In Situ Probing Unusual Protein Adsorption Behavior on Electrified Zwitterionic Conducting Polymers

Understanding the phenomenon of protein adsorption on electrified conducting polymer-based electrodes is an important issue in organic bioelectronics. To investigate both specific and nonspecific protein adsorption on electrified electrodes, C-reactive protein (CRP) binding behavior is measured in situ and is compared with the nonspecific binding of bovine serum albumin and lysozyme on electrified phosphorylcholine-functionalized poly(3,4-ethylenedioxythiophene) (poly(EDOT-PC)) by using an electrochemical quartz crystal microbalance with dissipation (EQCM-D) and an electrochemical atomic force microscopy (EC-AFM). According to the result of EQCM-D, an unexpected enhancement is observed in the CRP binding on the electrified poly(EDOT-PC) when both -0.5 and 0.5 V (versus Ag/AgCl) potentials are applied to poly(EDOT-PC). Furthermore, an EC-AFM is used to in situ map the surface topography and modulus of poly(EDOT-PC) under the application of surface potentials. Together with EQCM-D measurements, the large enhancement of CRP binding can be visualized as the formation of a loose and thick CRP multilayer of low surface modulus, high root-mean-square roughness, and high dissipation when a potential of 0.5 V is subjected to poly(EDOT-PC). It is concluded that the enhancement in CRP binding is mainly attributed to the synergistic effect of specific protein recognition and electrostatic interaction between the CRP and poly(EDOT-PC).