Quartz crystal microbalance viscoelastic properties

Galli Marxer, C., Collaud Coen, M., and Schlapbach, L. (2003). Study of adsorption and viscoelastic properties of proteins with a quartz crystal microbalance by measuring the oscillation amplitude. J. Colloid Interface Sci., 261, 291-298. 

Hook, F., Kasemo, B., Nylander, T., Fant, C., Sott, K., and Elwing, H. (2001). Variations in coupled water, viscoelastic properties, and film thickness of a Mefp-1 protein film during adsorption and cross-linking A quartz crystal microbalance with dissipation monitoring, ellipsometry, and surface plasmon resonance study.y4na/. Chem., 13, 5796-5804. 

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]. 

In this work we studied the regularities of a horseradish peroxidase (HRP) layer formation from its aqueous solutions on bare gold surface and that modified with a polyethyleneimine/polystyrene sulfonate bilayer using the quartz crystal microbalance (QCM) technique in liquid phase allowing to achieve highly sensitive mass detection and obtain information on viscoelastic properties of the adsorbed layers [3,4]. 

Hillman AR, Efimov I, Ryder KS (2005) Timescale-and temperature-dependent properties of viscoelastic PEDOT films. J Am Chem Soc 127 16611 Mohamoud MA, Hillman AR, Efimov I (2008) Film mechanical resonance phenomenon during electrochemical deposition of polyaniline. Electrochim Acta 53(21) 6235-6243 Hillman AR, Dong Q, Mohamoud MA, Efimov I (2010) Characterization of viscoelastic properties of composite films involving polyaniline and carbon nanotubes. Electrochim Acta 55(27) 8142-8153 Efimov I, Hillman AR, Schultze JW (2006) Sensitivity variation of the electrochemical quartz crystal microbalance in response to energy trapping. Electrochim Acta... 

The quartz crystal microbalance (QCM) consists of a quartz crystal that is electrically driven into oscillation. The resonance frequency of the crystal is monitored. This frequency is highly dependent on any mass added to the crystal surface. Hence the mass dependence of the QCM resonance frequency can be, in air, used to weigh minute amounts of material with a sensitivity of the order of 1 ng/cm. QCM can also be coupled with electrochemistry here, the quartz crystal surface is coated with an appropriate electrode material, for example, thin film gold. This electrochemical QCM (EQCM) configuration can be used to monitor electrochemically triggered surface processes associated with the deposition (or loss) of material at the working electrode surface. However, in liquid medium the frequency shift of the QCM crystal is not solely sensitive to added mass but is also influenced by changes in the local property of the medium associated with the surface electrochemical process of interest. For example, density or viscosity variation of the medium in the electrode vicinity, in addition to variation in the viscoelastic properties of the deposited layer, can cause shifts in the resonant frequency of QCM. 

A rather old example for switching deals again with ferrocene-modified polymer networks. Thin films on an electrochemical quartz crystal microbalance were tested for changes in their viscoelastic properties in response to an overpotential [350, 351]. In this example, the electrochemical properties are dependent on... 

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