CV measurements were performed in 2 mM K3[Fe(CN)6] solution
containing 0.1 M KCl with a scan rate of 50 mV/s. 
DPV measurements were performed in 0.1 M PBS by scanning from 0
to +0.40 V with an pulse amplitude of 10 mV, 
pulse width of 0.05 s,
and pulse period of 0.2 s. 
EIS was performed in a 0.1 M KCl solution
within the frequency range of 10−2 to 105 Hz using a 5.0 mM
K3[Fe(CN)6]/K4[Fe(CN)6] (1:1) mixture as an electroactive probe.
The amplitude and potential were 0.005 and 0.165 V, respectively