(201g) The Effect of Applied Potential On the Adsorption of Poly-L-Lysine On Platinum Electrodes

Due to its biocompatibility, the polyelectrolyte poly-l-lysine (PLL) has been extensively investigated in various procedures concerning surface modification, e.g. to make electrodes suitable for in vitro and in vivo biological experiments. Previous studies have indicated that an electric potential applied to a conducting substrate affects the rate of film growth, and that growth rate does not appear to saturate as the film becomes thicker. We have examined the deposition of PLL onto platinum electrodes with an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), a powerful combination of the simultaneous measurements of the change in frequency, dissipation and current in response to an applied potential. By combining EQCM-D with cyclic voltammetry (CV), we demonstrate the electrochemical nature of the rate-limiting step in the PLL film's growth, and suggest a possible chemical mechanism. This mechanism is further corroborated by X-ray photoelectron spectroscopy (XPS) measurements. These results appear to agree with previous work in the area using optical techniques.