A 1:0.25 (w/w) mixture of graphite powder and paraffin was blended in an agate mortar and pestled for 20 min until a homogeneous paste was obtained. Then the pretreated nichrome substrate was rubbed in the carbon paste to fabricate an inlaying ultrathin carbon paste electrode (IUCPE) with a layer thickness of about 100 nm carbon paste film. The carbon paste out of the tube was cleaned and rinsed with double distilled deionized water