The uniformity of the surface of bare GC electrode is observed with weak visible of crystalline structure on the SEM image (Fig. 4A), whereas Fig. 4B shows that MWCNTs coating created uniform and dense layer of on the surface of GCE. The AFM images show clearly that the GCE surface has a fine-grained microstructure with a grain size of about 15–50 nm. In the case of the GC/MWCNTs electrode, multi-walled carbon nanotubes are bent, twisted and tangled, and they covered the full surface of GCE. The phase images of both GCE and GCE modified with MWCNTs indicate that the surfaces are homogeneous in composition and do not contain contaminants. The surface roughness, calculated as RMS (root mean square of height deviations) from the recorded AFM high images for GCE and GCE/MWCNTs, was 0.25 ± 0.06 nm and 0.8 ± 0.1 nm, respectively.