Figure 2.

(a) Representative QCM-D data recording PrP^27–30 fibril attachment to Al₂O₃ at pH 6, I = 5 mM. Upward facing arrows indicate the time points that sensors were removed for AFM imaging (see Figure 4). (b) Areal mass densities of prion fibrils on Al₂O₃ as determined by QCM-D (m_QCM-D) and OWLS (m_OWLS). m_QCM-D was determined by applying a Kelvin-Voight viscoelastic model⁴⁵ to the Δf_i/i and ΔD_i/i data. The density of the adlayer and the density and dynamic viscosity of the bulk phase were set at 1025 kg·m⁻³, 0.997 kg·m⁻³ and 0.000910 Pa·s, respectively. m_QCM-D includes the mass of all molecules acoustically coupled to the vibrating sensor surface including analyte and solvent (viz. PrP^27–30 and water). m_OWLS was calculated by applying de Feijter’s equation (eq 1) to the refractive indices measured by the instrument. The experimental effective refractive indices are measured relative to their initial (protein-free buffer) values, m_OWLS corresponds to the mass of only the analyte molecules (e.g., PrP^27–30) not trapped solvent. Changes in solution chemistries are indicated by arrows above and dashed lines in each plot.