Jacques Pistre

A love-wave gas sensor coated with functionalized polysiloxane for sensing organophosphorus compounds

Love-wave devices based on quartz piezoelectric substrate and SiO2 guiding layer coated with a specific polysiloxane polymer are used to detect organophosphorus compounds. This allows to study affinities of the polysiloxane polymer coating towards organophosphorus compounds, and to demonstrate the high sensitivity of love-wave devices for gas detection. We also present a theoretical model which describe wave propagation in love devices and allow to design optimized structures. Then, we discuss experimental results, in terms of interactions between sensor and vapor and in comparison to SAW results.

Real time device for biosensing: design of a bacteriophage model using love acoustic waves.

Love wave sensors (ST-cut quartz substrate with interdigital transducers, SiO(2) guiding layer and sensitive coating) have been receiving a great deal of attention for a few years. Indeed, the wave coupled in a guiding layer confers a high gravimetric sensitivity and the shear horizontal (SH) polarization allows to work in liquid media. In this paper, an analytical method is proposed to calculate the Love wave phase velocity and the gravimetric sensitivity for a complete multilayer structure. This allows us to optimize the Love wave devices design in order to improve their gravimetric sensitivity in liquid media. As a model for virus or bacteria detection in liquids (drinking or bathing water, food em leader ) we design a model using M13 bacteriophage. The first step is the anti-M13 (AM13) monoclonal antibody grafting, on the device surface (SiO(2)). The second step is an immunoreaction in between the M13 bacteriophage and the AM13 antibody. The Love wave device allows to detect in real time the graft of the AM13 sensitive coating, as well as the immobilization of the M13 bacteriophages. With a pH change, the M13 bacteriophages can be removed from the sensor surface, in order to be numerated as plaque forming unit (pfu). Results on the sensitivity of Love waves are compared with similar immunological works with bulk acoustic wave devices, and demonstrate the high potentialities of Love waves sensors.

Microwave sensors: a new sensing principle. Application to humidity detection

Abstract We are presenting here a new approach to gas sensor, using the electromagnetic (e.m) properties variation of some sensitive materials in the presence of gas at ultrahigh frequencies (ca. 1 GHz). The chemical sensor basically consists of a microwave resonator to which a sensitive coating is added. The e.m perturbation can be seen through a frequency variation measurement when the sensor serves as feedback element in an oscillator chain. After the development of a narrow-band-pass filter, a permittivity variation study is done, thanks to an e.m simulator HP-MDS. Then a humidity sensor is designed and tested. A good sensitivity as well as a great reversibility are obtained.

Study of acoustic Love wave devices for real time bacteriophage detection

Abstract Acoustic wave devices have shown their good potentialities for real time monitoring of immunoreactions. Different acoustic wave devices (BAW, SHAPM, Love waves) were described for applications in liquid medium. Love wave delay line structures (ST cut quartz substrate with interdigital transducers, SiO2 guiding layer) present several advantages, in particular, the pure shear horizontal polarisation adapted to liquid medium, and its very high sensitivity related to the wave confining in the thin guiding layer. In this paper an analytical method based on multilayer propagating structure is first presented: it allows us to estimate the Love wave phase velocity and then the mass loading effect sensitivity. A few theoretical results are exposed; they show that this theoretical analysis can allow to optimise physical parameters in order to conceive powerful devices for detection applications in liquid medium. As a model for virus or bacteria detection in liquids (drinking or bathing water, food, etc.), we design a model using M13 bacteriophage. The first step is the anti-M13 antibody binding. By using a Labwindows CVI software, we can monitor in real time the graft of the anti-M13 antibody sensitive coating, as well as the detection of the M13 bacteriophages. Experimental results are exposed, analysed and discussed. Love waves sensors appear to be a powerful approach for immunodetection, as theoretically predicted.

SYNTHESIS AND EVALUATION OF FLUOROPOLYOL ISOMERS AS SAW MICROSENSOR COATINGS : ROLE OF HUMIDITY AND TEMPERATURE

Abstract A surface acoustic wave (SAW) organophosphorus gas detector has been designed, fabricated and tested. The gas detector consists of a dual delay line fabricated on a single quartz substrate. Each delay line is connected into the feedback path of a radio-frequency amplifier, to realize a SAW oscillator. The propagation path of one delay line is coated with fluoropolyol (FPOL). These polymers offer an interesting way to detect organophosphorus compounds like GB at low concentration levels. The absorption of vapors induces phase variations due to mass loading and stress effects. These variations result in corresponding frequency shifts. In this work, we have synthesised the four FPOL isomer combinations separately and characterized these materials by physico–chemical analysis. A series of SAW sensors have been coated with these materials and experimental results as a function of vapor concentration are presented. The influence of coating thickness, temperature and humidity are examined. Results showed on one hand that frequency variations are linear with GB gas concentrations from 0.5 to 10 ppm and on the other hand that sensitivity to organophosphorus compounds is two times greater in wet atmospheres (RH=60%) than in dry air. The sensitivity was also better at a working temperature close to the glass transition point ( T G ) of the polymer. Above T G , the modification of the polymer structure induced a great radiation of the acoustic energy in the coating.

A surface acoustic wave gas sensor: detection of organophosphorus compounds

Abstract Over the last decade, there has been great interest in chemical applications of acoustic wave devices, especially those using surface acoustic waves (SAWs). This work deals with the sensing of an organophosphorus gas using a SAW delay line spin-coated with a specific organic compound. The sensing cell as well as the measurement bench are completely described. Reproducible responses to pollutant concentrations from 10 to 100 ppm at various temperatures (25, 30 and 50 °C) are presented. The described sensor has a sensitivity of 27 Hz ppm − at 30 °C.

Detection of GB and DMMP vapors by Love wave acoustic sensors using strong acidic fluoride polymers

In this paper, we present a comparative study of GB and DMMP vapor detection using Love wave devices. Acoustic sensors are optimized versus the mass loading effect according to theoretical results, and a specific sensitive coating based on polysiloxane polymer is used to ensure selectivity. Experimental results allow us to compare the interactions between the coating and both gases. An estimation of the diffusion coefficient of each gas (GB and DMMP) was performed and we linked the dynamic of the responses with the sorption kinetics.

Love-waves to improve chemical sensors sensitivity: theoretical and experimental comparison of acoustic modes

Both a theoretical and experimental comparison of the sensitivities of various acoustic wave sensors is presented. From a theoretical point of view, several methods to calculate the sensors mass loading sensitivity are reviewed. Particular attention is turned on Love-wave devices which present a high sensitivity, and are very promising chemical sensors. Experimental tests of gas detection are presented for SAW, SH-APM and Love-wave sensors. The results are discussed. Experimental sensitivities are compared. Some hypotheses are given to explain the discrepancy between theoretical and experimental results.

A shear horizontal acoustic plate mode (SH-APM) sensor for biological media

Abstract Acoustic wave devices are often used as chemical sensors. Those described in the literature are merely based on bulk waves or on surface waves (SAW), also called Rayleigh waves. In this paper we describe another type of device, based on shear-horizontal acoustic plate mode (SH-APM) waves. Experimental results with various modes concerning the influence of the temperature, the viscosity and the concentration of NaCl and tris(hydroxymethyl)aminomethane (Tris) in aqueous solution are presented: they show the better sensitivity of higher-order modes. These results show that this device can be used as a sensor in a biological medium.

Thick film pellistor array with a neural network post-treatment

Abstract In pellistor gas sensors, the heat exhaust produced by the catalytic combustion of reducing gases increases the temperature of the device. A typical pellistor consists of a platinum wire supported in an alumina bead impregnated with a finely dispersed noble metal like palladium. The platinum wire serves as heater of the bead to its operating temperature and as a thermometer. In reality, the temperature measured by the resistance of the Pt wire is compared to that of a reference element which has a similar structure but without any catalytic activity. No selectivity of such a device has to be expected since the catalytic combustion of any combustible gas will lead to a temperature increase of the device. In order to try to achieve selectivity to methane, we have in a first step exploited the differential activity of palladium and platinum by using two screen-printed pellistors, one based on Pd and the other on Pt. At around 400 °C, all reducing gases including methane are oxidized by Pd whereas Pt oxidized all gases except methane. In order to extend the recognition process to combustible gases other than methane, that is to propane, and ethanol vapour, a small array of four pellistors with various percentages of Pd and Pt has been elaborated with thick film technology, which is very valuable for realizing series of similar sensors, required in arrays. The four microcalorimetric sensors are exposed to various gases and various concentration values. A recognition of methane, propane, and ethanol is obtained by neural network techniques. The network consists of three layers: an input layer; a hidden layer; and an output layer which permits gas identification. Back-propagation is used as the learning algorithm. In this case, the selectivity of the system is demonstrated.