Quartz crystal microbalance impedance

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

The monotonic increase of immobilized material vith the number of deposition cycles in the LbL technique is vhat allo vs control over film thickness on the nanometric scale. Eilm growth in LbL has been very well characterized by several complementary experimental techniques such as UV-visible spectroscopy [66, 67], quartz crystal microbalance (QCM) [68-70], X-ray [63] and neutron reflectometry [3], Fourier transform infrared spectroscopy (ETIR) [71], ellipsometry [68-70], cyclic voltammetry (CV) [67, 72], electrochemical impedance spectroscopy (EIS) [73], -potential [74] and so on. The complement of these techniques can be appreciated, for example, in the integrated charge in cyclic voltammetry experiments or the redox capacitance in EIS for redox PEMs The charge or redox capacitance is not necessarily that expected for the complete oxidation/reduction of all the redox-active groups that can be estimated by other techniques because of the experimental timescale and charge-transport limitations. 

Improving the accuracy of a quartz crystal microbalance with automatic determination of acoustic impedance ratio. 

Although less common, some third-order chemical sensors have found significant applications not only in sensing but also in research. One such example is Electrochemical Quartz Crystal Microbalance (EQCM). With EQCM, an electrochemical experiment can be performed in its inherently large experimental space, that is, various electrochemical waveforms, impedance analysis, gating, and different mass loading. As the dimensionality of the experiment is increased, so is its information content. 

Through the combination of SPR with a - poten-tiostat, SPR can be measured in-situ during an electrochemical experiment (electrochemical surface plasmon resonace, ESPR). Respective setups are nowadays commercially available. Voltammetric methods, coupled to SPR, are advantageously utilized for investigations of - conducting polymers, thin film formation under influence of electric fields or potential variation, as well as - electropolymerization, or for development of -> biosensors and - modified electrodes. Further in-situ techniques, successfully used with SPR, include electrochemical - impedance measurements and -+ electrochemical quartz crystal microbalance. 

As the readers may see, quartz crystal resonator (QCR) sensors are out of the content of this chapter because their fundamentals are far from spectrometric aspects. These acoustic devices, especially applied in direct contact to an aqueous liquid, are commonly known as quartz crystal microbalance (QCM) [104] and used to convert a mass ora mass accumulation on the surface of the quartz crystal or, almost equivalent, the thickness or a thickness increase of a foreign layer on the crystal surface, into a frequency shift — a decrease in the ultrasonic frequency — then converted into an electrical signal. This unspecific response can be made selective, even specific, in the case of QCM immunosensors [105]. Despite non-gravimetric contributions have been attributed to the QCR response, such as the effect of single-film viscoelasticity [106], these contributions are also showed by a shift of the fixed US frequency applied to the resonator so, the spectrum of the system under study is never obtained and the methods developed with the help of these devices cannot be considered spectrometric. Recent studies on acoustic properties of living cells on the sub-second timescale have involved both a QCM and an impedance analyser thus susceptance and conductance spectra are obtained by the latter [107]. 

A special type of hybrid measurements involving a quartz crystal microbalance (QCM) and an impedance analyser was used to study the variability of acoustic properties of living cells on the sub-second time scale. Changes in susceptance and conductance caused by changing the ultrasonic frequency were monitored in a fast mode in order to detect periodic, synchronous contractions of the cell layer in the quartz crystal the contractions were clearly reflected in periodic variations of the resonance frequency and bandwidth [117]. 

Jia, X., Xie, Q., Zhang, Y., Yao, S. (2007). Simultaneous quartz crystal microbalance-electrochemical impedance spectroscopy study on the adsorption of anti-human immunoglobulin G and its immunoreaction at nanomaterial-modified Au electrode surfaces. Anal. Sci., 23, 689-696. 

Patolsky, K, Zayats, M., Katz, E., and Willner, I. (1999) Precipitation of an insoluble product on enzyme monolayer electrodes for biosensor applications Characterization by faradaic impedance spectroscopy, cyclic voltammetry, and microgravimetric quartz crystal microbalance analyses. Anal. Chem. 71, 3171-3180... 

FIG. 7.30 Electronic and optical transduction of the formation of antigen-antibody affinity complexes on transducers (A) Amperometric transduction at an electrode (R /K Is a redox label In the electrolyte solution). (B) Transduction by faradic Impedance spectrosco . (C) Microgravimetric quartz crystal microbalance (QCM) transduction in the presence of a piezoelectric quartz crystal. (D) Surface plasmon resonance transduction. 

Figure 4.18 Principal construction of a quartz crystal microbalance with network analysis. WE working electrode, CE counter electrode, RE reference electrode, Po potentiostat, Na network analyzer, R and C for resistance and capacitance for impedance adaptation, and Nj inert gas purging.

When compared to other analysis methodologies such as surface plasmon resonance (SPR), quartz crystal microbalance (QCM) or impedance (EIS), voltammetry-based sensors provide short response time, less-expensive analysis about immobilization of molecules, and in many analj es they allow real-time measurements. 

Ever since Feldberg s original model separating faradaic and capacitance current associated with a conducting polymer that behaves like a porous metal, " there have been various attempts to rationalize experimentally the nature of the current at a conducting polymer. Apart from impedance models, there has not been so much effort placed on modeling the system. Experimental efforts to examine processes at conducting-polymer-modified electrodes consisted of voltam-metry, " impedance, " and quartz crystal microbalance. However the... 

In fact, ac electrogravimetry is the combination of electrochemical impedance spectroscopy with a fast quartz crystal microbalance. The fluxes of all mobile species are considered, and the usual conditions and treatments of EIS are applied. Beside the electrochemical impedance, an electrogravimetric transfer function, Aw/A ((o), can be derived which contains the dependences of the fluxes of anions, cations and solvent molecules, respectively, on the small potential perturbation. The complex plane plot representations of electrogravimetric transfer functions for PANI are shown in Figs. 3.17 and 3.18. 

R. Gabai, N. Sallacan, V. Chegel, T. Bourenko, E. Katz, I. Willner, Characterization of the swelling of acrylamidophenylboronic acid-acrylamide hydrogels upon interaction with glucose by faradaic impedance spectroscopy, chronopotentiometry, quartz crystal microbalance (QCM), and surface plas-mon resonance (SPR) experiments, Journal of Physical Chemistry B 2001, 105, 8196. 

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