Electric field effects on adsorption/desorption of proteins and colloidal particles on a gold film observed using surface plasmon resonance

We present results for the enhancement or retardation of the attachment of the protein soybean peroxidase to a gold substrate using electric fields. We detect the influence of the electric fields on the proteins using the surface plasmon resonance phenomenon. The gold surface on which the surface plasmon resonance is generated also acts as one of the electrodes required to apply the electric field. The second electrode has a semi-insulating layer that limits current flow, and limits electrolysis effects. The results show that at pH 7, when the soybean peroxidase is negatively charged, a greatly enhanced deposition of protein is obtained when a positive potential is applied to the gold electrode. A negative potential can inhibit protein attachment, or reduce the amount of protein attached; however, after repeated applications of a positive potential, a negative potential has little effect. Results are presented of experiments using colloidal silica that has negatively charged particles of similar size to soybean peroxidase, showing the attraction and repulsion of negatively charged particles by the gold surface.