A piezoelectric immunosensor for the determination of pesticide residues and metabolites in fruit juices

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Authors: C. March, J.J. Manclús, Y. Jiménez, A. Arnau, A. Montoya

Journal: Talanta (2008)

A quartz crystal microbalance (QCM) immunosensor was developed for the determination of the insecticide carbaryl and 3,5,6-trichloro-2-pyridinol (TCP), the main metabolite of the insecticide chlorpyrifos and of the herbicide triclopyr. The detection was based on a competitive conjugate-immobilized immunoassay format using monoclonal antibodies (MAbs). Hapten conjugates were covalently immobilized, via thioctic acid self-assembled monolayer (SAM), onto the gold electrode sensitive surface of the quartz crystal. This covalent immobilization allowed the reusability of the modified electrode surface for at least one hundred and fifty assays without significant loss of sensitivity. The piezoimmunosensor showed detection limits (analyte concentrations producing 10% inhibition of the maximum signal) of 11 and 7µg l-¹ for carbaryl and TCP, respectively. The sensitivity attained (I50 value) was around 30µg l-¹ for both compounds. Linear working ranges were 15–53µg l-¹for carbaryl and 13–83µg l-¹ for TCP. Each complete assay cycle took 20 min. The good sensitivity, specificity, and reusability achieved, together with the short response time, allowed the application of this immunosensor to the determination of carbaryl and TCP in fruits and vegetables at European regulatory levels, with high precision and accuracy.

Improved electronic interfaces for AT-cut quartz crystal microbalance sensors under variable damping and parallel capacitance conditions

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Authors: A. Arnau, J.V. García, Y. Jiménez, V. Ferrari, M. Ferrari

Journal: Review of Scientific Instruments, vol. 79 (2008)

A new configuration of automatic capacitance compensation ACC technique based on an oscillatorlike working interface, which permits the tracking of the series resonant frequency and the monitoring of the motional resistance and the parallel capacitance of a thickness-shear mode quartz crystal microbalance sensor, is introduced. The new configuration permits an easier calibration of the system which, in principle, improves the accuracy. Experimental results are reported with 9 and 10 MHz crystals in liquids with different parallel capacitances which demonstrate the effectiveness of the capacitance compensation. Some frequency deviations from the exact series resonant frequency, measured by an impedance analyzer, are explained by the specific nonideal behavior of the circuit components. A tentative approach is proposed to solve this problem that is also common to previous ACC systems.

Improved frequency/voltage converters for fast quartz crystal microbalance applications

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Authors: R. Torres, J.V. García, A. Arnau, H. Perrot, L. To Thi Kim, C. Gabrielli

Journal: Review of Scientific Instruments, vol. 79, (2008)

The monitoring of frequency changes in fast quartz crystal microbalance QCM applications is a real challenge in today’s instrumentation. In these applications, such as ac electrogravimetry, small frequency shifts, in the order of tens of hertz, around the resonance of the sensor can occur up to a frequency modulation of 1 kHz. These frequency changes have to be monitored very accurately both in magnitude and phase. Phase-locked loop techniques can be used for obtaining a high performance frequency/voltage converter which can provide reliable measurements. Sensitivity higher than 10 mV/ Hz, for a frequency shift resolution of 0.1 Hz, with very low distortion in tracking both the magnitude and phase of the frequency variations around the resonance frequency of the sensor are required specifications. Moreover, the resonance frequency can vary in a broad frequency range from 5 to 10 MHz in typical QCM sensors, which introduces an additional difficulty. A new frequency-voltage conversion system based on a double tuning analog-digital phase-locked loop is proposed. The reported electronic characterization and experimental results obtained with conducting polymers prove its reliability for ac-electrogravimetry measurements and, in general, for fast QCM applications.

A review of interface electronic systems for AT-cut Quartz Crystal Microbalance Applications in Liquids

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Authors: A. Arnau

Journal: Sensors: Special Issue: Piezolectric sensors for determination of analytes in solutions, 370-411 (2008)

 

From the first applications of AT-cut quartz crystals as sensors in solutions more than 20 years ago, the so-called quartz crystal microbalance (QCM) sensor is becoming into a good alternative analytical method in a great deal of applications such as biosensors, analysis of biomolecular interactions, study of bacterial adhesion at specific interfaces, pathogen and microorganism detection, study of polymer film-biomolecule or cell-substrate interactions, immunosensors and an extensive use in fluids and polymer characterization and electrochemical applications among others. The appropriate evaluation of this analytical method requires recognizing the different steps involved and to be conscious of their importance and limitations. The first step involved in a QCM system is the accurate and appropriate characterization of the sensor in relation to the specific application. The use of the piezoelectric sensor in contact with solutions strongly affects its behavior and appropriate electronic interfaces must be used for an adequate sensor characterization. Systems based on different principles and techniques have been implemented during the last 25 years. The interface selection for the specific application is important and its limitations must be known to be conscious of its suitability, and for avoiding the possible error propagation in the interpretation of results. This article presents a comprehensive overview of the different techniques used for AT-cut quartz crystal microbalance in insolution applications, which are based on the following principles: network or impedance analyzers, decay methods, oscillators and lock-in techniques. The electronic interfaces based on oscillators and phase-locked techniques are treated in detail, with the description of different configurations, since these techniques are the most used in applications for detection of analytes in solutions, and in those where a fast sensor response is necessary.

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Piezoelectric transducers and applications, Second Edition.

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piezoelectric transducers and applicationsAuthors: Arnau A., Brett C., Bittencourt, Ch., Calvo E., Canetti, R., Coelho, W., Ferrari V., Jiménez Y., Kanazawa K., Leija L., Luckmlum R., March, C., Montoya, A., Muñoz R., Negreira, C., Ocampo, A., Otero M., Perrot., Ramos A., San Emeterio J.L., Soares D., Sogorb T., Stipek S, Vera, A.

Published by: Springer-Verlag Berlin Heidelberg (2008).

Since the publication of the first edition, the richness of the study of piezoelectric transducers has resulted in a large number of studies dealing both with new understandings underlying the principles, with new technological advances in its applications and indeed with developing new areas of utility for these transducers. The motivations driving the publication of that first edition as described in its foreword (which follows) continues with increased validity. The value of a second edition to include these new developments has been prepared. During the interim, the contributors and their students have not only continued, but increased their mutual interactions resulting in an amazing energy and synergy which is revealed in this edition.

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