Colorimetric sensor arrays for volatile organic compounds

The development of a low-cost, sensitive colorimetric sensor array for the detection and identification of volatile organic compounds (VOCs) is reported. Using an array composed of chemoresponsive dyes, enormous discriminatory power is possible in a simple device that can be imaged easily with an ordinary flatbed scanner. Excellent differentiation of closely related organic compounds can be achieved, and a library of 100 VOCs is presented. The array discriminates among VOCs by probing a wide range of intermolecular interactions, including Lewis acid/base, Br?nsted acid/base, metal ion coordination, hydrogen bonding, and dipolar interactions. Importantly, by proper choice of dyes and substrate, the array is essentially nonresponsive to changes in humidity.     

Chip cleaning and regeneration for electrochemical sensor arrays

Sensing systems based on electrochemical detection have generated great interest because electronic readout may replace conventional optical readout in microarray. Moreover, they offer the possibility to avoid labelling for target molecules. A typical electrochemical array consists of many sensing sites. An ideal micro-fabricated sensor-chip should have the same measured values for all the equivalent sensing sites (or spots). To achieve high reliability in electrochemical measurements, high quality in functionalization of the electrodes surface is essential. Molecular probes are often immobilized by using alkanethiols onto gold electrodes. Applying effective cleaning methods on the chip is a fundamental requirement for the formation of densely-packed and stable self-assembly monolayers. However, the available well-known techniques for chip cleaning may not be so reliable. Furthermore, it could be necessary to recycle the chip for reuse. Also in this case, an effective recycling technique is required to re-obtain well cleaned sensing surfaces on the chip. This paper presents experimental results on the efficacy and efficiency of the available techniques for initial cleaning and further recycling of micro-fabricated chips. Piranha, plasma, reductive and oxidative cleaning methods were applied and the obtained results were critically compared. Some interesting results were attained by using commonly considered cleaning methodologies. This study outlines oxidative electrochemical cleaning and recycling as the more efficient cleaning procedure for electrochemical based sensor arrays.     

Processing technique for single-walled carbon nanotube-based sensor arrays

We investigated a selective assembly method of fabricating single-walled carbon nanotubes (SWCNTs) on a silicon-dioxide (SiO2) surface by using only a photolithographic process; then, we fabricated 8 x 8 field-emission transistor (FET) arrays for sensor applications. Photoresist (PR) patterns were made on a SiO2-grown Si substrate by using the photolithographic process. This PR-patterned substrate was dipped into a SWCNT solution dispersed in dichlorobenzene (DCB). The PR patterns were removed by using acetone. As a result, selectively-assembled SWCNT channels in 8 x 8 FET arrays could be fabricated between source and drain electrodes without complicated chemical steps using octadecyltrichlorosilane (OTS). Finally, we successfully fabricated 8 x 8 SWCNT-based multi-channel FET arrays by using our novel self-assembly method.     

Pin-printed chemical sensor arrays for simultaneous multianalyte quantification

A new approach to rapidly produce micrometer-scale sensor elements into reusable multianalyte chemical sensor arrays is demonstrated. By using pin printing technology in concert with sol-gel processing methods, we form discrete xerogel-based microsensors on a planar substrate. We illustrate the new approach by forming discrete 02- and pH-responsive sensing elements into arrays that allow one to simultaneously determine O2 and pH in aqueous samples. The pin printing method allows one to prepare sensor elements that are on the order of 100 microm in diameter, 1-2 microm thick, at a rate of approximately one sensor element per second with a single pin. Within a given calibrated array, the sensor element-to-sensor element response is reproducible to within 5%, the sensor element short- and long-term reproducibilities are 3 and 6%, respectively, and the array-to-array response reproducibility is 11%. These results demonstrate the potential of this methodology for rapidly forming ensembles of reusable sensor arrays for simultaneous multianalyte detection.     

Parameter identification for human body segment models

For the practical implementation of computer simulation or analysis of human motion in ergonomics, orthopaedics, sports, and other areas, the respective models must be individualized by assigning them subject-specific parameter values such as those for segment parameters. Several methods and their efficiency are discussed for determining this parameter set for a given subject. It is shown that the anthropometrico-computational method is presently the most accurate and reliable technique with potential for further improvement.     

Source separation based processing for integrated Hall sensor arrays

Integrated arrays of Hall-type magnetic sensors are generally subject to significant crosstalk due to poor spatial selectivity of very closely spaced sensors. In this paper, we explore blind source separation as a signal processing technique to unmix a number of magnetic sources that impinge on the array. The processing consists of two stages: the first one estimates the source number and projects the observations on the signal subspace; the second stage is a source separation algorithm. Experimental results from a silicon array of Hall sensors, interfaced with a DSP, demonstrate real-time separation of two magnetic sources even under ill-conditioning of the mixing matrix.     

Skin-like tactile sensor arrays for contact stress field extraction

Continuous scanning of variable contact forces occurring during object exploration and manipulation by means of miniature sensors is becoming increasingly important in medical prosthetics and orthotics, advanced robotics, teleoperation and telepresence. In this paper a system able to provide robots with tactile sensitivity is presented. Skin-like tactile sensor arrays, which are selectively sensitive to stress-tensor components and are based on piezoelectric polymer technology, have been implemented. The basic characteristics of the sensors, together with the mechanical devices and the electronics developed for setting up the artificial tactile system, are described. An investigation of the expected responses of the sensor has been carried out by modelling the mechanics of object-sensor interaction and by finding the stress solutions of a forward elastic contact problem. The system has been tested by comparing the theoretical results with data measured experimentally from the sensor.     

Aptamer-based sensor arrays for the detection and quantitation of proteins

Aptamer biosensors have been immobilized on beads, introduced into micromachined chips on the electronic tongue sensor array, and used for the detection and quantitation of proteins. Aptamer chips could detect proteins in both capture and sandwich assay formats. Unlike most protein-based arrays, the aptamer chips could be stripped and reused multiple times. The aptamer chips proved to be useful for screening aptamers from in vitro selection experiments and for sensitively quantitating the biothreat agent ricin.     

Radioluminescent light source for the development of optical sensor arrays

A radioluminescent (RL) light source is evaluated for the development of photonically based chemical-responsive sensor arrays (CRSAs). The RL light source is comprised of a strontium-90 (90Sr) radionuclide and a plastic scintillator. The beta particles emitted from the 90Sr generate blue light (lambda(max) = 435 nm) from the plastic scintillator, and the blue light excites the analyte-responsive luminophores within the CRSA. To assess the RL light source utility, we have determined the analytical figures of merit from two tris(4,7'-diphenyl-1,10'-phenathroline)ruthenium(II)-doped xerogel-based sensor platforms: (i) a planar 5 x 5 multielement array and (ii) a discrete sensor element formed on the proximal face of poly(styrene) pillars that have a frustrated cone (frustum) geometry. We compare the performance from each platform when it is excited by a He-Cd laser (442 nm), a blue light-emitting diode (460-470 nm), and the RL light source. The RL light source yields results that are statistically equivalent to results from either electrically powered light source. The RL light source consumes no electrical power, is compact and simple, and has an extremely stable time-averaged signal. The primary trade-offs for these advantages are the RL light source's lower radiant power and the corresponding longer data acquisition times.     

Capacitive sensor arrays in dimensional analysis of surfaces

The theoretical aspects of dimensional analysis and shape reconstruction of surfaces by means of displacement sensor arrays are investigated. Although this analysis is focused on surface profiles and linear arrays of capacitive sensors, its results could be easily extended to surfaces and bidimensional arrays of displacement sensors. Capacitance variations related to sensor-to-surface displacements during array scanning are used in the reconstruction equations obtained from the analysis. The reconstruction accuracy depends mainly on the dimensional stability of the array, and it is independent from the array trajectory. The problems raised by nonideal array and sensor behavior, such as fringe effects and geometry deviations are discussed. Capacitance variations due to such effects are calculated and taken into account by means of an energy method. A reconstruction system based on the theoretical results is proposed, and its performance in the reconstruction process is evaluated by a computer simulation which accounts for measurement uncertainties. Simulation results confirm both the effectiveness of the method and the feasibility of the system. Its features are compared with those of other noncontact surface-measuring instruments, and possible applications are outlined     

曲率波前传感器波前重构算法的研究

运用衍射理论计算出两个离焦面上的光强分布,从而获得波前曲率和孔径边缘的波前径向倾斜。根据Zernike多项式的微分特性,采用两种不同的方法分别处理曲率和倾斜,使用积分的方法解决了在边界上δ函数很难处理的问题。由探测器的几何分布预先算出控制矩阵,用Zernike多项式曲线拟合的方法重构出波前。计算机仿真表明,波前残差小于5％,验证了此波前重构算法的可行性。     

Optimization of the geometry and porosity of microelectrode arrays for sensor design

This paper describes the systematic investigation of a range of microelectrode arrays with varying dimensions fabricated by standard photolithographic and reactive-ion etching techniques. As expected from theory, the electrochemical behavior of microelectrode arrays with a constant individual diameter varied strongly with center-to-center spacing, the larger the spacing the more sigmoidal the recorded voltammogram. Furthermore, the behavior of arrays with a constant relative center-to-center spacing is shown to vary with individual electrode diameter, the arrays with the smallest electrodes producing strongly peaked voltammograms. Peak current densities and signal-to-noise ratios were also obtained for a variety of array geometries, and the use of electrodeposited platinum black electrodes was investigated. To demonstrate one advantage of using a loosely packed microelectrode array in electroanalysis, a ferrocene-mediated enzyme-linked assay involving the biocatalytic reduction of H2O2 was investigated. Results showed an improved temporal response, with current-time transients reaching a steady-state response more quickly using arrays with increased center-center spacings.     

A ray-tracing approach for simulating recognition abilities of active infrared sensor arrays

The construction and setup of sensors or sensor arrays determines their maximum resolution and recognition abilities. Therefore, the analysis of certain setups is an important and mandatory task during the design process of a new sensor system. This paper deals with the simulation and evaluation of the recognition abilities of active infrared sensors for autonomous systems. Additionally, the simulation method as well as the results provide useful information for other applications, where infrared sensors are used. The simulation method is based on a Monte Carlo algorithm, which uses ray tracing to calculate the impulse response of the optical channel consisting of the sending and receiving components and the environment. In order to allow a fast simulation of several configurations, an efficient and flexible computation is realized. This means that all rays contribute maximally to the final result, and different sensor characteristics can easily be calculated. Extensive experiments are carried out, and the results show different evaluation options.     

Hybrid Si nanowire/amorphous silicon FETs for large-area image sensor arrays

Silicon nanowire (SiNW) field-effect transistors (FETs) were fabricated from nanowire mats mechanically transferred from a donor growth wafer. Top- and bottom-gate FET structures were fabricated using a doped a-Si:H thin film as the source/drain (s/d) contact. With a graded doping profile for the a-Si:H s/d contacts, the off-current for the hybrid nanowire/thin-film devices was found to decrease by 3 orders of magnitude. Devices with the graded contacts had on/off ratios of ～10(5), field-effect mobility of ～50 cm(2)/(V s), and subthreshold swing of 2.5 V/decade. A 2 in. diagonal 160 × 180 pixel image sensor array was fabricated by integrating the SiNW backplane with an a-Si:H p-i-n photodiode.     

Two-dimensional encoding scheme for digital spatial domainmultiplexed large-scale optical fiber sensor arrays

This paper studies a novel two-dimensional (2-D) encoding scheme to increase the multiplexing capacity of the newly developed digital spatial domain multiplexing technique used for integration of large-scale interferometric fiber-sensor arrays. The feasibility of the scheme is assessed via computer simulation and a preliminary experiment which involved strain measurement at multipositions on a cantilever beam     

Convergent, self-encoded bead sensor arrays in the design of an artificial nose.

We report a new approach to designing an artificial nose based on high-density optical arrays that directly incorporate a number of structural and operational features of the olfactory system. The arrays are comprised of thousands of microsphere (bead) sensors, each belonging to a discrete class, randomly dispersed across the face of an etched optical imaging fiber. Beads are recognized and classified after array assembly by their unique, "self-encoded" response pattern to a selected vapor pulse. The high degree of redundancy built into the array parallels that found in nature and affords new opportunities for chemical-sensor signal amplification. Since each bead is independently addressable through its own light channel, it is possible to combine responses from same-type beads randomly distributed throughout the array in a manner reminiscent of the sensory-neuron convergence observed in the mammalian olfactory system. Signal-to-noise improvements of approximately n1/2 have been achieved using this method.     

Extending the longevity of fluorescence-based sensor arrays using adaptive exposure

Fluorescent microbead sensor arrays were prepared to determine sensor array longevity. Sensor longevity is limited by photobleaching of the dyes attached to the microbeads and presents one of the biggest drawbacks of most fluorescent dye-based arrays. Responses of an array of organic vapor sensors were acquired for 2 weeks to evaluate the sensor performance over time. Photobleaching effects were overcome in two ways: (1) by limiting the excitation light power and gradually increasing the power at a rate comparable to the sensor photobleaching rates and (2) by illuminating subsections of the array through an optical slit. Both approaches extended the longevity of a sensor array. During the longevity study, the sensor arrays were employed to test their ability to correctly distinguish between responses to seven vapors. A high classification accuracy (99.8%) was obtained after 17,700 exposures for vapor responses collected over two weeks using only approximately 8% of the array's surface area.     

Time-division multiplexing of large serial fiber-optic Bragg grating sensor arrays

Time-division multiplexing is a promising method for the interrogation of fiber-optic Bragg grating sensors arrays for measurement of strain and temperature. We examine the performance of these systems to determine the parameters for high-sensitivity, low-cross-talk operation. It is shown that the performance can be greatly improved by use of a short time resolution in the demultiplexing process. We propose a new method of demultiplexing with an electro-optic modulator to read out the sensor pulses by gating the signal with 400-ps resolution. The system is demonstrated experimentally to provide 0.15-muepsilon/ radicalHz strain resolution in a 50-Hz bandwidth within a full-scale range of 8000 muepsilon. The system parameters are capable of handling at least 50 time-addressed sensors on a single fiber.     

Multifrequency interrogation of nanostructured gas sensor arrays: a tool for analyzing response kinetics

This paper presents a unique perspective on enhancing the physicochemical mechanisms of two distinct highly sensitive nanostructured metal oxide micro hot plate gas sensors by utilizing an innovative multifrequency interrogation method. The two types of sensors evaluated here employ an identical silicon transducer geometry but with a different morphological structure of the sensitive film. While the first sensing film consists of self-ordered tungsten oxide nanodots, limiting the response kinetics of the sensor-chemical species pair only to the reaction phenomena occurring at the sensitive film surface, the second modality is a three-dimensional array of tungsten oxide nanotubes, which in turn involves both the diffusion and adsorption of the gas during its reaction kinetics with the sensitive film itself. By utilizing the proposed multifrequency interrogation methodology, we demonstrate that the optimal temperature modulation frequencies employed for the nanotubes-based sensors to selectively detect hydrogen, carbon monoxide, ethanol, and dimethyl methyl phosphonate (DMMP) are significantly higher than those utilized for the nanodot-based sensors. This finding helps understand better the amelioration in selectivity that temperature modulation of metal oxides brings about, and, most importantly, it sets the grounds for the nanoengineering of gas-sensitive films to better exploit their practical usage.