Abstract
While relatively successful theoretical models exist to link the signal of an acoustic biosensor to the mass and viscoelasticity of film-forming adsorbates, this is not the case for surfaces discretely covered by analytes such as proteins or DNA. This work extends and examines in detail the underlying physics of a previously published theory that links the response of microbalance sensors to the shapes and sizes of attached molecules, shedding light on the hydrodynamics and energy-dissipation processes. Their analysis offers further physical insight, and could be exploited to improve detection approaches relevant to biology and biomedicine.
Highlights
Shear-wave acoustic devices work by forcing a piezoelectric material at the core of the device to vibrate and following the changes of the crystal’s shear oscillatory motion that take place when biological or other matter is in contact with the moving surface
The presented model is formulated to hold for the quartz crystal microbalance (QCM-D) sensor and sheds new light in many standing questions regarding its operation with biological samples in liquid
Provided that the particle addition rate does not overlap with the inverse time scale, τp−1 related to the drag force [Eq (8a)], it will be possible for the system to retain its characteristics, namely an oscillatory motion of the fluid, as in Eq (4), and a wavelike pattern of the molecules’ motion that will tend to adapt to the fluid’s velocity profile, even at moderate surface coverage
Summary
Shear-wave acoustic devices work by forcing a piezoelectric material at the core of the device to vibrate and following the changes of the crystal’s shear oscillatory motion that take place when biological or other matter is in contact with the moving surface. Tsortos et al [22,23,24] followed a route that allowed to look at the role of the actual size and shape of rodlike molecules, such as DNA linear chains, or even more complex structures using nucleotides as building blocks They relied on solution viscosity theory to show that the ratio of change in wave-energy dissipation D, over frequency shift, − f, (termed “acoustic ratio,” D/ f ), is independent of surface coverage and proportional to the analyte’s intrinsic viscosity [η], a hydrodynamic quantity directly related to structure [23]. In Appendix B, an approximate expression is derived at the limit of vanishing analyte mass per unit surface area, leading to the original theory [22,23,24]
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