Compact and flexible optical sensor designed for on-line monitoring

A new on line optical sensor based on light scattering dedicated to real-time monitoring during processing of polymers blends and polymers nanocomposites has been developed. The sensor is designed to monitor the quality of a polymer melt or of a dispersion of nanofillers in a polymeric matrix during the process of extrusion. This sensor presents three openings: two for light sensor setups (one for transmission measurements and the other for 90°-scattered light measurements) and one for the incident laser beam. The experimental validation of this optical sensor has been realized on two materials: poly(methyl methacrylate) (PMMA) and on the nanocomposites obtained by the melt mixing of this polymer matrix with modified montmorillonite (MMT) clays. Experimental results proved the good results in terms of signal repeatability and sensitivity to organoclay particle concentration and structures of nanocomposites respectively.     

Integrated sensor array for analysis of multicomponent gas mixtures

A new device has been proposed and tested experimentally for the discrimination of gases in “electronic nose” systems. The device consists of an array of surface-acoustic wave (SAW) sensors positioned on a single anisotropic substrate with a common gas-sensitive coating for each sensor. The specificity of the sensors is provided entirely by the elastic anisotropy of the single-crystal substrate: changes in the direction of propagation of the wave through the gas-sensitive film deposited on the anisotropic substrate are accompanied by changes in the partial components of the mechanical displacement of the wave and corresponding contributions to the resultant SAW “response.” Pis’ma Zh. Tekh. Fiz. 24, 40–45 (August 26, 1998)     

Microfluidic electrochemical sensor array for characterizing protein interactions with various functionalized surfaces

We present a unique microfluidic platform to allow for quick and sensitive probing of protein adsorption to various functionalized surfaces. The ability to tailor a sensor surface for a specific analyte is crucial for the successful application of portable gas and fluid sensors and is of great interest to the drug screening community. However, choosing the correct surface chemistry to successfully passivate against nonspecific binding typically requires repeated trial and error experiments. The presented device incorporates an array of integrated electrochemical sensors for fast, sensitive, label-free detection of these binding interactions. The layout of the electrodes allows for loading various surface chemistries in one direction while sensing their interactions with particular compounds in another without any cross-contamination. Impedance data is collected for three commonly used passivation compounds (mercaptohexanol, polyethylene glycol, and bovine serum albumin) and demonstrates their interaction with three commonly studied proteins in genetic and cancer research (cAMP receptor protein, tumor necrosis factor α, and tumor necrosis factor β). The ability to quickly characterize various surface interactions provides knowledge for selecting optimal functionalization for any biosensor.     

Integrated force measurement for on-line cutting geometryinspection

A novel on-line cutting geometry inspection technique based on the integrated force-sensing method has been developed. A piezoelectric force sensor, mounted at the back of a single crystal diamond tool, was used to measure the cutting forces encountered by the tool system as it plunge-cut parallel micro flow channels on copper foils about 125 μm in thickness. The force data were then converted by a software code which calculates the geometrical dimensions (depth and width) of the micro channels that had been cut. A series of experiments were conducted for four different feeds: 0.1, 0.3, 1.0, and 5.0 μm/rev., at a constant workpiece speed of 2,400 rpm. Error analysis showed that the maximum relative error of the measurement, as compared to the results from the theoretical analysis, is 9.8%. By incorporating this force sensing technique into the machine tool control system, a real-time control unit can be implemented which conducts on-line adjustment of the diamond cutting performance to improve manufacturing quality     

Label-free electrochemical detection for aptamer-based array electrodes

An electrochemical impedance spectroscopy method of detection for aptamer-based array electrodes is reported in which the binding of aptamers immobilized on gold electrodes leads to impedance changes associated with target protein binding events. Human IgE was used as a model target protein and incubated with the aptamer-based array consisting of single-stranded DNA containing a hairpin loop. To increase the binding efficiency for proteins, a hybrid modified layer containing aptamers and cysteamine was fabricated on the photolithographic gold surface through molecular self-assembly. Atomic force microscopy analysis demonstrated that human IgE could be specifically captured by the aptamer and stand well above the self-assembled monolayer (SAM) surface. Compared to immunosensing methods using anti-human IgE antibody as the recognition element, impedance spectroscopy detection could provide higher sensitivity and better selectivity for aptamer-modified electrodes. The results of this method show good correlation for human IgE in the range of 2.5-100 nM. A detection limit of 0.1 nM (5 fmol in a 50-microL sample) was obtained, and an average of the relative standard deviation was <10%. The method herein describes the first label-free detection for arrayed electrodes utilizing electrochemical impedance spectroscopy.     

An addressable microelectrode array for electrochemical detection

Column and row electrodes on two different glass substrates were orthogonally arranged in order to assemble an addressable microelectrode device for the purpose of comprehensive electrochemical detection. Amperometric signal at the individual crossing point of the column and row electrodes was detected separately on the basis of redox cycling of localized electroactive species occurring between the electrodes. The addressable microelectrode device was simple and could be easily assembled; however, it comprised as many as 10 x 10 addressable detection points on a single chip. The basic electrochemical performance of the device was investigated by using the ferricyanide/ferrocyanide redox couple. Electrochemical responses at 100 individual points could be collected within 22 s. The present device was successfully used for imaging the spots of alkaline phosphatase on the array substrate. The results indicate that the device can be applied to comprehensive and high-throughput detection and imaging of biochemical species.     

Embedded spectroscopic fiber sensor for on-line arc-welding analysis

A new fiber sensor system designed for spectroscopic analysis and on-line quality assurance of arc-welding processes is presented here. Although several different approaches have been considered for the optical capture of plasma emission in arc-welding processes, they tend to be invasive and make use of optical devices such as collimators or photodiodes. The solution proposed here is based on the arrangement of an optical fiber, which is used at the same time as the optical capturing device and also to deliver the optical information to a spectrometer, embedded within an arc-welding torch. It will be demonstrated that, by using the shielding gas as a protection for the fiber end, the plasma light emission is efficiently collected, forming a sensor system completely transparent and noninvasive for the welding operator. The feasibility of the proposed sensor designed to be used as the input optics of a welding quality-assurance system based on plasma spectroscopy will be demonstrated by means of several welding tests.     

Integrated microdevice for long-term automated perfusion culture without shear stress and real-time electrochemical monitoring of cells

Electrochemical techniques based on ultramicroelectrodes (UMEs) play a significant role in real-time monitoring of chemical messengers' release from single cells. Conversely, precise monitoring of cells in vitro strongly depends on the adequate construction of cellular physiological microenvironment. In this paper, we developed a multilayer microdevice which integrated high aspect ratio poly(dimethylsiloxane) (PDMS) microfluidic device for long-term automated perfusion culture of cells without shear stress and an independently addressable microelectrodes array (IAMEA) for electrochemical monitoring of the cultured cells in real time. Novel design using high aspect ratio between circular "moat" and ring-shaped micropillar array surrounding cell culture chamber combined with automated "circular-centre" and "bottom-up" perfusion model successfully provided continuous fresh medium and a stable and uniform microenvironment for cells. Two weeks automated culture of human umbilical endothelial cell line (ECV304) and neuronal differentiation of rat pheochromocytoma (PC12) cells have been realized using this device. Furthermore, the quantal release of dopamine from individual PC12 cells during their culture or propagation process was amperometrically monitored in real time. The multifunctional microdevice developed in this paper integrated cellular microenvironment construction and real-time monitoring of cells during their physiological process, and would possibly provide a versatile platform for cell-based biomedical analysis.     

A carbon-nanotube-based sensor array for formaldehyde detection

We have fabricated a sensor array consisting of 32 sensor elements with pristine, doped and metal-loaded single-wall carbon nanotubes as sensing materials. The sensor elements consist of interdigitated electrodes with varying finger widths and gaps. The chemiresistor-type sensors provide a significant response to formaldehyde at concentrations down to 10 ppb in air with rapid response and recovery times.     

Soft microelectrode linear array for scanning electrochemical microscopy

A linear array of eight individual addressable microelectrodes has been developed in order to perform high-throughput scanning electrochemical microscopy (SECM) imaging of large sample areas in contact regime. Similar to previous reports, the soft microelectrode array was fabricated by ablating microchannels on a polyethylene terephthalate (PET) film and filling them with carbon ink. Improvements have been achieved by using a 5 μm thick Parylene coating that allows for smaller working distances, as the probe was mounted with the Parylene coating facing the sample surface. Additionally, the application of a SECM holder allows scanning in contact regime with a tilted probe, reducing the topographic effects and assuring the probe bending direction. The main advantage of the soft microelectrode array is the considerable decrease in the experimental time needed for imaging large sample areas. Additionally, soft microelectrode arrays are very stable and can be used several times, since the electrode surface can be regenerated by blade cutting. Cyclic voltammograms and approach curves were recorded in order to assess the electrochemical properties of the device. An SECM image of a gold on glass chip was obtained with high resolution and sensitivity, proving the feasibility of soft microelectrode arrays to detect localized surface activity. Finite element method (FEM) simulations were performed in order to establish the effect of diffusion layer overlapping between neighboring electrodes on the respective approach curves.     

Thin-film sensor for emergency shutdown of electrochemical generator

A thin-film sensor for detection of emergency situations in fuel cells of electrochemical generators is proposed. Experimental results of emergency modeling are presented. It is shown that the thin-film sensor can function as a high-speed warning device. A system is proposed for emergency shutdown by means of a thermal pulse from the thin-film sensor. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 64–65, July, 2000.     

Lab-on-a-Cable for electrochemical monitoring of phenolic contaminants

The "Lab-on-a-Cable" concept, based on scaling down an electrochemical flow system to a cable platform, is described. The system integrates the analyte collection and the sample handling, with the electrochemical detection of the reaction product in a sealed cylindrical unit, connected to a long shielded cable. An enzymatic assay, involving collection of a phenolic substrate, its mixing with an internally delivered tyrosinase solution, and amperometric detection of the liberated quinone product, is used for illustrating the operation of the flow probe and demonstrating its advantages over remote phenol sensors. The internal buffer solution ensures independence of sample conditions such as pH, ionic strength, or natural conditions, that commonly influences the performance of remote sensors. The "built-in" flow pulsation of the integrated micropump is exploited for a sensitive hydrodynamic-modulation voltammetric detection of hydrazine and peroxide pollutants.     

Integrated on-capillary electrochemical detector for capillary electrophoresis

An on-capillary electrochemical detector for capillary electrophoresis is described. It consists of a gold wire mounted permanently at the end of the capillary perpendicular to the direction of flow. This mode of detection eliminates the need for the micromanipulators or specially machined cell holders for alignment that are used for in-capillary detection modes. It also makes it possible to perform relatively fast CEEC separations using very short capillaries. The use of this detector for both off-column detection of catecholamines and end-column detection of carbohydrates by CE-PAD is described.     

Plasma-assisted cataluminescence sensor array for gaseous hydrocarbons discrimination

Combining plasma activation and cross-reactivity of sensor array, we have developed a plasma-assisted cataluminescence (PA-CTL) sensor array for fast sensing and discrimination of gaseous hydrocarbons, which can be potentially used for fast diagnosis of lung cancer. Based on dielectric barrier discharge, a low-temperature plasma is generated to activate gaseous hydrocarbons with low cataluminescence (CTL) activities. Extremely increased CTL responses have been obtained, which resulted in a plasma assistance factor of infinity (∞) for some hydrocarbons. On a 4 × 3 PA-CTL sensor array made from alkaline-earth nanomaterials, gaseous hydrocarbons showed robust and unique CTL responses to generate characteristic patterns for fast discrimination. Because of the difference in the component of hydrocarbons in breath, exhaled breath samples from donors with and without lung cancer were tested, and good discrimination has been achieved by this technique. In addition, the feasibility of multidimentional detection based on temperature was confirmed. It had good reproducibility and gave a linear range of 65-6500 ng/mL or 77-7700 ppmv (R > 0.98) for CH(4) with a detection limit of 33 ng/mL (38 ppmv) on MgO. The PA-CTL sensor array is simple, low-cost, thermally stable, nontoxic, and has an abundance of alkaline-earth nanomaterials to act as sensing elements. This has expanded the applications of CTL-based senor arrays and will show great potential in clinical fast diagnosis.     

Dynamic orthogonal projection. A new method to maintain the on-line robustness of multivariate calibrations. Application to NIR-based monitoring of wine fermentations

A new method is developed to maintain the on-line robustness of multivariate calibrations against unknown influence factors, especially in the case of spectroscopy. This method is based on the use of the calibration database and the periodical on-line reference measurements with their corresponding spectra to compute an orthogonal correction. The spectra that would have been obtained in the absence of influence factor occurrence are estimated from the calibration database using the reference measurements and a kernel function. The difference between the estimated and the on-line spectra is used to compute an orthogonal projection correction of the calibration database that is used for recalibration. The originality of this method is its capability to handle different kinds of perturbations (chemical, physical, and environmental) using the original calibration database. This method was applied for on-line monitoring of alcoholic wine fermentation in the presence of temperature variations as the influence factor, where it showed a good performance for temperature variation and batch effects. Also, this method provides an on-line diagnosis tool for the spectral causes of robustness problems thus providing a basis to better understand the process in order to perform adjustments, if necessary, at an earlier stage.     

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.     

Living bacterial cell array for genotoxin monitoring

A biosensor composed of a high-density living bacterial cell array was fabricated by inserting bacteria into a microwell array formed on one end of an imaging fiber bundle. The size of each microwell allows only one cell to occupy each well. In this biosensor, E. coli cells carrying a recA::gfp fusion were used as sensing components for genotoxin detection. Each fiber in the array has its own light pathway, enabling thousands of individual cell responses to be monitored simultaneously with both spatial and temporal resolution. The biosensor was capable of performing cell-based functional sensing of a genotoxin with high sensitivity and short incubation times (1 ng/mL mitomycin C after 90 min). Dose-response curves for several genotoxins were obtained. The biosensors demonstrated an active sensing lifetime of more than 6 h and a shelf lifetime of two weeks.     

Integrated microinterferometric sensor for in-plane displacement measurement

We present an integrated sensor based on a grating interferometer (GI) for in-plane displacement measurement in microregions of large engineering structures. The system concept and design, based on a monolithic version of Czarnek's GI, is discussed in detail. The technology chain of the GI measurement head (MH), including the master fabrication and further replication by means of hot embossing, is described. The numerical analyses of the MH by means of geometric ray tracing and scalar wave propagation are provided. They allow us to determine geometrical tolerance values as well as refractive index homogeneity and nonflatness of MH working surfaces, which provide proper beam guiding. Finally the demonstrative measurement performed with a model of the sensor is presented.