This paper presents a new paradigm in the analysis and methodology for Surface Acoustic Wave (SAW) devices for sensing application in a liquid medium. This new protocol encourages the analysis of the electrical and electro-acoustic behavior of the sensor rather than limiting the measurement interest to mechanical interactions between the sensor and the adjacent medium. This work focuses on a “holistic” approach, mainly seeking to achieve an improved understanding of the sensing phenomena and to enrich the global response and its analysis. Even though this work does not aim to enhance the general sensitivity, it could be used to improve the design of the sensor for a specific target. Our methodology is based on the separation of electrical and mechanical mechanisms with post-treatment analysis of experimental responses, using jointly frequency and time domains analysis. It is supported by an unconventional energy flow chart of the acoustic wave propagation in the SAW device which helped us extracting a few hypotheses. This new paradigm allows us to get information related to both dielectric and mechanical parameters of a liquid sample using a single sensor, thus enriching the response at no cost. In this paper, we applied the method to Love wave sensors with different technological characteristics influencing the electric and acoustic response, and numerous fluid solutions for a large diversity of dielectric constants and mechanical properties. The large set of measurement allows the extraction of both dielectric and mechanical parameters of a liquid medium on the Love wave sensor surface.

The present study aimed to develop and characterize new heavy metal sensors functionalized by extracellular polymeric substances (EPSs) isolated from a Tunisian thermophilic microalga strain Graesiella sp. The elaborated sensor showed a highly homogeneous character and revealed a microstructural lamellar arrangement, high crystalline nature, and several functional groups. Electrochemical impedance spectroscopy (EIS) and acoustic wave sensing were used as sensing techniques to explore the ability of microalgae-EPS-functionalized sensors to detect cadmium and mercury as heavy metals. For impedimetric measurements, a two-dipole circuit was adopted and showed good-fitted results with a low total error. The acoustic sensor platforms showed good compatibility with EPS in adjacent water. For both EPS-functionalized sensors, metal ions (Cd²⁺, Hg²⁺) were successfully detected in the concentration range from 10⁻¹⁰ M to 10⁻⁴ M. Impedimetric sensor was more sensitive to Cd²⁺ at low concentrations before saturation at 10⁻⁷ M, while the acoustic sensor exhibited more sensitivity to Hg²⁺ over the full range. The results highlight a new potential alternative to use microalgae EPSs as a sensitive coating material for the detection of heavy metals. However, its use in a real liquid medium requires further investigation of its selectivity in the presence of other compounds.

Love wave (LW) acoustic sensors are promising devices for biochemical detection in the liquid media. However, their application for in-situ biochemical detection especially in the turbid liquid medium is not yet explored. Turbid liquids are complex in nature with both mechanical and electrical characteristics. These characteristics could be reliably estimated with LW acoustic sensor response, where some of the dedicated sensors based on electrochemistry or optical principle show limitations. This paper presents experimental responses of LW acoustic sensor to turbid liquids based on Formazin solutions and its comparison to the spectrophotometer response. Analysis of sensor’s electro-acoustic response is used to better characterize the sensor performance with turbid liquids. Further, this paper demonstrates the feasibility of LW acoustic sensor as a multiparameter sensing unit by estimating the influence of electro-mechanical parameters of the turbid liquids on the overall response of the sensor.

Capacitive sensors are based on the principle of capacitance and have wide applications in industrial, environmental, and biomedical fields, standing out for their cost-effectiveness and efficiency. Recently, their use as biosensors has gained relevance due to the incorporation of sensitive and selective layers that detect specific targets, such as bacteria, viruses, heavy metals, and organic pollutants. Studies demonstrate their high sensitivity, surpassing traditional methods, while also offering reduced manufacturing costs and time, making them ideal for applications in locations with limited technological facilities. Among recent technologies, capacitive sensors with interdigitated electrodes offer a larger interaction area with the analyzed medium, increasing accuracy and efficiency in biomarker detection. However, gaps in understanding their application in complex systems indicate the need for improved sensor integration strategies and in-depth investigations into their performance under variable environmental and biological conditions. This article presents a literature review on interdigitated capacitive sensors, focusing on devices applied as biosensors in liquid media. It discusses their operating principles, technological advances, and recent applications to consolidate the state of the art and identify future trends in the field, particularly in the context of sensors that can be fabricated using conventional and low-cost methods.

This paper presents an extended work on the Finite Element Method (FEM) simulation of Love Wave (LW) sensors in a liquid medium. Two models are proposed to simulate the multiphysical response of the sensor. Both are extensively described in terms of principle, composition and behavior, making their applications easily reproducible by the sensor community. The first model is a Representative Volume Element (RVE) simulating the transducer and the second focuses on the sensor’s longitudinal (OXZ) cut which simulates the multiphysical responses of the device. Sensitivity of the LW device to variations in the rheological and dielectric properties of liquids is estimated and then compared to a large set of measurements issued from LW sensors presenting different technological characteristics. This integral approach allows for a deeper insight into the multiphysical behavior of the LW sensor. This article also explores the advantages and drawbacks of each model. Both are in good accordance with the measurements and could be used for various applications, for which a non-exhaustive list is proposed in the conclusion.

Les capteurs à ondes de Love sont utilisés dans une large gamme d’applications en milieu liquide, avec des sensibilités très importantes. Néanmoins, ceux-ci ne permettent pas, encore aujourd’hui, de détecter des molécules de très faibles poids telles que les cyanotoxines. Ces travaux de thèse portent sur l’utilisation de couches mésoporeuses d’oxyde de titane sur un capteur à ondes de Love afin d’améliorer sa sensibilité. Après avoir obtenu un nouveau modèle conceptuel du capteur permettant d’enrichir sa réponse, sa sensibilité à des effets de variations rhéologiques et diélectriques est quantifiée en milieu liquide. Ces résultats sont ensuite utilisés pour obtenir un ensemble de modèles par éléments finis, venant compléter notre « boite à outils ». Enfin, plusieurs méthodes de dépôt de couches mésostructurées en films minces sont étudiées. Les capteurs ainsi obtenus sont caractérisés en milieu liquide et permettent de conclure sur une amélioration des performances en sensibilité sous un certain nombre de conditions. Ces conditions sont étudiées à l'aide des modèles par éléments finis et permettent de tracer une voie d’optimisation des capteurs à ondes de Love utilisant des couches mésostructurées.