Before modification, pre-treatment of AuE was performed
according to Siddiquee et al. [31] procedure with some modifications.
Firstly, the AuE was polished with 3 lM aluminium slurry
for 2 min. After that, the AuE was sonicated for 2 min and rinsed
with deionized water for about 2 min. Later, 10 lL of the CHIT/
CaONPs/[EMIM][Otf] suspensions was casted onto the AuE and
then dried at room temperature for at least 4 h in order to obtain
a uniform coated membrane of CHIT/CaONPs/[EMIM][Otf]/AuE.
After successful immobilization, the surface of the modified AuE
was soaked in 0.001 M of MB for 2 min followed by washing with
Tris–HCl buffer (pH 7.0) to remove unspecific physically adsorption.
The electrochemical measurements of the modified AuE and
bare AuE were conducted in 50 mM Tris–HCl, 20 mM NaCl buffer
solutions (pH 7.0) containing 1.0 mM of MB using CV and DPV
methods.