Experimental and numerical estimations into the force distribution on an occlusal surface utilizing a flexible force sensor array

This study presents a novel flexible force sensor array for measuring the distribution of the force distribution over the first molar. The developed force sensor array is composed of a flexible polyimide electrode and barium-titanate-based multilayer ceramic capacitors (MLCCs). The piezoelectric and material properties of industrial-grade MLCCs are ideal for measuring large-force loadings. The sensors are cheap and easy to integrate with automated manufacturing processes. Prior to experimental measurements, the force responses for the MLCC sensor cells were systematically measured and evaluated, confirming their high fracture strength and good sensing properties. Finite element (FE) simulations were used to calculate the force distribution over the tooth crown from the measurement results of the 3×3 force sensor array. Results indicate that the sensor has great sensitivity and linearity under a high-speed cycle loading of 500 N/s conducted to simulate normal chewing. The total force measured using the developed sensor array within the artificial tooth had an error of less than 5%. In addition, the force distributions over the molar crown obtained using a numerical method of FE analysis agree well with those obtained from experiments. The developed flexible force sensor array thus has potential for in-situ bite force measurements that are low-cost and reliable.     

A composite sensor array impedentiometric electronic tongue Part I. Characterization

A study aimed at the characterization of five compounds with different chemical characteristics and gustative perceptions by measuring the variations of the electrical impedance of a composite sensor array is presented. The array was composed of five sensors of three different types based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes. Measurements were carried out by evaluating the electrical impedance of the sensor array at a frequency of 150 Hz, and the data acquisition process was automated; a mechanical arm and a rotating platform controlled by a data acquisition card and a dedicated software allowed the sequential dipping of sensors in the test solutions. Fifty different solutions eliciting the 5 basic tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter, respectively) at 10 concentration levels comprising the human perceptive range were analysed. More than 100 measurements were carried for each sample in a 4-month period to evaluate the system repeatability and robustness. The impedentiometric composite sensor array is shown to be sensitive, selective and stable for use in an electronic tongue.     

Nanosized gamma-Al2O3 + Nd2O3-based cataluminescence sensor for ethylene dichloride.

A gas-sensor utilizing cataluminescence (CTL) on nanosized gamma-Al2O3 + Nd2O3 for measuring low concentrations of gaseous ethylene dichloride (EDC) was developed. The results showed that gamma-Al2O3 nanoparticles as a catalyst offered high sensitivity and selectivity in the detection of EDC. The addition of a small quantity of Nd2O3 increased the intensity of CTL more than two-fold. Quantitative analysis was performed at a wavelength of 400 nm and at an optimal temperature of 279 degrees C, and the optimal flow rate of carrier gas was 320 mL/min. Under the optimized conditions, the linear range of CTL intensity vs. concentration is 6-5000 ppm (R = 0.9996; n = 7), with a detection limit of 2 ppm. The response time is <5 s. No interference or only very low levels of significant interference were observed when substances such as formaldehyde, n-hexane, methyl benzene, carbon tetrachloride, chloroform and benzene were passed through the sensor.     

A composite sensor array impedentiometric electronic tongue Part II. Discrimination of basic tastes

An impedentiometric electronic tongue based on the combination of a composite sensor array and chemometric techniques aimed at the discrimination of soluble compounds able to elicit different gustative perceptions is presented. A composite array consisting of chemo-sensitive layers based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes was used. The electrical impedance of the sensor array was measured at a frequency of 150 Hz by means of an impedance meter. The experimental set-up was designed in order to allow the automatic selection of a test solution and dipping of the sensor array following a dedicated measurement protocol. Measurements were carried out on 15 different solutions eliciting 5 different tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter, respectively) at 3 concentration levels comprising the human perceptive range. In order to avoid over-fitting, more than 100 repetitions for each sample were carried in a 4-month period. Principal component analysis (PCA) was used to detect and remove outliers. Classification was performed by linear discriminant analysis (LDA). A fairly good degree of discrimination was obtained.     

Development of micropost force sensor array with culture experiments for determination of cell traction forces

Cell traction forces (CTFs) are critical for cell motility and cell shape maintenance. As such, they play a fundamental role in many biological processes such as angiogenesis, embryogenesis, inflammation, and wound healing. To determine CTFs at the sub-cellular level with high sensitivity, we have developed high density micropost force sensor array (MFSA), which consists of an array of vertically standing poly(dimethylsiloxane) (PDMS) microposts, 2 microm in diameter and 6 microm in height, with a center-to-center distance of 4 microm. In combination with new image analysis algorithms, the MFSA can achieve a spatial resolution of 40 nm and a force sensitivity of 0.5 nN. Culture experiments with various types of cells showed that this MFSA technology can effectively determine CTFs of cells with different sizes and traction force magnitudes.     

Repair replication in human cells. Simplified determination utilizing hydroxyurea.

A simplified and shortened procedure has been developed for the determination of repair replication of DNA in cultured mammalian cells. The procedure, using the bromodeoxyuridine density label and a radio-isotopic label has been applied to normal diploid human cells (WI38) and to their SV40 transformants (VA13). After incubation with the repair label the cells are lysed and digested for two hours at 50 degrees C with proteinase K. This digest can then be immediately subjected to alkaline cesium chloride density gradient centrifugation with no need for DNA extraction. Hydroxyurea is used to reduce the level of semi-conservative synthesis that a quantitative determination of repair replication can be accomplished by a single centrifugation. The method is not affected by variation in the effectiveness of the inhibitor although a small amount of semi-conservative synthesis normally occurs in the presence of the drug. The time course of repair replication in WI38 cells is unaffected by the drug. The apparent amount of repair synthesis in ultraviolet irradiated cells is increased 25 to 40% in the presence of hydroxyurea when thymidine is used as tracer. Under certain conditions in which the level of semiconservative synthesis is low (e.g., contact inhibited cells, high ultraviolet doses) the use of hydroxyurea is unnecessary.     

Separation and determination of mass and radioactivity of fermentation gases.

A procedure is described for the separation of permanent gases on a gas chromatograph, the determination of each component by means of a thermal conductivity detector and the simultaneous measurement of radioactivity in each peak by means of a proportional counter.Procedures for calibration of the apparatus and for calculation of absolute radioactivities in samples are given.The capabilities of the apparatus are illustrated by some results of experiments with an artificial rumen using ¹⁴C- and ³H-labeled compounds.     

Potentiometric sensor for on line glucose determination

Summary An enzymatic biosensor, with a flow-through sensor for continuous monitoring of glucose coupled to a Flow Injection Analysis (FIA) sampling line has been used to determine glucose over the range of 5 to 120 g/l. without sample dilution. The system can analyse 10 samples per hour. Calibration and reproducibility analysis have shown a good linearity and excellent results as compared to a commercial glucose analyser.     

A new floating sensor array to detect electric near fields of beating heart preparations

A new flexible sensor for in vitro experiments was developed to measure the surface potential, Φ, and its gradient, E (electric near field), at given sites of the heart. During depolarisation, E describes a vector loop from which direction and magnitude of local conduction velocity θ can be computed. Four recording silver electrodes (14 μm × 14 μm) separated by 50 μm, conducting leads, and solderable pads were patterned on a 50 μm thick polyimide film. The conductive structures, except the electrodes, were isolated with polyimide, and electrodes were chlorided. Spacer pillars mounted on the tip fulfil two functions: they keep the electrodes 70 μm from the tissue allowing non-contact recording of Φ and prevent lateral slipping. The low mass (9.1 mg) and flexibility (6.33 N/m) of the sensor let it easily follow the movement of the beating heart without notable displacement. We examined the electrodes on criteria like rms-noise of Φ, signal-to-noise ratio of Φ and E, maximum peak-slope recording dΦ/dt, and deviation of local activation time (LAT) from a common signal and obtained values of 24–28 μV, 46 and 41 dB, 497–561 V/s and no differences, respectively. With appropriate data acquisition (sampling rate 100 kHz, 24-bit), we were able to record Φ and to monitor E and θ on-line from beat-to-beat even at heart rates of 600 beats/min. Moreover, this technique can discriminate between uncoupled cardiac activations (as occur in fibrotic tissue) separated by less than 1 mm and 1 ms.     

A novel sensor based on electrochemical polymerization of diglycolic acid for determination of acetaminophen

Diglycolic acid (DA) polymer was coated on glassy carbon (GC) electrode by cyclic voltammetry (CV) technique for the first time. The electrochemical performances of the modified electrode were investigated by CV and electrochemical impedance (EIS). The obtained electrode showed an excellent electrocatalytic activity for the oxidation of acetaminophen (ACOP). A couple of well-defined reversible electrochemical redox peaks were observed on the ploy(DA)/GC electrode in ACOP solution. Compared with bare GC electrode, the oxidation peak potential of ACOP on ploy(DA)/GC electrode moved from 0.289 V to 0.220 V. Meanwhile, the oxidation peak current was much higher on the modified electrode than that on the bare GC electrode, indicating DA polymer modified electrode possessed excellent performance for the oxidation of ACOP. This kind of capability of the modified electrode can be enlisted for the highly sensitive and selective determination of ACOP. Under the optimized conditions, a wide linear range from 2 × 10(-8) to 5.0 × 10(-4)M with a correlation coefficient 0.9995 was obtained. The detection limit was 6.7 × 10(-9)M (at the ratio of signal to noise, S/N=3:1). The modified electrode also exhibited very good stability and reproducibility for the detection of ACOP. The established method was applied to the determination of ACOP in samples. An average recovery of 100.1% was achieved. These results indicated that this method was reliable for determining ACOP.     

Characterization of multicomponent monosaccharide solutions using an enzyme-based sensor array

We report the development of a sensor for rapidly and simultaneously measuring multiple sugars in aqueous samples. In this strategy, enzyme-based assays are localized within an array of individually addressable sites on a micromachined silicon chip. Microspheres derivatized with monosaccharide-specific dehydrogenases are distributed to pyramidal cavities anisotropically etched in a wafer of silicon (100) and are exposed to sample solution that is forced through the cavities by a liquid chromatography pumping system. Production of fluorescent reporter molecules is monitored under stopped-flow conditions when localized dehydrogenase enzyme systems are exposed to their target sugars. We demonstrate the capability of this analysis strategy to quantify beta-D-glucose and beta-D-galactose at low micromolar to millimolar levels, with no detectable cross-talk between assay sites. Analysis is achieved either through fluorescence detection of an initial dehydrogenase product (NADH, NADPH) or by production of a secondary fluorescent product created by hydride transfer from the reduced nicotinamide cofactor to a fluorogenic reagent. The array format of this sensor provides capabilities for redundant analysis of sugars and for monitoring levels of other solution components known to affect the activity of enzymes. The use of this strategy to normalize raw fluorescence signals is demonstrated by the determination of glucose and pH on a single chip. Alternatively, uncertainties in the activity of an immobilized enzyme can be accounted for using standard additions, an approach used here in the determination of serum glucose.     

A microelectronic pH sensor.

This paper presents preliminary data on a new integrated circuit microelectronic pH sensor. The device is extremely miniaturized by the use of integrated circuit technology, and uses the intrinsic hydrogen ion selective properties of the gate insulator material. In order to make the device compatible with aqueous solution monitoring, the silicon dioxide-silicon nitride gate insulator structure is used. The integrated circuit chip was designed, processed, and packaged by a variety of techniques which protect all metal parts from the aqueous solution. Test data are reported on leakage current, sensitivity, reproducibility, linearity, stability, response time, and life. The results indicate that this type of pH sensor may have many significant advantages for biomedical research and application.     

Microbial sensor for selective determination of sulphide

A microbial sensor consisting of immobilized Thiobacillus thiooxidans, a gas-permeable membrane, and an O₂ electrode was prepared for the determination of sulphide. When a sample solution containing sulphide was passed into the flow cell, the output of the microbial sensor decreased markedly with time until a steady state was reached. The total time required for an assay was 20–30 min by the steady-state method. In the pulse method, the total time required for an assay was about 5 min. A linear relationship was obtained between the sensor output and the concentration of sodium sulphide below 0.40 mm. The minimum detectable concentration of sodium sulphide was 0.02 mm. Selectivity of the sensor was satisfactory. The microbial sensor was applied to the determination of sulphide in spring water. A good agreement was obtained between the microbial sensor and the methylene blue method. The regression coefficient was 0.97 for five experiments. The activity of the microbial membrane was stable for more than 25 days. The response was reproducible with 2.5% of the relative standard deviation when a sample solution containing 0.2 mm sodium sulphide was employed. *** DIRECT SUPPORT *** AG903053 00005     

Real-time odor discrimination using a bioelectronic sensor array based on the insect electroantennogram

Current trends in artificial nose research are strongly influenced by knowledge of biological olfactory systems. Insects have evolved over millions of years to detect and maneuver toward a food source or mate, or away from predators. The insect olfactory system is able to identify volatiles on a time scale that matches their ability to maneuver. Here, biological olfactory sense organs, insect antennae, have been exploited in a hybrid-device biosensor, demonstrating the ability to identify individual strands of odor in a plume passing over the sensor on a sub-second time scale. A portable system was designed to utilize the electrophysiological responses recorded from a sensor array composed of male or female antennae from four or eight different species of insects (a multi-channel electroantennogram, EAG). A computational analysis strategy that allows discrimination between odors in real time is described in detail. Following a training period, both semi-parametric and k-nearest neighbor (k-NN) classifiers with the ability to discard ambiguous responses are applied toward the classification of up to eight odors. EAG responses to individual strands in an odor plume are classified or discarded as ambiguous with a delay (sensor response to classification report) on the order of 1 s. The dependence of classification error rate on several parameters is described. Finally, the performance of the approach is compared to that of a minimal conditional risk classifier.     

Label-free antibody-antigen binding detection by optical sensor array based on surface-synthesized gold nanoparticles

Gold nanoparticles grown in situ from printed seed particles on a glass substrate have been fabricated into a biosensor array. The light-scattering properties of the resulting surfaces show sensitivity to changes in the local refractive index. Each array spot is functionalized with fibrinogen or bovine serum albumin and scattered radiation is used to monitor the refractive index change on label-free binding of the antibodies to their antigens from whole blood antiserum. Data were collected real-time and the association rate constants for the specific antibody-antigen binding were derived from a kinetic analysis. The minimum antibody concentration detection sensitivity is of 100 nM.     

Investigation of selective protein immobilization on charged protein array by wavelength interrogation-based SPR sensor

We have investigated the use of multilayer films of polyelectrolytes as selective surfaces to analyze protein interactions with a self-assembled SPR wavelength-shift sensor. Charged arrays were prepared by alternating adsorption of the charged polyelectrolytes, poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS). Multilayer formation was monitored with the SPR wavelength-shift sensor and a Spreeta SPR sensor. Protein immobilization on the charged surfaces, which was also analyzed by the SPR sensors, was dependent on the pI of the proteins. Tissue transglutaminase (tTGase) and beta-galactosidase (pIs, 5.1 and 5.3, respectively) were preferentially bound to the positively charged PDDA surface, whereas lysozyme (pI, 11.0) was selectively bound to the negatively charged PSS surface. Immobilization of tTGase on the PDDA surface was also dependent on the buffer pH. The interaction of tTGase with RhoA(V14), a constitutively active form of Rho, could be detected on the charged arrays with the wavelength-shift sensor. The arrays could be reutilized at least 5 times. Thus, it is likely that charged surfaces, assembled by the layer-by-layer method using polyelectrolytes, will prove useful for preparing selective protein arrays.     

A new amperometric nanostructured sensor for the analytical determination of hydrogen peroxide

A new amperometric, nanostructured sensor for the analytical determination of hydrogen peroxide is proposed. This sensor was constructed by immobilizing silver nanoparticles in a polyvinyl alcohol (PVA) film on a platinum electrode, which was performed by direct drop-casting silver nanoparticles that were capped in a PVA colloidal suspension. UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy were used to give a complete characterization of the nanostructured film. Cyclic voltammetry experiments yielded evidence that silver nanoparticles facilitate hydrogen peroxide reduction, showing excellent catalytic activity. Moreover, the cronoamperometric response of modified sensors was dependent on nanoparticle lifetime. Experiments were performed, using freshly prepared solutions, after 4 and 8 days. Results concerning the quantitative analysis of hydrogen peroxide, in terms of detection limit, linear range, sensitivity and standard deviation (STD), are discussed for each tested sensor type. Utilization of two different linear ranges (40 microM to 6mM and 1.25 microM to 1.0mM) enabled the assessment of concentration intervals having up to three orders of magnitude. Moreover, the electrode made using a 4-day-old solution showed the maximal sensitivity of 128 nA microM(-1)(4090 nA microM(-1)cm(-2)), yielding a limit of detection of 1 microuM and STD of 2.5 microAmM(-1). All of these analytical parameters make the constructed sensors suitable for peroxide determination in aqueous solution.     

Microbial sensor system which usesMethylomonas sp. for the determination of methane

Summary Pseudomonas putida (ATCC 111 72) was studied in a continuous culture at various dilution rates with asparagine as the sole carbon source and limiting factor. Under the experimental conditions applied, a considerable number of the cells became attached to the fermentor walls and equipment. The viable count of the attached cells was of the same magnitude as those in suspension. The following steady-state characteristics were obtained: The cell-mass (OD₆₂₀ and dry weight) versus dilution rate (D) had maxima at 0.63 and 1.1 h⁻¹. The corresponding plot of viable count had a minimum at 0.94 h⁻¹ whereafter it reached a maximum at 1.3 h⁻¹. Largest yield coefficient obtained was 0.44 g dry weight/g asparagine (D=1.1 h⁻¹). The productivity of the culture increased with D up to 1.1 h⁻¹, which is far above the D corresponding to the maximum specific growth rate (^μmax) of a batch culture (0.59 h⁻¹). The cell mass was not completly washed-out of the fermentor even at a D of 2.2 h⁻¹. The influence of attached growth for the steady-state characteristics, and the significance of the results in relation to chemostate as an instrument for testing environmental factors, are discussed. It is suggested that the attached cells had a significantly higher (^μmax) value than the suspended ones.     

Electrochemical sensor based on Arthrobacter globiformis for cholinesterase activity determination

The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type oxygen probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type oxygen probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 x 10(-4) moldm(-3), with detection limit of 8 x 10(-8) moldm(-3) and sensitivity of 4 x 10(-1) microAcm(3)mol(-1), at pH 6, temperature of 25 degrees C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mUcm(-3), with a slope of 1.97 x 10(-2) microAcm(3)mU(-1), at pH 6, temperature of 25 degrees C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.