Authors: J.V. García, C. March, A. Sánchez, Y. Montagut, Y. Jiménez, A. Montoya, A. Arnau

Event: Biosensors 2012, 22 World Congress on Biosensors. Cancún, México (2012)

A 50 MHz quartz crystal microbalance (QCM) immunosensor has been developed for the determination of pesticides. High fundamental frequency (HFF) inverted mesa quartz crystal resonators were used. To provide mechanical stability and robustness quartz crystal resonators were attached permanently to a PEEK chip holder. This also allowed easy manipulation in all experimental processes. An automated flow injection analysis system was developed. The system consists of: the flow cell for the sensor chips; a flow circuit with automated syringe pumps, distribution and injection valves; and an electronic characterization system, based on the phase mass measurement at constant frequency. Carbaryl pesticide was chosen as a model analyte. Due to the low molecular weight of this insecticide, the immunoassay format chosen was a competitive one, with monoclonal antibodies (MAbs). The hapten conjugate was covalently immobilized, via mercaptohexadecanoic acid (MHA) self assembled monolayer (SAM), onto the sensor electrode surface. The immunosensor results showed an improvement of one order of magnitude in terms of sensitivity (I₅₀ ≈ 2 μg/L) and two orders of magnitude in terms of limit of detection (LOD < 0,2 μg/L), compared with results obtained with standard 10MHz QCM sensors previously reported by our group. The automated analysis system allowed a very good reproducibility of measurements. Further improvement in terms of sensitivity and limit of detection could be easily accomplished working with higher fundamental frequency sensors (100-150 MHz), which can be directly used with the developed system.

Authors: J. Fochtmann, C. Peters, R. Fernández, R. Lucklum, D. McCann, J. Vetelino, A. Arnau

Journal: Sensors and actuators B: Chemical (2012)

Investigating the electrical sensitivity of lateral field excited resonators (LFE) we observed two characteristics to highly impact sensitivity. First, an increase of the piezoelectric coupling factor k enhances the viscosity measurement range. Higher coupling factors are provided by the use of new materials, namely lithium tantalite (LiTaO3) and lithium niobate (LiNbO3) with coupling factors of 0.43 and 0.91 respectively. Since the sensitivity to electrical load parameters is governed by relative permittivity of the resonator material itself, the sensitivity to electrical parameters is found to decrease for new materials. Second, an electrode pattern that reveals higher energy trapping in the center of crystal was investigated. Compared to common LFE pattern, a third electrode was introduced in center between bite wing electrodes. Finite element modeling in ANSYS© shows enhanced sensitivity to low relative permittivity in range from 1 to 8. We performed experiments to verify the simulation results. Although an increased frequency shift compared to common LFE resonators was not observed, significantly higher conductance amplitudes occurred, which enhances the measurement range to high viscosity liquids, too.

Authors: Y. Montagut, J.V. García, Y. Jiménez, C. March, A. Montoya, A. Arnau

Journal: Review of Scientific Instruments (2011)

The improvement of sensitivity in quartz crystal microbalance (QCM) applications has been addressed in the last decades by increasing the sensor fundamental frequency, following the increment of the frequency/mass sensitivity with the square of frequency predicted by Sauerbrey. However, this sensitivity improvement has not been completely transferred in terms of resolution. The decrease of frequency stability due to the increase of the phase noise, particularly in oscillators, made impossible to reach the expected resolution. A new concept of sensor characterization at constant frequency has been recently proposed. The validation of the new concept is presented in this work. An immunosensor application for the detection of a low molecular weight contaminant, the insecticide carbaryl, has been chosen for the validation. An, in principle, improved version of a balanced-bridge oscillator is validated for its use in liquids, and applied for the frequency shift characterization of the QCM immunosensor application. The classical frequency shift characterization is compared with the new phase-shift characterization concept and system proposed.

Authors: Ilya Reviakine, Diethelm Johannsmann and Ralf P. Richter

Journal: Analytical Chemistry, 2011

Authors: R. Torres, Y. Jiménez, A. Arnau, C. Gabrielli, S. Joiret, H. Perrot, T.K.L. To, X. Wang

Journal: Electrochimica Acta (2010)

For many years, polyaniline films have appeared to be one of the most studied conducting polymers. At the same time, ac-electrogravimetry has been used as a powerful technique for different polymer films but in general for slow perturbation rates. Two reasons for that: on the one hand, high frequency mass transfer responses are not expected and on the other hand, the electronic interfaces dedicated for ac-electrogravimetry are not prepared to follow, without distortion, high rate frequency shifts, faster than a few hertz. This paper shows that high ionic transfer responses can be detected by using a new ac-electrogravimetry concept. The experiments conducted with PANI tried to verify whether high frequency responses in conducting polymers are possible or not. The main interest of the new device is to reach the high frequency values directly and to demonstrate an ionic transfer contribution at 1 kHz which was not predicted with old systems.