Potential dependence of ferritin monomer, dimer and oligomer adsorption on a polycrystalline Au surface

An electrochemical quartz crystal microbalance (EQCM) was used to measure the effects of in situ potential changes on the adsorption and desorption of ferritin on polycrystalline Au. As-received horse-spleen ferritin, and purified ferritin monomer, dimer and higher oligomer fractions separated by gel chromatography were compared. Experiments were carried out at pH 5 where the ferritin is expected to have a net negative charge. Despite electrostatic repulsion, significant adsorption was observed on Au even at the most negative potentials studied, though it could be suppressed by using a low ionic strength electrolyte. This adsorption was attributed to hydrophobic interactions caused by partial denaturation of the protein, and it was greater for as-received ferritin containing higher oligomers than for monomeric ferritin. The reversibility of the adsorption was also lower when higher oligomers were present. Potential dependent adsorption/desorption could be useful as a diagnostic method for protein solutions.