A two-electrode electrochemical surface plasmon resonance sensor for investigating the electropolymerization of polyaniline

A novel electrochemical surface plasmon resonance (EC-SPR) sensor has been developed based on the surface plasmon resonance (SPR) combined with a two-electrode electrochemical configuration. The theory of potential-modulated for EC-SPR was described, and several factors which can induce the change of the SPR resonance angle were revealed. Comparing with the conventional three-electrode electrochemical system, the reference electrode has been eliminated in this design, and the active carbon (AC) electrode employed as the counter electrode. Due to the large specific surface area, AC presents considerable double layer capacitance at the interface of electrode and electrolyte, which can provide a constant potential during the electrochemical reactions. Using an angle modulation SPR sensor and the resolution of that is 5 x 10(-6) RIU (refractive index units), a real-time data-smoothing algorithm is adopted to reduce the noise of the data, which can guarantee an accurate result of the resonance angle of SPR. The EC-SPR setup was used for investigating the electropolymerization of polyaniline by applying a potential of cyclic voltammetry, both of the electrochemical current and the resonance angle shift of SPR are recorded to monitor the growth process of the polymer. Comparing with the three-electrode configuration, the novel AC two-electrode system can also obtain detailed information about the polymerization process from the resonance angle shift curves, including the change of thickness and dielectric constant, deposition and transitions between different redox states of the polymer film. Experimental results demonstrated that this two-electrode EC-SPR configuration is suitable for analyzing the electropolymerization process of a conducting polymer.