(A) CVs of 5 mM K3Fe(CN)6/0.1 M KCl at GCE (curve 1) and OMC/GCE (curve 2). Scan rate: 50 mV/s. (B) Nyquist plots at GCE (curve 1), OMC/GCE (curve 2) in 5 mM K3Fe(CN)6/0.1 M KCl. Inset a and b are the equivalent circuit and the amplification of OMC at higher frequencies, respectively.