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

Event: IBERSENSORS 2006. Montevideo, Uruguay (2006)

A Monoclonal Antibody-based Piezoelectric Immunosensor for the analysis of pesticides was developed. Functionalized AT-cut 9 MHz quartz crystals integrated in a flow-through system were used as the transducer element. Pesticide detection was accomplished by competitive immunoassay in the conjugate-coated format, using specific monoclonal antibodies. Working in the microgravimetric mode, the frequency variations of the piezoelectric crystal were measured and correlated with the concentration of the pesticide in the sample. Frequency signals were inversely proportional to the pesticide concentrations, thus providing decreasing sigmoidal calibration curves. The immunosensor sensitivity (estimated as the assay I₅₀ value) was around 30 µg/l. The limits of detection ( I₉₀ values) were around 7 µg/l. A complete assay cycle, including regeneration, was performed in 20 min. and each sensor could be reliably reused for one hundred times. These analytical performance would allow the detection of pesticides in fruits and vegetables at European regulatory levels.

Authors: R. Torres, A. Arnau, H. Perrot, J. García, C. Gabrielli

Journal: Electronics Letters, Vol 42, N. 22, pp 1272-1273 (2006)

Requirements for frequency–voltage conversion in alternating current (AC) electrogravimetry are introduced. A new frequency–voltage conversion system based on a double tuning analogue–digital phaselocked loop is proposed. The reported results prove its reliability for AC electrogravimetry measurements.

Introduction: AC electrogravimetry is based on an electrochemical quartz crystal microbalance (EQCM) used in dynamic regime. In EQCM one of the deposited gold electrodes of the quartz crystal resonator can be coated with an electroactive polymer film and can be used as the working electrode (WE) following a classical electrochemical configuration. The frequency shift of the quartz crystal microbalance (QCM) allows obtaining of the mass response associated with the charge transfer, which occurs at polymer=electrolyte interface. AC electrogravimetry was proposed to characterise and separately identify ions and solvent motion at the film=electrolyte interface. In this technique the mass response to a small potential perturbation is analysed in the frequency domain thanks to a fast QCM used in dynamic regime; for that, a continuous voltage with a superimposed small potential sinusoidal perturbation is applied between the reference electrode and the WE of the electrochemical cell. Thus, the so-called electrogravimetric transfer function (EGTF), defined as the ratio (Dm=DE) between the amplitude of induced mass change (Dm) and the perturbation amplitude (DE), can be plotted in a complex plane for the entire range of perturbation frequencies. The various species involved are characterised by a loop in the complex plane and can be separately identified when the loops do not overlap.

Authors: C. March, A. Abad, A. Arnau, Y. Jiménez, T. Sogorb, A. Montoya

Event: 4th MGPR International Symposium of pesticides in food and the environment in Mediterranean Countries. Pine Bay Holiday Resort Kusadasi-Aydin. Turkey (2005)

Immunosensors combine immunoassay selectivity with the high sensitivity often provided by electronic signal transducers. In this communication, the development of a monoclonal antibody-based Piezoelectric Immunosensor for the analysis of carbaryl is described and coupled to BSA were covalently attached to gold coated AT- cut 9 MHz quartz crystals, previously functionalized with a self-assembled alkanethiol monolayer. The crystal was inserted in a homemade Arnite cell that allowed only one face of the crystal to be in contact with the reagents. The cell was integrated in a flow-through system and pesticide detection was accomplished by competitive immunoassay in the conjugate-coated format. The assay consisted of the incubation of the analyte with a specific monoclonal antibody, followed by the immunoreaction of the mixture with the carbaryl derivative immobilized on the sensor surface. The frequency variations of the piezoelectric crystal were measured with a commercial Research Quartz Crystal Microbalance (RQCM) and correlated with the carbaryl concentration in the standards. The total time required for a complete assay cycle, including regeneration, was 20 min. As it corresponds to binding inhibition immunoassays, the frequency signal provided by the sensor was inversely proportional to the analyte concentration. A sigmoidal calibration curve was obtained by fitting experimental points to a four-parameter equation. The immunoassay sensitivity, expressed as the carbaryl concentration that reduced the assay signal by 50% (I50), was around 25 µg/l. The inhibition curve would allow the detection of carbaryl in fruits and vegetables at European regulatory levels.

Authors: A. Arnau, Y. Jiménez, R. Torres

Event: 5th edition of Acoustic Wave Based Sensors: Fundamentals, Concepts, New Applications. Physikzentrum Bad Honnef, Germany (2005)

An Electrochemical Quartz Crystal Microbalance is used for a continuous monitoring of the growth of the polymer poly(3,4-ethylenedioxy) thiopene tetrabutyammonium perchlorate (PEDT-TBAP), which is electro-polymerized in acetonitrile of a gold electrode of a 10 MHz quartz crystal resonator. The surface acoustic impedance of the resonator is analyzed starting from the electrical admittance continuously measured by means of a network analyzer. Changes in the acoustic impedance suggest that a mechanical resonance phenomenon occurs during the electro-deposition of the coating. In order to determine the origin of this effect, the evolution of the physical properties of the coating is analyzed. The extraction of the physical properties of the coating is carried out by means of an algorithm recently developed by the authors. Four sets of coating properties are obtained with the algorithm in four different conditions. In one of them an additional technique, ellipsometry, is used to have an alternative measurement of the coating thickness, no additional techniques are necessary in the rest of the cases. All the cases show a significant change in the viscoelastic properties of the coating during the time-interval of the suspected mechanical resonance. Changes in the surface roughness of the coating during the experiment are confirmed by scanning electron microscopy (SEM). The analysis of the surface roughness of the coating and its effect on the effective values of the coating properties, seem to indicate that the changes in the viscoelastic properties are due to the changes in the surface roughness of the coating, and that these changes are responsible for the mechanical resonance effect. This analysis is carried out by means of the same algorithm which is used, in this case, as a simulation tool.

Authors: Y. Jiménez, A. Arnau, T. Sogorb, M. Otero, E. Calvo

Event: 4th Acoustic Wave Sensor Workshop. Salbris, France (2003)

A new algorithmic strategy which permits an unambiguous extraction of the effective surface mass density, loss tangent and characteristic impedance of the first coating layer in AT cut quartz crystal resonators (QCR) is introduced. A preliminary analysis of the propagating error in the determination of these effective physical parameters, due to practical errors in the admittance measuring system or due to a lack of precision in the admittance model for describing the real admittance of the sensor, is presented as well. This analysis makes clear the necessity of a standard indicating the specifications of the measuring system including the cell interface for an appropriate sensor characterization.