A new surface plasmon resonance sensor for high-throughput screening applications

We report a new high-throughput surface plasmon resonance (SPR) sensor based on combination of SPR imaging with polarization contrast and a spatially patterned multilayer SPR structure. We demonstrate that this approach offers numerous advantageous features including high-contrast SPR images suitable for automated computer analysis, minimum crosstalk between neighboring sensing channels and inherent compensation for light level fluctuations. Applications of a laboratory prototype of the high-throughput SPR sensor with 108 sensing channels for refractometry and biosensing are described. In refractometric experiments, the noise-limited refractive index resolution of the system has been established to be 3 x 10(-6) refractive index unit (RIU). Experimental data on detection of human choriogonadotropin (hCG) suggest that in conjunction with monoclonal antibodies against hCG, the reported SPR imaging sensor is capable of detecting hCG at concentrations lower than 500 ng/ml.     

Plasmonic Sensors Based on Funneling Light Through Nanophotonic Structures

We present a refractometric sensor realized as a stack of metallic gratings with subwavelength features and embedded within a low-index dielectric medium. Light is strongly confined through funneling mechanisms and excites resonances that sense the analyte medium. Two terminations of the structure are compared. One of them has a dielectric medium in contact with the analyte and exploits the selective spectral transmission of the structure. The other design has a metallic continuous layer that generates surface plasmon resonances at the metal/analyte interface. Both designs respond with narrow spectral features that are sensible to the change in the refractive index of the analyte and can be used for sensing biomedical samples.

     

STUDIES IN RESPIROMETRY : I. A COMBINED GAS BURETTE-INTERFEROMETER RESPIROMETER

A machine has been described which combines volumetric and refractometric means of observing changes in carbon dioxide and oxygen concentrations and amounts in a closed system suitable for containing a respiring system. A means of thermoregulation has been described briefly. The theory upon which estimation is based has been outlined in considerable detail and generality; indicating how dependence upon absorption of gases by reagents can be eliminated completely, although they may be used in certain instances as a means of independent check. An experiment of this nature has been reported as an illustration of one use of the machine. Data of other experiments in which a moist environment was employed for the respiring system will be given in another communication.     

Application of an image and environmental sensor network for automated greenhouse insect pest monitoring

This work presents an automated insect pest counting and environmental condition monitoring system using integrated camera modules and an embedded system as the sensor node in a wireless sensor network. The sensor node can be used to simultaneously acquire images of sticky paper traps and measure temperature, humidity, and light intensity levels in a greenhouse. An image processing algorithm was applied to automatically detect and count insect pests on an insect sticky trap with 93% average temporal detection accuracy compared with manual counting. The integrated monitoring system was implemented with multiple sensor nodes in a greenhouse and experiments were performed to test the system’s performance. Experimental results show that the automatic counting of the monitoring system is comparable with manual counting, and the insect pest count information can be continuously and effectively recorded. Information on insect pest concentrations were further analyzed temporally and spatially with environmental factors. Analyses of experimental data reveal that the normalized hourly increase in the insect pest count appears to be associated with the change in light intensity, temperature, and relative humidity. With the proposed system, laborious manual counting can be circumvented and timely assessment of insect pest and environmental information can be achieved. The system also offers an efficient tool for long-term insect pest behavior observations, as well as for practical applications in integrated pest management (IPM).     

Rapid alignment of schlieren and interference optics in the analytical ultracentrifuge

A systematic procedure is described for the complete alignment of the refractometric optical system of the Beckman analytical ultracentrifuge.     

Detection of Staphylococcus aureus enterotoxin B at femtomolar levels with a miniature integrated two-channel surface plasmon resonance (SPR) sensor

Surface plasmon resonance (SPR) biosensors offer the capability for continuous real-time monitoring. The commercial instruments available have been large in size, expensive, and not amenable to field applications. We report here an SPR sensor system based on a prototype two-channel system similar to the single channel Spreeta devices. This system is an ideal candidate for field use. The two-channel design provides a reference channel to compensate for bulk refractive index (RI), non-specific binding and temperature variations. The SPR software includes a calibration function that normalizes the response from both channels, thus enabling accurate referencing. In addition, a temperature-controlled enclosure utilizing a thermo-electric module based on the Peltier effect provides the temperature stability necessary for accurate measurements of RI. The complete SPR sensor system can be powered by a 12V battery. Pre-functionalized, disposable, gold-coated thin glass slides provide easily renewable sensor elements for the system. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detectable at sub-nanomolar levels and with amplification at femtomolar levels. A regeneration procedure for the sensor surface allowed for over 60 direct detection cycles in a 1-month period.     

Multiplex bacterial growth monitoring in 24-well microplates using a dual optical sensor for dissolved oxygen and pH

Non-invasive, simultaneous optical monitoring of oxygen and pH during bacterial cultivation in 24-well microplates is presented using an integrated dual sensor for dissolved oxygen and pH values. The dual sensor is based on oxygen-sensitive organosilica microparticles and pH-sensitive microbeads from a polymethacrylate derivative embedded into a polyurethane hydrogel. The readout is based on a phase-domain fluorescence lifetime-based method referred to as modified frequency domain dual lifetime referencing using a commercially available detector system for 24-well microplates. The sensor was used for monitoring the growth of Pseudomonas putida bacterial cultures. The method is suitable for parallelized, miniaturized bioprocessing, and cell-based high-throughput screening applications.     

A Service Approach for Architecting Application Independent Wireless Sensor Networks

The current sensor networks are assumed to be designed for specific applications, having data communication protocols strongly coupled to applications. The future sensor networks are envisioned as comprising heterogeneous devices assisting to a large range of applications. To achieve this goal, a new architecture approach is needed, having application specific features separated from the data communication protocol, while influencing its behavior. We propose a Web Services approach for the design of sensor network, in which sensor nodes are service providers and applications are clients of such services. Our main goal is to enable a flexible architecture in which sensor networks data can be accessed by users spread all over the world.     

Dependence of the root suction force on the soil water content

The suction force of active roots ofFraxinus excelsior L. was estimated by the refractometric compensation method (compensation in a sucrose solution) and its dependence on the water content of soil was determined. Where differences in the soil humidity were excluded within the root system, the dependence could be expressed by a curve resembling the dependence of the suction force of soil on its water content. This dependence was valid both for the minimal gradients of suction forces between the over-and underground parts of the plant (pot experiments), as well as when transpiration and hence gradients were present (under field conditions). Where differences in soil humidity were formed within the root system, the dependence did not correspond to this basic curve, due to the compensation of root suction forces within the root system.     

Cataluminescence‐based sensors: principle,instrument and application

The cataluminescence (CTL)‐based sensor is a new promising type of chemical transducer, and has attracted much attention of researchers for its potential versatile applications in public safety, emission control and environmental protection. In this review, we briefly introduce the development history of CTL‐based sensors and summarize existing explanations of the CTL reaction mechanism as well as three research strategies for mechanism the CTL mechanism. In the following, all the function units of a typical CTL‐based sensor system are described and the investigation of the sensor materials. CTL‐based sensor arrays, are discussed in detail. We classify the recent novel hyphenated techniques based on CTL coupled to other analysis techniques into the preconcentration‐CTL hyphenated technique, nebulization‐CTL hyphenated technique, plasma‐assisted CTL technique and tandem CTL technique according to the type of analysis combined with CTL and provide a detailed account of novel hyphenated techniques. Owing to the appearance of these novel techniques, the application range of CTL has been expanded as well as the sensitivity and selectivity of CTL system has been greatly improved. Finally, the applications of CTL‐based sensor and sensor arrays in the last several years are classified and summarized. Copyright © 2014 John Wiley & Sons, Ltd.     

An inertial and magnetic sensor based technique for joint angle measurement

This paper describes the design and evaluation of a miniature kinematic sensor based three dimensional (3D) joint angle measurement technique. The technique uses a combination of rate gyroscope, accelerometer and magnetometer sensor signals. The technique enables 3D inter-segment joint angle measurement and could be of benefit in a variety of applications which require monitoring of joint angles. The technique is not dependent on a fixed reference coordinate system and thus may be suitable for use in a dynamic system such as a moving vehicle. The technique was evaluated by applying it to joint angle measurement of the ankle joint. Experimental results show that accurate measurement of ankle joint angles is achieved by the technique during a variety of lower leg exercises including walking.     

Multi-Parametric Clustering for Sensor Node Coordination in Cognitive Wireless Sensor Networks

The deployment of wireless sensor networks for healthcare applications have been motivated and driven by the increasing demand for real-time monitoring of patients in hospital and large disaster response environments. A major challenge in developing such sensor networks is the need for coordinating a large number of randomly deployed sensor nodes. In this study, we propose a multi-parametric clustering scheme designed to aid in the coordination of sensor nodes within cognitive wireless sensor networks. In the proposed scheme, sensor nodes are clustered together based on similar network behaviour across multiple network parameters, such as channel availability, interference characteristics, and topological characteristics, followed by mechanisms for forming, joining and switching clusters. Extensive performance evaluation is conducted to study the impact on important factors such as clustering overhead, cluster joining estimation error, interference probability, as well as probability of reclustering. Results show that the proposed clustering scheme can be an excellent candidate for use in large scale cognitive wireless sensor network deployments with high dynamics.     

Wideband Optical Detector of Ultrasound for Medical Imaging Applications

Optical sensors of ultrasound are a promising alternative to piezoelectric techniques, as has been recently demonstrated in the field of optoacoustic imaging. In medical applications, one of the major limitations of optical sensing technology is its susceptibility to environmental conditions, e.g. changes in pressure and temperature, which may saturate the detection. Additionally, the clinical environment often imposes stringent limits on the size and robustness of the sensor. In this work, the combination of pulse interferometry and fiber-based optical sensing is demonstrated for ultrasound detection. Pulse interferometry enables robust performance of the readout system in the presence of rapid variations in the environmental conditions, whereas the use of all-fiber technology leads to a mechanically flexible sensing element compatible with highly demanding medical applications such as intravascular imaging. In order to achieve a short sensor length, a pi-phase-shifted fiber Bragg grating is used, which acts as a resonator trapping light over an effective length of 350 µm. To enable high bandwidth, the sensor is used for sideway detection of ultrasound, which is highly beneficial in circumferential imaging geometries such as intravascular imaging. An optoacoustic imaging setup is used to determine the response of the sensor for acoustic point sources at different positions.     

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.

     

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.     

Development and characterization of a fiber optical fluorescence sensor for the online monitoring of biofilms and their microenvironment

The growth of microorganisms on surfaces and interfaces as a biofilm is very common and plays important role in various areas such as material science, biomedicine, or waste treatment among others. Due to their inhomogeneous structure and the variance in the microorganism consortium, the analysis of biofilms represents a significant challenge. An online fluorescence sensor was developed that is able to measure the most important biological fluorophores (proteins, nicotinamide adenine dinucleotide, and flavin) in a noninvasive manner in biofilms, e.g. in bioelectrochemical applications. The sensor gives the opportunity to continuously draw conclusions on the metabolic state of the biofilm. The developed sensor has a diameter of 1 mm at the sensor tip and can be moved on and into the biofilm surface. In the first experiment, the measuring range of the sensor and the long‐term stability could be determined and the system applicability was confirmed. In addition, measurements in biofilm‐like structures could be performed. The formation of a wastewater‐based biofilm was monitored using the developed sensor, demonstrating the functionality of the sensor in a proof‐of‐principle experiment.     

Highly sensitive optical chip immunoassays in human serum

Over the past decade the ability of refractometric optical sensors to quantitatively measure a wide range of biomolecules has been demonstrated. These include proteins, nucleic acids, microorganisms, and in competitive formats small molecules such as drugs and pesticides. Furthermore, by using high refractive index nanoparticles to amplify the biomolecular binding signal, sensitivities approaching those of well established diagnostic assays have been achieved. However, to date it has not been possible to show rapid detection of analytes in complex bodily fluids such as serum, in a one-step procedure, due to the interference resulting from non-specific binding (NSB) to the sensor surface. We have carried out preliminary work on the control of interference due to NSB using an optical chip based on the Hartman interferometer. This interferometer configuration employs a reference sensing region that can be functionalized separately from the specific sensing region. Optical chips were stored dry after surface functionalization, and rehydrated in serum. The observed level of background drift in serum was reduced by an order of magnitude when an exposed reference was used, compared to a reference which was blind to the sample. An additional 70% reduction in signal drift in serum was achieved by controlling the surface chemistry of the optical chip using a biotin-poly(ethylene glycol) (PEG) blocking agent. This functionalization procedure was combined with a sandwich assay using gold nanoparticles to develop a one-step assay for human chorionic gonadotropin (hCG) in human serum with a detection limit of 0.1 ng/ml for a 35 min assay.     

Miniaturized multi-enzyme biosensors integrated with pH sensors on flexible polymer carriers for in vivo applications

An electrochemical glucose sensor has been integrated, together with a pH sensor, on a flexible polyimide substrate for in vivo applications. The glucose sensor is based on the measurement of H₂O₂ produced by the membrane-entrapped enzyme glucose oxidase (GOD). To minimize electrochemical interference, an electrode configuration was designed to perform differential measurements. The solid-state pH sensor employs a PVC-based neutral carrier membrane. The enzymes GOD and catalase were immobilized into two layers of photolithographically patterned hydrogels. The intended use of this device is the short-term monitoring of glucose and pH in intensive care units and operating theatres, especially for neurosurgical applications. The developed immobilization technique can also be used to create integrated multi-sensor chips for clinical analysers. The glucose and pH sensor exhibited excellent performance during tests in buffer solutions, serum and whole blood.     

A novel sensor concept for optimization of loosening diagnostics in total hip replacement

The main reason for the revision of total hip replacements is aseptic loosening, caused by stress shielding and wear particle induced osteolysis. In order to detect an implant loosening early, the osseointegration of endoprosthetic implants must be measured exactly. Currently applied diagnostic methods, such as standard radiographs and clinical symptomatology, often result in an imprecise diagnosis. A novel radiation-free method to improve the diagnostic investigation of implant loosening is presented. The osseointegration of an implant can be identified using mechanical magnetic sensors (oscillators), which impinge on small membranes inside an implant component, e.g., the femoral hip stem. The maximum velocity after impingement of the oscillator depends on the osseointegration of the implant. Excitation of the oscillator is realized by a coil outside the human body. Another external coil is used to detect the velocity of the oscillator. To demonstrate the principle of the novel loosening sensor, an overdimensioned test device was designed to measure simulated loosening phases in the first experimental tests with different material layers. The overdimensioned test device of the loosening sensor showed significant differences in the various phases of fixation. Analysis of the membrane without any material layer in the case of advanced loosening resulted in a 23% higher maximum velocity compared to an attached artificial bone layer. Based on these preliminary results, the sensor system shows potential for the detection of implant loosening. Moreover, the proposed system could be used in experimental applications to determine the quality of bioactive coatings and new implant materials.     

Design and fabrication of a largely deformable sensorized polymer actuator

Polypyrrole (PPy), with its biomimetic properties such as high power density, large strain, and biocompatibility, is an excellent candidate for a biomimetic microactuator in microrobotics and bioengineering. A polyvinylidene fluorid (PVDF) sensor is also biocompatible, flexible, and chemically stable. Therefore, a PPy actuator is integrated with a PVDF sensor to realize a sensorized polymer actuator. A novel sensorized polymer actuator can accurately measure its bending motion precisely with real time. Experimental results demonstrate the feasibility of the sensorized polymer actuator. The polymer actuator can be actuated while it senses signals induced from the bending motion. In addition, the position of the sensorized polymer actuator can be controlled and adjusted precisely with feedback signals from its embedded sensor at the time of operation. If this system becomes more robust and reliable, its applications are promising and can be realized in cell handling, microrobotics, and microsurgery with the integration of standard microfabrication techniques.