March 15th 2021: AWSensors is pleased to invite you to take a look to the its new Application Note on Potentiostat Integration entitled “Potentiostat integration with AWSensors equipment“.

Summary of the Note

Seamless integration of QCMD and electrochemistry in the AWSensors EQCMD systems allows simultaneous measurements of the amount, electrochemical properties, and organization of material at the air/liquid interface accessed through the changes in the resonance frequency and dissipation measured by QCMD and the potential/current relationships measured with an integrated potentiostat or a galvanostat. The capabilities of the integrated AWSensors electrochemical EQCMD systems are illustrated here using the electropolymerization of aniline as an example.

Introduction

Investigation of complex interfacial processes benefit from combinations of complementary surface-analytical techniques that are based on different principles and approach the interface from complementary perspectives. [1,2] In this regard, the electrochemical quartz crystal microbalance with dissipation measurements, or EQCMD, has a venerable history. [3-5] Indeed, one of the incentives for immersing QCMD in liquids in the 1980s was to perform combined EQCMD measurements [6]. The two approaches are complementary in terms of the information they provide about the solid-liquid interface: interfacial mass transfer and structural changes are accessed with QCMD, while electrochemistry is concerned with the interfacial charge transfer and surface potential changes. Of particular interest is the quantitative characterization of electrochemically driven structural or viscoelastic transitions in interfacial layers, e.g., in battery research [7].

To accommodate the needs of researchers working with electrochemical applications in a wide variety of fields, AWSensors developed QCMD instruments with integrated potentiostat/galvanostat control for synchronizing QCMD and electrochemical experiments with appropriate BioLogic potentiostat or galvanostat. To illustrate the functionality, we use a straight-forward aniline polymerization experiment.

Electropolymerization of aniline to form polyaniline (PANI), and its electrochemical properties, have been widely studied, including by electrochemical quartz crystal microbalance (ref. [8-10], and references therein). Here, we go through the necessary steps for setting up an electrochemical experiment with the integrated QCMD/potentiostat combination for following aniline electropolymerization on the gold electrode surface of a QCMD sensor. The gravimetric and electrochemical results are presented, and the gravimetric results are compared with the cyclic voltammetry.

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You can download the full Application Note in pdf file from this link or download it from our Applications Web Page where you can find this and the rest of our Technology Notes.

Other references about the Note

• Combination of Quartz Crystal Microbalance with other Techniques, in Piezoelectric Transducers and Applications, A.A. Vives (ed.), 2008, doi: 10.1007/978-3-540-77508-9_13, Springer-Verlag Berlin Heidelberg.

• Electrochemical Quartz Crystal Microbalance with Dissipation Real- Time Hydrodynamic Spectroscopy of Porous Solids in Contact with Liquids. 2016, Anal. Chem. 88, 10151 – 10157.

 

February 15th 2021: AWSensors is pleased to invite you to take a look to the its new Technology Note on Love-SAW sensors “AWSensors Love-SAW sensors“.

Summary of the Note

Advanced Wave Sensors (AWSensors) develops and markets various types of sensors: classical QCM, High Fundamental Frequency QCM, and Love-Surface Acoustic Wave (Love-SAW). Love-SAW sensors do not measure love, but they do measure other interesting properties of interfacial layers. This Note is dedicated to explaining the basics of the operation of these less known acoustic sensors.

 

Introduction to Love-SAW sensors

Love waves are shear horizontally (SH) polarized surface acoustic waves. They are named after Augustus Edward Hough Love, who predicted them mathematically in 1911, and appear in fields as distinct as seismology and sensing [1].

Figure 1. a) Piezoelectric material, such as quartz, cut at a certain angle relative to the crystallographic axis, is used as a substrate in the construction of the Love-SAW sensors which basic structure is shown in b) (Taken from [2]).

Love-SAW sensors use a piezoelectric substrate (like quartz), in which the surface acoustic waves are excited by applying electrical current in a specific direction relative the crystallographic orientation of the piezoelectric material (see Figure 1a). The waves are then confined into the guiding layer overlaying the piezoelectric substrate. The structure of such a sensor is shown in Figure 1b where the current is applied through the so-called interdigitated transducers (IDTs), located between the substrate and the guiding layer. A standing Love wave is generated in the space between the IDTs (D in Figure 2), defining the sensing area. The condition for the existence of these waves is that the shear velocity in the guiding layer is less than that in the substrate. It is this difference in the mechanical properties between the guiding layer and the substrate that slows down the wave propagation velocity and traps the acoustic energy in the guiding layer keeping the wave energy near the surface. The sensitivity of this device is determined by the degree of wave confinement in the guiding layer. Thus, the higher the confinement of the wave in the guiding layer, the higher the sensitivity of the device is.

Love-SAW sensors typically operate at frequencies of hundreds of MHz. The operating frequency of a Love-SAW sensor is defined by the materials of its structure, the periodicity of the IDTs, λ in Figure 2, and the guiding layer thickness, d [2].

Key advantages of Love-SAW devices include efficient operation in liquids, mechanical stability (robustness), and high sensitivity (due to the high operating frequency by only changing the IDTs periodicity). Key limitations include a need for calibration due to the lack of simple, predictive model describing SAW wave propagation akin to the Sauerbrey relationship in QCMD or Lorentz-Lorenz and de Feijter’s relationships in ellipsometry. [3–5]

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Download the Full Technology Note

You can download the full Love-SAW Technology Note in pdf format from this link. A list of our Technology Notes can be found on our Technology Web Page.

Other references about Love-SAW sensors

• Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

• Love Wave Immunosensor for the Detection of Carbaryl Pesticide