Spectral measurements with hybrid LMR and SAW platform for dual parameter sensing.

Lossy mode resonance (LMR)-based optical sensors change their wavelength upon contact with substances or gases. This allows developing applications to detect the refractive index of the surrounding medium and even the thickness of the biolayers deposited on the waveguide. In the same way, when acoustic sensors are in contact with a liquid, it is possible to determine parameters, especially mechanical ones such as shape of the particle or molecule, mass load, elastic constants and viscosity of the liquid. This work reports the development of a system that combines LMR with surface acoustic wave (SAW) technologies to characterize a liquid in terms of its refractive index and viscosity simultaneously. Conveniently prepared glucose solutions are used for sensor calibration. The refractive index of the solutions ranges from 1.33 to 1.41 and its viscosity ranges from 1.005 mPa·s to 9 mPa·s, respectively. A sensitivity of 332 nm per RIU has been achieved with the optical sensor while the acoustic sensor has shown a sensitivity of -1.5 dB/(mPa·s). This new combinational concept could be expanded to the development of more demanding applications such as chemical sensors or biosensors.

Trends and Applications of Surface and Bulk Acoustic Wave Devices: A Review.

The past few decades have witnessed the ultra-fast development of wireless telecommunication systems, such as mobile communication, global positioning, and data transmission systems. In these applications, radio frequency (RF) acoustic devices, such as bulk acoustic waves (BAW) and surface acoustic waves (SAW) devices, play an important role. As the integration technology of BAW and SAW devices is becoming more mature day by day, their application in the physical and biochemical sensing and actuating fields has also gradually expanded. This has led to a profusion of associated literature, and this article particularly aims to help young professionals and students obtain a comprehensive overview of such acoustic technologies. In this perspective, we report and discuss the key basic principles of SAW and BAW devices and their typical geometries and electrical characterization methodology. Regarding BAW devices, we give particular attention to film bulk acoustic resonators (FBARs), due to their advantages in terms of high frequency operation and integrability. Examples illustrating their application as RF filters, physical sensors and actuators, and biochemical sensors are presented. We then discuss recent promising studies that pave the way for the exploitation of these elastic wave devices for new applications that fit into current challenges, especially in quantum acoustics (single-electron probe/control and coherent coupling between magnons and phonons) or in other fields.

CNT-Based Inkjet-Printed RF Gas Sensor: Modification of Substrate Properties during the Fabrication Process.

This paper presents the feasibility of a fully inkjet-printed, microwave flexible gas sensor based on a resonant electromagnetic transducer in microstrip technology and the impact of the printing process that affects the characteristics of the gas sensor. The sensor is fabricated using silver ink and multi-wall carbon nanotubes (MWCNTs) embedded in poly (3,4-ethylenedioxythiophene) polystyrene (PEDOT: PSS-MWCNTs) as sensitive material for Volatile Organic Compounds (VOCs) detection. Particular attention is paid to the characterization of the printed materials and the paper substrate. The manufacturing process results in a change in relative permittivity of the paper substrate by nearly 20%. Electrical characterization, made in the presence of gas, validates our theoretical approach and the radiofrequency (RF) gas sensor proof of concept.

Converting Any Faradaic Current Generated at an Electrode under Potentiostatic Control into a Remote Fluorescence Signal.

We describe the development of an original faradaic current-to-fluorescence conversion scheme. The proposed instrumental strategy consists of coupling the electrochemical reaction of any species at an electrode under potentiostatic control with the fluorescence emission of a species produced at the counter electrode. In order to experimentally validate this scheme, the fluorogenic species resazurin is chosen as a fluorescent reporter molecule, and its complex reduction mechanism is first studied in unprecedented detail. This kinetic study is carried out by recording simultaneous cyclic voltammograms and voltfluorograms at the same electrode. Numerical simulations are used to account for the experimental current and fluorescence signals, to analyze their degree of correlation, and to decipher their relation to resazurin reduction kinetics. It is then shown that, provided that the reduction of resazurin takes place at a micrometer-sized electrode, the fluorescence emission perfectly tracks the faradaic current. By implementing this ideal configuration at the counter electrode of a potentiostatic setup, it is finally demonstrated that the oxidation reaction of a nonfluorescent species at the working electrode can be quantitatively transduced into simultaneous emission of fluorescence.

Love Acoustic Wave-Based Devices and Molecularly-Imprinted Polymers as Versatile Sensors for Electronic Nose or Tongue for Cancer Monitoring.

Cancer is a leading cause of death worldwide and actual analytical techniques are restrictive in detecting it. Thus, there is still a challenge, as well as a need, for the development of quantitative non-invasive tools for the diagnosis of cancers and the follow-up care of patients. We introduce first the overall interest of electronic nose or tongue for such application of microsensors arrays with data processing in complex media, either gas (e.g., Volatile Organic Compounds or VOCs as biomarkers in breath) or liquid (e.g., modified nucleosides as urinary biomarkers). Then this is illustrated with a versatile acoustic wave transducer, functionalized with molecularly-imprinted polymers (MIP) synthesized for adenosine-5'-monophosphate (AMP) as a model for nucleosides. The device including the thin film coating is described, then static measurements with scanning electron microscopy (SEM) and electrical characterization after each step of the sensitive MIP process (deposit, removal of AMP template, capture of AMP target) demonstrate the thin film functionality. Dynamic measurements with a microfluidic setup and four targets are presented afterwards. They show a sensitivity of 5 Hz·ppm(-1) of the non-optimized microsensor for AMP detection, with a specificity of three times compared to PMPA, and almost nil sensitivity to 3'AMP and CMP, in accordance with previously published results on bulk MIP.