Guido Huyberechts

Nanoscaled interdigitated electrode arrays for biochemical sensors

Abstract Nanoscaled interdigitated electrode arrays were made with deep UV lithography. Electrode widths and spacings from 500 down to 250 nm were achieved on large active areas (0.5×1 mm). These electrodes allow for the detection of affinity binding of biomolecular structures (e.g. antigens, DNA) by impedimetric measurements. Such a sensor with Pd electrodes on SiO 2 is developed and theoretically analysed. It was experimentally characterised in KCl solutions demonstrating its bulk-insensitive behaviour and the immobilisation of glucose oxidase (GOD) could be monitored by measuring the double layer impedance.

Simultaneous quantification of carbon monoxide and methane in humid air using a sensor array and an artificial neural network

Abstract The simultaneous quantification of carbon monoxide and methane in humid air is presented. The response of a three-sensor array, including an undoped and a platinum doped tin dioxide sensor showing non-ideal selectivity and a humidity sensor is fed into an optimised feed forward back propagation artificial neural network in order to obtain the carbon monoxide and methane concentration as network output. The gaseous environments under study were ternary mixtures in the concentration ranges of 0–0.5% methane, 0–1000 ppm carbon monoxide and 0–60% relative humidity at 20°C. The network structure, network output with respect to a priori known test concentrations and the influence of the size of the training data set is discussed.

Stochastic simulation of chemically activated unimolecular reactions

The kinetic master equation for the title processes can be formulated as a traditional deterministic set of coupled differential reaction-rate equations, or, alternatively, as a stochastic process in which each reaction is a random–walk transition in energy–species space. This stochastic description is the basis for three methods we describe here to numerically solve the kinetic master equation for chemically activated unimolecular reactions. The first method allows the calculation of the complete time evolution within a given mechanism, and is based on Gillespie’s exact stochastic method (ESM). It is essentially a Monte Carlo simulation of the stochastic reaction processes. The second method allows for the direct calculation of the steady-state product distribution (DCPD). It describes the random walk within the framework of a discrete time Markov chain, and reduces the calculation of the steady-state product distribution to a fairly simple matrix algebra problem. The third method calculates the steady-s...

Synthesis and characterization of tin dioxide powders for the realization of thick-film gas sensors

Abstract Semiconductor gas sensors produced with screen-printing techniques and based on home-made tin dioxide inks are presented. The ink consists of home-made tin dioxide powder added to a polymer solution to make it screen printable on 96% alumina substrates. The major work is performed on the preparation and the characterization of pure undoped tin dioxide powder produced by two different synthetic pathways. Inks prepared with powders from each method are consecutively handled in an identical way to obtain gas sensors. The sensor response towards different gases is measured and compared for both types of starting materials.

Characterisation of strontium containing tin dioxide based thick film humidity sensors

Abstract Humidity is an important process parameter in a variety of industrial and agro-industrial processes. Ceramic based humidity sensors find an application in these domains where relatively high humidity levels are frequently encountered. Humidity sensitive materials based on tin dioxide, strontium carbonate and zinc borosilicate mixtures are used to prepare precursors powders for thick film humidity sensors. The responses of sensors based on well defined ink formulations are analysed by impedance spectroscopy. The influence of composition of the sensing material and operating frequency is studied in order to obtain optimum sensing conditions at room temperature. Over the range of compositions studied the sensor materials show an appreciable variation in humidity sensitivity, film adhesion, optimum operating frequency, etc. It is concluded that notwithstanding a drastic increase in sensitivity due to the addition of zinc borosilicate, sensor materials containing approximately equal weights of tin dioxide and strontium carbonate show the best acceptable overall properties for sensor applications in relatively humid environments.

In situ formation of humidity-sensitive devices for the evaluation of solar panel encapsulations

A certain deterioration of solar panels under long-term working conditions can be attributed to the effect of humidity entrapment or penetration in the encapsulate polymer. Afterwards, corrosion of contacts can be initiated, with device failure as a consequence. A measuring technique that allows the monitoring of humidity changes inside the finished solar panel is described. The electrical characteristics of the encapsulating polymer are monitored by electrochemical impedance spectroscopy, using screen-printed interdigitated electrodes as electrical contacts. The alumina substrate containing the sensing structure is encapsulated under circumstances identical to those used for the solar cells, and the humidity-related electrical characteristics of the encapsulating polymer itself are used as the sensor signal. The influence of the construction of multilayer structures with different protective top layers (glass, Tedlar®) on humidity is reported.

Studies on the Relationship between Esophageal Acid Exposure, Mucosal Lesions and Heartburn Using an Acid Exposure Sensor

Background: In vitro studies of a recently developed acid exposure sensor show that the sensor response (SR) to acid < pH 4 is linearly determined by the duration and degree of acidity. The aim was to determine whether SR correlates with the severity of acid-induced esophageal mucosal lesions and acid-induced heartburn. Methods: HCl pH 1.5 or saline was infused into the feline esophagus for 5-20 min. Simultaneously, sensor measurements were performed below the infusion port. The histological damage was scored by an independent pathologist. In 15 normal subjects, HCl pH 1 was infused into the esophagus and the severity of the heartburn (0-5) was scored at 5-min intervals. In 10 subjects who experienced heartburn during acid perfusion, initial perfusion with HCl was repeated during heartburn induction time minus 5 min, followed by perfusion with the subjects own gastric juice, titrated to pH 2; heartburn severity was again scored at 5-min intervals. Acid exposure sensors positioned below the infusion port were removed at heartburn scores 1, 2 and 3. Results: A good correlation was found between SR and the histological score for mucosal damage in the cat esophagus ( r = 0.64, P < 0.005). There was a good relation between heartburn severity score and acid exposure time ( r = 0.84, P < 0.001), and a significant but weaker relation between heartburn severity and SR. Conclusion: In cats, there is a good relation between the severity of acid-induced esophageal mucosal lesions and SR. In men, there is a significant correlation between the severity of acid-induced heartburn and the simultaneously measured SR. Therefore, SR measurement has the potential of yielding clinically relevant information in the investigation of GERD.

Development of a disposable probe for the evaluation of acid-induced damage of the oesophageal mucosa

Abstract The development of a disposable probe to measure the acid burden over an extended period of time is reported. The probe consists of a screen-printed matrix that shows decomposition as a function of pH and exposure time. The concept development and realisation of the probe is discussed, and experimental results, both in vitro and under pre-clinical in vivo conditions, are presented. The in vitro experiments prove the validity of the concept and the feasibility of the approach. The in vivo experiments indicate that there is a good correlation between the probe response and the oesophageal epithelial cell damage produced by oesophageal acid perfusion of the feline oesophagus.

Validation of a New Method of Measuring Esophageal Acid Exposure: Comparison with 24-Hour pH Monitoring

Recently, we developed a disposable acid exposure sensor whose in vitro response to acid below pH 4 is linearly determined by the duration of exposure and the degree of acidity. The aim of the present study was to compare the SR to simultaneous esophageal pH and duodenogastroesophageal reflux (DGER) monitoring (Bilitec) in patients investigated for presumed gastroesophageal reflux disease (GERD). Twenty-six patients (16 men, mean age 46 ± 2 years) with symptoms suggestive of GERD underwent 24-hr ambulatory pH monitoring and SR monitoring at 5 cm proximal to the LES. DGER monitoring was performed in 21 patients. Exposure of the esophagus to acid and to DGER were analyzed. These data were compared to SR. A significant correlation was found between the exposure of the distal esophagus to acid and SR (R = 0.85; P < 0.0001). Similarly, the area below a cutoff pH 4 was significantly correlated to SR (r = 0.81; P < 0.0001). SR was not correlated to DGER (r = 0.16; NS). At a cutoff of 50, the sensitivity and specificity of SR to predict esophageal acid exposure >5% of time were 91% and 93%, respectively conclusion, the response of the acid exposure sensor is strongly correlated with the results of simultaneous esophageal pH monitoring. The sensor seems able to reliably predict pathological esophageal acid exposure. These findings warrant larger studies of the clinical potential of the acid exposure sensor in the diagnosis and quantification of GERD.

Gas sensor arrays for quantitative analysis and alarm generation

The use of different approaches for analysing the response of a small sensor array based on artificial neural networks is presented. In one case the quantification of all compounds in a three component mixture is discussed. Based on the same gas sensor array (and data) an approach for extracting safety information directly from the sensor array response is illustrated. Carbon monoxide and methane have been selected as target gases in this study because of their importance in domestic environments.