Surface adsorption

A quartz crystal microbalance (OpenQCM, Novaetech S.r.l, Italy) was employed to determine the adsorption of full-length human plasma fibronectin on the different SAMs surfaces. SAM-coated QCM crystals were loaded onto the QCM before introducing the fibronectin solution (25 µg mL⁻¹ in PBS pH 7.4) at a flow of 1 µL s⁻¹ using an Ismatec IPC-N 4 peristaltic pump (Ismatec, Wertheim, Germany). Masses of adsorbed hydrated protein were calculated using the Sauerbrey equation⁴⁷ (Eq. ¹):

here Δf_m is the measured resonant frequency (Hz), f₀ is the intrinsic resonant frequency of the unloaded crystal (Hz), Δm is the mass change (g), A is the mass sensitive area of the electrode (cm²), ρ_q is the density of quartz (2.648 g cm³), µ_q is the shear modulus of the quartz crystal (2.947 × 10¹¹ g cm⁻¹ s⁻²⁾ and C_f is the quartz sensitivity factor or constant (Hz g⁻¹). The negative sign in the formula implies that an increase in mass on the surface of the crystal results in a reduction of the measured resonant frequency. A total of seven measurements were performed for each SAM surface.