Viscoelasticity evolution in protein layers during binding reactions evaluated using high-frequency wireless and electrodeless quartz crystal microbalance biosensor without dissipation

In this study, we demonstrate the effectiveness of a resonance acoustic microbalance with a naked embedded quartz (RAMNE-Q) biosensor for evaluating viscoelastic property changes in thin protein layers during protein deposition reactions without dissipation measurement. Quartz crystal microbalance (QCM) biosensors have conventionally been adopted for the viscoelasticity evaluation of adsorbed protein layers by measuring dissipation as well as resonance frequency. However, dissipation, or the vibrational energy loss, is easily affected by many factors and is rarely measured with sufficiently high accuracy. To evaluate viscoelasticity only from a reliable frequency response, one needs to perform an ultrahigh-frequency measurement, which is here achieved using the RAMNE-Q biosensor. Simultaneous frequency measurement is performed for fundamental and overtone modes up to 406 MHz of a 58 MHz RAMNE-Q biosensor during various binding reactions, and evolutions of viscosity, shear modulus, and thickness of adsorbed protein layers are inversely evaluated. A marked difference is observed in the viscosity evolution between specific and nonspecific binding reactions. Furthermore, the reversed frequency response appears, which indicates the modification of the protein structure into a rigid structure.