Hydration and Energy Dissipation Measurements of Biomolecules on a Piezoelectric Quartz Oscillator by Admittance Analyses

Abstract

By using a 27-MHz piezoelectric quartz oscillator connected with a vector network analyzer, we obtained resonance frequency decreases (−ΔF_water) and energy dissipation increases (ΔD_water) during binding of biotinylated bovine serum albumin, biotinylated ssDNA, biotinylated dsDNA, and biotinylated pullulan to a NeutrAvidin-immobilized 27-MHz quartz crystal microbalance (QCM) plate in aqueous solution, as well as in the wet air phase (98% humidity, −ΔF_wet and ΔD_wet) and in the dry air phase (−ΔF_air and ΔD_air). −ΔF_water indicates the total mass of the molecule, bound water, and vibrated water in aqueous solutions. −ΔF_wet indicates the total mass of the molecule and bound water. −ΔF_air simply shows the real mass of the molecule on the QCM. In terms of results, (−ΔF_wet)/(−ΔF_air) values indicated the bound water ratios per unit biomolecular mass were on the order of pullulan (2.1−2.2) > DNAs = proteins (1.4−1.6) > polystyrene (1.0). The (−ΔF_water)/(−ΔF_air) values indicated the hydrodynamic water (bound and vibrated water) ratios per unit biomolecular mass were on the order of dsDNA (6.5) > ssDNA = pullulan (3.5−4.4) > proteins (2.4−2.5) > polystyrene (1.0). Energy dissipation parameters per unit mass in water (ΔD_water/(−ΔF_air)) were on the order of pullulan > dsDNA > ssDNA > proteins > polystyrene. Energy dissipation in the wet and dry air phases (ΔD_wet and ΔD_air) were negligibly small, which indicates even these biomolecules act as elastic membranes in the air phase (without aqueous solution). We obtained a good linear relationship between [(−ΔF_water)/(−ΔF_air) − 1], which is indicative of hydration and ΔD_water/(−ΔF_air) of proteins. The aforementioned values suggest that the energy dissipation of proteins was mainly caused by hydration and that proteins themselves are elastic molecules without energy dissipation in aqueous solutions. On the contrary, plots in cases of denatured proteins, DNAs, and pullulans were relatively deviant toward the large hydration and energy dissipation from the theoretical line as perfect elastic materials, meaning that the large energy dissipation occurs because of viscoelastic properties of denatured proteins, linear DNAs, and pullulans in the water phase, in addition to energy dissipation due to the hydration of molecules. These two parameters could characterize various biomolecules with structural properties in aqueous solutions.