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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 5x10-6 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.
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