εr is the relative permittivity of the buffer at 76.64, ε0 is the permittivity of vacuum of 8.854 x10 -12 C V -1 m -1 , f(ka) is the Henry function, approximated to 1.5 by the Smoluchowski approximation , and η is the viscosity of the buffer (0.904 mPa s). The samples were diluted 20 -100-fold and vortexed before being measured five times, applying a voltage of 50 V. At the same time, the current I was measured on the same samples at the applied voltage V. From this, the conductivity σ is calculated (Eq. 9), where L is the distance between the electrodes and S is the surface area.