 30 | Viewed by 4147 | PDF Full-text (629 KB) | HTML Full-text | XML Full-text
Abstract
Different classes of polymeric materials such as nanomaterials, sol-gel materials, conducting polymers, functional polymers and biomaterials have been used in the design of sensors and biosensors. Various methods have been used, for example from direct adsorption, covalent bonding, crossing-linking with glutaraldehyde on composites [...] Read more.
Different classes of polymeric materials such as nanomaterials, sol-gel materials, conducting polymers, functional polymers and biomaterials have been used in the design of sensors and biosensors. Various methods have been used, for example from direct adsorption, covalent bonding, crossing-linking with glutaraldehyde on composites to mixing the enzymes or use of functionalized beads for the design of sensors and biosensors using these polymeric materials in recent years. It is widely acknowledged that analytical sensing at electrodes modified with polymeric materials results in low detection limits, high sensitivities, lower applied potential, good stability, efficient electron transfer and easier immobilization of enzymes on electrodes such that sensing and biosensing of environmental pollutants is made easier. However, there are a number of challenges to be addressed in order to fulfill the applications of polymeric based polymers such as cost and shortening the long laboratory synthetic pathways involved in sensor preparation. Furthermore, the toxicological effects on flora and fauna of some of these polymeric materials have not been well studied. Given these disadvantages, efforts are now geared towards introducing low cost biomaterials that can serve as alternatives for the development of novel electrochemical sensors and biosensors. This review highlights recent contributions in the development of the electrochemical sensors and biosensors based on different polymeric material. The synergistic action of some of these polymeric materials and nanocomposites imposed when combined on electrode during sensing is discussed. Full article
(This article belongs to the Section Biosensors)
Open AccessArticle Sheathless Size-Based Acoustic Particle Separation
Sensors 2012, 12(1), 905-922; https://doi.org/10.3390/s120100905
Received: 23 November 2011 / Revised: 4 January 2012 / Accepted: 14 January 2012 / Published: 16 January 2012
Cited by 47 | Viewed by 6239 | PDF Full-text (1680 KB) | HTML Full-text | XML Full-text
Abstract
Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence [...] Read more.
Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined up at the center of the channel without introducing any external sheath flow. The particles are then entered into the second stage where particles are driven towards the off-center pressure nodes for size based separation. The larger particles are exposed to more lateral displacement in the channel due to the acoustic force differences. Consequently, different-size particles are separated into multiple collection outlets. The prominent feature of the present microfluidic platform is that the device does not require the use of the sheath flow for positioning and aligning of particles. Instead, the sheathless flow focusing and separation are integrated within a single microfluidic device and accomplished simultaneously. In this paper, we demonstrated two different particle size-resolution separations; (1) 3 µm and 10 µm and (2) 3 µm and 5 µm. Also, the effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. These technologies have potential to impact broadly various areas including the essential microfluidic components for lab-on-a-chip system and integrated biological and biomedical applications. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle Phantom with Pulsatile Arteries to Investigate the Influence of Blood Vessel Depth on Pulse Oximeter Signal Strength
Sensors 2012, 12(1), 895-904; https://doi.org/10.3390/s120100895
Received: 29 November 2011 / Revised: 29 December 2011 / Accepted: 10 January 2012 / Published: 16 January 2012
Cited by 9 | Viewed by 4251 | PDF Full-text (446 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes a three-layer head phantom with artificial pulsating arteries at five different depths (1.2 mm, 3.7 mm, 6.8 mm, 9.6 mm and 11.8 mm). The structure enables formation of spatially and temporally varying tissue properties similar to those of living tissues. [...] Read more.
This paper describes a three-layer head phantom with artificial pulsating arteries at five different depths (1.2 mm, 3.7 mm, 6.8 mm, 9.6 mm and 11.8 mm). The structure enables formation of spatially and temporally varying tissue properties similar to those of living tissues. In our experiment, pressure pulses were generated in the arteries by an electronically controlled pump. The physical and optical parameters of the layers and the liquid in the artificial arteries were similar to those of real tissues and blood. The amplitude of the pulsating component of the light returning from the phantom tissues was measured at each artery depth mentioned above. The build-up of the in-house-developed pulse oximeter used for performing the measurements and the physical layout of the measuring head are described. The radiant flux generated by the LED on the measuring head was measured to be 1.8 mW at 910 nm. The backscattered radiant flux was measured, and found to be 0.46 nW (0.26 ppm), 0.55 nW (0.31 ppm), and 0.18 nW (0.10 ppm) for the 1.2 mm, 3.7 mm and 6.8 mm arteries, respectively. In the case of the 9.6 mm and 11.8 mm arteries, useful measurement data were not obtained owing to weak signals. We simulated the phantom with the arteries at the above-mentioned five depths and at two additional ones (2.5 mm and 5.3 mm in depth) using the Monte Carlo method. The measurement results were verified by the simulation results. We concluded that in case of 11 mm source-detector separation the arteries at a depth of about 2.5 mm generate the strongest pulse oximeter signal level in a tissue system comprising three layers of thicknesses: 1.5 mm (skin), 5.0 mm (skull), and > 50 mm (brain). Full article
(This article belongs to the Special Issue Optical Sensors in Medicine)
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Open AccessEditorial Paper Withdrawn Before the Issue Release
Sensors 2012, 12(1), 878-894; https://doi.org/10.3390/s120100878
Received: 8 December 2011 / Revised: 11 January 2012 / Accepted: 11 January 2012 / Published: 16 January 2012
Viewed by 2980 | PDF Full-text (97 KB) | HTML Full-text | XML Full-text
Abstract
The following paper “Juan V. Capella, Alberto Bonastre, Miguel Peris and Rafael Ors. Distributed In-Line Analysis of Water Pollution in a Spanish Lake. Sensors 2012, 12, 878-894” has been withdrawn at the request of the authors before the issue release of [...] Read more.
The following paper “Juan V. Capella, Alberto Bonastre, Miguel Peris and Rafael Ors. Distributed In-Line Analysis of Water Pollution in a Spanish Lake. Sensors 2012, 12, 878-894” has been withdrawn at the request of the authors before the issue release of Sensors Volume 12, Issue 1. We apologize for any inconvenience this may cause. Full article
Open AccessArticle Real Time Corner Detection for Miniaturized Electro-Optical Sensors Onboard Small Unmanned Aerial Systems
Sensors 2012, 12(1), 863-877; https://doi.org/10.3390/s120100863
Received: 6 December 2011 / Revised: 28 December 2011 / Accepted: 29 December 2011 / Published: 12 January 2012
Cited by 12 | Viewed by 3814 | PDF Full-text (500 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the target detection algorithm for the image processor of a vision-based system that is installed onboard an unmanned helicopter. It has been developed in the framework of a project of the French national aerospace research center Office National d’Etudes et [...] Read more.
This paper describes the target detection algorithm for the image processor of a vision-based system that is installed onboard an unmanned helicopter. It has been developed in the framework of a project of the French national aerospace research center Office National d’Etudes et de Recherches Aérospatiales (ONERA) which aims at developing an air-to-ground target tracking mission in an unknown urban environment. In particular, the image processor must detect targets and estimate ground motion in proximity of the detected target position. Concerning the target detection function, the analysis has dealt with realizing a corner detection algorithm and selecting the best choices in terms of edge detection methods, filtering size and type and the more suitable criterion of detection of the points of interest in order to obtain a very fast algorithm which fulfills the computation load requirements. The compared criteria are the Harris-Stephen and the Shi-Tomasi, ones, which are the most widely used in literature among those based on intensity. Experimental results which illustrate the performance of the developed algorithm and demonstrate that the detection time is fully compliant with the requirements of the real-time system are discussed. Full article
(This article belongs to the Section Remote Sensors)
Open AccessArticle A Low-Complexity Geometric Bilateration Method for Localization in Wireless Sensor Networks and Its Comparison with Least-Squares Methods
Sensors 2012, 12(1), 839-862; https://doi.org/10.3390/s120100839
Received: 12 December 2011 / Revised: 9 January 2012 / Accepted: 10 January 2012 / Published: 12 January 2012
Cited by 17 | Viewed by 5643 | PDF Full-text (2334 KB) | HTML Full-text | XML Full-text
Abstract
This research presents a distributed and formula-based bilateration algorithm that can be used to provide initial set of locations. In this scheme each node uses distance estimates to anchors to solve a set of circle-circle intersection (CCI) problems, solved through a purely geometric [...] Read more.
This research presents a distributed and formula-based bilateration algorithm that can be used to provide initial set of locations. In this scheme each node uses distance estimates to anchors to solve a set of circle-circle intersection (CCI) problems, solved through a purely geometric formulation. The resulting CCIs are processed to pick those that cluster together and then take the average to produce an initial node location. The algorithm is compared in terms of accuracy and computational complexity with a Least-Squares localization algorithm, based on the Levenberg–Marquardt methodology. Results in accuracy vs. computational performance show that the bilateration algorithm is competitive compared with well known optimized localization algorithms. Full article
(This article belongs to the Special Issue Collaborative Sensors)
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Open AccessArticle Reliability and Availability Evaluation of Wireless Sensor Networks for Industrial Applications
Sensors 2012, 12(1), 806-838; https://doi.org/10.3390/s120100806
Received: 9 December 2011 / Revised: 5 January 2012 / Accepted: 10 January 2012 / Published: 12 January 2012
Cited by 97 | Viewed by 7333 | PDF Full-text (746 KB) | HTML Full-text | XML Full-text
Abstract
Wireless Sensor Networks (WSN) currently represent the best candidate to be adopted as the communication solution for the last mile connection in process control and monitoring applications in industrial environments. Most of these applications have stringent dependability (reliability and availability) requirements, as a [...] Read more.
Wireless Sensor Networks (WSN) currently represent the best candidate to be adopted as the communication solution for the last mile connection in process control and monitoring applications in industrial environments. Most of these applications have stringent dependability (reliability and availability) requirements, as a system failure may result in economic losses, put people in danger or lead to environmental damages. Among the different type of faults that can lead to a system failure, permanent faults on network devices have a major impact. They can hamper communications over long periods of time and consequently disturb, or even disable, control algorithms. The lack of a structured approach enabling the evaluation of permanent faults, prevents system designers to optimize decisions that minimize these occurrences. In this work we propose a methodology based on an automatic generation of a fault tree to evaluate the reliability and availability of Wireless Sensor Networks, when permanent faults occur on network devices. The proposal supports any topology, different levels of redundancy, network reconfigurations, criticality of devices and arbitrary failure conditions. The proposed methodology is particularly suitable for the design and validation of Wireless Sensor Networks when trying to optimize its reliability and availability requirements. Full article
(This article belongs to the Section Sensor Networks)
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Open AccessArticle Smart Sensor for Real-Time Quantification of Common Symptoms Present in Unhealthy Plants
Sensors 2012, 12(1), 784-805; https://doi.org/10.3390/s120100784
Received: 16 November 2011 / Revised: 7 January 2012 / Accepted: 10 January 2012 / Published: 11 January 2012
Cited by 17 | Viewed by 5502 | PDF Full-text (2677 KB) | HTML Full-text | XML Full-text
Abstract
Plant responses to physiological function disorders are called symptoms and they are caused principally by pathogens and nutritional deficiencies. Plant symptoms are commonly used as indicators of the health and nutrition status of plants. Nowadays, the most popular method to quantify plant symptoms [...] Read more.
Plant responses to physiological function disorders are called symptoms and they are caused principally by pathogens and nutritional deficiencies. Plant symptoms are commonly used as indicators of the health and nutrition status of plants. Nowadays, the most popular method to quantify plant symptoms is based on visual estimations, consisting on evaluations that raters give based on their observation of plant symptoms; however, this method is inaccurate and imprecise because of its obvious subjectivity. Computational Vision has been employed in plant symptom quantification because of its accuracy and precision. Nevertheless, the systems developed so far lack in-situ, real-time and multi-symptom analysis. There exist methods to obtain information about the health and nutritional status of plants based on reflectance and chlorophyll fluorescence, but they use expensive equipment and are frequently destructive. Therefore, systems able of quantifying plant symptoms overcoming the aforementioned disadvantages that can serve as indicators of health and nutrition in plants are desirable. This paper reports an FPGA-based smart sensor able to perform non-destructive, real-time and in-situ analysis of leaf images to quantify multiple symptoms presented by diseased and malnourished plants; this system can serve as indicator of the health and nutrition in plants. The effectiveness of the proposed smart-sensor was successfully tested by analyzing diseased and malnourished plants. Full article
(This article belongs to the Section Biosensors)
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Open AccessArticle Local Area Water Removal Analysis of a Proton Exchange Membrane Fuel Cell under Gas Purge Conditions
Sensors 2012, 12(1), 768-783; https://doi.org/10.3390/s120100768
Received: 9 December 2011 / Revised: 24 December 2011 / Accepted: 4 January 2012 / Published: 11 January 2012
Cited by 4 | Viewed by 3288 | PDF Full-text (1360 KB) | HTML Full-text | XML Full-text
Abstract
In this study, local area water content distribution under various gas purging conditions are experimentally analyzed for the first time. The local high frequency resistance (HFR) is measured using novel micro sensors. The results reveal that the liquid water removal rate in a [...] Read more.
In this study, local area water content distribution under various gas purging conditions are experimentally analyzed for the first time. The local high frequency resistance (HFR) is measured using novel micro sensors. The results reveal that the liquid water removal rate in a membrane electrode assembly (MEA) is non-uniform. In the under-the-channel area, the removal of liquid water is governed by both convective and diffusive flux of the through-plane drying. Thus, almost all of the liquid water is removed within 30 s of purging with gas. However, liquid water that is stored in the under-the-rib area is not easy to remove during 1 min of gas purging. Therefore, the re-hydration of the membrane by internal diffusive flux is faster than that in the under-the-channel area. Consequently, local fuel starvation and membrane degradation can degrade the performance of a fuel cell that is started from cold. Full article
(This article belongs to the Special Issue Ultra-Small Sensor Systems and Components)
Open AccessArticle Soil Moisture Sensing via Swept Frequency Based Microwave Sensors
Sensors 2012, 12(1), 753-767; https://doi.org/10.3390/s120100753
Received: 24 November 2011 / Revised: 28 December 2011 / Accepted: 29 December 2011 / Published: 11 January 2012
Cited by 10 | Viewed by 4101 | PDF Full-text (272 KB) | HTML Full-text | XML Full-text
Abstract
There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive [...] Read more.
There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications. Full article
(This article belongs to the Section Physical Sensors)
Open AccessReview The Evolution of the Bacterial Luciferase Gene Cassette (lux) as a Real-Time Bioreporter
Sensors 2012, 12(1), 732-752; https://doi.org/10.3390/s120100732
Received: 26 November 2011 / Revised: 30 December 2011 / Accepted: 9 January 2012 / Published: 11 January 2012
Cited by 36 | Viewed by 5311 | PDF Full-text (749 KB) | HTML Full-text | XML Full-text
Abstract
The bacterial luciferase gene cassette (lux) is unique among bioluminescent bioreporter systems due to its ability to synthesize and/or scavenge all of the substrate compounds required for its production of light. As a result, the lux system has the unique ability [...] Read more.
The bacterial luciferase gene cassette (lux) is unique among bioluminescent bioreporter systems due to its ability to synthesize and/or scavenge all of the substrate compounds required for its production of light. As a result, the lux system has the unique ability to autonomously produce a luminescent signal, either continuously or in response to the presence of a specific trigger, across a wide array of organismal hosts. While originally employed extensively as a bacterial bioreporter system for the detection of specific chemical signals in environmental samples, the use of lux as a bioreporter technology has continuously expanded over the last 30 years to include expression in eukaryotic cells such as Saccharomyces cerevisiae and even human cell lines as well. Under these conditions, the lux system has been developed for use as a biomedical detection tool for toxicity screening and visualization of tumors in small animal models. As the technologies for lux signal detection continue to improve, it is poised to become one of the first fully implantable detection systems for intra-organismal optical detection through direct marriage to an implantable photon-detecting digital chip. This review presents the basic biochemical background that allows the lux system to continuously autobioluminesce and highlights the important milestones in the use of lux-based bioreporters as they have evolved from chemical detection platforms in prokaryotic bacteria to rodent-based tumorigenesis study targets. In addition, the future of lux imaging using integrated circuit microluminometry to image directly within a living host in real-time will be introduced and its role in the development of dose/response therapeutic systems will be highlighted. Full article
(This article belongs to the Special Issue Live Cell-Based Sensors)
Open AccessArticle Underwater Sensor Networks: A New Energy Efficient and Robust Architecture
Sensors 2012, 12(1), 704-731; https://doi.org/10.3390/s120100704
Received: 30 November 2011 / Revised: 5 January 2012 / Accepted: 9 January 2012 / Published: 10 January 2012
Cited by 35 | Viewed by 5650 | PDF Full-text (2128 KB) | HTML Full-text | XML Full-text
Abstract
The specific characteristics of underwater environments introduce new challenges for networking protocols. In this paper, a specialized architecture for underwater sensor networks (UWSNs) is proposed and evaluated. Experiments are conducted in order to analyze the suitability of this protocol for the subaquatic transmission [...] Read more.
The specific characteristics of underwater environments introduce new challenges for networking protocols. In this paper, a specialized architecture for underwater sensor networks (UWSNs) is proposed and evaluated. Experiments are conducted in order to analyze the suitability of this protocol for the subaquatic transmission medium. Moreover, different scheduling techniques are applied to the architecture in order to study their performance. In addition, given the harsh conditions of the underwater medium, different retransmission methods are combined with the scheduling techniques. Finally, simulation results illustrate the performance achievements of the proposed protocol in end-to-end delay, packet delivery ratio and energy consumption, showing that this protocol can be very suitable for the underwater medium. Full article
(This article belongs to the Special Issue Underwater Sensor Nodes and Underwater Sensor Networks)
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Open AccessArticle A Feedfordward Adaptive Controller to Reduce the Imaging Time of Large-Sized Biological Samples with a SPM-Based Multiprobe Station
Sensors 2012, 12(1), 686-703; https://doi.org/10.3390/s120100686
Received: 18 November 2011 / Revised: 5 January 2012 / Accepted: 6 January 2012 / Published: 10 January 2012
Cited by 3 | Viewed by 3212 | PDF Full-text (3948 KB) | HTML Full-text | XML Full-text
Abstract
The time required to image large samples is an important limiting factor in SPM-based systems. In multiprobe setups, especially when working with biological samples, this drawback can make impossible to conduct certain experiments. In this work, we present a feedfordward controller based on [...] Read more.
The time required to image large samples is an important limiting factor in SPM-based systems. In multiprobe setups, especially when working with biological samples, this drawback can make impossible to conduct certain experiments. In this work, we present a feedfordward controller based on bang-bang and adaptive controls. The controls are based in the difference between the maximum speeds that can be used for imaging depending on the flatness of the sample zone. Topographic images of Escherichia coli bacteria samples were acquired using the implemented controllers. Results show that to go faster in the flat zones, rather than using a constant scanning speed for the whole image, speeds up the imaging process of large samples by up to a 4x factor. Full article
(This article belongs to the Special Issue Control Systems and Robotics in Bioengineering)
Open AccessReview Multipath Routing in Wireless Sensor Networks: Survey and Research Challenges
Sensors 2012, 12(1), 650-685; https://doi.org/10.3390/s120100650
Received: 8 November 2011 / Revised: 3 January 2012 / Accepted: 4 January 2012 / Published: 9 January 2012
Cited by 176 | Viewed by 8244 | PDF Full-text (516 KB) | HTML Full-text | XML Full-text
Abstract
A wireless sensor network is a large collection of sensor nodes with limited power supply and constrained computational capability. Due to the restricted communication range and high density of sensor nodes, packet forwarding in sensor networks is usually performed through multi-hop data transmission. [...] Read more.
A wireless sensor network is a large collection of sensor nodes with limited power supply and constrained computational capability. Due to the restricted communication range and high density of sensor nodes, packet forwarding in sensor networks is usually performed through multi-hop data transmission. Therefore, routing in wireless sensor networks has been considered an important field of research over the past decade. Nowadays, multipath routing approach is widely used in wireless sensor networks to improve network performance through efficient utilization of available network resources. Accordingly, the main aim of this survey is to present the concept of the multipath routing approach and its fundamental challenges, as well as the basic motivations for utilizing this technique in wireless sensor networks. In addition, we present a comprehensive taxonomy on the existing multipath routing protocols, which are especially designed for wireless sensor networks. We highlight the primary motivation behind the development of each protocol category and explain the operation of different protocols in detail, with emphasis on their advantages and disadvantages. Furthermore, this paper compares and summarizes the state-of-the-art multipath routing techniques from the network application point of view. Finally, we identify open issues for further research in the development of multipath routing protocols for wireless sensor networks. Full article
(This article belongs to the Section Sensor Networks)
Open AccessArticle Toward Sensor-Based Context Aware Systems
Sensors 2012, 12(1), 632-649; https://doi.org/10.3390/s120100632
Received: 12 December 2011 / Revised: 31 December 2011 / Accepted: 3 January 2012 / Published: 9 January 2012
Cited by 14 | Viewed by 4064 | PDF Full-text (363 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a methodology for sensor data interpretation that can combine sensor outputs with contexts represented as sets of annotated business rules. Sensor readings are interpreted to generate events labeled with the appropriate type and level of uncertainty. Then, the appropriate context [...] Read more.
This paper proposes a methodology for sensor data interpretation that can combine sensor outputs with contexts represented as sets of annotated business rules. Sensor readings are interpreted to generate events labeled with the appropriate type and level of uncertainty. Then, the appropriate context is selected. Reconciliation of different uncertainty types is achieved by a simple technique that moves uncertainty from events to business rules by generating combs of standard Boolean predicates. Finally, context rules are evaluated together with the events to take a decision. The feasibility of our idea is demonstrated via a case study where a context-reasoning engine has been connected to simulated heartbeat sensors using prerecorded experimental data. We use sensor outputs to identify the proper context of operation of a system and trigger decision-making based on context information. Full article
(This article belongs to the Special Issue Selected Papers from FGIT 2010)
Open AccessReview Aptamers and Their Biological Applications
Sensors 2012, 12(1), 612-631; https://doi.org/10.3390/s120100612
Received: 29 November 2011 / Revised: 31 December 2011 / Accepted: 4 January 2012 / Published: 9 January 2012
Cited by 274 | Viewed by 9397 | PDF Full-text (922 KB) | HTML Full-text | XML Full-text
Abstract
Recently, aptamers have attracted the attention of many scientists, because they not only have all of the advantages of antibodies, but also have unique merits, such as thermal stability, low cost, and unlimited applications. In this review, we present the reasons why aptamers [...] Read more.
Recently, aptamers have attracted the attention of many scientists, because they not only have all of the advantages of antibodies, but also have unique merits, such as thermal stability, low cost, and unlimited applications. In this review, we present the reasons why aptamers are known as alternatives to antibodies. Furthermore, several types of in vitro selection processes, including nitrocellulose membrane filtration, affinity chromatography, magnetic bead, and capillary electrophoresis-based selection methods, are explained in detail. We also introduce various applications of aptamers for the diagnosis of diseases and detection of small molecules. Numerous analytical techniques, such as electrochemical, colorimetric, optical, and mass-sensitive methods, can be utilized to detect targets, due to convenient modifications and the stability of aptamers. Finally, several medical and analytical applications of aptamers are presented. In summary, aptamers are promising materials for diverse areas, not just as alternatives to antibodies, but as the core components of medical and analytical equipment. Full article
(This article belongs to the Special Issue Biomarkers and Nanosensors: New Approaches for Biology and Medicine)
Open AccessArticle FPGA Implementation for Real-Time Background Subtraction Based on Horprasert Model
Sensors 2012, 12(1), 585-611; https://doi.org/10.3390/s120100585
Received: 10 December 2011 / Revised: 28 December 2011 / Accepted: 3 January 2012 / Published: 5 January 2012
Cited by 23 | Viewed by 4438 | PDF Full-text (6181 KB) | HTML Full-text | XML Full-text
Abstract
Background subtraction is considered the first processing stage in video surveillance systems, and consists of determining objects in movement in a scene captured by a static camera. It is an intensive task with a high computational cost. This work proposes an embedded novel [...] Read more.
Background subtraction is considered the first processing stage in video surveillance systems, and consists of determining objects in movement in a scene captured by a static camera. It is an intensive task with a high computational cost. This work proposes an embedded novel architecture on FPGA which is able to extract the background on resource-limited environments and offers low degradation (produced because of the hardware-friendly model modification). In addition, the original model is extended in order to detect shadows and improve the quality of the segmentation of the moving objects. We have analyzed the resource consumption and performance in Spartan3 Xilinx FPGAs and compared to others works available on the literature, showing that the current architecture is a good trade-off in terms of accuracy, performance and resources utilization. With less than a 65% of the resources utilization of a XC3SD3400 Spartan-3A low-cost family FPGA, the system achieves a frequency of 66.5 MHz reaching 32.8 fps with resolution 1,024 x 1,024 pixels, and an estimated power consumption of 5.76 W. Full article
(This article belongs to the Section Physical Sensors)
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Open AccessArticle Visual Sensor Based Abnormal Event Detection with Moving Shadow Removal in Home Healthcare Applications
Sensors 2012, 12(1), 573-584; https://doi.org/10.3390/s120100573
Received: 2 November 2011 / Revised: 27 December 2011 / Accepted: 3 January 2012 / Published: 5 January 2012
Cited by 29 | Viewed by 3462 | PDF Full-text (821 KB) | HTML Full-text | XML Full-text
Abstract
Vision-based abnormal event detection for home healthcare systems can be greatly improved using visual sensor-based techniques able to detect, track and recognize objects in the scene. However, in moving object detection and tracking processes, moving cast shadows can be misclassified as part of [...] Read more.
Vision-based abnormal event detection for home healthcare systems can be greatly improved using visual sensor-based techniques able to detect, track and recognize objects in the scene. However, in moving object detection and tracking processes, moving cast shadows can be misclassified as part of objects or moving objects. Shadow removal is an essential step for developing video surveillance systems. The goal of the primary is to design novel computer vision techniques that can extract objects more accurately and discriminate between abnormal and normal activities. To improve the accuracy of object detection and tracking, our proposed shadow removal algorithm is employed. Abnormal event detection based on visual sensor by using shape features variation and 3-D trajectory is presented to overcome the low fall detection rate. The experimental results showed that the success rate of detecting abnormal events was 97% with a false positive rate of 2%. Our proposed algorithm can allow distinguishing diverse fall activities such as forward falls, backward falls, and falling asides from normal activities. Full article
(This article belongs to the Section Physical Sensors)
Open AccessReview Exploring Transduction Mechanisms of Protein Transduction Domains (PTDs) in Living Cells Utilizing Single-Quantum Dot Tracking (SQT) Technology
Sensors 2012, 12(1), 549-572; https://doi.org/10.3390/s120100549
Received: 30 November 2011 / Revised: 30 December 2011 / Accepted: 31 December 2011 / Published: 5 January 2012
Cited by 15 | Viewed by 3864 | PDF Full-text (1211 KB) | HTML Full-text | XML Full-text
Abstract
Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and to [...] Read more.
Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and to identify the rate-limiting steps. Because of technical limitations for imaging PTD behavior on cells with conventional fluorescent-dyes, how PTDs enter the cells has been a topic of much debate. Utilizing quantum dots (QDs), we recently tracked the behavior of PTD that was derived from HIV-1 Tat (TatP) in living cells at the single-molecule level with 7-nm special precision. In this review article, we initially summarize the controversy on TatP entry mechanisms; thereafter, we will focus on our recent findings on single-TatP-QD tracking (SQT), to identify the major sequential steps of intracellular delivery in living cells and to discuss how SQT can easily provide direct information on TatP entry mechanisms. As a primer for SQT study, we also discuss the latest findings on single particle tracking of various molecules on the plasma membrane. Finally, we discuss the problems of QDs and the challenges for the future in utilizing currently available QD probes for SQT. In conclusion, direct identification of the rate-limiting steps of PTD entry with SQT should dramatically improve the methods for enhancing transduction efficiency. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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